Silver nanoflower–reduced graphene oxide composite based micro-disk electrode for insulin detection in serum

A cucurbit[7]uril-mediated crosslinking-amplified microchannel resistance immunoassay via magnetic interception for point of care testing of insulin

Insulin is the only hormone that lowers blood glucose levels, the abnormal insulin secretion leads to various diseases such as diabetes. Herein, we present a cucurbit[7]uril (CB[7])-mediated crosslinking-amplified microchannel resistance immunoassay (MCRI) via magnetic interception for point of care (POC) testing of insulin in human serum samples. In the developed MCRI, the CB[7] coated gold magnetic nanoparticles (AuMNP@CB[7]) are used for extracting insulin from complex samples by host-guest interaction. The formed AuMNP@CB[7]-insulin plays a role of crosslinker to induce the aggregation of the antibody modified polystyrene microspheres (PS-Ab) through immune recognition. The aggregates are then trapped in a microchannel via magnetic interception, resulting in a decrease in the current intensity, which is quantitatively correlated with the insulin level. Benefiting from the CB[7]-mediated extraction, enrichment, and crosslinking amplification, a satisfactory analytical performance is obtained and the limit of detection (LOD) is as low as 0.35 pg/mL. Thus, the MCRI is appropriate for sensitive detection of insulin and can be extended to POC application by integrating the CB[7]-mediated amplification with the simple MCRI device.

An Electrochemical Nickel-Cobalt (Ni-Co)/Graphene Oxide-Polyvinyl Alcohol (GO-PVA) Sensor for Glucose Detection

This paper presents a non-enzymatic sensor for glucose detection in an environment where glucose and insulin coexist. The sensor is based on a three-electrode chip fabricated by etching the copper foil of a printed circuit board. The working electrode is coated with a graphene oxide-polyvinyl alcohol composite film, followed by the electroplating of a nickel-cobalt layer and an additional surface treatment using O2 plasma. The experimental results indicate that within a glucose concentration of 2 mM to 10 mM and an insulin concentration of 0.1 mM to 1 mM, the measured current exhibits a linear relationship with the concentration of glucose or insulin, regardless of whether cyclic voltammetry or linear sweep voltammetry is used. However, the detection limit for insulin is 0.01 mM, ensuring that glucose detection remains unaffected by insulin interference. In this sensor, nickel-cobalt serves as a catalyst for glucose and insulin detection, while the graphene oxide-polyvinyl alcohol composite enhances sensing performance.

Gold nanourchin on multiple-point dielectrode for glucose biosensing by current-potential measurement

Gestational diabetes (GD) is a condition characterized by elevated blood sugar levels during pregnancy. GD poses various health risks, such as serious birth injuries, the need for cesarean delivery, and the necessity of newborn care. Monitoring glucose levels is essential for ensuring safe delivery and reducing the risks to both the mother and fetus. Various sensors are readily available for monitoring glucose levels, and researchers are continually working to develop highly sensitive glucose sensors. This research aimed to develop a gold nanourchin (AuNU)-hybrid biosensor for quantifying glucose on a multi-point electrode sensor. Glucose oxidase (GOx) was attached to the AuNU and seeded on the sensing surface using an amine linker. The current-potential (1-2 V at 0.1 V sweep) was recorded for the GOx-glucose interaction, with a limit of detection of 560 μM and a regression coefficient (R2) of 0.9743 [y = 0.9106x - 0.9953] on the linear curve. The sensitivity was estimated to be 3.5 mAcm-2M-1. Furthermore, control experiments with galactose, sucrose, and fructose did not yield an increase in current-potential, confirming specific glucose detection. This experiment helps in monitoring glucose levels to manage conditions associated with GD.

Progress in nanoparticle-based electrochemical biosensors for hormone detection

Hormones are chemical messengers that regulate a wide range of physiological processes including metabolism, development, growth, reproduction and mood. The concentration of hormones that orchestrate the numerous bodily functions is very low (1 nM or less). Efforts have been made to develop highly sensitive tools to detect them. This review represents a critical comparison between different types of nanoparticle-based electrochemical biosensors for the detection of various hormones, namely cortisol, sex hormones (estradiol, progesterone, testosterone), insulin, thyroid-stimulating hormone (TSH) and growth hormone (GH). The electrochemical biosensors investigated for each hormone are first divided on the basis of the biological fluid tested for their detection, and successively on the basis of the electrochemical transducer utilized in the device (voltammetric or impedimetric). Focus is placed on the nanoparticles employed and the successive electrode modification developed in order to improve detection sensitivity and specificity and biosensor stability. Limit of detection (LOD), linear range, reproducibility and possibility of regeneration for continuous reuse are also investigated and compared. The review also addresses the recent trends in the development of wearable biosensors and point-of-care testing for hormone detection in clinical diagnostics useful for endocrinology research, and the future perspectives regarding the integration of nanomaterials, microfluidics, near field communication (NFC) technology and portable devices.

Electrochemical Assays for the Determination of Antidiabetic Drugs-A Review

This article presents the current state of knowledge regarding electrochemical methods for determining the active substances within drugs that are used in the treatment of type 1 and type 2 diabetes. Electrochemical methods of analysis, due to their sensitivity and easiness, are a great alternative to other, usually more expensive analytical assays. The determination of active substances mentioned in this review is based on oxidation or reduction processes on the surface of the working electrode. A wide variety of working electrodes, often modified with materials such as nanoparticles or conducting polymers, have been used for the highly sensitive analysis of antidiabetic drugs. The presented assays allow us to determine the compounds of interest in various samples, such as pharmaceutical products or different human bodily fluids.

A Sandwich-Type Electrochemical Immunosensor for Insulin Detection Based on Au-Adhered Cu5 Zn8 Hollow Porous Carbon Nanocubes and AuNP Deposited Nitrogen-Doped Holey Graphene

Rapid, accurate, and sensitive insulin detection is crucial for managing and treating diabetes. A simple sandwich-type electrochemical immunosensor is engineered using gold nanoparticle (AuNP)-adhered metal-organic framework-derived copper-zinc hollow porous carbon nanocubes (Au@Cu₅ Zn₈ /HPCNC) and AuNP-deposited nitrogen-doped holey graphene (NHG) are used as a dual functional label and sensing platform. The results show that identical morphology and size of Au@Cu₅ Zn₈ /HPCNC enhance the electrocatalytic active sites, conductivity, and surface area to immobilize the detection antibodies (Ab₂ ). In addition, AuNP/NHG has the requisite biocompatibility and electrical conductivity, which facilitates electron transport and increases the surface area of the capture antibody (Ab₁ ). Significantly, Cu₅ Zn₈ /HPCNC exhibits necessary catalytic activity and sensitivity for the electrochemical reduction of H₂ O₂ using (i-t) amperometry and improves the electrochemical response in differential pulse voltammetry. Under optimal conditions, the immunosensor for insulin demonstrates a wide linear range with a low detection limit and viable specificity, stability, and reproducibility. The platform's practicality is evaluated by detecting insulin in human serum samples. All these characteristics indicate that the Cu₅ Zn₈ /HPCNC-based biosensing strategy may be used for the point-of-care assay of diverse biomarkers.

Emerging Theranostic Nanomaterials in Diabetes and Its Complications

Diabetes mellitus (DM) refers to a group of metabolic disorders that are characterized by hyperglycemia. Oral subcutaneously administered antidiabetic drugs such as insulin, glipalamide, and metformin can temporarily balance blood sugar levels, however, long-term administration of these therapies is associated with undesirable side effects on the kidney and liver. In addition, due to overproduction of reactive oxygen species and hyperglycemia-induced macrovascular system damage, diabetics have an increased risk of complications. Fortunately, recent advances in nanomaterials have provided new opportunities for diabetes therapy and diagnosis. This review provides a panoramic overview of the current nanomaterials for the detection of diabetic biomarkers and diabetes treatment. Apart from diabetic sensing mechanisms and antidiabetic activities, the applications of these bioengineered nanoparticles for preventing several diabetic complications are elucidated. This review provides an overall perspective in this field, including current challenges and future trends, which may be helpful in informing the development of novel nanomaterials with new functions and properties for diabetes diagnosis and therapy.

Aptamer-binding zirconium-based metal-organic framework composites prepared by two conjunction approaches with enhanced bio-sensing for detecting isocarbophos

A novel label-free and enzyme-free detection strategy has been developed for the electrochemical biosensor detection of isocarbophos (ICP) using UiO-66-NH₂ and aptamer as the signal transducers. In this work, the ICP aptamers were attached to UiO-66-NH₂ through physical mixing and chemical combination methods. In the presence of ICP, the aptamers could undergo conformational change and bind to them, which prevent the electron transfer to the surface of electrode. By comparing the two conjunction approaches of aptasensors, these proposed strategies could selectively and sensitively detect ICP with a detection limit of 6 ng mL^-1 (20.74 nM) and 0.9 ng mL^-1 (3.11 nM). Furthermore, we have also demonstrated the capability of this strategy in the detection of ICP in real samples from vegetable and fruit extract, indicating the potential application of this strategy in food safety issues.

NiO Nanoparticles for Electrochemical Insulin Detection

Diabetes mellitus represents one of the most widespread diseases in civilization nowadays. Since the costs for treating and diagnosing of diabetes represent several billions of dollars per year, a cheap, fast, and simple sensor for diabetes diagnosis is needed. Electrochemical insulin sensors can be considered as a novel approach for diabetes diagnosis. In this study, carbon electrode with electrodeposited NiO nanoparticles was selected as a suitable electrode material for insulin determination. The morphology and surface composition were studied by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, and X-ray photoelectron spectroscopy (XPS). For a better understanding of insulin determination on NiO-modified electrodes, the mechanism of electrochemical reaction and the kinetic parameters were studied. They were calculated from both voltammetric and amperometric measurements. The modified carbon electrode displayed a wide linear range from 600 nM to 10 µM, a low limit of detection of 19.6 nM, and a high sensitivity of 7.06 µA/µM. The electrodes were stable for 30 cycles and were able to detect insulin even in bovine blood serum. Additionally, the temperature stability of this electrode and its storage conditions were studied with appropriate outcomes. The above results show the high promise of this electrode for detecting insulin in clinical samples.

A Label-free Electrochemical Immunosensor for Highly Sensitive Detection of TNF α, Based on Star Polymer-modified disposable ITO Electrode

Background:

Biomarkers are very important disease-related biomolecules which should be analyzed sensitive and selective in related physiological fluids or tissues. Tumor necrosis factor-α is a type of cytokine which plays vitlly important roles in different methabolic pathways such as cell death, survival, differentiation, proliferation and migration, and infectious and inflammatory diseases including rheumatoid arthritis, diabetes.

Objective:

In this study, it was aimed to develop a reliable tool based on star-shaped poly(glycidyl methacrylate) polymer coated disposable indium tin oxide electrode for determination of Tumor necrosis factor-α, an important disease biomarker.

Methods:

Star shaped polymer was used as an interface material for anti- Tumor necrosis factor α antibodies immobilization. The antibodies were immobilized covalently onto polymer coated indium tin oxide electrode. Electrochemical impedance spectroscopy and cyclic voltammetry techniques were used for all electrochemical measurements.

Results:

The suggested immunosensor exhibited a linear range between 0.02 and 4 pg/mL Tumor necrosis factor-α, and the detection limit was found as 6 fg/mL. Scanning electron microscopy and atomic force microscopy were used for electrode surface characterization. In addition, the suggested immunosensor was used for Tumor necrosis factor-α sensing in human serum samples. The results displayed recoveries between 97.07 and 100.19%. Moreover, this immunosensor had a simple fabrication procedure and a long storage-stability.

Conclusion:

A new biosensor based on a Star shaped polymer for the ultra sensitive determination of a biomarker Tumor necrosis factor-α was developed. The biosensor presented excellent repeatability and reproducubility, and also wide calibration range for Tumor necrosis factor- α.

Design and fabrication of a smart sensor using in silico epitope mapping and electro-responsive imprinted polymer nanoparticles for determination of insulin levels in human plasma

A robust and highly specific sensor based on electroactive molecularly imprinted polymer nanoparticles (nanoMIP) was developed. The nanoMIP tagged with a redox probe, combines both recognition and reporting capabilities. The developed nanoMIP replaces enzyme-mediator pairs used in traditional biosensors thus, offering enhanced molecular recognition for insulin, improving performance in complex biological samples, and yielding high stability. Also, most of existing sensors show poor performance after storage. To improve costs of the logistics and avoid the need of cold storage in the chain supply, we developed an alternative to biorecognition system that relies on nanoMIP. NanoMIP were computationally designed using "in-silico" insulin epitope mapping and synthesized by solid phase polymerisation. The characterisation of the polymer nanoparticles was performed by transmission electron microscopy (TEM), dynamic light scattering (DLS), Fourier-transform Infrared (FT-IR) and surface plasmon resonance (SPR). The electrochemical sensor was developed by chemical immobilisation of the nanoMIP on screen printed platinum electrodes. The insulin sensor displayed satisfactory performances and reproducible results (RSD = 4.2%; n = 30) using differential pulse voltammetry (DPV) in the clinically relevant concentration range from 50 to 2000 pM. The developed nanoMIP offers the advantage of large number of specific recognition sites with tailored geometry, as the resultant, the sensor showed high sensitivity and selectivity to insulin with a limit of detection (LOD) of 26 and 81 fM in buffer and human plasma, respectively, confirming the practical application for point of care monitoring. Moreover, the nanoMIP showed adequate storage stability of 168 days, demonstrating the robustness of sensor for several rounds of insulin analysis.

Bioelectrocatalysis of Hemoglobin on Electrodeposited Ag Nanoflowers toward H2O2 Detection

Hydrogen peroxide (H2O2) is a partially reduced metabolite of oxygen that exerts a diverse array of physiological and pathological activities in living organisms. Therefore, the accurate quantitative determination of H2O2 is crucial in clinical diagnostics, the food industry, and environmental monitoring. Herein we report the electrosynthesis of silver nanoflowers (AgNFs) on indium tin oxide (ITO) electrodes for direct electron transfer of hemoglobin (Hb) toward the selective quantification of H2O2. After well-ordered and fully-grown AgNFs were created on an ITO substrate by electrodeposition, their morphological and optical properties were analyzed with scanning electron microscopy and UV-Vis spectroscopy. Hb was immobilized on 3-mercaptopropionic acid-coated AgNFs through carbodiimide cross-linking to form an Hb/AgNF/ITO biosensor. Electrochemical measurement and analysis demonstrated that Hb retained its direct electron transfer and electrocatalytic properties and acted as a H2O2 sensor with a detection limit of 0.12 µM and a linear detection range of 0.2 to 3.4 mM in phosphate-buffered saline (PBS). The sensitivity, detection limit, and detection range of the Hb/AgNF/ITO biosensor toward detection H2O2 in human serum was also found to be 0.730 mA mM-1 cm-2, 90 µM, and 0.2 to 2.6 mM, indicating the clinical application for the H2O2 detection of the Hb/AgNF/ITO biosensor. Moreover, interference experiments revealed that the Hb/AgNF/ITO sensor displayed excellent selectivity for H2O2.

Preparation of graphene nanocomposites from aqueous silver nitrate using graphene oxide's peroxidase-like and carbocatalytic properties

The present study evaluates the role of graphene oxide’s (GO’s) peroxidase-like and inherent/carbocatalytic properties in oxidising silver nitrate (AgNO₃) to create graphene nanocomposites with silver nanoparticles (GO/Ag nanocomposite). Activation of peroxidase-like catalytic function of GO required hydrogen peroxide (H₂O₂) and ammonia (NH₃) in pH 4.0 disodium hydrogen phosphate (Na₂HPO₄). Carbocatalytic abilities of GO were triggered in pH 4.0 deionised distilled water (ddH₂O). Transmission electron microscope (TEM), scanning electron microscope (SEM), cyclic voltammetry (CV) and UV-Vis spectroscopy aided in qualitatively and quantitatively assessing GO/Ag nanocomposites. TEM and SEM analysis demonstrated the successful use of GO’s peroxidase-like and carbocatalytic properties to produce GO/Ag nanocomposite. UV-Vis analysis indicated a higher yield in optical density values for GO/Ag nanocomposites created using GO’s carbocatalytic ability rather than its peroxidase-like counterpart. Additionally, CV demonstrated that GO/Ag nanocomposite fabricated here is a product of an irreversible electrochemical reaction. Our study outcomes show new opportunities for GO as a standalone catalyst in biosensing. We demonstrate a sustainable approach to obtain graphene nanocomposites exclusive of harmful chemicals or physical methods.

Electrochemical Detection of C-Reactive Protein in Human Serum Based on Self-Assembled Monolayer-Modified Interdigitated Wave-Shaped Electrode

An electrochemical capacitance immunosensor based on an interdigitated wave-shaped micro electrode array (IDWµE) for direct and label-free detection of C-reactive protein (CRP) was reported. A self-assembled monolayer (SAM) of dithiobis (succinimidyl propionate) (DTSP) was used to modify the electrode array for antibody immobilization. The SAM functionalized electrode array was characterized morphologically by atomic force microscopy (AFM) and energy dispersive X-ray spectroscopy (EDX). The nature of gold-sulfur interactions on SAM-treated electrode array was probed by X-ray photoelectron spectroscopy (XPS). The covalent linking of anti-CRP-antibodies onto the SAM modified electrode array was characterized morphologically through AFM, and electrochemically through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The application of phosphate-buffered saline (PBS) and human serum (HS) samples containing different concentrations of CRP in the electrode array caused changes in the electrode interfacial capacitance upon CRP binding. CRP concentrations in PBS and HS were determined quantitatively by measuring the change in capacitance (ΔC) through EIS. The electrode immobilized with anti-CRP-antibodies showed an increase in ΔC with the addition of CRP concentrations over a range of 0.01-10,000 ng mL-1. The electrode showed detection limits of 0.025 ng mL-1 and 0.23 ng mL-1 (S/N = 3) in PBS and HS, respectively. The biosensor showed a good reproducibility (relative standard deviation (RSD), 1.70%), repeatability (RSD, 1.95%), and adequate selectivity in presence of interferents towards CRP detection. The sensor also exhibited a significant storage stability of 2 weeks at 4 °C in 1× PBS.

Reflectance aptasensor based on metal salphen label for rapid and facile determination of insulin

An optical aptasensor-based sensing platform for rapid insulin detection was fabricated. Aminated porous silica microparticles (PSiMPs) were synthesized via a facile mini-emulsion method to provide large surface area for covalent immobilization of insulin-binding DNA aptamer (IGA3) by glutaraldehyde cross-linking protocol. A Nickel-salphen type complex with piperidine side chain [Ni(II)-SP] was synthesized with a simple one-pot reaction, and functionalized as an optical label due to strong π-π interaction between aromatic carbons of G-quadruplex DNA aptamer and planar aromatic groups of Ni(II)-SP to form the immobilized IGA3-Ni(II)-SP complex, i.e. the dye-labeled aptamer, thereby bringing yellow colouration to the immobilized G-quartet plane. Optical characterization of aptasensor towards insulin binding was carried out with a fiber optic reflectance spectrophotometer. The maximum reflectance intensity of the immobilized IGA3-Ni(II)-SP complex at 656 nm decreased upon binding with insulin as aptasensor changed to brownish orange colouration in the background. This allows optical detection of insulin as the colour change of aptasensor is dependent on the insulin concentration. The linear detection range of the aptasensor is obtained from 10 to 50 μIU mL^-1 (R² = 0.9757), which conformed to the normal fasting insulin levels in human with a limit of detection (LOD) at 3.71 μIU mL^-1. The aptasensor showed fast response time of 40 min and long shelf life stability of >3 weeks. Insulin detection using healthy human serums with informed consent provided by participants suggests the DNA aptamer biosensor was in good agreement with ELISA standard method using BIOMATIK Human INS (Insulin) ELISA Kit.

Robust Bioengineered Apoferritin Nanoprobes for Ultrasensitive Detection of Infectious Pancreatic Necrosis Virus

Infectious pancreatic necrosis virus (IPNV) has been identified as a viral pathogen for many fish diseases that have become a huge hurdle for the growing fishing industry. Thus, in this work, we report a label-free impedance biosensor to quantify IPNV in real fish samples at point-of-care (POC) level. High specificity IPNV sensor with a detection limit of 2.69 TCID₅₀/mL was achieved by conjugating IPNV antibodies to portable Au disk electrode chips using human heavy chain apoferritin (H-AFN) nanoprobes as a binding agent. H-AFN probes were bioengineered through PCR by incorporating pET-28b(+) resulting in 24 subunits of 6 × his-tag and protein-G units on its outer surface to increase the sensitivity of the IPNV detection. The biosensor surface modifications were characterized by differential pulse voltammetry (DPV) and EIS methods for each modification step. The proposed nanoprobe based sensor showed three-fold enhancement in charge transfer resistance toward IPNV detection in comparison with the traditional linker approach when measured in a group of similar virus molecules. The portable sensor exhibited a linear range of 100-10000 TCID₅₀/mL and sensitivity of 5.40 × 10^-4 TCID₅₀/mL in real-fish samples. The performance of the proposed IPNV sensor was fully validated using an enzyme-linked immunosorbent assay (ELISA) technique with a sensitivity of 3.02 × 10^-4 TCID₅₀/mL. Results from H-AFN nanoprobe based IPNV sensor indicated high selectivity, sensitivity, and stability could be a promising platform for the detection of similar fish viruses and other biological molecules of interest.

Non-Enzymatic Impedimetric Sensor Based on 3-Aminophenylboronic Acid Functionalized Screen-Printed Carbon Electrode for Highly Sensitive Glucose Detection

A highly sensitive glucose sensor was prepared by a one-step method using 3-aminophenyl boronic acid as a unit of recognition and a screen-printed carbon electrode (SPCE) as an electrochemical transducer. Scanning Electron Microscopy confirmed the success of the functionalization of the SPCE due to the presence of clusters of boronic acid distributed on the carbon surface. In agreement with the Electrochemical Impedance Spectroscopy (EIS) tests performed before and after the functionalization, Cyclic Voltammetry results indicated that the electroactivity of the electrode decreased 37.9% owing to the presence of the poly phenylboronic acid on the electrode surface. EIS revealed that the sensor was capable to selectively detect glucose at a broad range of concentrations (limit of detection of 8.53 × 10-9 M), not recognizing fructose and sucrose. The device presented a stable impedimetric response when immediately prepared but suffered the influence of the storage time and some interfering species (dopamine, NaCl and animal serum). The response time at optimized conditions was estimated to be equal to 4.0 ± 0.6 s.

Amyloid beta in nasal secretions may be a potential biomarker of Alzheimer's disease

We investigated the level of amyloid beta (Aβ) in nasal secretions of patients with Alzheimer’s disease dementia (ADD) using interdigitated microelectrode (IME) biosensors and determined the predictive value of Aβ in nasal secretions for ADD diagnosis. Nasal secretions were obtained from 35 patients with ADD, 18 with cognitive decline associated with other neurological disorders (OND), and 26 cognitively unimpaired (CU) participants. Capacitance changes in IMEs were measured by capturing total Aβ (ΔC_tAβ). After 4-(2-hydroxyethyl)-1-piperazinepropanesulfonic acid (EPPS) was injected, additional capacitance changes due to the smaller molecular weight Aβ oligomers disassembled from the higher molecular weight oligomeric Aβ were determined (ΔC_oAβ). By dividing two values, the capacitance ratio (ΔC_oAβ/ΔC_tAβ) was determined and then normalized to the capacitance change index (CCI). The CCI was higher in the ADD group than in the OND (p = 0.040) and CU groups (p = 0.007). The accuracy of the CCI was fair in separating into the ADD and CU groups (area under the receiver operating characteristic curve = 0.718, 95% confidence interval = 0.591–0.845). These results demonstrate that the level of Aβ in nasal secretions increases in ADD and the detection of Aβ in nasal secretions using IME biosensors may be possible in predicting ADD.

Facile Synthesis of Cu2O@TiO2-PtCu Nanocomposites as a Signal Amplification Strategy for the Insulin Detection

Novel ultrasensitive sandwich-type electrochemical immunosensor was proposed for the quantitative detection of insulin, a representative biomarker for diabetes. To this end, molybdenum disulfide nanosheet-loaded gold nanoparticles (MoS₂/Au NPs) were used as substrates to modify bare glassy carbon electrodes. MoS₂/Au NPs not only present superior biocompatible and large specific surface area to enhance the loading capacity of primary antibody (Ab₁) but also present good electrical conductivity to accelerate electron transfer rate. Moreover, the amino-functionalized cuprous oxide decorated with titanium dioxide octahedral composites (Cu₂O@TiO₂-NH₂) were prepared to load dendritic platinum-copper nanoparticles (PtCu NPs) to realize signal amplification strategy. The resultant nanocomposites (cuprous oxide decorated with titanium dioxide octahedral loaded dendritic platinum-copper nanoparticles) demonstrate uniform octahedral morphology and size, which effectively increases the catalytically active sites and specific surface area to load the secondary antibody (Ab₂), even increases conductivity. Most importantly, the resultant nanocomposites possess superior electrocatalytic activity for hydrogen peroxide (H₂O₂) reduction, which present the signal amplification strategy. Under the optimal conditions, the proposed immunosensor exhibited a linear relationship between logarithm of insulin antigen concentration and amperometric response within a broad range from 0.1 pg/mL to 100 ng/mL and a limit detection of 0.024 pg/mL. Meanwhile, the immunosensor was employed to detect insulin in human serum with satisfactory results. Furthermore, it also presents good reproducibility, selectivity, and stability, which exhibits broad application prospects in biometric analysis.

Electrochemical Impedance Characterization of Cell Growth on Reduced Graphene Oxide–Gold Nanoparticles Electrodeposited on Indium Tin Oxide Electrodes

The improved binding ability of graphene–nanoparticle composites to proteins or molecules can be utilized to develop new cell-based assays. In this study, we fabricated reduced graphene oxide–gold nanoparticles (rGO-AuNP) electrodeposited onto a transparent indium tin oxide (ITO) electrode and investigated the feasibility of the electrochemical impedance monitoring of cell growth. The electrodeposition of rGO–AuNP on the ITO was optically and electrochemically characterized in comparison to bare, rGO-, and AuNP-deposited electrodes. The cell growth on the rGO–AuNP/ITO electrode was analyzed via electrochemical impedance measurement together with the microscopic observation of HEK293 cells transfected with a green fluorescent protein expression vector. The results showed that rGO–AuNP was biocompatible and induced an increase in cell adherence to the electrode when compared to the bare, AuNP-, or rGO-deposited ITO electrode. At 54 h cultivation, the average and standard deviation of the saturated normalized impedance magnitude of the rGO–AuNP/ITO electrode was 3.44 ± 0.16, while the value of the bare, AuNP-, and rGO-deposited ITO electrode was 2.48 ± 0.15, 2.61 ± 0.18, and 3.01 ± 0.25, respectively. The higher saturated value of the cell impedance indicates that the impedimetric cell-based assay has a broader measurement range. Thus, the rGO–AuNP/ITO electrode can be utilized for label-free and real-time impedimetric cell-based assays with wider dynamic range.

Label-Free Impedance Sensing of Aflatoxin B₁ with Polyaniline Nanofibers/Au Nanoparticle Electrode Array

Aflatoxin B1 (AFB₁) is produced by the Aspergillus flavus and Aspergillus parasiticus group of fungi which is most hepatotoxic and hepatocarcinogenic and occurs as a contaminant in a variety of foods. AFB₁ is mutagenic, teratogenic, and causes immunosuppression in animals and is mostly found in peanuts, corn, and food grains. Therefore, novel methodologies of sensitive and expedient strategy are often required to detect mycotoxins at the lowest level. Herein, we report an electrochemical impedance sensor that selectively detects AFB₁ at the lowest level by utilizing polyaniline nanofibers (PANI) coated with gold (Au) nanoparticles composite based indium tin oxide (ITO) disk electrodes. The Au-PANI nanocomposites were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) spectroscopy, and electrochemical impedance spectroscopy (EIS). The composite electrode exhibited a 14-fold decrement in |Z|1Hz in comparison with the bare electrode. The Au-PANI acted as an effective sensing platform having high surface area, electrochemical conductivity, and biocompatibility which enabled greater loading deposits of capture antibodies. As a result, the presence of AFB₁ was screened with high sensitivity and stability by monitoring the changes in impedance magnitude (|Z|) in the presence of a standard iron probe which was target specific and proportional to logarithmic AFB₁ concentrations (CAFB₁). The sensor exhibits a linear range 0.1 to 100 ng/mL with a detection limit (3) of 0.05 ng/mL and possesses good reproducibility and high selectivity against another fungal mycotoxin, Ochratoxin A (OTA). With regard to the practicability, the proposed sensor was successfully applied to spiked corn samples and proved excellent potential for AFB₁ detection and development of point-of-care (POC) disease sensing applications.

Silver@Nitrogen-Doped Carbon Nanorods as a Highly Efficient Electrocatalyst for the Oxygen Reduction Reaction in Alkaline Media

In recent years, various platinum-free catalysts for the oxygen reduction reaction (ORR) have attracted great attention due to the limited natural abundance and high cost of platinum. Herein, Ag@N-C (N-C: nitrogen-doped carbon) nanorods for the ORR were synthesized through chemical polymerization and pyrolysis methods by using pyrrole and silver nitrate as raw materials. Pyrolysis could significantly increase the specific surface area of as-synthesized catalysts and convert pyrrolic-N into graphitic-N and pyridinic-N. The results of electrochemical tests show that the Ag@N-C-900 catalyst (pyrolyzed at 900 °C) exhibits highly efficient ORR catalytic activity, improved stability, and better methanol resistance in comparison to that of Pt/C catalyst in alkaline media.

A novel electrochemical immunosensor based on ITO modified by carboxyl-ended silane agent for ultrasensitive detection of MAGE-1 in human serum

A new, low-cost electrochemical immunosensor was developed for rapid detection of Melanoma-associated antigen 1 (MAGE-1), a cancer biomarker. The fabrication procedure of immunosensor was based on the covalent immobilization of anti-MAGE-1, biorecognition molecule, on ITO electrode by carboxyethylsilanetriol (CTES) monolayer. The biosensing MAGE-1 antigen was monitored by using electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) technique. Apart from these techniques, single frequency impedance (SFI) was used for investigation of antibody-antigen interactions. Scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) were utilized for characterization of the proposed biosensor. To fabricate highly sensitive, good stability immunosensor, some parameters were optimized. Under optimal conditions, the developed electrochemical immunosensor for MAGE-1 exhibited a dynamic range of 4 fg/mL and 200 fg/mL with a low detection limit of 1.30 fg/mL. It had acceptable repeatability (5.05%, n = 20) and good storage stability (3.58% loss after 10 weeks). Moreover, this electrochemical immunosensor has been successfully applied to the determination of MAGE-1 in human serum samples.

Carbon Nanomaterial Based Biosensors for Non-Invasive Detection of Cancer and Disease Biomarkers for Clinical Diagnosis

The early diagnosis of diseases, e.g., Parkinson's and Alzheimer's disease, diabetes, and various types of cancer, and monitoring the response of patients to the therapy plays a critical role in clinical treatment; therefore, there is an intensive research for the determination of many clinical analytes. In order to achieve point-of-care sensing in clinical practice, sensitive, selective, cost-effective, simple, reliable, and rapid analytical methods are required. Biosensors have become essential tools in biomarker sensing, in which electrode material and architecture play critical roles in achieving sensitive and stable detection. Carbon nanomaterials in the form of particle/dots, tube/wires, and sheets have recently become indispensable elements of biosensor platforms due to their excellent mechanical, electronic, and optical properties. This review summarizes developments in this lucrative field by presenting major biosensor types and variability of sensor platforms in biomedical applications.

Aptamer-Embedded Zirconium-Based Metal-Organic Framework Composites Prepared by De Novo Bio-Inspired Approach with Enhanced Biosensing for Detecting Trace Analytes

A series of Zr-based metal-organic framework (MOF) composites embedded with three kinds of aptamer strands (509-MOF@Apt) were achieved by a one-step de novo synthetic approach. A platform for ultrasensitive detection of analytes, namely, thrombin, kanamycin, and carcinoembryonic antigen (CEA), was also established. Considering the conformational changes caused by the binding interactions between aptamer strands and targeted molecules, the label-free electrochemical aptasensors based on 509-MOF@Apt composites could be developed to detect various target molecules. By comparing the common fabrication approaches of aptasensors, a distinct determination mechanism was presented through analysis of the electrochemical measurements on different interaction behaviors between probe aptamer strands and 509-MOF materials. The optimized aptasensors based on 509-MOFs@Apt demonstrated excellent sensitivity (with the detection limit of 0.40, 0.37, and 0.21 pg mL^-1 for CEA, thrombin, and kanamycin, respectively), stability, repeatability, and applicability. This work will provide a new platform for direct and feasible detection in biosensing related to clinical diagnostics and therapeutics, and further, extend the scope of potential applications for MOF materials.

Ultrasensitive multiplexed immunoassay of autophagic biomarkers based on Au/rGO and Au nanocages amplifying electrochemcial signal

A novel sandwich-assay electrochemical immunosensor for simultaneous determination of autophagic biomarkers was introduced for the first time, the gold-reduced grapheme oxide nanocomposite (Au/r-GO) set as a good conductive platform with super high specific area, and provided more binding sites for the both antibodies of Beclin-1 and LC3B-II. While Au nanocages (AuNCs) served as good conductive platform to encapsulate a large amount of redox probe and secondary antibodies for signal amplification, due to the abundant reactive oxygen functional groups on its surface. Through differential pulse voltammetry (DPV) measurements, two separate signals can be detected directly in a single run, which represent the existence of Belin-1 and LC3B-II. Under optimized conditions, the electrochemical immunosensor exhibited good sensitivity and selectivity for the simultaneous determination of Beclin-1 and LC3B-II with linear ranges of 0.1-100 ng/mL. The detection limit for Beclin-1 and LC3B-II is 0.02 and 0.03 ng/mL respectively. This method was also applied for the analysis of Beclin-1 and LC3B-II levels in experimental cellular protein lysates, and the results were in good agreement with those of enzyme linked immunosorbent assay. This approach gives a promising simple, sensitive and quantitative strategy for the detection of autophagy.