Label-free Electrochemical Immunosensor Research Articles

Label-Free Electrochemical Immunosensor for Monitoring Kidney Transplant Rejection With Electroactive Antibiofouling Hydrogel

Label-Free Electrochemical Immunosensor for Monitoring Kidney Transplant Rejection With Electroactive Antibiofouling Hydrogel

Electrochemical Detection of Myoglobin Using an Ultrasensitive Label-free Sensor Derived from Cubic-ZIF67@Au-rGOF-NH2 Composite of MOF and GOF

Markers of myocardial injury, such as myoglobin (Mb), are substances swiftly released into the peripheral bloodstream upon myocardial cell injury or altered cardiac activity. During the onset of acute myocardial infarction, patients experience a significant surge in serum Mb levels. Given this, precise detection of Mb is essential, necessitating the development of innovative assays to optimize detection capabilities. This study introduces the synthesis of a three-dimensional hierarchical nanocomposite, Cubic-ZIF67@Au-rGOF-NH2, utilizing aminated reduced graphene oxide and zeolite imidazolium ester framework-67 (ZIF67) as foundational structures. Notably, this novel material, applied in a label-free electrochemical immunosensor, presents a groundbreaking approach for detecting myocardial injury markers. Experimental outcomes revealed ZIF67 and AuNPs exhibit enhanced affinity and growth on the 3D-rGOF-NH2 matrix, thus amplifying electrical conductivity while preserving the inherent electrochemical attributes of ZIF67. As a result, the Cubic-ZIF67@Au-rGOF-NH2 label-free electrochemical immunosensor exhibited a broad detection range and high sensitivity for Mb. The derived standard curve was ΔIp=16.67552lgC+275.245 (R=0.993) with a detection threshold of 3.47 fg/ml. Moreover, recoveries of standards spiked into samples ranged between 96.3% to 108.7%. Importantly, the devised immunosensor retained notable selectivity against non-target proteins, proving its potential clinical utility based on exemplary sample analysis performance.

Synthesis of flower-like ZnO nanoparticles for label-free point of care detection of carcinoembryonic antigen

In this work, flower-like ZnO nanoparticles (ZnONPs) were synthesized using zinc nitrate (Zn(NO3)2 6H2O) as a precursor with KOH. The morphology of the ZnONPs was controlled by varying the synthesis temperature at 50, 75 and 95°C. The morphology and structure of ZnONPs were characterized using scanning electron microscopy (SEM), and X-ray diffraction (XRD) and Brunauer-Emmett Teller (BET) analysis. ZnONPs were successfully synthesized by a simple chemical precipitation method. A synthesis temperature of 75°C produced the most suitable flower-like ZnONPs, which were combined with graphene nanoplatelets (GNPs) to develop a label-free electrochemical immunosensor for the detection of the colon cancer biomarker carcinoembryonic antigen (CEA) in human serum. Under optimum conditions, the developed immunosensor showed a linear range of 0.5 to 10 ng mL-1 with a limit of detection (LOD) of 0.44 ng mL-1. The label-free electrochemical immunosensor exhibited good selectivity, reproducibility, and repeatability, and recoveries were excellent. The immunosensor is used with a Near-Field Communication (NFC) potentiostat connected to a smartphone to facilitate POC cancer detection in low-resource locations.

A dual-mode label-free electrochemical immunosensor for ultrasensitive detection of procalcitonin by on-site vulcanization of dual-MOF heterostructure

Detection of procalcitonin (PCT) is crucial for the early identification of sepsis. PCT is primarily utilized in the multiple diagnosis of bacterial and viral illnesses along with to guide the application of antibiotics. Considering their advantages of high specificity and straightforward usage, electrochemical immunosensors offer significant application prospects in the detection of disease indicators. A dual-mode electrochemical immunosensor was constructed in this study to reliably identify PCT. In light of the synergistic effect of the dual-MOF derived heterostructure, the immunosensor demonstrating excellent square wave voltammetry (SWV) signals as well as significant catalytic activity for the H2O2 redox process. In addition to maintaining a low detection limit (SWV: 0.31 fg/mL and i-t: 0.098 fg/mL), the immunosensor offers an extensive linear response range (0.000001–100 ng/mL). The excellent performance is on account of the introduction of the local on-site sulfurized dual-MOF heterostructure with abundant metal chalcogenides/MOF interfaces, which boosts the specific surface area, offers an abundance of active sites, enhances conductivity, and raises catalytic activity. Furthermore, the immunosensor exhibits outstanding specificity, stability and reproducibility for the determination of PCT in serum, which is of great crucial for the clinical screening and diagnosis of sepsis.

Hydrangea-like TiO2/Bi2MoO6 porous nanoflowers triggering highly sensitive electrochemical immunosensing to tumor marker.

Rapid and sensitive detection of carcinoembryonic antigen (CEA) is of great significance for cancer patients. Here, molybdenum (Mo) was doped into bismuth oxide (Bi2O3) by one-pot hydrothermal method forming porous tremella Bi2MoO6 nanocomposites with a larger specific surface area than the spherical structure. Then, a new kind of hydrangea-like TiO2/Bi2MoO6 porous nanoflowers (NFs) was prepared by doping titanium into Bi2MoO6, where titanium dioxide (TiO2) grew in situ on the surface of Bi2MoO6 nanoparticles (NPs). The hydrangea-like structure provides larger specific surface area, higher electron transfer ability and biocompatibility as well as more active sites conducive to the attachment of anti-carcinoembryonic antigen (anti-CEA) to TiO2/Bi2MoO6 NFs. A novel label-free electrochemical immunosensor was then constructed for the quantitative detection of CEA using TiO2/Bi2MoO6 NFs as sensing platform, showing a good linear relationship with CEA in the concentration range 1.0pg/mL ~ 1.0mg/mL and a detection limit of 0.125pg/mL (S/N = 3). The results achieved with the designed immunosensor are comparable with many existing immunosensors used for the detection of CEA in real samples.

Ultrasensitive Label-Free Electrochemical Immunosensor for Carbohydrate Antigen-125 (CA125) Employing Cu(II)-Polyethyleneimine (PEI)/Silica Nanoparticle@Overoxidized Polypyrrole (OPPy)/Multi-Walled Carbon Nanotubes (MWNTs) Hybrid Nanomaterial

Novel electroactive nanotags of Cu(II) functionalized polyethylenimine (PEI)/SiO2 nanoparticles (abbreviated as Cu2+/PEI/SiO2 NPs) were conveniently synthesized using a strong coordination reaction between Cu(II) and the multi-amino groups of PEI. These electroactive nanotags were easily coated on the overoxidized polypyrrole (OPPy) modified Nafion/multi-walled carbon nanotubes (abbreviated as Nafion/MWNTs) electrode surface through Cu-N bonds and strong electrostatic interactions. The Cu2+/PEI/SiO2 NPs@OPPy/MWNTs hybrid nanomaterial was formed without the addition of extra membrane-forming substances. The experimental results demonstrate that the OPPy/MWNTs composite membrane coupled with electrocatalytic Cu(Tris)4 2+ complexes in tris(hydroxymethyl)aminomethane (Tris)-HCl buffer medium amplified the electrochemical signals of nanotags based on the mutual synergistic effects. As an application, a label-free electrochemical immunosensor for epithelial ovarian cancer biomarker-carbohydrate antigen-125 (CA125) was constructed by covalently immobilizing CA125 antibody onto the hybrid nanomaterial modified electrode. With the increasing concentrations of CA125 antigen, different decreases in the electrochemical signals of the nanotags were observed due to the formation of antigen-antibody immune complexes. The electrochemical immunosensor showed a linear relationship from 0.001 to 500 U·mL−1 for CA125 with a detection limit of 3.4 × 10−4 U·mL−1. In addition, the proposed immunosensor was applied to the determination of CA125 in human serum with satisfactory results.

Label-free simultaneous detection of quinolone antibiotic residues using an origami paper–based electrochemical immunosensor

Label-free electrochemical sensors have gained popularity as point-of-care devices because they do not require complicated labeling procedures. However, they have difficulties detecting multiple analytes simultaneously. In this study, we developed a novel label-free electrochemical immunosensor on an origami paper–based analytical device (oPAD) for the simultaneous detection of quinolone antibiotics, in which norfloxacin (Nor) and enrofloxacin (Enr) were used as a model. The oPAD was designed with two antibody zones, each zone contains different antibodies. The oPAD has two thionine- and ferrocenecarboxylic acid-coated reagent zones, as redox species, which will generate the response current signals for the detection of quinolone antibiotics. The simultaneous current responses of thionine and ferrocenecarboxylic acid decreased proportionately when exposed to Nor and Enr concentrations, respectively. Under optimal conditions, this device provided linear range at concentrations of 0.01–10 µg/mL for the detection of Nor and Enr and limit of detection was calculated as 2.02 and 1.70 ng/mL, respectively. Moreover, this device demonstrates performance comparable to standard methods for the simultaneous detection of Nor and Enr in milk, honey, and fish. Therefore, label-free electrochemical immunosensors provide a highly potent, inexpensive, and portable method for detecting multiple quinolone antibiotics simultaneously on a single device.

Regulation of triazine-COF and CoAl-LDH substrates in composites for high-performance neurofilament-light chains electrochemical immunosensors

Early diagnosis of Alzheimer’s disease (AD) can be achieved through the detection of neurofilament light chain (NfL) biomarker, which can slow down the progress of AD and improve quality of life for patients. In this paper, polyvalent Tb-metal organic frameworks (Tb-MOF) and CoAl-layered double hydroxides (CoAl-LDH) are directly acceded to the synthesis system of triazine-covalent organic frameworks (triazine-COF) using one-pot synthesis to obtain the COF-based composite (COF/MOF-LDH). Similarly, the composite of LDH-based (LDH/MOF-COF) is acquired by integrating Tb-MOF and triazine-COF into the synthesis system of CoAl-LDH via hydrothermal procedure. COF/MOF-LDH and LDH/MOF-COF are used as electrode modification materials to construct label-free electrochemical immunosensors for anchoring and detecting NfL. Under optimal conditions for detecting NfL, both modified sensors exhibit high degree of selectivity, stability and reproducibility. However, the COF/MOF-LDH sensor displays a wider linear concentration range (0.05 pg/mL - 100 ng/mL) with lower limit detection of 0.017 pg/mL (S/N=3), and high sensitivity of 130.8 μA·ng−1·mL·cm−2, attributing to large conjugation system of triazine-COF used for substrate modulation and the immobilisation of the anti-NfL through strong π-π* affect and hydrogen bonding. Likely, the incorporation of polyvalent Tb-MOF and CoAl-LDH in COF/MOF-LDH considerably enhance sensitivity via improving active sites and response signals. Furthermore, the morphology, pore size and specific surface area differences of the composites are a reflection of the results of the substrate material control strategy. Especially, the N2 adsorption/desorption tests indicate the larger mesoporous structure of COF/MOF-LDH which facilitate the electron transfer and anti-NfL immobilization. Taken together, the immunosensor based on COF/MOF-LDH shows excellent detection performance which provides a pathway for early screening of AD.

Concanavalin A as carrier for sensitive electrochemical immunosensor based on AgNPs-rGO signal amplification

Concanavalin A (ConA), as a carrier for immobilizing antibodies, was used for the first time in electrochemical immunosensor. In this work, a label-free electrochemical immunosensor based on Ag nanoparticles-reduced graphene oxide (AgNPs-rGO) nanocomposite and ConA was successfully prepared to detect arsanilic acid (ASA). AgNPs-rGO nanocomposite displayed superior conductivity and redox capability. Specially, ConA showed excellent binding ability with monoclonal antibody of ASA through lectin-sugar interactions. Under the optimized conditions, the proposed electrochemical immunosensor showed a linear dependence over ASA concentrations ranging from 0.025 ng/mL to 25 ng/mL with a low detection limit of 0.011 ng/mL. Furthermore, the immunosensor was used to monitor ASA in chicken and egg with good precision and accuracy. In conclusion, the simple and low-cost immunosensor was desirably applied as a useful candidate for detection of ASA in animal derived food.

Fabrication of a label-free electrochemical immunosensor by functionalized nanofiber membrane for the ultrasensitive detection of quinalphos

The accumulation of quinalphos pesticide in agricultural products have detrimental effects to human body and environment, hence, an efficient and sensitive detection approach is desirable. In this study, a label-free electrochemical immunosensor based on the directly immobilizing nanobody onto functionalized polyvinyl alcohol/gelatin-gold nanoparticles nanofiber membrane (PVA/G-AuNPs NFM) was fabricated. First, a homogeneous PVA/G-AuNPs NFM with multiple-porosity structure and appropriate hydrophilicity was prepared. Then, the electrochemical immunosensor was assembled and under the optimized conditions, the prepared biosensor exhibited good detection performance towards quinalphos with the linear range and limit of detection being 0.06–1000 ng/mL and 50.74 pg/mL (S/N = 3), respectively. Moreover, the sensor presented good specificity, regenerability and stability, maintaining more than 90% activity after 5 times of regeneration and about 90% activity after 6 weeks of storage. Finally, the average recoveries of quinalphos from food samples were 89.68%–110.88% with the coefficient of variation being 1.65%–7.81%, showing good correlation with UPLC-MS/MS (R2 = 0.9859), indicating the accuracy of the proposed electrochemical immunosensor assay. Overall, the label-free electrochemical immunosensor presents a novel approach for the rapid and sensitive detection of quinalphos and other pesticide residues.

Ultrasensitive Electrochemical Immunosensor for Multiplex Sandwich Bioassaying Based on the Functional Antibodies.

In vitro diagnostics (IVDs) based on electrochemical immunosensors are crucial for disease screening, diagnosis, prognosis, and treatment monitoring. However, label-free electrochemical immunosensors commonly suffer from poor specificity, leading to false positives. To address this issue, we propose a highly sensitive and precise electrochemical immunosensor for protein marker detection. This approach involves directly labeling the detection antibodies (Ab2) with thionine (Thi). The Ab2 labeled by Thi exhibits a distinct redox peak upon targeted voltage stimulation, enabling accurate quantification of protein biomarkers. Thi-modified antibodies provide significant advantages over traditional antibody modification methods, such as enhanced detection sensitivity, improved accuracy, and specificity in protein marker identification. The method is straightforward and efficient, ensuring specific analyte detection while minimizing interference from other substances in the sample. Additionally, a multielectrode detection method was employed, achieving remarkably low limits of detection (LoDs) for tumor necrosis factor-alpha (TNF-alpha), cardiac troponin I (cTnI), and interleukin-6 (IL-6), with LoDs of 9.38 fg/mL, 1.70 fg/mL, and 8.14 fg/mL, respectively. The proposed electrochemical immunosensor also exhibited high selectivity and repeatability, with relative standard deviations (RSD) of 6.39% for TNF-alpha, 2.42% for cTnI, and 2.72% for IL-6 (n = 5). Moreover, it demonstrated high sensitivity and was evaluated for serum detection using the standard addition method. The results highlight the great potential of the proposed electrochemical immunosensor for clinical applications, offering a novel approach for future utilization in clinical settings.

Ultrasensitive and label-free electrochemical immunosensor for the detection of the ovarian cancer biomarker CA125 based on CuCo-ONSs@AuNPs nanocomposites

Cancer antigen 125 (CA125) is pivotal as a tumor marker in early ovarian cancer prevention and diagnosis. In this work, we introduced an ultrasensitive label-free electrochemical immunosensor tailored for CA125 detection, leveraging nanogold-functionalized copper-cobalt oxide nanosheets (CuCo-ONSs@AuNPs) as nanocomposites. For the inaugural application, copper-cobalt oxide nanosheets delivered the requisite DPV electrochemical response for the immunosensors. Their large specific surface area and commendable electrical conductivity amplify electron transfer and enable significant gold nanoparticle loading. Concurrently, AuNPs offer a plethora of active sites, facilitating easy immobilization of biomolecules via the bond between amino groups and AuNPs. We employed scanning electron microscopy, transmission electron microscopy, and x-ray photoelectron spectroscopy to characterize the nanomaterials' surface morphology and elemental composition. The electrochemical sensor response signals were ascertained using differential pulse voltammetry. Under optimal conditions, the immunosensor exhibited a linear detection range from 1×10−7 U/mL to 1×10−3 U/mL and a detection limit of 3.9×10−8 U/mL (S/N=3). The proposed label-free electrochemical immunosensor furnishes a straightforward, dependable, and sensitive approach for CA125 quantification and stands as a promising method for clinical detection of other tumor markers.

Label-Free Electrochemical Immunosensor Based on Conjugated Polymer Film Coated Disposable Electrode for Ultrasensitive Determination of Resistin Potential Obesity Biomarker.

A new label-free immunosensor was designed for sensitive detection of resistin obesity biomarker in human biological fluids. To construct a sensing interface, the monomer of double epoxy groups-substituted thiophene (TdiEpx) was synthesized for the fabrication of the biosensing system. A disposable indium tin oxide sheet was first modified by electrochemical polymerization of the TdiEpx monomer, and this robust and novel surface was characterized using different spectroscopic and electrochemical analyses. The double epoxy ends were linked to the amino ends of anti-resistin, and they served as binding points for the covalent binding of biomolecules. The double epoxy ends present in each TdiEpx monomer ensured an extensive surface area, which improved the quantity of attached anti-resistin. The determination of resistin antigen was based on the specific coupling of resistin with anti-resistin, and this interaction hindered the electron transfer reaction. The immunosensor introduced a wide linear range of 0.0125-15 pg/mL, a low detection limit of 4.17 fg/mL, and an excellent sensitivity of 1.38 kohm pg mL-1 cm2. In this study, a sandwich enzyme-linked immunosorbent assay spectrophotometric method was utilized as a reference technique for the quantitative analysis of resistin in human serum and saliva samples. Both measurements in clinical samples displayed correlations and high-correlation coefficients. In addition, this immunosensor had good storage stability, acceptable repeatability and reproducibility, high specificity, and good accuracy. The proposed immunosensor provided a simple and versatile impedimetric immunosensing platform and a promisingly sensitive way for clinical applications.

A Label-free Electrochemical Immunosensor Based on Gold Nanoparticles-poly(ferriporphyrin-co-acrylamide)-reduced Graphene Oxide and the Application in Prostate Specific Antigen Detection

A Label-free Electrochemical Immunosensor Based on Gold Nanoparticles-poly(ferriporphyrin-co-acrylamide)-reduced Graphene Oxide and the Application in Prostate Specific Antigen Detection

A Novel Label-Free Electrochemical Immunosensor for the Detection of Thyroid Transcription Factor 1 Using Ribbon-like Tungsten Disulfide-Reduced Graphene Oxide Nanohybrids and Gold Nanoparticles.

Thyroid transcription factor 1 (TTF1) is an important cancer-related biomarker for clinical diagnosis, especially for carcinomas of lung and thyroid origin. Herein, a novel label-free electrochemical immunosensor was prepared for TTF1 detection based on nanohybrids of ribbon-like tungsten disulfide-reduced graphene oxide (WS2-rGO) and gold nanoparticles (AuNPs). The proposed immunosensor employed H2O2 as the electrochemical probe because of the excellent peroxidase-like activity of ribbon-like WS2-rGO. The introduction of AuNPs not only enhanced the electrocatalytic activity of the immunosensor, but also provided immobilization sites for binding TTF1 antibodies. The electrochemical signals can be greatly amplified due to their excellent electrochemical performance, which realized the sensitive determination of TTF1 with a wide linear range of 0.025-50 ng mL-1 and a lower detection limit of 0.016 ng mL-1 (S/N = 3). Moreover, the immunosensor exhibited high selectivity, good reproducibility, and robust stability, as well as the ability to detect TTF1 in human serum with satisfactory results. These observed properties of the immunosensor enhance its potential practicability in clinical applications. This method can also be used for the detection of other tumor biomarkers by using the corresponding antigen-antibody complex.

Label-free electrochemical immunosensor employing new redox probes/porous organic polymers/graphene oxide nanocomposite towards multiplex detection of three SARS-COV2-induced storming proteins for severe COVID-19 diagnosis

Since an outbreak of severe acute respiratory disease caused by coronavirus 2 (SARS-CoV-2) in the province of Wuhan, China, coronavirus disease 2019 (COVID-19) has tremendously evolved into a global pandemic. COVID-19 causing serious failures in organ functions is found to be involved in many groups or kinds of “cytokine storm effect” protein biomarkers resulting from the human immunological responses to the virus. The in-body abnormalities and clinical features relevant to COVID-19 exhibit a wide range and it is difficult to forecast the severity of infection in patients. Consequently, the development of a fast and highly accurate method for screening, diagnosis, monitoring, rapid identification, and isolation of COVID-19-infected patients, and monitoring its severity is urgently needed. This work aims to develop a highly sensitive multiplex label-free electrochemical immunosensor based on a porous organic polymer (POP-AQ)/graphene oxide (GO) electrode to screen and diagnose COVID-19 severity. The screen-printed carbon electrode (SPCE) consisting of three working electrodes is modified by a new POP-AQ/GO nanocomposite to enhance its specific surface area and electrochemical reactivity. The resultant platform is functionalized with three different chitosan-encapsulated redox probes (m-cresol purple (mCP), thymol blue (TMB), and polydopamine (PDA)), followed by three different antibodies, which are employed to quantitatively detect the corresponding proteins from the immunological response. This novel platform allows for the simultaneous measurement of critical illness biomarkers (IL-6, D-dimer, and ferritin), with high sensitivities and low detection limits (LODs). The biosensor displays an excellent analytical performance with wide linear dynamic ranges of 0.005–5, 2.5−100, and 2.5−100 ng mL−1, and LODs of 0.0040, 0.844, and 0.806 ng mL−1 for IL-6, D-dimer, and ferritin, respectively. Moreover, this platform reveals high reproducibility and stability, while maintaining low instrumentation complexity, and cost-effectiveness. This proposed multiplex immunosensor has excellent potential for fast COVID-19 diagnosis and severity screening in infected patients. Additionally, its versatility suggests applicability in diagnosing other diseases and emerging pathogens.

Realizing the label-free sensitive detection of carcinoembryogenic antigen (CEA) in blood serum via a MNC-decorated flexible immunosensor.

A label-free electrochemical immunosensor utilising nitrogen-rich mesoporous carbon (MNC) as the substrate material was developed for the sensitive quantification of carcinoembryonic antigen (CEA). The synergic interactions between MNC and AbCEA also eliminated the need for coupling agents such as EDC/NHS. The novel immunosensor demonstrated a wide detection range from 500 fM (9.04 pg mL-1) to 50 nM (1 μg mL-1) and a low detection limit (LOD) of 500 fM. Moreover, the immunosensor showed sensitivities of 12.27 mA nM-1 cm-2 and 0.066 mA nM-1 cm-2 for detecting CEA in the linear ranges 10 pM to 1 nM and 2 nM to 50 nM, respectively, while maintaining long-term storage stability of 6 weeks. Analysis of real serum sample analysis yielded highly accurate results with recovery rates ranging from 99.3% to 103.7%. Furthermore, the developed paper-based screen-printed electrode exhibited a similar detection range, suggesting its potential for use in point-of-care detection devices in future applications.

A NiFe PBA/AuNPs nanocomposite sensitive immunosensor for electrochemical detection of PSA.

In this paper, a label-free electrochemical immunosensor for sensitive detection of prostate antigen (PSA) was developed based on a NiFe PBA/AuNPs composite. The prostate antigen antibody was immobilized and the immunosensor was constructed by using a glassy carbon electrode modified with a nanocomposite consisting of nickel-iron Prussian blue analog (NiFe PBA) and gold nanoparticles (AuNPs). Due to the good biological affinity of AuNPs for biomolecules, as well as the porous nanostructure and regular shape of NiFe PBA, NiFe PBA/AuNPs nanocomposites significantly improve the electron transport rate, while achieving excellent performance for the sensor. Due to the interaction between the antibody and the antigen on the modified electrode, the current signal of the NiFe PBA itself is reduced due to the redox changes in Fe2+ and Fe3+, which can be determined by differential pulse voltammetry (DPV). Therefore, the monitoring of prostate antigen detection is realized. Under optimal experimental conditions, the immunosensor exhibited excellent detection performance with a dynamic response range from 0.5 pg mL-1 to 1000 pg mL-1 for the PSA concentration and a detection limit of 0.23 pg mL-1 (S/N = 3). In addition, the PSA aptasensor has good selectivity, high stability, and satisfactory reproducibility and has broad potential in clinical research and diagnostic applications.

The effect of gold nanostructure morphology on label-free electrochemical immunosensor design

In this research, various electrodeposition techniques were used to form gold nanostructures (AuNSs) on the surface of graphite rod electrode (GE). Three distinct AuNS morphologies on GE have been achieved based on the composition of electrodeposition solution. The use of H2SO4 as a supporting electrolyte resulted in the formation of smaller but more numerous AuNSI with a modified electrode’s electroactive surface area (EASA) of 0.213 cm2. Exchanging the supporting electrolyte to KNO3 and increasing HAuCl4 concentration facilitated the formation of bigger AuNSII particles with electrode EASA of 0.116 cm2. Finally, a partial coverage of GE by branched gold nanostructures (AuNSIII) was achieved with an estimated EASA of 0.110 cm2, when the HAuCl4 and KNO3 concentrations were increased. Estimated values of heterogeneous electron transfer rate constant did not depend on AuNS morphology. Electrode modified with AuNSI exhibited the highest bovine serum albumin (BSA) immobilization efficiency and the highest relative response for the detection of specific polyclonal antibodies against BSA (p-anti-BSA) compared to other modified electrodes. The limit of p-anti-BSA detection in PBS buffer was calculated as 0.63 nM, while in blood serum it was 0.71 nM. Linear ranges were from 1 to 7 nM and from 1 to 5 nM, respectively.

Advances and Challenges in Nanomaterial-Based Electrochemical Immunosensors for Small Cell Lung Cancer Biomarker Neuron-Specific Enolase.

Early and rapid detection of neuron-specific enolase (NSE) is highly significant, as it is putative biomarker for small-cell lung cancer as well as COVID-19. Electrochemical techniques have attracted substantial attention for the early detection of cancer biomarkers due to the important properties of simplicity, high sensitivity, specificity, low cost, and point-of-care detection. This work reviews the clinically relevant labeled and label-free electrochemical immunosensors developed so far for the analysis of NSE. The prevailing role of nanostructured materials as electrode matrices is thoroughly discussed. Subsequently, the key performances of various immunoassays are critically evaluated in terms of limit of detection, linear ranges, and incubation time for clinical translation. Electrochemical techniques coupled with screen-printed electrodes developing market level commercialization of NSE sensors is also discussed. Finally, the review concludes with the current challenges associated with available methods and provides a future outlook toward commercialization opportunities for easy detection of NSE.