Sensing of gene expression in live cells using electrical impedance spectroscopy and DNA-functionalized gold nanoparticles

A novel electrical impedance spectroscopy-based method for non-destructive sensing of gene expression in living cells is presented. The approach used takes advantage of the robustness and responsiveness of electrical impedance spectroscopy and the highly specific and selective nature of DNA hybridization. The technique uses electrical impedance spectroscopy and gold nanoparticles functionalized with single-stranded DNA complementary to an mRNA of interest to provide reliable, real-time, and quantifiable data on gene expression in live cells. The system was validated by demonstrating specific detection of the uidA mRNA, which codes for the β-glucuronidase (GUS) enzyme, in Solanum lycopersicum MsK8 cells. Gold nanoparticles were functionalized with single-stranded DNA oligonucleotides consisting of either a sequence complementary to uidA mRNA or an arbitrary sequence. The DNA-functionalized gold nanoparticles were mixed with cell suspensions, allowing the gold nanoparticles to penetrate into the cells. The impedance spectra of suspensions of cells with gold nanoparticles inserted within them were then studied. In suspensions of uidA-expressing cells and gold nanoparticles functionalized with the complementary single-stranded DNA oligonucleotide, the impedance magnitude in the frequency range of interest was significantly higher (146 %) in comparison to all other controls. Due to its highly selective nature, the methodology has the potential to be used as a precision agricultural sensing system for accurate and real-time detection of markers of stress, viral infection, disease, and normal physiological activities.

Microcavity well-plate for automated parallel bioelectronic analysis of 3D cell cultures

Three-dimensional (3D) in vitro cell culture models serve as valuable tools for accurately replicating cellular microenvironments found in vivo. While cell culture technologies are rapidly advancing, the availability of non-invasive, real-time, and label-free analysis methods for 3D cultures remains limited. To meet the demand for higher-throughput drug screening, there is a demanding need for analytical methods that can operate in parallel. Microelectrode systems in combination with microcavity arrays (MCAs), offer the capability of spatially resolved electrochemical impedance analysis and field potential monitoring of 3D cultures. However, the fabrication and handling of small-scale MCAs have been labour-intensive, limiting their broader application. To overcome this challenge, we have established a process for creating MCAs in a standard 96-well plate format using high-precision selective laser etching. In addition, to automate and ensure the accurate placement of 3D cultures on the MCA, we have designed and characterized a plug-in tool using SLA-3D-printing. To characterize our new 96-well plate MCA-based platform, we conducted parallel analyses of human melanoma 3D cultures and monitored the effect of cisplatin in real-time by impedance spectroscopy. In the following we demonstrate the capabilities of the MCA approach by analysing contraction rates of human pluripotent stem cell-derived cardiomyocyte aggregates in response to cardioactive compounds. In summary, our MCA system significantly expands the possibilities for label-free analysis of 3D cell and tissue cultures, offering an order of magnitude higher parallelization capacity than previous devices. This advancement greatly enhances its applicability in real-world settings, such as drug development or clinical diagnostics.

Development of an electrochemical impedance spectroscopy immunosensor for insulin monitoring employing pyrroloquinoline quinone as an ingestible redox probe

Contemporary electrochemical impedance spectroscopy (EIS)-based biosensors face limitations in their applicability for in vivo measurements, primarily due to the necessity of using a redox probe capable of undergoing oxidation and reduction reactions in solution. Although previous investigations have demonstrated the effectiveness of EIS-based biosensors in detecting various target analytes using potassium ferricyanide as a redox probe, its unsuitability for blood or serum measurements, attributed to its inherent toxicity, poses a significant challenge. In response to this challenge, our study adopted a unique approach, focusing on the use of ingestible materials, by exploring naturally occurring substances within the body, with a specific emphasis on pyrroloquinoline quinone (PQQ). Following an assessment of PQQ's electrochemical attributes, we conducted a comprehensive series of EIS measurements. This involved the thorough characterization of the sensor's evolution, starting from the bare electrode and progressing to the immobilization of antibodies. The sensor's performance was then evaluated through the quantification of insulin concentrations ranging from 1 pM to 100 nM. A single frequency was identified for insulin measurements, offering a pathway for potential in vivo applications by combining PQQ as a redox probe with EIS measurements. This innovative approach holds promise for advancing the field of in vivo biosensing based on the EIS method.

Constructing Novel High Dielectric Constant Polyimides Containing Dipolar Pendant Groups with Enhanced Orientational Polarization

Polymer dielectrics with high dielectric constant are urgently demanded for potential electrical and pulsed power applications. The design of polymers with side chains containing dipolar groups is considered an effective method for preparing materials with a high dielectric constant and low loss. This study synthesizes and comprehensively compare the dielectric properties of novel polyimides with side chains containing urea (BU-PI), carbamate (BC-PI), and sulfonyl (BS-PI) functional groups. The novel polyimides exhibit relatively high dielectric constant and low dielectric loss values due to the enhanced orientational polarization and suppressed dipole-dipole interactions of dipolar groups. In particular, BU-PI containing urea pendant groups presents the highest dielectric constant of 6.14 and reasonably low dielectric loss value of 0.0097. The strong γ transitions with low activation energies derived from dielectric spectroscopy measurements have been further evaluated to demonstrate the enhanced free rotational motion of urea pendant dipoles. In energy storage applications, BU-PI achieves a discharged energy density of 6.92 J cm-3 and a charge-discharge efficiency above 83% at 500 MV m-1. This study demonstrates that urea group, as dipolar pendant group, can provide polymers with better dielectric properties than the most commonly used sulfonyl groups.

The Use of Virtual Tissue Constructs That Include Morphological Variability to Assess the Potential of Electrical Impedance Spectroscopy to Differentiate between Thyroid and Parathyroid Tissues during Surgery

Electrical impedance spectroscopy (EIS) has been proposed as a promising noninvasive method to differentiate healthy thyroid from parathyroid tissues during thyroidectomy. However, previously reported similarities in the in vivo measured spectra of these tissues during a pilot study suggest that this separation may not be straightforward. We utilise computational modelling as a method to elucidate the distinguishing characteristics in the EIS signal and explore the features of the tissue that contribute to the observed electrical behaviour. Firstly, multiscale finite element models (or 'virtual tissue constructs') of thyroid and parathyroid tissues were developed and verified against in vivo tissue measurements. A global sensitivity analysis was performed to investigate the impact of physiological micro-, meso- and macroscale tissue morphological features of both tissue types on the computed macroscale EIS spectra and explore the separability of the two tissue types. Our results suggest that the presence of a surface fascia layer could obstruct tissue differentiation, but an analysis of the separability of simulated spectra without the surface fascia layer suggests that differentiation of the two tissue types should be possible if this layer is completely removed by the surgeon. Comprehensive in vivo measurements are required to fully determine the potential for EIS as a method in distinguishing between thyroid and parathyroid tissues.

Synergy of Active Sites and Charge Transfer in Branched WO3/W18O49 Heterostructures for Enhanced NO2 Sensing

Achieving reliable detection of trace levels of NO2 gas is essential for environmental monitoring and protection of human health protection. Herein, a thin-film gas sensor based on branched WO3/W18O49 heterostructures was fabricated. The optimized WO3/W18O49 sensor exhibited outstanding NO2 sensing properties with an ultrahigh response value (1038) and low detection limit (10 ppb) at 50 °C. Such excellent sensing performance could be ascribed to the synergistic effect of accelerated charge transfer and increased active sites, which is confirmed by electrochemical impedance spectroscopy and temperature-programmed desorption characterization. The sensor exhibited an excellent detection ability to NO2 under different air quality conditions. This work provides an effective strategy for constructing WO3/W18O49 heterostructures for developing NO2 gas sensors with an excellent sensing performance.

Porous Membrane Electrical Cell-Substrate Impedance Spectroscopy for Versatile Assessment of Biological Barriers In Vitro

Cell culture models of endothelial and epithelial barriers typically use porous membrane inserts (e.g., Transwell inserts) as a permeable substrate on which barrier cells are grown, often in coculture with other cell types on the opposite side of the membrane. Current methods to characterize barrier function in porous membrane inserts can disrupt the barrier or provide bulk measurements that cannot isolate barrier cell resistance alone. Electrical cell-substrate impedance sensing (ECIS) addresses these limitations, but its implementation on porous membrane inserts has been limited by costly manufacturing, low sensitivity, and lack of validation for barrier assessment. Here, we present porous membrane ECIS (PM-ECIS), a cost-effective method to adapt ECIS technology to porous substrate-based in vitro models. We demonstrate high fidelity patterning of electrodes on porous membranes that can be incorporated into well plates of a variety of sizes with excellent cell biocompatibility with mono- and coculture set ups. PM-ECIS provided sensitive, real-time measurement of isolated changes in endothelial cell barrier impedance with cell growth and barrier disruption. Barrier function characterized by PM-ECIS resistance correlated well with permeability coefficients obtained from simultaneous molecular tracer permeability assays performed on the same cultures, validating the device. Integration of ECIS into conventional porous cell culture inserts provides a versatile, sensitive, and automated alternative to current methods to measure barrier function in vitro, including molecular tracer assays and transepithelial/endothelial electrical resistance.

Design of sonochemical assisted synthesis of Zr-MOF/g-C3N4-modified electrode for ultrasensitive detection of antipsychotic drug chlorpromazine from biological samples

The rapid fabrication is described of binary electrocatalyst based on a highly porous metal-organic framework with zirconium metal core (Zr-MOF) decorated over the graphitic carbon nitride (g-C3N4) nanosheets via facile ultrasonication method. It is used for the robust determination of antipsychotic drug chlorpromazine (CLP) from environmental samples. The electrochemical behaviour of 2D Zr-MOF@g-C3N4 was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) studies. The crystalline and porous nature of the composite was characterized by XRD and SEM analysis. The functional groups and surface characteristics were investigated by FT-IR, Raman and XPS. The major electrochemical properties of the Zr-MOF@g-C3N4 composite towards CLP detection were analyzed by CV, chronocoulometric (CC), chronoamperometric (CA) and differential pulse voltammetry (DPV) techniques. The composite exhibits a low detection limit (LOD) of 2.45 nM with a linear range of 0.02 to 2.99 µM and attractive sensitivity for CLP. The sensor system shows higher selectivity towards the possible interferences of CLP drug and exhibits better repeatability and stability. Finally, the fabricated sensor system shows a high recovery range varying from 96.2 to 98.9% towards the real samples. The proposed electrochemical probe might be a promising alternative to the prevailing diagnostic tools for the detection of CLP.

Electrical Impedance Spectroscopy with Bacterial Biofilms: Neuronal-like Behavior

Negative capacitance at low frequencies for spiking neurons was first demonstrated in 1941 (K. S. Cole) by using extracellular electrodes. The phenomenon subsequently was explained by using the Hodgkin-Huxley model and is due to the activity of voltage-gated potassium ion channels. We show that Escherichia coli (E. coli) biofilms exhibit significant stable negative capacitances at low frequencies when they experience a small DC bias voltage in electrical impedance spectroscopy experiments. Using a frequency domain Hodgkin-Huxley model, we characterize the conditions for the emergence of this feature and demonstrate that the negative capacitance exists only in biofilms containing living cells. Furthermore, we establish the importance of the voltage-gated potassium ion channel, Kch, using knock-down mutants. The experiments provide further evidence for voltage-gated ion channels in E. coli and a new, low-cost method to probe biofilm electrophysiology, e.g., to understand the efficacy of antibiotics. We expect that the majority of bacterial biofilms will demonstrate negative capacitances.

A low-cost miniature immunosensor for haemoglobin as a device for the future detection of gastrointestinal bleeding

Gastrointestinal bleeding (GIB) is a serious medical condition, which requires immediate attention to establish the cause of the bleeding. Here, we present the development of a miniaturised electrochemical impedance spectroscopy (EIS) device for the detection of GIB. The device performs EIS measurements up to 100 kHz. Following the development of an immunosensor for haemoglobin (Hb) on screen printed electrodes, the EIS device was used for detecting Hb as an early indication of bleeding. The sensor was able to detect Hb in a redox solution in a linear range between 5 μg mL-1 and 60 μg mL-1, with a limit of detection of 13.3 μg mL-1. It was also possible to detect Hb in simulated intestinal fluid, without the need for a redox solution, within a range of 10 μg mL-1 to 10 mg mL-1 with a limit of detection of 2.31 mg mL-1. The miniature EIS device developed in this work is inexpensive, with an estimated cost per unit of £30, and has shown a comparable performance to existing commercial tools, demonstrating its potential to be used in the future as an ingestible sensor to detect GIB. All these measurements were carried out in a purpose built flow cell with supporting hardware electronics outside the cell. Integration of the hardware and the sensing electrodes was demonstrated in pill form. This pill after integration sampling fluidics has potential to be used in detecting gastrointestinal bleeding.

Impedance-Readout Integrated Circuits for Electrical Impedance Spectroscopy: Methodological Review

This review article provides a comprehensive overview of impedance-readout integrated circuits (ICs) for electrical impedance spectroscopy (EIS) applications. The readout IC, a crucial component of on-chip EIS systems, significantly affects key performance metrics of the entire system, such as frequency range, power consumption, accuracy, detection range, and throughput. With the growing demand for portable, wearable, and implantable EIS systems in the Internet-of-Things (IoT) era, achieving high energy efficiency while maintaining a wide frequency range, high accuracy, wide dynamic range, and high throughput has become a focus of research. Furthermore, to enhance the miniaturization and convenience of EIS systems, many emerging systems utilize two-electrode or dry electrode configurations instead of the conventional four-electrode configuration with wet electrodes for impedance measurement. In response to these trends, various technologies have been developed to ensure reliable operations even at two- or dry-electrode interfaces. This article reviews the principles, advantages, and disadvantages of techniques employed in state-of-the-art impedance-readout ICs, aiming to achieve high energy efficiency, wide frequency range, high accuracy, wide dynamic range, low noise, high throughput, and/or high input impedance. The thorough review of these advancements will provide valuable insights into the future development of impedance-readout ICs and systems for IoT and biomedical applications.

Surface modification of nanofiltration membrane using polyoxometalates for improved separation and antifouling performance

In this study, polyoxometalates (POMs) as a core-modifying material was used to fabricate the nanofiltration (NF) membrane on the polyvinylidene fluoride (PVDF) microfiltration membrane substrate via a novel interfacial polymerization (IP) method. The formation mechanism of the POMs-modified composite membrane was proposed. The separation and antifouling properties were further investigated. After cross-linking with POMs through the new IP reaction, the modified composite membrane showed improved hydrophilicity, water flux, and salt rejection. In the humic acid fouling experiment, the POMs-modified membrane exhibited the best antifouling performance, with a flux recovery rate of up to 91.3%. Electrochemical impedance spectroscopy was further used to investigate the antifouling performance of the membranes. Nyquist and Bode plots of the POMs-modified membranes showed no significant change before and after fouling compared to the PVDF membrane substrate, indicating reduced fouling attachment on the modified membrane, which was consistent with the fouling index and flux variation observed during the fouling experiment. Our findings provide a simple and valuable route for fabricating POMs-functionalized NF membranes with desirable separation and antifouling performance.

Pathogen Detection via Impedance Spectroscopy-Based Biosensor

This paper presents the development of a miniaturized sensor device for selective detection of pathogens, specifically Influenza A Influenza virus, as an enveloped virus is relatively vulnerable to damaging environmental impacts. In consideration of environmental factors such as humidity and temperature, this particular pathogen proves to be an ideal choice for our study. It falls into the category of pathogens that pose greater challenges due to their susceptibility. An impedance biosensor was integrated into an existing platform and effectively separated and detected high concentrations of airborne pathogens. Bio-functionalized hydrogel-based detectors were utilized to analyze virus-containing particles. The sensor device demonstrated high sensitivity and specificity when exposed to varying concentrations of Influenza A virus ranging from 0.5 to 50 μg/mL. The sensitivity of the device for a 0.5 μg/mL analyte concentration was measured to be 695 Ω· mL/μg. Integration of this pathogen detector into a compact-design air quality monitoring device could foster the advancement of personal exposure monitoring applications. The proposed sensor device offers a promising approach for real-time pathogen detection in complex environmental settings.

Electrical impedance spectroscopy detects skin barrier dysfunction in childhood atopic dermatitis

BACKGROUND

Skin barrier dysfunction is associated with the development of atopic dermatitis (AD), however methods to assess skin barrier function are limited. We investigated the use of electrical impedance spectroscopy (EIS) to detect skin barrier dysfunction in children with AD of the CARE (Childhood AlleRgy, nutrition, and Environment) cohort.

METHODS

EIS measurements taken at multiple time points from 4 months to 3-year-old children, who developed AD (n = 66) and those who did not (n = 49) were investigated. Using only the EIS measurement and the AD status, we developed a machine learning algorithm that produces a score (EIS/AD score) which reflects the probability that a given measurement is from a child with active AD. We investigated the diagnostic ability of this score and its association with clinical characteristics and age.

RESULTS

Based on the EIS/AD score, the EIS algorithm was able to clearly discriminate between healthy skin and clinically unaffected skin of children with active AD (area under the curve 0.92, 95% CI 0.85-0.99). It was also able to detect a difference between healthy skin and AD skin when the child did not have active AD. There was no clear association between the EIS/AD score and the severity of AD or sensitisation to the tested allergens. The performance of the algorithm was not affected by age.

CONCLUSIONS

This study shows that EIS can detect skin barrier dysfunction and differentiate skin of children with AD from healthy skin and suggests that EIS may have the ability to predict future AD development.

Assessment of freeze damage in tuber starch with electrical impedance spectroscopy and thermodynamic, rheological, spectrographic techniques

In this study, we aimed to use electrical impedance spectroscopy (EIS) to assess the freeze-damage level of starches from potato tubers treated with multiple freezing-thawing (FT) cycles. The results showed that the relationship between the physicochemical properties of starches and the impedance characteristics of starch paste is temperature-dependent. As the temperature rises to 70-90 °C, the impedance modules show a significant correlation with the amylose and mineral contents, gelatinization and pasting properties, short-range ordered structure, relative crystallinity, and damage level within the range of 10-1 MHz (p < 0.01). This could be because FT leads to a reduction in amylose and ion content. Compared to a high level of freeze-damaged starch (FDS), a low level of FDS has less amylopectin and more amylose. Additionally, the ions could be typically evenly distributed throughout the unbranched linear amylose structure in starch paste. At the peak gelatinization temperature, the starch paste made from a low level of FDS exhibits a weakened network structure, allowing more unbound water for ion movement and enhancing electric conduction. In conclusion, EIS can predict the damage level and properties of FDS, which can benefit the frozen starchy food industry.

Phenotypic Characterization of 2D and 3D Prostate Cancer Cell Systems Using Electrical Impedance Spectroscopy

Prostate cancer is the second leading cause of death in men. A challenge in treating prostate cancer is overcoming cell plasticity, which links cell phenotype changes and chemoresistance. In this work, a microfluidic device coupled with electrical impedance spectroscopy (EIS), an electrode-based cell characterization technique, was used to study the electrical characteristics of phenotype changes for (1) prostate cancer cell lines (PC3, DU145, and LNCaP cells), (2) cells grown in 2D monolayer and 3D suspension cell culture conditions, and (3) cells in the presence (or absence) of the anti-cancer drug nigericin. To validate observations of phenotypic change, we measured the gene expression of two epithelial markers, E-cadherin (CDH1) and Tight Junction Protein 1 (ZO-1). Our results showed that PC3, DU145, and LNCaP cells were discernible with EIS. Secondly, moderate phenotype changes based on differences in cell culture conditions were detected with EIS and supported by the gene expression of CDH1. Lastly, we showed that EIS can detect chemoresistant-related cell phenotypes with nigericin drug treatment. EIS is a promising label-free tool for detecting cell phenotype changes associated with chemoresistance. Further development will enable the detection and characterization of many other types of cancer cells.

Dielectric Spectroscopy Studies of Conformational Relaxation Dynamics in Molecular Glass-Forming Liquids

We review experimental results obtained with broadband dielectric spectroscopy concerning the relaxation times and activation energies of intramolecular conformational relaxation processes in small-molecule glass-formers. Such processes are due to the interconversion between different conformers of relatively flexible molecules, and generally involve conformational changes of flexible chain or ring moieties, or else the rigid rotation of planar groups, such as conjugated phenyl rings. Comparative analysis of molecules possessing the same (type of) functional group is carried out in order to test the possibility of assigning the dynamic conformational isomerism of given families of organic compounds to the motion of specific molecular subunits. These range from terminal halomethyl and acetyl/acetoxy groups to both rigid and flexible ring structures, such as the planar halobenzene cycles or the buckled saccharide and diazepine rings. A short section on polyesters provides a generalisation of these findings to synthetic macromolecules.

Temperature-dependent dielectric relaxation and hydrophobicity of aqueous alanine using time domain reflectometry

Physical, chemical and microbiological stability of the materials is affected by the rotational and translational mobility of free and hydrated water. The role of water in areas such as protein hydration and enzyme activity, food technology, lyophilization and polymers hydration is, therefore, important and can be well understood in terms of dielectric relaxation spectroscopy. Concentration and temperature-dependent hydrophobicity of amino acid is reflected in their tendencies to appear in appropriate positions in proteins. Therefore, to gain more insights on the temperature and concentration dependence of hydrophobicity and structural properties of amino acid, dielectric relaxation of aqueous alanine have been studied in the temperature region 303.15 K to 278.15 K. Time domain spectroscopy have been used in the frequency range of 10 MHz to 30 GHz and in the concentration range 0.18708 ≤ c/M ≤ 0.74831. Two relaxation processes namely the low-frequency relaxation (l) and the high-frequency relaxation (h) has been detected for the aqueous alanine. Dielectric parameters such as static dielectric constant (εj), relaxation time (τj) dipole moments (û) and correlation factor (g) have been studied to investigate molecular interaction between alanine and water. The number of water molecules irrotationally bond by the solute molecules (Zib) was also determined to examine the hydrophobicity of alanine which was found more hydrophobic towards low temperatures and concentrations. Thermodynamic parameters calculated are also supported well for the hydrophobic behaviour of alanine towards low temperatures and concentrations.Communicated by Ramaswamy H. Sarma.

Bio-Impedance Spectroscopy of Retained Cells Using a Micro-Perforated Sensing Membrane Filtrating Whole Blood Samples under High Flowrate

Blood filtration using micro-fabricated devices is an interdisciplinary topic of research and innovation driven by clinical applications in cytapheresis, cardiovascular disease monitoring, or liquid biopsy. In this paper, we demonstrate that a micro-perforated membrane can be equipped with sensing microelectrodes for detecting, in situ and in real-time, the capture of cellular material during ex vivo filtration of whole blood under high flow rates. This work describes the fabrication process of the sift and detection microdevice. We demonstrate that reliable electrical signals can be measured in whole blood samples flowing inside a fluidic system at typical flow rates, as large as 11.5 mL/min, hence allowing for large-volume sample processing. The in situ monitoring of the electrical impedance of the microelectrodes is shown to characterize the accumulation of living circulating cells retained by the filtrating membrane, opening interesting applications for monitoring blood filtration processes.

Added value of electrical impedance spectroscopy in adjunction of colposcopy: a prospective cohort study

OBJECTIVE

To assess whether electrical impedance spectroscopy (EIS) as an adjunctive technology enhances the performance of colposcopy.

DESIGN

Prospective cohort study.

SETTING

University Hospital colposcopy clinic.

PARTICIPANTS

Colposcopy with EIS for 647 women and conventional colposcopy for 962 women.

INTERVENTIONS

Comparison of the performance of colposcopy by referral cervical cytology in two cohorts, with and without EIS as an adjunctive technology.

OUTCOME MEASURES

Prevalence of cervical intraepithelial neoplasia grade 2 or worse (CIN2+), diagnostic testing accuracy to detect CIN2+ with and without EIS and their relative differences between cohorts.

RESULTS

The prevalence of CIN2+ varied between the cohorts according to referral cytology: 17.0% after abnormal squamous cells of unknown significance referral cytology in EIS cohort and 9.1% in the reference cohort, 16.5% and 18.9% after low-grade squamous intraepithelial lesion (LSIL), 44.3% and 58.2% after atypical squamous cells, cannot exclude high-grade squamous intraepithelial lesion (HSIL) (atypical squamous cells that cannot exclude HSIL), and 81.9% and 77.0% after HSIL cytology, respectively. Sensitivity to detect CIN2+ was higher in the EIS cohort, varying from 1.79 (95% CI 1.30 to 2.45) after LSIL referral cytology to 1.16 (95% CI 1.09 to 1.23) after HSIL referral cytology, with correspondingly lower specificity after any referral cytology.

CONCLUSIONS

Colposcopy with EIS had overall higher sensitivity but lower specificity to detect CIN2+ than conventional colposcopy. CIN2+ prevalence rates were, however, not consistently higher in the EIS cohort, suggesting innate differences between the cohorts or truly lower detection rates of CIN2+ for EIS, highlighting the need for randomised controlled trials on the effectiveness of EIS.

A battery-less implantable glucose sensor based on electrical impedance spectroscopy

The ability to perform accurate continuous glucose monitoring without blood sampling has revolutionised the management of diabetes. Newer methods that can allow measurements during longer periods are necessary to substantially improve patients' quality of life. This paper presents an alternative method for glucose monitoring which is based on electrical impedance spectroscopy. A battery-less implantable bioimpedance spectroscope was designed, built, and used in an in vivo study on pigs. After a recovery period of 14 days post surgery, a total of 236 subcutaneous bioimpedance measurements obtained from intravenous glucose tolerance tests, with glucose concentration ranges between 77.4 and 523.8 mg/dL, were analyzed. The results show that glucose concentrations estimated by subcutaneous bioimpedance measurements correlate very well to the blood glucose reference values. The pigs were clinically healthy throughout the study, and the postmortem examinations revealed no signs of adverse effects related to the sensor. The implantation of the sensor requires minor surgery. The implant, being externally powered, could in principle last indefinitely. These encouraging results demonstrate the potential of the bioimpedance method to be used in future continuous glucose monitoring systems.

Development of a label-free impedimetric aptasensor for the detection of Acinetobacter baumannii bacteria

Acinetobacter baumannii (A. baumannii) is responsible for various nosocomial infections, which is known as a clinically crucial opportunistic pathogen. Therefore, rapid detection of this pathogen is critical to prevent the spread of infection and appropriate treatment. Biological detection probes, such as aptamers and synthetic receptors can be used as diagnostic layers to detect bacteria. In this work, an electrochemical aptasensor was developed for the ultrasensitive detection of A. baumannii by electrochemical impedance spectroscopy (EIS). The aptamer was immobilized on the surface of a CSPE modified with the nanocomposite Fe3O4@SiO2@Glyoxal (Gly) for selective and label-free detection of A. baumannii. The charge transfers resistance (Rct) between redox couple [Fe(CN)63-/4-] and the surface of aptasensor in the Nyquist plot of EIS study was used as electroanalytical signal for detection and determination of A. baumannii. The obtained results showed that the constructed aptasensor could specifically detect A. baumannii in the concentration range from 1.0 × 103-1.0 × 108 Colony-forming unit (CFU)/mL and with a detection limit of 150 CFU/mL (S/N = 3). In addition to its sensitivity, the biosensor exhibits high selectivity over some other pathogens. Therefore, a simple, inexpensive, rapid, label-free, selective, and sensitive electrochemical aptasensor was developed to detect A. baumannii.

Glass transition phenomena and dielectric relaxations in supercooled d-lyxose aqueous solutions

Differential scanning calorimeter and broadband dielectric spectroscopy in a broad range of temperatures (150-300 K) were employed to study the d-lyxose aqueous mixture at different hydration levels. Two relaxation processes were observed in all investigated d-lyxose aqueous mixtures. A relaxation process (process-I) usually known as the primary relaxation mode which is accountable for the collective motion of d-lyxose aqueous solution, was observed above the glass transition temperature (Tg). Below Tg, another process designated as process-II was found which is mainly related to the water molecule relaxation inside the d-lyxose matrix. The average relaxation times as a function of temperature and dielectric strengths of both observed relaxation processes (I & II) were analyzed for all hydration levels in d-lyxose. It was identified that the relaxation amplitude of process-II in the d-lyxose aqueous mixture was increased drastically and their activation energies were found to be approximately independent of the content of water above critical concentration, xc = 0.28. This suggests that the dynamical process observed above xc was dominated by the presence of water clusters. In the current aqueous mixture, the critical content of water (xc) is slightly higher as compared to previously reported aqueous mixtures, indicating a more cooperative nature of water molecules with a d-lyxose matrix. Additionally, the Tg of pure water was estimated at 128 ± 5.8 K from the extrapolation of DSC Tg data of the d-lyxose aqueous solution by using the well-known Gordon-Taylor equation. Our current result gives further support to the well-accepted glass transition (Tg) of pure water.

Full-electric microfluidic platform to capture, analyze and selectively release single cells

Current single-cell technologies require large and expensive equipment, limiting their use to specialized labs. In this paper, we present for the first time a microfluidic device which demonstrates a combined method for full-electric cell capturing, analyzing, and selectively releasing with single-cell resolution. All functionalities are experimentally demonstrated on Saccharomyces cerevisiae. Our microfluidic platform consists of traps centered around a pair of individually accessible coplanar electrodes, positioned under a microfluidic channel. Using this device, we validate our novel Two-Voltage method for trapping single cells by positive dielectrophoresis (pDEP). Cells are attracted to the trap when a high voltage (VH) is applied. A low voltage (VL) holds the already trapped cell in place without attracting additional cells, allowing full control over the number of trapped cells. After trapping, the cells are analyzed by broadband electrochemical impedance spectroscopy. These measurements allow the detection of single cells and the extraction of cell parameters. Additionally, these measurements show a strong correlation between average phase change and cell size, enabling the use of our system for size measurements in biological applications. Finally, our device allows selectively releasing trapped cells by turning off the pDEP signal in their trap. The experimental results show the techniques potential as a full-electric single-cell analysis tool with potential for miniaturization and automation which opens new avenues towards small-scale, high throughput single-cell analysis and sorting lab-on-CMOS devices.

An electrochemical sensor based on CS-MWCNT and AuNPs for the detection of mycophenolic acid in plasma

For patients receiving organ transplants, monitoring the blood concentration of MPA can provide timely information on whether MPA has reached the effective therapeutic window to better function while reducing the incidence of rejection or adverse reactions. In this study, an electrochemical sensor for the detection of MPA was built using a nanocomposite made of CS-MWCNT and AuNPs. At the same time, the high performance liquid phase (HPLC) method for MPA was established and compared with this sensor. The surface morphology, structure, and roughness of the material on the electrode were characterized by scanning electron microscopy (SEM), Fourier transforms infrared spectroscopy (FTIR), and atomic force microscopy (AFM). In addition, the electrochemical behavior of the modified electrode was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The standard curve was obtained in blank plasma, not pure buffer solution. The peak current was linearly related to the MPA concentration in the linear range of 0.001-0.1 mM with a detection limit of 0.05 μM and good anti-interference ability. Moreover, the sensor was employed with success for the determination of MPA in rat plasma with good recovery. The electrochemical sensor presented here is eco-friendly, and sensitive, and offers a great possibility for practical applicability.

Determination of urea, phosphate, and potassium in agricultural runoff waters using electrochemical impedance spectroscopy

Large-scale use of chemical fertilizers has resulted in the contamination of agricultural runoff waters by soil macronutrients NPK, whose detection is of significant interest. This work reports the determination of macronutrients in the form of urea (N), orthophosphate PO43- (P), and potassium K+ (K) in simulated agricultural runoff waters. Their solutions were prepared by extracting water-soluble constituents of soil. This 'base' solution contains high concentrations of various species, including Cl-, SO42-, NO3-, PO43-, Na+, K+, and NH4+ along with natural organic matter. Predetermined amounts of urea (4 to 22.5 ppm), PO43- (7 to 50 ppm), and potassium K+ (25 to 250 ppm) were added to the base simulated runoff water to prepare standard stock solutions. Using stainless steel working and counter electrodes, a small AC perturbation (±10 mV vs. OCP, vs. Ag/AgCl) was applied and the frequency response of the working electrode-solution interface was measured from 1 Hz to 1 MHz. The interface itself was modeled as a suitable equivalent electrical circuit, and the magnitudes of its components were fitted from experimental data using nonlinear regression. It is observed that PO43- concentration is a linear function of charge transfer resistance arising from redox reaction, K+ concentration is a quadratic function of double-layer capacitance arising from its higher mobility, and urea concentration can be correlated as a linear function of constant phase element arising from its polarization in the presence of an applied electric field. The sensor exhibits good sensitivity, repeatability, and excellent performance against interfering species. These preliminary results show significant potential for development of a real-time or on-site sensing device.

Structural and impedance spectroscopic investigations of eco-friendly alkali phosphoborate glass-ceramics containing zirconium ion

Glass-ceramics with novel composition xZrO2.7P2O5.19CaO.24Na2O.(50-x)B2O3 (x = 0, 2, 4, 6, and 8 mol%) have been synthesized using melt quench technique. The synthesized compositions were characterized and analyzed by X-ray diffraction, field emission scanning electron microscopy, infrared absorption, and impedance spectroscopy. X-ray diffraction profiles of prepared samples confirm the existence of phases corresponding to Na3Ca6(PO4)5 crystal (with crystallite size ~ 23 nm). Infrared absorbance spectra reveal the presence of phosphate and borate units (PO3, PO4, BO3, BO4) in the glass matrix. Different dielectric parameters such as dielectric loss, electric modulus, and tangent loss were evaluated. Their variations with temperature and frequency confirm the non- Debye relaxation behavior of prepared samples. A phenomenal description of the capacitive behavior was studied by considering the circuit having a parallel combination of constant phase element and bulk resistance. The conduction is found to be governed by overlapping large polaron tunneling (OLPT) and follow OLPT model. The results indicate that ZrO2 substituted alkali phosphoborate glass-ceramics can be used as eco-friendly and safe dielectric materials.

Calibration-Free, Seconds-Resolved In Vivo Molecular Measurements using Fourier-Transform Impedance Spectroscopy Interrogation of Electrochemical Aptamer Sensors

Electrochemical aptamer-based (EAB) sensors are capable of measuring the concentrations of specific molecules in vivo, in real time, and with a few-second time resolution. For their signal transduction mechanism, these sensors utilize a binding-induced conformational change in their target-recognizing, redox-reporter-modified aptamer to alter the rate of electron transfer between the reporter and the supporting electrode. While a variety of voltammetric techniques have been used to monitor this change in kinetics, they suffer from various drawbacks, including time resolution limited to several seconds and sensor-to-sensor variation that requires calibration to remove. Here, however, we show that the use of fast Fourier transform electrochemical impedance spectroscopy (FFT-EIS) to interrogate EAB sensors leads to improved (here better than 2 s) time resolution and calibration-free operation, even when such sensors are deployed in vivo. To showcase these benefits, we demonstrate the approach's ability to perform real-time molecular measurements in the veins of living rats.

A Facile Method for the Fabrication of the Microneedle Electrode and Its Application in the Enzymatic Determination of Glutamate

Herein, a simple method has been used in the fabrication of a microneedle electrode (MNE). To do this, firstly, a commercial self-dissolving microneedle patch has been used to make a hard-polydimethylsiloxane-based micro-pore mold (MPM). Then, the pores of the MPM were filled with the conductive platinum (Pt) paste and cured in an oven. Afterward, the MNE made of platinum (Pt-MNE) was characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). To prove the electrochemical applicability of the Pt-MNE, the glutamate oxidase enzyme was immobilized on the surface of the electrode, to detect glutamate, using the cyclic voltammetry (CV) and chronoamperometry (CA) methods. The obtained results demonstrated that the fabricated biosensor could detect a glutamate concentration in the range of 10-150 µM. The limits of detection (LODs) (three standard deviations of the blank/slope) were also calculated to be 0.25 µM and 0.41 µM, using CV and CA, respectively. Furthermore, the Michaelis-Menten constant (KMapp) of the biosensor was calculated to be 296.48 µM using a CA method. The proposed biosensor was finally applied, to detect the glutamate concentration in human serum samples. The presented method for the fabrication of the mold signifies a step further toward the fabrication of a microneedle electrode.

Microwave hydrothermal preparation of reduced graphene oxide-induced p-AgO/n-MoO3 heterostructures for enhanced photocatalytic activity through S-scheme mechanism and its electronic performance

Through a powerful and modest closed system Microwave hydrothermal process, a methodological analysis is made in the rational synthesis of the reduced graphene oxide-induced p-AgO/n-MoO3 (RGAM) heterostructures. These have strong p-n junction heterostructures with considerable electron-hole recombination functioning as solar catalysts. The enhanced photocatalytic activity through the plasmonic step scheme (S-scheme mechanism) describes the effective charge recombination process. The energy band positions, bandgap, and work function are determined to understand the Fermi level shifts; this describes the S-scheme mechanism by UPS analysis which assessed an electron transfer between AgO and MoO3, yielding work function values of 6.34 eV and 6.62eV, respectively. This photocatalytic activity aids in dye removal by 94.22%, and heavy metals such as chromium (Cr) are eliminated by the surface action of sunlight on the produced material during solar irradiation. Electrochemical studies such as photocurrent response, cyclic voltammogram, and electrochemical impedance spectroscopy for RGAM heterostructures were also carried out. The study helps to broaden the search for and development of new hybrid carbon composites for electrochemical applications.

A Multimodality Electrochemical and Impedance Spectroscopy System-on-a-Chip With Temperature Sensing and Impedance-Boosting Techniques

This article presents a multimodal electrochemical sensing system-on-chip (SoC), including the functions of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and temperature sensing. CV readout circuitry achieves an adaptive readout current range of 145.5 dB through an automatic range adjustment and resolution scaling technique. EIS has an impedance resolution of 9.2 m Ω/√ Hz at a sweep frequency of 10 kHz and an output current of up to 120 μA. With an impedance boost mechanism, the maximum detectable load impedance is extended to 22.95 k Ω, while the total harmonic distortion is less than 1%. A resistor-based temperature sensor using a swing-boosted relaxation oscillator can achieve a resolution of 31 mK in 0-85 °C. The design is implemented in a 0.18 μm CMOS process. The total power consumption is 1 mW.

Electrochemical Impedance Spectroscopy-Based Sensing of Biofilms: A Comprehensive Review

Biofilms are complex communities of microorganisms that can form on various surfaces, including medical devices, industrial equipment, and natural environments. The presence of biofilms can lead to a range of problems, including infections, reduced efficiency and failure of equipment, biofouling or spoilage, and environmental damage. As a result, there is a growing need for tools to measure and monitor levels of biofilms in various biomedical, pharmaceutical, and food processing settings. In recent years, electrochemical impedance sensing has emerged as a promising approach for real-time, non-destructive, and rapid monitoring of biofilms. This article sheds light on electrochemical sensing for measuring biofilms, including its high sensitivity, non-destructive nature, versatility, low cost, and real-time monitoring capabilities. We also discussed some electrochemical sensing applications for studying biofilms in medical, environmental, and industrial settings. This article also presents future perspectives for research that would lead to the creation of reliable, quick, easy-to-use biosensors mounted on unmanned aerial vehicles (UAVs), and unmanned ground vehicles (UGVs), utilizing artificial intelligence-based terminologies to detect biofilms.

Multi-Walled Carbon Nanotube Array Modified Electrode with 3D Sensing Interface as Electrochemical DNA Biosensor for Multidrug-Resistant Gene Detection

Drug resistance in cancer is associated with overexpression of the multidrug resistance (MDR1) gene, leading to the failure of cancer chemotherapy treatment. Therefore, the establishment of an effective method for the detection of the MDR1 gene is extremely crucial in cancer clinical therapy. Here, we report a novel DNA biosensor based on an aligned multi-walled carbon nanotube (MWCNT) array modified electrode with 3D nanostructure for the determination of the MDR1 gene. The microstructure of the modified electrode was observed by an atomic force microscope (AFM), which demonstrated that the electrode interface was arranged in orderly needle-shaped protrusion arrays. The electrochemical properties of the biosensor were characterized by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS). Chronocoulometry (CC) was used for the quantitative detection of the MDR1 gene. Taking advantage of the good conductivity and large electrode area of the MWCNT arrays, this electrochemical DNA sensor achieved a dynamic range from 1.0 × 10-12 M to 1.0 × 10-8 M with a minimal detection limit of 6.4 × 10-13 M. In addition, this proposed DNA biosensor exhibited high sensitivity, selectivity, and stability, which may be useful for the trace analysis of the MDR1 gene in complex samples.

Graphene loaded TiO2 submicron spheres scattering layer for efficient dye-sensitized solar cell

Dye-Sensitized Solar Cells (DSSCs) have attracted great attention due to environmentally friendly low-cost processing, excellent working ability in diffuse light, and potential to meet the power demands of future buildings due the true class of building integrated photovoltaics (BIPV). Nevertheless, DSSCs have relatively low photoconversion efficiency (PCE) due to multiple issues. Several strategies have been employed to enhance its PCE. For instance, bi-layered structure of photoelectrode i.e., mesoporous TiO₂ transparent layer with top scattering layer was introduced which scatter light inside on large angles improves the harvesting ability of photoelectrode thus enhanced PCE. However, scattering layer is composed of aggregated small particles which offer sluggish electron transport due to multiple grain boundaries, consequently, unwanted recombination reaction which leads to poor PCE. This issue has been addressed for transparent layer immensely but ignored for scattering layer. Mostly for scattering layer in previous studies novel structures have been proposed to enhance scattering properties and dye adsorption only. Therefore, in this study for the first time presenting dual functional graphene/TiO₂ scattering layer in which solvent exfoliated graphene is incorporated in TiO₂ submicron spheres which enhanced electron transport properties, while submicron spheres scatter light effectively. Scattering and electron transport characteristics of DSSCs are thoroughly investigated with the function of graphene loading. Electrochemical impedance spectroscopy (EIS) has revealed that diffusion coefficient length and coefficient and conductivity attained maximum value at 0.01 wt%. while other important parameters such as electron lifetime and electron density in conduction band have been improved till 0.020 wt% graphene loading. However, results indicated that with 0.01 w% graphene 33% higher PCE was achieved than without scattering layer and 13% higher than scattering layer without graphene. The depraving in PCE at >0.01 wt% graphene despite of excellent electron transport improvement is attributed to the loss of diffuse reflectance and higher optical absorption by graphene.

Organ-on-a-chip with integrated semitransparent organic electrodes for barrier function monitoring

Organs-on-a-chip (OoC) are cell culture platforms that replicate key functional units of tissues in vitro. Barrier integrity and permeability evaluation are of utmost importance when studying barrier-forming tissues. Impedance spectroscopy is a powerful tool and is widely used to monitor barrier permeability and integrity in real-time. However, data comparison across devices is misleading due to the generation of a non-homogenous field across the tissue barrier, making impedance data normalization very challenging. In this work, we address this issue by integrating PEDOT:PSS electrodes for barrier function monitoring with impedance spectroscopy. The semitransparent PEDOT:PSS electrodes cover the entire cell culture membrane providing a homogenous electric field across the entire membrane making the cell culture area equally accountable to the measured impedance. To the best of our knowledge, PEDOT:PSS has never been used solely to monitor the impedance of cellular barriers while enabling optical inspection in the OoC. The performance of the device is demonstrated by lining the device with intestinal cells where we monitored barrier formation under flow conditions, as well as barrier disruption and recovery under exposure to a permeability enhancer. The barrier tightness and integrity, and the intercellular cleft have been evaluated by analyzing the full impedance spectrum. Furthermore, the device is autoclavable paving the way toward more sustainable OoC options.

Measuring the effects of diethyl phthalate microplastics on marine algae growth using dielectric spectroscopy

This paper presents the development of a dielectric spectroscopy-based method using a customized, transmission line probe, fabricated on a printed circuit board (PCB), for monitoring the effect of diethyl phthalate (DEP) microplastics on marine algae growth. Experiments were performed by exposing marine algae (Chlorella pyrenoidosa) to DEP (0-50 mg) for up to 6 days. In order to amplify the electrophysiological effects and improve the sensing, a glutaraldehyde crosslinking agent was used and encapsulated on the surface of the probe. The reflection coefficient (S₁₁) and the complex permittivity (ɛ' & ɛ″) of the Medium Under Test (MUT) were investigated in the frequency range of 30 kHz-800 MHz. Without the presence of DEP, the number of algae (10⁴ cells/mL) and chlorophyll content (mg/L) increased at the rates of 207.73 × 10⁴ cells/mL and 148.1 mg/L per day, respectively. After 6 days of exposing Chlorella pyrenoidosa (C. pyrenoidosa) algae to different DEP concentrations, the growth rate decreased down to -11.92 × 10⁴ cells/mL and -19.19 mg/L (50 mg DEP), respectively. Additionally, the linearity of the relationship kept decreasing as the DEP content increased from R² = 0.9716 to R² = 0.1050 and from R² = 0.9293 to R² = 0.4961, respectively. Dielectric spectroscopy using the custom, transmission line probe, at 740 MHz, showed linear relationship (-1.22 dB/day) between the reflection coefficient (S₁₁) and hence complex permittivity (ɛ' & ɛ″) without the presence of DEP. However, as the DEP content increased, algae growth was prohibited more intensely, shown both from the number of algae and the chlorophyll content. This trend was reflected on S₁₁ and subsequently on the complex permittivity. This relationship confirms the capability of this method to monitor the growth of marine algae in almost real-time. This dielectric spectroscopy method could be a potential, low-cost tool to examine the impact of microplastic pollutants on marine microorganisms.

Electrochemical detection of enrofloxacin in meat using bimetallic organic framework-derived NiCo2O4@NiO

A novel electrochemical aptasensor based on a bimetallic organic frame-derived carbide nanostructure of Co and Ni (NiCo₂O₄@NiO) was prepared for rapid and sensitive enrofloxacin (ENR) detection of sheep and pork liver meats. The composite was fabricated by solvothermal and direct pyrolysis methods and dropped onto a modified electrode to improve the electron transfer efficiency. Furthermore, different techniques such as scanning electron microscopy and X-ray photoelectron spectroscopy were used to characterize the morphology and structure of the materials. Electrochemical impedance spectroscopy and cyclic voltammetry were used to evaluate the performance of the electrochemical sensor. As a result, the electrochemical aptasensor based on NiCo₂O₄@NiO exhibited excellent sensing performances for ENR with an extremely low detection limit of 1.67 × 10^-2 pg mL^-1 and a broad linear range of 5 × 10^-2 to 5 × 10⁴ pg mL^-1, as well as great selectivity, excellent reproducibility, high stability and applicability. In addition, the relative standard deviation for real samples was in the range of 93.83 to 100.09% and 94.95 to 100.01% for sheep and pork liver. The results showed that the composite can be expected to greatly facilitate ENR detection and practical applications in harmful food due to the advantages of simple fabrication, controllable, large-area uniformity, environmental friendliness, and trace detection.

Highly selective electrochemical impedance spectroscopy-based graphene electrode for rapid detection of microplastics

The widespread occurrence of microplastics (MPs) in aquatic ecosystems that caused environmental pollution has attracted worldwide attention. Herein, graphene electrode was initially derived from petroleum waste. Then the electrochemical responses of the electrode were evaluated using electrochemical impedance spectroscopy (EIS) toward polystyrene (PS) under various optimum conditions. For the quantitative measurement of PS concentration, principal component analysis (PCA) score images displayed that the data points offered the best discrimination of the classes, and singular value decomposition (SVD) showed that a good linearity was achieved between Z"u(1) and lgC_ps in the concentration range of 0.01-25 mg L^-1. Especially for PS with particle size of 1 μm, the highest correlation coefficient (R² = 0.9914) was obtained. The sensor ability to determine the polystyrene concentration in real samples was evaluated with the recovery of 98.4-113.3 % and reliable reproducibility (RSD < 9.72 %). For the quantitative measurement of the particle size of PS, SVD images exhibited that a linearity was obtained between Z'u(1)and lgD_ps in the particle size range of 0.08-20 μm. A good linearity with R² = 0.9877 was obtained when the concentration was 1 mg L^-1. The recovery was in the range of 100.8-118.0 % with the RSD < 6.38 %. Therefore, a novel method is established for the rapid detection of PS MPs.

Novel Sensing Technique for Stem Cells Differentiation Using Dielectric Spectroscopy of Their Proteins

Dielectric spectroscopy (DS) is the primary technique to observe the dielectric properties of biomaterials. DS extracts complex permittivity spectra from measured frequency responses such as the scattering parameters or impedances of materials over the frequency band of interest. In this study, an open-ended coaxial probe and vector network analyzer were used to characterize the complex permittivity spectra of protein suspensions of human mesenchymal stem cells (hMSCs) and human osteogenic sarcoma (Saos-2) cells in distilled water at frequencies ranging from 10 MHz to 43.5 GHz. The complex permittivity spectra of the protein suspensions of hMSCs and Saos-2 cells revealed two major dielectric dispersions, β and γ, offering three distinctive features for detecting the differentiation of stem cells: the distinctive values in the real and imaginary parts of the complex permittivity spectra as well as the relaxation frequency in the β-dispersion. The protein suspensions were analyzed using a single-shell model, and a dielectrophoresis (DEP) study was performed to determine the relationship between DS and DEP. In immunohistochemistry, antigen-antibody reactions and staining are required to identify the cell type; in contrast, DS eliminates the use of biological processes, while also providing numerical values of the dielectric permittivity of the material-under-test to detect differences. This study suggests that the application of DS can be expanded to detect stem cell differentiation.

Fabrication of a Novel CNT-COO-/Ag3PO4@AgIO4Composite with Enhanced Photocatalytic Activity under Natural Sunlight

In this study, a carboxylated carbon nanotube-grafted Ag₃PO₄@AgIO₄ (CNT-COO^-/Ag₃PO₄@AgIO₄) composite was synthesized through an in situ electrostatic deposition method. The synthesized composite was characterized by Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflectance spectroscopy (DRS), and energy-dispersive X-ray spectroscopy (EDS). The electron transfer ability of the synthesized composite was studied using electrochemical impedance spectroscopy (EIS). The CNT-COO^-/Ag₃PO₄@AgIO₄ composite exhibited higher activity than CNT/Ag₃PO₄@AgIO₄, Ag₃PO₄@AgIO₄, and bare Ag₃PO₄. The material characterization and the detailed study of the various parameters thataffect the photocatalytic reaction revealed that the enhanced catalytic activity is related to the good interfacial interaction between CNT-COO and Ag₃PO₄. The energy band structure analysis is further considered as a reason for multi-electron reaction enhancement. The results and discussion in this study provide important information for the use of the functionalized CNT-COOH in the field of photocatalysis. Moreover, providinga new way to functionalize CNT viadifferent functional groups may lead to further development in the field of photocatalysis. This work could provide a new way to use natural sunlight to facilitate the practical application of photocatalysts toenvironmental issues.

Electrical impedance spectroscopy significantly enhances correct biopsy choice for pigmented skin lesions beyond clinical evaluation and dermoscopy

The purpose of this study was to investigate whether EIS technology can further improve correct biopsy choices beyond clinical and dermoscopic evaluation for melanoma (MM), severe dysplastic nevi (SDN) and benign PSLs. Images of 49 MMs, SDNs and benign PSLs were randomly selected from a prior study and were provided in a reader-type survey study to dermatologists to evaluate for biopsy. A total of 33,957 biopsy decisions were analyzed. Respondents significantly improved on the correct biopsy choice with the addition of dermoscopy versus clinical image alone for melanoma and severely dysplastic nevi. Respondents also showed a statistically significant improvement in correct biopsy choice beyond their dermoscopic evaluation when integrating the EIS score versus dermoscopy with clinical images for MM, SDN and benign lesions. Respondents also made fewer incorrect biopsy choices with the addition of the EIS score versus dermoscopy and clinical image for MM and benign lesions. Sub-analyses of biopsy choices were also conducted based on experience and practice type. The findings from this study demonstrate that the integration of EIS technology into PSL biopsy decisions has the potential to significantly improve the accuracy of lesion selection for biopsy beyond clinical and dermoscopic evaluation alone.

Improved Tool for Predicting Skin Irritation on Reconstructed Human Epidermis Models Based on Electrochemical Impedance Spectroscopy

The rabbit skin irritation test has been the standard for evaluating the irritation potential of chemicals; however, alternative methods that do not use animal testing are actively encouraged. Reconstructed human epidermis (RhE) models mimic the biochemical and physiological properties of the human epidermis and can be used as an alternative method. On RhE methods, the metabolic activity of RhE models is used to predict skin irritation, with a reduction in metabolic activity indicating a reduced number of viable cells and linking cell death to skin irritation processes. However, new challenges have emerged as the use of RhE models increases, including the need for non-invasive and marker-free methodologies to assess cellular states. Electrochemical impedance spectroscopy (EIS) is one such methodology that can meet these requirements. In this study, our results showed that EIS can differentiate between irritant and non-irritant chemicals, with a significant increase in the capacitance values observed in the irritant samples. A ROC curve analysis showed that the prediction method based on EIS met OECD TG 439 requirements at all time points and had 95% within-laboratory reproducibility. Comparison with the MTT viability assay showed that prediction using EIS achieved higher sensitivity, specificity, and accuracy. These results suggest that EIS could potentially replace animal testing in the evaluation of irritation potential and could be a valuable addition to in vitro testing strategies.

Single-Cell Classification Based on Population Nucleus Size Combining Microwave Impedance Spectroscopy and Machine Learning

Many recent efforts in the diagnostic field address the accessibility of cancer diagnosis. Typical histological staining methods identify cancer cells visually by a larger nucleus with more condensed chromatin. Machine learning (ML) has been incorporated into image analysis for improving this process. Recently, impedance spectrometers have been shown to generate all-inclusive lab-on-a-chip platforms to detect nucleus abnormities. In this paper, a wideband electrical sensor and data analysis paradigm that can identify nuclear changes shows the realization of a single-cell microfluidic device to detect nuclei of altered sizes. To model cells of altered nucleus, Jurkat cells were treated to enlarge or shrink their nucleus followed by broadband sensing to obtain the S-parameters of single cells. The ability to deduce important frequencies associated with nucleus size is demonstrated and used to improve classification models in both binary and multiclass scenarios, despite a heterogeneous and overlapping cell population. The important frequency features match those predicted in a double-shell circuit model published in prior work, demonstrating a coherent new analytical technique for electrical data analysis. The electrical sensing platform assisted by ML with impressive accuracy of cell classification looks forward to a label-free and flexible approach to cancer diagnosis.

Design of electrical impedance spectroscopy sensing surgical drill using computational modelling and experimental validation

Electrical Impedance Spectroscopy (EIS) sensing surgical instruments could provide valuable and real-time feedback to surgeons about hidden tissue boundaries, therefore reducing the risk of iatrogenic injuries. In this paper, we present an EIS sensing surgical drill as an example instrument and introduce a strategy to optimize the mono-polar electrode geometry using a finite element method (FEM)-based computational model and experimental validation. An empirical contact impedance model and an adaptive mesh refinement protocol were developed to accurately preserve the behaviour of sensing electrodes as they approach high impedance boundaries. Specifically, experiments with drill-bit, cylinder, and conical geometries suggested a 15%-35% increase in resistance as the sensing electrode approached a high impedance boundary. Simulations achieved a maximum mean experiment-to-simulation mismatch of +1.7% for the drill-bit and +/-11% range for other electrode geometries. The simulations preserved the increase in resistance behaviour near the high impedance boundary. This highly accurate simulation framework allows us a mechanism for optimizing sensor geometry without costly experimental evaluation.

Gold Leaf-Based Microfluidic Platform for Detection of Essential Oils Using Impedance Spectroscopy

Drug delivery systems are engineered platforms for the controlled release of various therapeutic agents. This paper presents a conductive gold leaf-based microfluidic platform fabricated using xurography technique for its potential implication in controlled drug delivery operations. To demonstrate this, peppermint and eucalyptus essential oils (EOs) were selected as target fluids, which are best known for their medicinal properties in the field of dentistry. The work takes advantage of the high conductivity of the gold leaf, and thus, the response characteristics of the microfluidic chip are studied using electrochemical impedance spectroscopy (EIS) upon injecting EOs into its micro-channels. The effect of the exposure time of the chip to different concentrations (1% and 5%) of EOs was analyzed, and change in electrical resistance was measured at different time intervals of 0 h (the time of injection), 22 h, and 46 h. It was observed that our fabricated device demonstrated higher values of electrical resistance when exposed to EOs for longer times. Moreover, eucalyptus oil had stronger degradable effects on the chip, which resulted in higher electrical resistance than that of peppermint. 1% and 5% of Eucalyptus oil showed an electrical resistance of 1.79 kΩ and 1.45 kΩ at 10 kHz, while 1% and 5% of peppermint oil showed 1.26 kΩ and 1.07 kΩ of electrical resistance at 10 kHz respectively. The findings obtained in this paper are beneficial for designing suitable microfluidic devices to expand their applications for various biomedical purposes.

Cervical Tissue Hydration Level Monitoring by a Resonant Microwave Coaxial Probe

Cervical tissue hydration level is one of the most important parameters to monitor in the early diagnosis of preterm birth. Electrical-impedance-spectroscopy-based techniques are often used, but they suffer from limited accuracy. Open microwave coaxial probes have been widely used as a broadband dielectric characterization technique for human tissue samples due to their versatility, but with limited accuracy due to their nonresonant nature. In this work, a resonant microwave open coaxial probe with multiple harmonic resonances is proposed as a sensing platform for tissue-hydration-level monitoring. The mechanical design was analyzed and verified by finite-element full 3D electromagnetic simulation and experiments. Dominant sources of errors and the ways to mitigate them were discussed. In vitro experiments were carried out on human cervix samples to verify the precision and accuracy by comparing the results to a commercial skin-hydration sensor. The proposed sensor shows mean fractional frequency shift of (3.3 ± 0.3) × 10^-4 per unit % over the entire data. This translates into an absolute frequency shift (ΔfN) of 252 ± 23 kHz/%, 455 ± 41 kHz/%, and 647 ± 57 kHz/% at second, fourth, and sixth harmonic resonance, respectively.

Measurement System for Piezoelectric Resonance Impedance Spectroscopy Under Combined AC and High-Voltage DC Loading

Piezoelectric resonance impedance spectroscopy is a standardized measurement technique for determining the electromechanical, elastic, and dielectric parameters of piezoceramics. However, commercial measurement setups are designed for small-signal measurements and encounter difficulties when constant driving voltages/currents are required at resonances, higher fields, or combined AC and DC loading. The latter is particularly important to evaluate the DC bias-hardening effect of piezoelectrics. Here, we propose a novel measurement system for piezoelectric resonance impedance spectroscopy under combined AC and high-voltage DC loading that complies with established standards. The system is based on two separate output amplifier stages and includes voltage/current probes, a laser vibrometer, custom protection components, and control software with optimization algorithm. In its current form, the measurement setup allows the application of AC frequencies up to 500 kHz and DC signals up to ±10 kV on samples with impedance between 10-1 and 10⁶ Ω . The operation of the proposed setup was benchmarked against commercial impedance analyzers in the small-signal range and reference equivalent circuits. Test measurements under combined AC and DC loading were performed on a soft Pb(Zr,Ti)O3 piezoceramic. The results revealed that a DC bias voltage applied along the polarization direction ferroelectrically hardens the material, while the material softens and eventually depolarizes when the DC bias voltage is applied in the opposite direction. The results confirm the suitability of the designed measurement system and open new exciting possibilities for tuning the piezoelectric properties by DC bias fields.

An Experimental Framework for Developing Point-of-Need Biosensors: Connecting Bio-Layer Interferometry and Electrochemical Impedance Spectroscopy

Biolayer interferometry (BLI) is a well-established laboratory technique for studying biomolecular interactions important for applications such as drug development. Currently, there are interesting opportunities for expanding the use of BLI in other fields, including the development of rapid diagnostic tools. To date, there are no detailed frameworks for implementing BLI in target-recognition studies that are pivotal for developing point-of-need biosensors. Here, we attempt to bridge these domains by providing a framework that connects output(s) of molecular interaction studies with key performance indicators used in the development of point-of-need biosensors. First, we briefly review the governing theory for protein-ligand interactions, and we then summarize the approach for real-time kinetic quantification using various techniques. The 2020 PRISMA guideline was used for all governing theory reviews and meta-analyses. Using the information from the meta-analysis, we introduce an experimental framework for connecting outcomes from BLI experiments (KD, kon, koff) with electrochemical (capacitive) biosensor design. As a first step in the development of a larger framework, we specifically focus on mapping BLI outcomes to five biosensor key performance indicators (sensitivity, selectivity, response time, hysteresis, operating range). The applicability of our framework was demonstrated in a study of case based on published literature related to SARS-CoV-2 spike protein to show the development of a capacitive biosensor based on truncated angiotensin-converting enzyme 2 (ACE2) as the receptor. The case study focuses on non-specific binding and selectivity as research goals. The proposed framework proved to be an important first step toward modeling/simulation efforts that map molecular interactions to sensor design.

Electric Impedance Spectroscopy in Trees Condition Analysis: Theory and Experiment

Electric impedance spectroscopy is an alternative technology to existing methods that shows promising results in the agro-food industry and plant physiology research. For example, this technology makes it possible to monitor the condition of plants, even in the early stages of development, and to control the quality of finished products. However, the use of electric impedance spectroscopy is often associated with the need to organize special laboratory conditions for measurements. Our aim is to extract information about the state of health of the internal tissues of a plant's branches from impedance measurements. Therefore, we propose a new technique using the device and model developed by us that makes it possible to monitor the condition of tree branch tissues in situ. An apple tree was chosen as the object under study, and the dependence of the impedance of the apple tree branch on the signal frequency and branch length was analyzed. The change in the impedance of an apple tree branch during drying was also analyzed. It was shown that, when a branch dries out, the conductivity of the xylem mainly decreases. The developed technique was also applied to determine the development of the vascular system of an apple tree after grafting. It was shown that the processing of the scion and rootstock sections with the help of cold atmospheric plasma and a plasma-treated solution contributes to a better formation of graft unions.

Scalable two-tier protruding micro-/nano-optoelectrode arrays with hybrid optical-electrical modalities by hierarchical modular design

In situ spatiotemporal characterization of correlated bioelectrical and biochemical processes in living multicellular systems remains a formidable challenge but can offer crucial opportunities in biology and medicine. A promising approach is to develop bio-interfaced multifunctional micro-/nano-sensor arrays with complementary biophotonic-bioelectronic modalities and biomimetic topology to achieve combined bioelectrical and biochemical detection and tight device-cell coupling. However, a system-level engineering strategy is still missing to create multifunctional micro-/nano-sensor arrays that meet the multifaceted design requirements for in situ spatiotemporal characterizations of living systems. Here, we demonstrate a hierarchical modular design and fabrication approach to develop scalable two-tier protruding micro-/nano-optoelectrode arrays that extend the design space of biomimetic micro-/nano-pillar topology, plasmonic nanoantenna-based biophotonic function in surface-enhanced Raman spectroscopy (SERS), and micro-/nano-electrode-based bioelectronics function in electrochemical impedance spectroscopy (EIS). Notably, two-tier protruding micro-/nano-optoelectrode arrays composed of nanolaminate nanoantenna arrays on top of micropillar electrode arrays can support plasmonic nanocavity modes with high SERS enhancement factors (≈10⁶) and large surface-to-volume ratio with significantly reduced interfacial impedance in EIS measurements. We envision that scalable two-tier protruding micro-/nano-optoelectrode arrays can potentially serve as bio-interfaced multifunctional micro-/nano-sensor arrays for in situ correlated spatiotemporal bioelectrical-biochemical measurements of living multicellular systems such as neuronal network cultures, cancerous organoids, and microbial biofilms.