Gold nanourchin enhances detection of Alzheimer's disease biomarker "miRNA-137" on dual electrode sensing surface

Diagnosis of Alzheimer's disease (AD) is a complex task, and at present, neuroimaging such as magnetic resonance imaging and positron emission tomography is commonly used for the diagnosis of AD. This research work developed a new biosensing method with gold nanomaterial to identify AD biomarker of miRNA-137. Gold nanourchin (GNU) was attached on the interdigitated electrode through the silane linker and COOH-ended capture oligonucleotide was immobilized on the GNU surface. This surface helps to quantify the target sequence of miRNA-137 and the detection limit reached to 0.01 pM on the linear range of 0.01-100 pM. With 3δ calculation on the linearity, the determination coefficient was noticed as y = 1.2867x - 2.2697; R²  = 0.9059. The control performances did not show a significant response, indicating the specific identification of target.

Hydration Assessment Using the Bio-Impedance Analysis Method

Body hydration is considered one of the most important physiological parameters to measure and one of the most challenging. Current methods to assess hydration are invasive and require costly clinical settings. The bio-impedance analysis offers a noninvasive and inexpensive tool to assess hydration, and it can be designed to be used in wearable health devices. The use of wearable electronics in healthcare applications has received increased attention over the last decade. New, emerging medical devices feature continuous patient monitoring and data collection to provide suitable treatment and preventive actions. In this paper, a model of human skin is developed and simulated to be used as a guide to designing a dehydration monitoring system based on a bio-impedance analysis technique. The study investigates the effect of applying different frequencies on the dielectric parameters of the skin and the resulting measured impedance. Two different interdigitated electrode designs are presented, and a comparison of the measurements is presented. The rectangular IDE is printed and tested on subjects to validate the bio-impedance method and study the interpretation of its results. The proposed design offers a classification criterion that can be used to assess dehydration without the need for a complex mathematical model. Further clinical testing and data are needed to refine and finalize the criteria.

Cardiovascular biomarker troponin I biosensor: Aptamer-gold-antibody hybrid on a metal oxide surface

Myocardial infarction (MI) is highly related to cardiac arrest leading to death and organ damage. Radiological techniques and electrocardiography have been used as preliminary tests to diagnose MI; however, these techniques are not sensitive enough for early-stage detection. A blood biomarker-based diagnosis is an immediate solution, and due to the high correlation of troponin with MI, it has been considered to be a gold-standard biomarker. In the present research, the cardiac biomarker troponin I (cTnI) was detected on an interdigitated electrode sensor with various surface interfaces. To detect cTnI, a capture aptamer-conjugated gold nanoparticle probe and detection antibody probe were utilized and compared through an alternating sandwich pattern. The surface metal oxide morphology of the developed sensor was proven by microscopic assessments. The limit of detection with the aptamer-gold-cTnI-antibody sandwich pattern was 100 aM, while it was 1 fM with antibody-gold-cTnI-aptamer, representing 10-fold differences. Further, the high performance of the sensor was confirmed by selective cTnI determination in serum, exhibiting superior nonfouling. These methods of determination provide options for generating novel assays for diagnosing MI.

A Digital Microfluidic Device Integrated with Electrochemical Impedance Spectroscopy for Cell-Based Immunoassay

The dynamic immune response to various diseases and therapies has been considered a promising indicator of disease status and therapeutic effectiveness. For instance, the human peripheral blood mononuclear cell (PBMC), as a major player in the immune system, is an important index to indicate a patient's immune function. Therefore, establishing a simple yet sensitive tool that can frequently assess the immune system during the course of disease and treatment is of great importance. This study introduced an integrated system that includes an electrochemical impedance spectroscope (EIS)-based biosensor in a digital microfluidic (DMF) device, to quantify the PBMC abundance with minimally trained hands. Moreover, we exploited the unique droplet manipulation feature of the DMF platform and conducted a dynamic cell capture assay, which enhanced the detection signal by 2.4-fold. This integrated system was able to detect as few as 10⁴ PBMCs per mL, presenting suitable sensitivity to quantify PBMCs. This integrated system is easy-to-operate and sensitive, and therefore holds great potential as a powerful tool to profile immune-mediated therapeutic responses in a timely manner, which can be further evolved as a point-of-care diagnostic device to conduct near-patient tests from blood samples.

Size-Selective Detection of Nanoparticles in Solution and Air by Imprinting

Monitoring of nanoparticles (NPs) in air and aquatic environments is an unmet challenge accentuated by the rising exposure to anthropogenic or engineered NPs. The inherent heterogeneity in size, shape, and the stabilizing shell of NPs makes their selective recognition a daunting task. Thus far, only a few technologies have shown promise in detecting NPs; however, they are cumbersome, costly, and insensitive to the NPs morphology or composition. Herein, we apply an approach termed nanoparticle-imprinted matrices (NAIM), which is based on creating voids in a thin layer by imprinting NPs followed by their removal. The NAIM was formed on an interdigitated electrode (IDE) and used for the size-selective detection of silica NPs. Three- and 5-fold increases in capacitance were observed for the reuptake of NPs with similar diameter, compared to smaller or larger NPs, in air and liquid phase, respectively. En masse, the proposed approach lays the foundation for the emergence of field-effective, inexpensive, real-life applicable sensors that will allow online monitoring of NPs in air and liquids.

Effects of Seed-Layer N2O Plasma Treatment on ZnO Nanorod Based Ultraviolet Photodetectors: Experimental Investigation with Two Different Device Structures

The crystalline quality of ZnO NR (nanorod) as a sensing material for visible blind ultraviolet PDs (photodetectors) critically depends on the SL (seed layer) material of properties, which is a key to high-quality nanocrystallite growth, more so than the synthesis method. In this study, we fabricated two different device structures of a gateless AlGaN/GaN HEMT (high electron mobility transistor) and a photoconductive PD structure with an IDE (interdigitated electrode) pattern implemented on a PET (polyethylene terephthalate) flexible substrate, and investigated the impact on device performance through the SL N₂O plasma treatment. In case of HEMT-based PD, the highest current on-off ratio (~7) and spectral responsivity R (~1.5 × 10⁵ A/W) were obtained from the treatment for 6 min, whereas the IDE pattern-based PD showed the best performance (on-off ratio = ~44, R = ~69 A/W) from the treatment for 3 min and above, during which a significant etch damage on PET substrates was produced. This improvement in device performance was due to the enhancement in NR crystalline quality as revealed by our X-ray diffraction, photoluminescence, and microanalysis.

Advancement in biosensor: "Telediagnosis" and "remote digital imaging"

Current developments in sensors and actuators are heralding a new era to facilitate things to happen effortlessly and efficiently with proper communication. On the other hand, Internet of Things (IoT) has been boomed up with er potential and occupies a wide range of disciplines. This study has choreographed to design of an algorithm and a smart data-processing scheme to implement the obtained data from the sensing system to transmit to the receivers. Technically, it is called "telediagnosis" and "remote digital monitoring," a revolution in the field of medicine and artificial intelligence. For the proof of concept, an algorithmic approach has been implemented for telediagnosis with one of the degenerative diseases, that is, Parkinson's disease. Using the data acquired from an improved interdigitated electrode, sensing surface was evaluated with the attained sensitivity of 100 fM (n = 3), and the limit of detection was calculated with the linear regression value coefficient. By the designed algorithm and data processing with the assistance of IoT, further validation was performed and attested the coordination. This proven concept can be ideally used with all sensing strategies for immediate telemedicine by end-to-end communications.

Identification of osteosarcoma by microRNA-coupled nuclease digestion on interdigitated electrode sensor

Osteosarcoma is a type of tumor originating from the bone cells, most often from long bones. Children and adolescents are mainly affected by osteosarcoma. Identifying the condition with osteosarcoma is mandatory to provide proper treatment to the affected patients. This research work has introduced an identification of an osteosarcoma biomarker "miRNA-21" on the interdigitated electrochemical sensor by nuclease digestion. The target RNA sequence of miRNA-21 was hybridized to the capture DNA and placed on the sensing electrode surface with the aid of the biotin-streptavidin interaction. The unhybridized immobilized single-standard capture DNA was digested by S1-nuclease. The current response of the digestion level was considered as the duplex formation between the target and capture DNA. Using this technique, the detection limit of the target was reached to 1 fM and a similar response of current was noted with the target RNA-spiked human serum, indicating the selective identification of target RNA. Further, single mismatched, triple mismatched, and random miRNA sequences (miRNA-195) failed to interact with the immobilized capture DNA, representing the specific identification of target RNA. This nuclease digestion technique with miRNA-21 identification helps in detecting osteosarcoma and related issues.

Development of an Interdigitated Electrode-Based Disposable Enzyme Sensor Strip for Glycated Albumin Measurement

Glycated albumin (GA) is an important glycemic control marker for diabetes mellitus. This study aimed to develop a highly sensitive disposable enzyme sensor strip for GA measurement by using an interdigitated electrode (IDE) as an electrode platform. The superior characteristics of IDE were demonstrated using one microelectrode of the IDE pair as the working electrode (WE) and the other as the counter electrode, and by measuring ferrocyanide/ferricyanide redox couple. The oxidation current was immediately reached at the steady state when the oxidation potential was applied to the WE. Then, an IDE enzyme sensor strip for GA measurement was prepared. The measurement of fructosyl lysine, the protease digestion product of GA, exhibited a high, steady current immediately after potential application, revealing the highly reproducible measurement. The sensitivity (2.8 nA µM⁻¹) and the limit of detection (1.2 µM) obtained with IDE enzyme sensor strip were superior compared with our previously reported sensor using screen printed electrode. Two GA samples, 15 or 30% GA, corresponding to healthy and diabetic levels, respectively, were measured after protease digestion with high resolution. This study demonstrated that the application of an IDE will realize the development of highly sensitive disposable-type amperometric enzyme sensors with high reproducibility.

Myocardial infarction biomarker C-reactive protein detection on nanocomposite aptasensor

Myocardial infarction (MI) is considered as one of the major life-threatening health issues worldwide. Growing number of cases every year is demanding rapid, portable, and early detection by the sensing devices for the identification of MI. This research work introduces a modified interdigitated electrode (IDE) sensing surface constructed with single-walled carbon nanotube (SWCN) to detect the cardiac biomarker, C-reactive protein (CRP). CRP-specific aptamer was conjugated with gold nanoparticle and attached on SWCN-constructed IDE surface. This probe-modified sensing surface has reached the limit of CRP detection to 10 pM on a linear regression curve with the regression coefficient of R² = 0.9223 [y = 0.9198x - 0.4326]. Further, control molecules, such as random aptamer sequence and nontarget cardiac biomarker (Troponin I), did not show the current response, indicating the specific CRP detection. This sensing strategy helps to detect the lower level of CRP and diagnose the MI at its earlier stages.

Bio-Compatibility and Bio-Insulation of Implantable Electrode Prosthesis Ameliorated by A-174 Silane Primed Parylene-C Deposited Embedment

Microelectrodes for pain management, neural prosthesis or assistances have a huge medical demand, such as the application of pain management chip or retinal prosthesis addressed on age-related macular degeneration (AMD) and the retinitis pigmentosa (RP). Due to lifelong implanted in human body and direct adhesion of neural tissues, the electrodes and associated insulation materials should possess an ideal bio-compatibility, including non-cytotoxicity and no safety concern elicited by immune responses. Our goal intended to develop retinal prosthesis, an electrical circuit chip used for assisting neural electrons transmission on retina and ameliorating the retinal disability. Therefore, based on the ISO 10993 guidance for implantable medical devices, the electrode prosthesis with insulation material has to conduct bio-compatibility assessment including cytotoxicity, hemolysis, (skin) irritation and pathological implantation examinations. In this study, we manufactured inter-digitated electrode (IDE) chips mimic the electrode prosthesis through photolithography. The titanium and platinum composites were deposited onto a silicon wafer to prepare an electric circuit to mimic the electrode used in retinal prosthesis manufacture, which further be encapsulated to examine the bio-compatibility in compliance with ISO 10993 and ASTM guidance specifically for implantable medical devices. Parylene-C, polyimide and silicon carbide were selected as materials for electrode encapsulation in comparison. Our data revealed parylene-C coating showed a significant excellence on bio-insulation and bio-compatibility specifically addressed on implantable neuron stimulatory devices and provided an economic procedure to package the electrode prosthesis. Therefore, parylene C encapsulation should serve as a consideration for future application on retinal prosthesis manufacture and examination.

Sensitive identification of prostate-specific antigen by iron oxide nanoparticle antibody conjugates on the gap-finger electrode surface

Researches have proved that increasing level of prostate-specific antigen (PSA) is an indicator for the progression of prostate cancer. The present study was focused to determine the PSA level by using anti-PSA antibody conjugated iron oxide nanoparticles, as the probe immobilized on the gap-fingered electrode sensing surface. The detection limit and sensitivity were found at the level of 1.9 pg/mL on the linear regression curve (y = 1.6939x - 0.5671; R² = 0.9878). A dose-dependent liner range was found from 1.9 until 60 pg/mL. Further, PSA was spiked in human serum and did not affect the interaction of PSA and its antibody. This method of detection quantifies the level of PSA, which helps to diagnose prostate cancer at its earlier stage.

Silica nanoparticle assists determining liver cancer gene sequence on interdigitated electrode surface

A high-performance interdigitated electrode (IDE) biosensing surface was reported here by utilizing self-assembled silica nanoparticle (SiNP). The modified surface was used to evaluate the complementation of hairpin forming region from Mitoxantrone resistance gene 7 (MXR7; liver cancer-related short gene). The conjugated SiNPs on 3-aminopropyl triethoxysilane functionalization were captured with probe sequence on IDE biosensing surface. The physical and chemically modified surface was used to quantify MXR7 and an increment in the current response upon complementation was noticed. Limit of target DNA detection was calculated (1-10 fM) and this label-free detection is at the comparable level to the fluorescent-based sensing. A linear regression was calculated [y = 0.243x - 0.0773; R² = 0.9336] and the sensitivity was 1 fM on the linear range of 1 fM to 10 pM. With the strong attachment of capture DNA on IDE through SiNP, the surface clearly discriminates the specificity (complementary) versus nonspecificity (complete-, single-, and triple-mismatched sequences). This detection strategy helps to determine liver cancer progression and the similar strategy can be followed for other gene sequence complementation.

Immunodetection of urinary C-terminal telopeptide fragment of type II collagen: An osteoarthritis biomarker analysis

The urinary C-terminal telopeptide fragment of type II collagen (uCTX-II) has been reported as the efficient blood-based biomarker for osteoarthritis, which affects knees, hands, spine, and hips. This study reports a sensing strategy with antibody-conjugated gold nanoparticles (GNP) on an interdigitated electrode (IDE) to determine uCTX-II. The GNP-antibody complex was chemically immobilized on the IDE surface through the amine linker. uCTX-II was determined by monitoring the alteration in current upon interacting the GNP-complexed antibody. This strategy was improved the detection by attracting higher uCTX-II molecules, and the detection limit falls in the range of 10-100 pM with an acceptable regression value [y = 0.6254x - 0.4073, R² = 0.9787]. The sensitivity of the detection was recognized at 10 pM. Additionally, upon increasing the uCTX-II concentration, the current changes were increased in a linear fashion. Control detection with nonimmune antibody and control protein do not increase the current level, confirming the specific detection of uCTX-II. This method of detection helps in diagnosing osteoarthritis and its follow-up treatment.

DNA-RNA complementation on silicon wafer for thyroid cancer determination

One of the current issues with thyroid tumor is early diagnosis as it makes the higher possibility of curing. This research was focused to detect and quantify the level of specific target sequence complementation of miR-222 with capture DNA sequence on interdigitated electrode (IDE) sensor. The aluminum electrode with the gap and finger sizes of 10 µm was fabricated on silicon wafer, further the surface was amine-functionalized for accommodating carboxylated-DNA probe. With DNA-target RNA complementation, the detection limit was attained to be 1 fM as estimated by a linear regression analysis [y = 1.5325x - 2.1171 R² = 0.9065] and the sensitivity was at the similar level. Current responses were higher by increasing the target RNA sequence concentrations. Control experiments with mismatched/noncomplementary sequences were failed to complement the capture DNA sequence immobilized on IDE, indicating the specific target validation. This research helps diagnosing and identifying the progression with thyroid tumor and miRNA being a potential "marker" in atypia diagnosis.

Aerosol-Jet-Printed Graphene Immunosensor for Label-Free Cytokine Monitoring in Serum

Graphene-based inks are becoming increasingly attractive for printing low-cost and flexible electrical circuits due to their high electrical conductivity, biocompatibility, and manufacturing scalability. Conventional graphene printing techniques, such as screen and inkjet printing, are limited by stringent ink viscosity requirements properties and large as-printed line width that impedes the performance of printed biosensors. Here, we report an aerosol-jet-printed (AJP) graphene-based immunosensor capable of monitoring two distinct cytokines: interferon gamma (IFN-γ) and interleukin 10 (IL-10). Interdigitated electrodes (IDEs) with 40 μm finger widths were printed from graphene-nitrocellulose ink on a polyimide substrate. The IDEs were annealed in CO₂ to introduce reactive oxygen species on the graphene surface that act as chemical handles to covalently link IFN-γ and IL-10 antibodies to the graphene surfaces. The resultant AJP electrochemical immunosensors are capable of monitoring cytokines in serum with wide sensing range (IFN-γ: 0.1-5 ng/mL; IL-10: 0.1-2 ng/mL), low detection limit (IFN-γ: 25 pg/ml and IL-10: 46 pg/ml) and high selectivity (antibodies exhibited minimal cross-reactivity with each other and IL-6) without the need for sample prelabeling or preconcentration. Moreover, these biosensors are mechanically flexible with minimal change in signal output after 250 bending cycles over a high curvature (Φ = 5 mm). Hence, this technology could be applied to numerous electrochemical applications that require low-cost electroactive circuits that are disposable and/or flexible.

Glucose oxidase complexed gold-graphene nanocomposite on a dielectric surface for glucose detection: a strategy for gestational diabetes mellitus

BACKGROUND

Gestational diabetes mellitus is a commonly occurring metabolic disorder during pregnancy, affecting >4% of pregnant women. It is generally defined as the intolerance of glucose with the onset or initial diagnosis during pregnancy. This illness affects the placenta and poses a threat to the baby as it affects the supply of proper oxygen and nutrients.

PURPOSE

Due to the high percentage of affected pregnant women, it should be mandatory to evaluate glucose levels during pregnancy and there is a need for a continuous monitoring system.

METHODS

Herein, the investigators modified the interdigitated (di)electrodes (IDE) sensing surface to detect the glucose on covalently immobilized glucose oxidase (GOx) with the graphene. The characterization of graphene and gold nanoparticle (GNP) was performed by high-resolution microscopy.

RESULTS

Sensitivity was found to be 0.06 mg/mL and to enhance the detection, GOx was complexed with GNP. GNP-GOx was improved the sensitive detection twofold from 0.06 to 0.03 mg/mL, and it also displayed higher levels of current changes at all the concentrations of glucose that were tested. High-performance of the above IDE sensing system was attested by the specificity, reproducibility and higher sensitivity detections. Further, the linear regression analysis indicated the limit of detection to be between 0.02 and 0.03 mg/mL.

CONCLUSION

This study demonstrated the potential strategy with nanocomposite for diagnosing gestational diabetes mellitus.

DEP-on-a-Chip: Dielectrophoresis Applied to Microfluidic Platforms

Dielectric particles in a non-uniform electric field are subject to a force caused by a phenomenon called dielectrophoresis (DEP). DEP is a commonly used technique in microfluidics for particle or cell separation. In comparison with other separation methods, DEP has the unique advantage of being label-free, fast, and accurate. It has been widely applied in microfluidics for bio-molecular diagnostics and medical and polymer research. This review introduces the basic theory of DEP, its advantages compared with other separation methods, and its applications in recent years, in particular, focusing on the different electrode types integrated into microfluidic chips, fabrication techniques, and operation principles.

High-Density Redox Amplified Coulostatic Discharge-Based Biosensor Array

High-density biosensor arrays are essential for many cutting-edge biomedical applications including point-of-care vaccination screening to detect multiple highly-contagious diseases. Typical electrochemical biosensing techniques are based on the measurement of sub-pA currents for micron-sized sensors requiring highly-sensitive readout circuits. Such circuits are often too complex to scale down for high-density arrays. In this paper, a high-density 4,096-pixel electrochemical biosensor array in 180 nm CMOS is presented. It uses a coulostatic discharge sensing technique and interdigitated electrode geometry to reduce both the complexity and size of the readout circuitry. Each biopixel contains an interdigitated microelectrode with a 13 aA low-leakage readout circuit directly underneath. Compared to standard planar electrodes, the implemented interdigitated electrodes achieve a maximum amplification factor of 10.5× from redox cycling. The array's sensor density is comparable to state-of-the-art arrays, all without augmenting the sensors with complex post-processing. The detection of anti-Rubella and anti-Mumps antibodies in human serum is demonstrated.

Reduced Graphene Oxide Modified the Interdigitated Chain Electrode for an Insulin Sensor

Insulin is a key regulator in glucose homeostasis and its deficiency or alternations in the human body causes various types of diabetic disorders. In this paper, we present the development of a reduced graphene oxide (rGO) modified interdigitated chain electrode (ICE) for direct capacitive detection of insulin. The impedance properties of rGO-ICE were characterized by equivalent circuit modeling. After an electrochemical deposition of rGO on ICE, the electrode was modified with self-assembled monolayers and insulin antibodies in order to achieve insulin binding reactions. The impedance spectra and capacitances were measured with respect to the concentrations of insulin and the capacitance change (ΔC) was analyzed to quantify insulin concentration. The antibody immobilized electrode showed an increment of ΔC according to the insulin concentration in human serum ranging from 1 ng/mL to 10 µg/mL. The proposed sensor is feasible for label-free and real-time measuring of the biomarker and for point-of-care diagnosis.