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In this study, we designed a Pt/CoFe 2 O 4 /NC composite material as an excellent electrocatalyst for hydrogen evolution reaction (HER) and used the HER signal to construct an electrochemical immunosensor for carcinoembryonic antigen (CEA) detection. Remarkably, Pt/CoFe 2 O 4 /NC demonstrated superior HER performance compared to alternative Pt-based materials. It exhibited a low overpotential of only 42 mV and a Tafel slope of 253 mV dec−1 in acidic medium. Furthermore, due to the excellent conductivity, large surface area, and superior HER performance of Pt/CoFe 2 O 4 /NC, it was used as secondary antibody (Ab 2) label to achieve signal amplification in the electrochemical immunosensor. The results showed that this immunosensor possessed high selectivity and sensitivity. The linear detection range is 1.0 × 10−4–5.0 ng mL−1, and the detection limit is 0.0134 pg mL−1. It has potential applications in the clinical analysis field. Due to the excellent conductivity, large surface area, and superior HER performance of Pt/CoFe 2 O 4 /NC, it was used as an Ab 2 label to achieve signal amplification in the electrochemical immunosensor. The results showed that this immunosensor possessed high selectivity and sensitivity. The linear detection range is 1.0 × 10−4–5.0 ng mL−1, and the detection limit is 0.0134 pg mL−1. It has potential applications in the clinical analysis field. [Display omitted] • Pt is loaded onto the CoFe 2 O 4 /NC by photoreduction method. • The Pt/CoFe 2 O 4 /NC with low Pt loading presents low overpotential and Tafel slope in the HER. • A novel electrochemical immunosensor based on Pt/CoFe 2 O 4 /NC was constructed for CEA detection. [ABSTRACT FROM AUTHOR]

In terms of medicine, the prevention, diagnosis, and assessment of acute myocardial infarction (AMI) as well as the effectiveness of therapy all depend on the sensitive and early detection of human heart-type fatty acid–binding protein (H-HABP). The synthetic material used in this study, Ni-TCPP(Fe), has a unique structure that resembles a rifter with many thorns. When exposed to PSS-Gr, Ni-TCPP(Fe) would unfold into a sheet structure, exposing a lot of active sites and improving the catalytic active surface area, making it easier to detect H-FABP. We have successfully synthesized an electrochemical immunosensor based on Ni-TCPP(Fe)@PSS-Gr and Ag@Au/Pt as a signal label which demonstrated excellent sensor performance. A broad linear range of 10 fg/mL to 100 ng/mL with a low detection limit of 5.75 fg/mL (S/N = 5) for detecting H-FABP was obtained under ideal conditions. Furthermore, the detection results from the human serum samples were positive, suggesting that the made-up immunosensor could be useful for early clinical analysis. [ABSTRACT FROM AUTHOR]

A natural stress response induces elevated cortisol levels in biological fluids, such as saliva. While current sensor technologies can detect cortisol in real time, their sensitivity and reliability for human subjects have not been assured. This is due to relatively low concentrations of salivary cortisol, which fluctuate throughout the day and vary significantly between individuals. To address these challenges, we present an improved electrochemical biosensor leveraging graphene's exceptional conductivity and physicochemical properties. A 1-pyrenebutyric acid N-hydroxysuccinimide ester (PBASE-NHS)–modified commercial graphene foam (GF) electrode is presented to realize an ultra-sensitive biosensor for cortisol detection directly in human saliva. The biosensor fabrication process entails the attachment of anti-cortisol monoclonal antibodies (mAb-cort) onto a PBASE-NHS/GF electrode through noncovalent immobilization on the vertically stratified graphene foam electrode surface. This unique immobilization strategy preserves graphene's structural integrity and electrical conductivity while facilitating antibody immobilization. The binding of cortisol to immobilized mAb-cort is read out via differential pulse voltammetry using ferri/ferro redox reactions. The immunosensor demonstrates an exceptional dynamic range of 1.0 fg mL−1 to 10,000 pg mL−1 (R2 = 0.9914) with a detection limit of 0.24 fg mL−1 (n = 3) for cortisol. Furthermore, we have established the reliability of cortisol sensors in monitoring human saliva. We have also performed multiple modes of validation, one against the established enzyme-linked immunosorbent assay (ELISA) and a second by a third-party service Salimetric on 16 student volunteers exposed to different stress levels, showing excellent correlation (r = 0.9961). These findings suggest the potential for using mAb-cort/PBASE-NHS/GF-based cortisol electrodes for monitoring salivary cortisol in the general population. [ABSTRACT FROM AUTHOR]

A novel approach is presented that combines filtration and the direct immunomagnetic separation of the retained bacteria Legionella in filters, for further electrochemical immunosensing. This strategy allows for the separation and preconcentration of the water-borne pathogen from high-volume samples, up to 1000 mL. The limit of detection of the electrochemical immunosensor resulted in 100 CFU mL−1 and improved up to 0.1 CFU mL−1 when the preconcentration strategy was applied in 1 L of sample (103-fold improvement). Remarkably, the immunosensor achieves the limit of detection in less than 2.5 h and simplified the analytical procedure. This represents the lowest concentration reported to date for electrochemical immunosensing of Legionella cells without the need for pre-enrichment or DNA amplification. Furthermore, the study successfully demonstrates the extraction of bacteria retained on different filtering materials using immunomagnetic separation, highlighting the high efficiency of the magnetic particles to pull out the bacteria directly from solid materials. This promising feature expands the applicability of the method beyond water systems for detecting bacteria retained in air filters of air conditioning units by directly performing the immunomagnetic separation in the filters. [ABSTRACT FROM AUTHOR]

An ultrasensitive electrochemical immunosensor was developed for detection of the cervical squamous cell carcinoma antigen (SCCA) biomarker using graphene-chitosan nanocomposites. Graphene oxide (GO) synthesized by a modified Hummer's method was functionalized with chitosan biopolymer (CS) to produce CS-GO nanocomposites. Characterization by SEM, FTIR, Raman, XPS confirmed successful grafting of CS onto GO by electrostatic interactions. The CS-GO composite exhibited improved conductivity and biocompatibility. After optimizing the GO:CS ratio to 1:1, the nanocomposite was deposited on glassy carbon electrodes (GCE). Anti-SCCA antibodies were then immobilized covalently using pyrenebutyric acid crosslinker. The immunosensor fabrication was analyzed by EIS, CV, and DPV electrochemical techniques. The conditions including CS-GO ratio, antibody concentration, incubation time, pH, and voltage parameters were systematically optimized using orthogonal experimental design. Under optimal conditions, the immunosensor showed a linear detection range from 1 pg/mL to 100 ng/mL with a sensitivity of 196 μA/(ng/mL/cm2). The low limit of detection of 1 pg/mL was attributed to the high surface area and conductivity of the CS-GO transducer. Analysis of human serum samples spiked with SCCA demonstrated the reliability of the immunosensor for clinical applications. The graphene-nanocomposite electrochemical biosensing platform provides a rapid, low-cost, and ultrasensitive alternative to ELISA for SCCA detection in cervical cancer diagnostics. [ABSTRACT FROM AUTHOR]

This work created a simple electrochemical cortisol sensing method based on ZnO nanostructures to track high-performance athletes' stress levels and recuperation times. ZnO nanorods (ZnO NRs) were deposited on the surface of a glassy carbon electrode (ZnO/GCE) using an electrodeposition technique. Subsequently, 3-aminopropyltriethoxysilane (APTES) was applied to the electrode surface in order to improve cortisol antibody (C-M ab) immobilization and stability (C-M ab/APTES/ZnO/GCE). Successful immobilization of C-M ab on APTES/ZnO/GCE and electrodeposition of ZnO NRs on GCE were confirmed by structural investigations conducted using XRD, FT-IR, and FE-SEM. Cortisol was detected using an electrochemical immunosensor (C-M ab/APTES/ZnO/GCE) by monitoring the change in DPV and CV currents following cortisol binding to C-M ab. According to electrochemical experiments, the immunosensor exhibited a steady, selective, and sensitive response when it detected cortisol at concentrations between 10−6 nM and 106 nM, with a detection limit of 2 × 10−4 nM. It was assessed if the C-M ab/APTES/ZnO/GCE combination could identify cortisol in human serum. The samples' relative standard deviation (RSD) values range from 3.63% to 4.30%, and their recovery rates range from 90.00% to 98.50%, according to the analytical study. These findings imply that the C-M ab/APTES/ZnO/GCE offers accurate evaluations for cortisol detection in human serum samples. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Interferon-γ (IFN-γ) is a vital part of the immune system, and a critical biomarker determining the progression of several diseases, like tuberculosis, HIV, and multiple sclerosis. This work presents an electrochemical immunosensor for detecting IFN-γ based on an indium–tin oxide electrode modified with a nanocomposite of gold nanorods and reduced graphene oxide (AuNR-rGO). The antibodies are immobilized on the modified electrode. Subsequent addition of analyte proteins causes a drop in the peak current in the differential pulse voltammetry (DPV) since the proteins hinder electron transfer. The DPV peak current values are proportional to logarithmic IFN-γ concentrations in the dynamic range of 5–1000 pg/mL with a detection limit of 2.5 pg/mL. In addition, this immunosensor shows high specificity to IFN-γ in the presence of competent inflammatory proteins (IL-4 and TNF-α) in phosphate-buffered saline and human blood samples. Our results demonstrate the potential of AuNR-rGO nanocomposite as an effective electrode material for improved sensor performance, providing a simple, sensitive, and specific detection of IFN-γ. [ABSTRACT FROM AUTHOR]

A new conductive ink based on the addition of carbon black to a poly(vinyl alcohol) matrix is developed and investigated for electrochemical sensing and biosensing applications. The produced devices were characterized using morphological and electrochemical techniques and modified with Pd nanoparticles to enhance electrical conductivity and reaction kinetics. With the aid of chemometrics, the parameters for metal deposition were investigated and the sensor was applied to the determination of Parkinson's disease biomarkers, specifically epinephrine and α-synuclein. A linear behavior was obtained in the range 0.75 to 100 μmol L-1 of the neurotransmitter, and the device displayed a limit of detection (LOD) of 0.051 μmol L-1. The three-electrode system was then tested using samples of synthetic cerebrospinal fluid. Afterward, the device was modified with specific antibodies to quantify α-synuclein using electrochemical impedance spectroscopy. In phosphate buffer, a linear range was obtained for α-synuclein concentrations from 1.5 to 15 μg mL-1, with a calculated LOD of 0.13 μg mL-1. The proposed immunosensor was also applied to blood serum samples, and, in this case, the linear range was observed from 6.0 to 100.5 μg mL-1 of α-synuclein, with a LOD = 1.3 µg mL-1. Both linear curves attend the range for the real diagnosis, demonstrating its potential application to complex matrices. [ABSTRACT FROM AUTHOR]

The design of a novel electrochemical impedimetric biosensor for label-free analysis of resistin, a biomarker for obesity, is reported. For the fabrication of the immunosensor, a novel approach composed of electrochemical copolymerization of double epoxy groups-substituted thiophene (ThidEp) and 3,4-Ethylenedioxythiophene (EDOT) monomers was utilized. Anti-resistin antibodies were covalently attached to the copolymer-coated electrode. The capture of resistin antigens by anti-resistin antibodies caused significant variations in charge transfer resistance (Rct) because of the immunoreactions between these proteins. Under optimum experimental variables, the changes in impedance signals were employed for the determination of resistin antigen concentration, and the prepared immunosensor based on conjugated copolymer illustrated a wide linear range between 0.0125 and 22.5 pg/mL, a low detection limit (LOD) of 3.71 fg/mL, and a good sensitivity of 1.22 kΩ pg−1mL cm2. The excellent analytical performance of the resistin immunosensor in terms of selectivity, sensitivity, repeatability, reproducibility, storage stability, and low detection limit might be attributed to the conductive copolymer film layer generation on the disposable indium tin oxide (ITO) platform. The capability of this system for the determination of resistin in human serum and saliva samples was also tested. The immunosensor results were in accordance with the enzyme-linked immunosorbent assay (ELISA) results. The matrix effects of human serum and saliva were also investigated, and the proposed immunosensor displayed good recovery ranging from 95.91 to 106.25%. The engineered immunosensor could open new avenues for obesity monitoring. [ABSTRACT FROM AUTHOR]

To detect the dengue virus NS1 protein with high sensitivity, this research suggests an electrochemical immunosensor based on the Al-TCPP adsorption aggregation signal amplification approach. We created a type of metal-organic framework (MOF) material called astrophytum myriostigma, which resembles a cactus plant and has a large specific surface area. In addition, it can produce electrostatic attraction with the amino groups on methylene blue (MB), firmly fix MB on the MOF material, and manage MB reunion after adsorption, which is helpful for electron transmission and amplifies the electrical signal. The cationic dye methylene blue has redox characteristics. It possesses a high electron transfer rate, electrochemical reversibility, and strong biocompatibility. The generated electrochemical immunosensor has good reproducibility and stability, and the relationship between the analyte concentration and electrical signal strength is linear. The suggested immunosensor has a broad detection range from 10 fg/mL to 100 ng/mL with a low detection limit of 9.12 fg/mL under ideal conditions. [ABSTRACT FROM AUTHOR]

Evaluating the levels of the biomarker carbohydrate antigen 19-9 (CA19-9) is crucial in early cancer diagnosis and prognosis assessment. In this study, an antifouling electrochemical immunosensor was developed for the label-free detection of CA19-9, in which bovine serum albumin (BSA) and graphene were cross-linked with the aid of glutaraldehyde to form a 3D conductive porous network on the surface of an electrode. The electrochemical immunosensor was characterized through the use of transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscope (AFM), UV spectroscopy, and electrochemical methods. The level of CA19-9 was determined through the use of label-free electrochemical impedance spectroscopy (EIS) measurements. The electron transfer at the interface of the electrode was well preserved in human serum samples, demonstrating that this electrochemical immunosensor has excellent antifouling performance. CA19-9 could be detected in a wide range from 13.5 U/mL to 1000 U/mL, with a detection limit of 13.5 U/mL in human serum samples. This immunosensor also exhibited good selectivity and stability. The detection results of this immunosensor were further validated and compared using an enzyme-linked immunosorbent assay (ELISA). All the results confirmed that this immunosensor has a good sensing performance in terms of CA19-9, suggesting its promising application prospects in clinical applications. [ABSTRACT FROM AUTHOR]

The rampant spread and death rate of the recent coronavirus pandemic related to the SARS-CoV-2 respiratory virus have underscored the critical need for affordable, portable virus diagnostics, particularly in resource-limited settings. Moreover, efficient and timely monitoring of vaccine efficacy is needed to prevent future widespread infections. Electrochemical immunosensing poses an effective alternative to conventional molecular spectroscopic approaches, offering rapid, cost-effective, sensitive, and portable electroanalysis of disease biomarkers and antibodies; however, efforts to improve binding efficiency and sensitivity are still being investigated. Graphene quantum dots (GQDs) in particular have shown promise in improving device sensitivity. This study reports the development of a GQD-functionalized point-of-contamination device leveraging the selective interactions between SARS-CoV-2-specific Spike (S) Protein receptor binding domain (RBD) antigens and IgG anti-SARS-CoV-2-specific S-protein antibodies at screen-printed carbon electrode (SPCE) surfaces. The immunocomplexes formed at the GQD surfaces result in the interruption of the redox reactions that take place in the presence of a redox probe, decreasing the current response. Increased active surface area, conductivity, and binding via EDC/NHS chemistry were achieved due to the nanomaterial inclusion, with 5 nm, blue luminescent GQDs offering the best results. GQD concentration, EDC/NHS ratio, and RBD S-protein incubation time and concentration were optimized for the biosensor, and inter- and intra-screen-printed carbon electrode detection was investigated by calibration studies on multiple and single electrodes. The single electrode used for the entire calibration provided the best results. The label-free immunosensor was able to selectively detect anti-SARS-CoV-2 IgG antibodies between 0.5 and 100 ng/mL in the presence of IgM and other coronavirus antibodies with an excellent regression of 0.9599. A LOD of 2.028 ng/mL was found, offering comparable findings to the literature-reported values. The detection sensitivity of the sensor is further compared to non-specific IgM antibodies. The developed GQD immunosensor was compared to other low-oxygen content carbon nanomaterials, namely (i) carbon quantum dot (CQD), (ii) electrochemically reduced graphene oxide, and (iii) carbon black-functionalized devices. The findings suggest that improved electron transfer kinetics and increased active surface area of the CNs, along with surface oxygen content, aid in the detection of anti-SARS-CoV-2 IgG antibodies. The novel immunosensor suggests a possible application toward monitoring of IgG antibody production in SARS-CoV-2-vaccinated patients to study immune responses, vaccine efficacy, and lifetime to meet the demands for POC analysis in resource-limited settings. [ABSTRACT FROM AUTHOR]

[Display omitted] This study proposes the fabrication of a highly sensitive electrochemical immunosensor for label-free detection of EpCAM antigen. MXenes, novel 2D materials have become popular owing to their unique electrochemical properties. Unlike conventional immunosensors, which are unable to detect the carcinoma at primary stage and also time consuming, the use of highly conducting MXene provides a label-free and highly sensitive immunosensor. Herein, we develop a unique immunosensor, which is based on the in-situ growth of 2D-TiO 2 onto the novel 2D-Ti 3 C 2 T x sheets by hydrothermal treatment. The 2D/2D TiO 2 /Ti 3 C 2 T x hybrid provides a platform having a large effective surface area, and more number of electrochemically active sites to enhance the electron transfer rate through the redox probe. The designed sensing platform, BSA/anti-EpCAM/TiO 2 /Ti 3 C 2 T x @ITO shows a broad linear range (1 ag/mL to 10 ng/mL) with high sensitivity (6.661 µA ag−1 mL cm−2), and low detection limit (0.7 ag/mL) for EpCAM antigen detection under optimized conditions. The proposed immunosensor possesses good reproducibility, long-term stability, and outstanding selectivity and specificity. Moreover, the clinical applicability of the novel immunosensor is tested in spiked human serum showing good recovery. [ABSTRACT FROM AUTHOR]

We report here the results of studies related to the fabrication of an electrochemical immunosensor for the detection of Escherichia coli ATCC 25922 using AuNPs-GCE-avidin-Ab-E. coli based on complex compound. In the presence of targeted bacteria, the specific antibody was coated on the surface with gold nanoparticles (AuNPs). The detailed morphology of synthesized AuNPs was confirmed using analytical techniques. The proposed immunosensor revealed a high electrocatalytic activity and linear response at the peak potential value over a wide concentration of E. coli ATCC 25922 from 101 to 105 CFU/mL. The results were correlated with the linear equation of (R2 = 0.991). The recorded results were responded in the presence of targeted E. coli ATCC 25922 with other bacterial strains such as Salmonella typhi, Klebsiella aerogenes, and E. coli O57:H7 indicating a high selectivity of electrochemical immunosensor. A combined artificial neural network (ANN) approach serves as a powerful model to understand and analyze the intelligent data of the digital transformation output. The determined regression method of the fabricated sensor was selected for evaluation of the ANN-based technique that initiated to be a superior known method. The applied technique confirmed a great practical approach to targeted bacteria in spiked samples of the sandwich complex. Therefore, the satisfactory result demonstrates the feature of simulation data attainment and analysis is highly reliable and attractive. Moreover, the constructed immunosensor may be used to screen contaminated water and prevents an epidemic of life-threatening infectious disease. [ABSTRACT FROM AUTHOR]

The progression of Alzheimer's disease (AD) is positively correlated with the phosphorylation damage of Tau-441 protein, which is the marker with the most potential for the early detection of AD. The low content of Tau-441 in human serum is a major difficulty for the realization of content detection. Herein, we prepared an electrochemical immunosensor modified with Poly(3,4-ethylene-dioxythiophene)-poly (styrene sulfonate) (PEDOT: PSS)/Carboxylated multi-walled carbon nanotube (MWCNTs-COOH) nanocomposites based on electrochemical immunoassay technology for the low-concentration detection of Tau-441. The immunosensor based on the nanocomposite can take advantage of the characteristics of conductive polymers to achieve electrical signal amplification and use MWCNTs-COOH to increase the contact area of the active site and bond with the Tau-441 antibodies on the electrode. The physicochemical and electrical properties of PEDOT: PSS/MWCNTs-COOH were studied by in situ characterization techniques and electrochemical characterization methods, indicating that the immunosensor has high selectivity and sensitivity to the Tau-441 immune reaction. Under optimized optimal conditions, the electrochemical immunosensor detected a range of concentrations of Tau-441 to obtain a low detection of limit (0.0074 ng mL−1) and demonstrated good detection performance through actual human serum sample testing experiments. Therefore, the study provides an effective reference value for the early diagnosis of AD. [ABSTRACT FROM AUTHOR]

Gelatin derived from porcine sources raises significant ethical and religious concerns worldwide, particularly due to its increasing use in food-based products without adequate monitoring and control. Once gelatin is incorporated into processed food items, determining its source animal becomes challenging, which consequently increases the risks of adulteration and mislabeling. In this study, we propose the utilization of a novel nanocomposite comprising multi-walled carbon nanotubes (MWCNTs), chitosan (CS), and gold nano-urchins (AuNUs) for constructing a label-free electrochemical immunosensor. The purpose of this immunosensor is to effectively detect Porcine skin gelatin (PSG) in food samples using differential pulse voltammetry (DPV) with a 5 mM [K3Fe(CN6)] redox probe. Under optimized conditions, the fabricated biosensor demonstrates superior sensitivity to PSG, exhibiting a linear detection range of 50 pg/mL to 1000 a pg/mL and a limit of detection (LOD) of 23.079 pg/mL. Moreover, the constructed biosensor exhibits excellent reproducibility, acceptable selectivity, and interference resistance. Notably, it achieves outstanding recovery rates when applied to real food samples spiked with PSG, thus indicating its potential for practical implementation in food safety monitoring.

Previous studies confirm that aberrant expression of cytokeratin 19 fragment antigen 21-1 (cyfra-21-1) is highly correlated with non-small cell lung cancer (NSCLC). Herein, a proportional electrochemical immunosensor based upon a methylene blue/cadmium telluride/molybdic sulfide (MB/CdTe/MoS2) nanocomposite was successfully fabricated for detecting tumor marker cyfra-21-1. The result indicates that MB/CdTe/MoS2 modified on the surface of a glassy carbon electrode (GCE) supplies a large surface area for immobilizing primary antibodies (Ab1), ensuring high selectivity and sensitivity. To further amplify the sensitivity of the biosensor, ferrocenecarboxylic acid (Fc-COOH) linked with amino-functionalized secondary antibodies through amido bond (Ab2-Fc) as the "signal-on" probe and MB-modified with MoS2 with a large specific surface area as the "signal-off" probe increase the number of active sites for integration of Ab2-Fc/Ag/BSA/Ab1/MB/CdTe/MoS2/GCE electrode with the linker cyfra-21-1 (Ag). Meanwhile, CdTe accelerates the electron transfer and enhances the MB current, improving the sensitivity and detection limit. The presence of cyfra-21-1 led to both the decreasing response of MB and increasing current responses of Fc upon the electrode. Based upon this strategy, the determination of cyfra-21-1 was achieved in a linear range from 10 pg/mL to 10,000 ng/mL with the lowest detectable concentration of 10 pg/mL (signal-to-noise ratio of 3). The electrochemical immunosensor performs a sensitive determination of cyfra-21-1, possibly providing a practical strategy for the clinical analysis of lung cancer. [ABSTRACT FROM AUTHOR]

A novel electrochemical sensing platform based on Fe3O4-antibody conjugate was developed for the rapid and sensitive determination of Salmonella typhimurium antigen in model suspensions. The conjugates Fe3O4-antibody were synthesized via carbodiimide cross-linking and characterized by infrared spectroscopy and cyclic voltammetry. The electrochemical properties of Fe3O4 magnetic nanoparticles in water were investigated; the possible mechanism of direct electrochemical reduction was proposed and justified as an analytical signal. The design of an electrochemical sensing platform with magnetically controlled flows has been proposed. Under the most appropriate conditions, the developed portable device was provided the linear response as I (µA) = (7.20 ± 0.35) × (–lg CAg) − (23.77 ± 1.95) in the concentration range 1 × 10−7–1 × 10−4 mg/mL. The detection limit was 390 ng/mL and was comparable to other works. [ABSTRACT FROM AUTHOR]

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Based on an indirect competitive method, a novel nano-Au/fluticasone propionate electrochemical immunosensor was successfully fabricated by combining the nanoscale effect, superior conductivity of nano-Au, stable Au−S chemical bond as well as strong interaction between glucocorticoid and the receptor, which was used to simultaneously detect eight kinds of glucocorticoids. The modified immunosensors' electrochemical properties were explored by means of a cyclic voltammetry (CV) method and electrochemical impedance spectroscopy (EIS) measurements. Two factors (glucocorticoid receptor concentration, incubation time) were studied in order to obtain the optimal results. The immunosensor presents attractive electrochemical performance with a wide linear range (between 0.1 and 1500 ng⋅mL−1) and low detection limit (between 0.057 and 0.357 ng⋅mL−1), realizing the rapid multi-residue detection of a large class of glucocorticoids. Two glucocorticoids (hydrocortisone, triamcinolone) were detected in actual skincare samples, which obtained satisfactory detection results. [ABSTRACT FROM AUTHOR]

An electrochemical immunosensor based on carbon nanofibers (CNFs) and gold nanoparticles (AuNPs) was developed for detecting anti-Toxoplasma gondii antibodies (anti-T. gondii) IgG in human serum. CNFs were produced using electrospinning and carbonization processes. Screen-printed carbon electrode (SPCE) surface was modified with CNFs and AuNPs which were electrodeposited onto the CNFs. Then, T. gondii antigen was immobilized onto the AuNPs/CNFs/SPCE. Afterward, anti-T. gondii IgG positive serum samples were coated on the modified electrode and assessed via adding anti-human IgG labeled with horseradish peroxidase (HRP) enzyme. The morphology of SPCE, CNFs, and AuNPs/CNFs/SPCE surface was characterized using field emission scanning electron microscopy (FESEM) equipped with energy dispersive spectroscopy (EDS). Characterization of CNFs was evaluated by Raman spectroscopy and X-ray diffraction (XRD). Electrochemical characterization of the immunosensor was verified using cyclic voltammetry (CV), and electrochemical response of modified electrode for anti-T. gondii IgG was detected via differential pulse voltammetry (DPV). This immunosensor was detected in the range 0–200 U mL−1 with a low detection limit (9 × 10−3 U mL−1). In addition, the proposed immunosensor was exhibited with high selectivity, strong stability, and acceptable reproducibility and repeatability. Furthermore, there was a strong correlation between results obtained via the designed immunosensor and enzyme-linked immunosorbent assay (ELISA) as gold standard. In conclusion, the developed immunosensor is a promising route for rapid and accurate clinical diagnosis of toxoplasmosis. [ABSTRACT FROM AUTHOR]

The screen-printed carbon electrode (SPCE) is a useful technology that has been widely used in the practical application of biosensors oriented to point-of-care testing (POCT) due to its characteristics of cost-effectiveness, disposability, miniaturization, wide potential window, and simple electrode design. Compared with gold or platinum electrodes, surface modification is difficult because the carbon surface is chemically or physically stable. Oxygen plasma (O2) can easily produce carboxyl groups on the carbon surface, which act as scaffolds for covalent bonds. However, the effect of O2-plasma treatment on electrode performance remains to be investigated from an electrochemical perspective, and sensor performance can be improved by clarifying the surface conditions of plasma-treated biosensors. In this research, we compared antibody modification by plasma treatment and physical adsorption, using our novel immunosensor based on gold nanoparticles (AuNPs). Consequently, the O2-plasma treatment produced carboxyl groups on the electrode surface that changed the electrochemical properties owing to electrostatic interactions. In this study, we compared the following four cases of SPCE modification: O2-plasma-treated electrode/covalent-bonded antibody (a); O2-plasma-treated electrode/physical adsorbed antibody (b); bare electrode/covalent-bonded antibody (c); and bare electrode/physical absorbed antibody (d). The limits of detection (LOD) were 0.50 ng/mL (a), 9.7 ng/mL (b), 0.54 ng/mL (c), and 1.2 ng/mL (d). The slopes of the linear response range were 0.039, 0.029, 0.014, and 0.022. The LOD of (a) was 2.4 times higher than the conventional condition (d), The slope of (a) showed higher sensitivity than other cases (b~d). This is because the plasma treatment generated many carboxyl groups and increased the number of antibody adsorption sites. In summary, the O2-plasma treatment was found to modify the electrode surface conditions and improve the amount of antibody modifications. In the future, O2-plasma treatment could be used as a simple method for modifying various molecular recognition elements on printed carbon electrodes.

We reported a highly efficient electrochemical immunosensor utilizing chitosan–graphene nanosheets (CS-GNs) nanocomposites for the detection of aflatoxin B1 (AFB1) in corn samples. The CS-GNs nanocomposites, serving as a modifying layer, provide a significant specific surface area and biocompatibility, thereby enhancing both the electron transfer rate and the efficiency of antibody immobilization. The electrochemical characterization was conducted utilizing both differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). Moreover, the antibody concentration, pH, antibody immobilization time, and immunoreaction time, were optimized. The results showed that the current change (ΔI) before and after the immunoreaction demonstrated a strong linear relationship (R2=0.990) with the AFB1 concentration, as well as good specificity and stability. The linear range extended from 0.05 to 25 ng/mL, with a detection limit of 0.021 ng/mL (S/N=3). The immunosensor exhibited a recovery rate ranging from 97.3% to 101.4% in corn samples, showing a promising performance using an efficient method, and indicating a remarkable prospect for the detection of fungal toxins in grains.

This research is focused on enhancing the capabilities of scanning electrochemical impedance microscopy (SEIM) for detecting gold nanoparticle-labelled antibodies using electrochemically modified platinum ultramicroelectrode. The primary objective was to address the high resistance issue encountered in previous measurements with SEIM via the utilization of SEIM probes based on micro-electrodes modified by platinum microstructures, which improved the sensitivity and precision of the detection of targeted biomolecules. The modified probe resulted in a lowered charge transfer resistance by over ten times and a decrease in detection to around 100 fg/mL. We suggest potential applications in various biotechnological and biomedical fields, with future research expected to further refine this technique.

In this study, we report a highly sensitive electrochemical immunosensor for carcinoembryonic antigen (CEA) detection based on the electrodeposited platinum nanoparticles (Pt NPs) confined in the ultrasmall nanochannels of vertically ordered mesoporous silica film (VMSF). VMSF bearing amine groups (NH2-VMSF) can be prepared on the indium tin oxide electrode surface via a one-step co-condensation route using an electrochemically assisted self-assembly method, which renders a strong electrostatic effect for [PtCl6]2- and leads to the spatial confinement of Pt NPs inside the silica nanochannels after electrodeposition. The external surface of NH2-VMSF is functionalized with CEA antibodies using glutaraldehyde as a coupling agent, resulting in an electrochemical immunosensing interface with good specificity for CEA detection. Under optimal experimental conditions, high affinity between the CEA antibody and CEA produces a steric hindrance effect for the accessibility of the electrochemical probe ([Fe(CN)6]3-) in the bulk solution to the underlying indium tin oxide surface, eventually resulting in the attenuated electrochemical signal and enabling the detection of the CEA with a wide linear range of 0.01 pg/mL∼10 ng/mL and a pretty low limit of detection of 0.30 fg/mL. Owing to the signal amplification ability of Pt NPs and the anti-biofouling property of NH2-VMSF, the as-prepared electrochemical immunosensor based on the Pt NPs@NH2-VMSF displays an accurate analysis of the CEA in human serum samples, holding significant promise for health monitoring and clinical diagnosis.

Non-small cell lung cancer (NSCLC) is the most common type of lung cancer accounting for 85% of all newly diagnosed cases. Its prognosis remains poor as most patients are diagnosed at an advanced stage. In this study, we report the development of an electrochemical immunosensor for quantitative detection of Yamaguchi sarcoma viral oncogene homolog 1 (v-YES1) protein, comprised of a glassy carbon electrode modified with gold nanoparticles (AuNP), thiolated protein G (TPG), YES1 antibody (AB1) and glutaraldehyde (GA), which was used as a cross linker. Cyclic voltammetry (CV) and Differential pulse voltammetry (DPV) were used to measure the response and characterization of the fabricated immunosensor. The fabricated immunosensor, glassy carbon electrode (GCE)/AuNP/TPG/GA/Ab1) was optimized for pH, response time, antibody concentration and temperature. Under optimum conditions, the immunosensor displayed high sensitivity, recording a limit of detection (LOD) of 0.0014 ng/mL and was noted to have negligible cross reactivity. The proposed immunosensor proved to be stable for up to 2 weeks, which means that it can be used as an alternative diagnostic tool for the rapid, sensitive and specific detection of YES1 antigen in clinical samples for clinical monitoring of cancer progression.

Phenanthrene (PHE), as a structurally simple, tricyclic, polycyclic aromatic hydrocarbon (PAHs), is widely present in marine environments and organisms, with serious ecological and health impacts. It is crucial to study fast and simple high-sensitivity detection methods for phenanthrene in seawater for the environment and the human body. In this paper, a immunosensor was prepared by using a multi-wall carbon nanotube (MWCNTs)-chitosan oligosaccharide (COS) nanocomposite membrane loaded with phenanthrene antibody. The principle was based on the antibody–antigen reaction in the immune reaction, using the strong electron transfer ability of multi-walled carbon nanotubes, coupled with chitosan oligosaccharides with an excellent film formation and biocompatibility, to amplify the detection signal. The content of the phenanthrene in seawater was studied via differential pulse voltammetry (DPV) using a potassium ferricyanide system as a redox probe. The antibody concentration, pH value, and probe concentration were optimized. Under the optimal experimental conditions, the response peak current of the phenanthrene was inversely proportional to the concentration of phenanthrene, in the range from 0.5 ng·mL−1 to 80 ng·mL−1, and the detection limit was 0.30 ng·mL−1. The immune sensor was successfully applied to the detection of phenanthrene in marine water, with a recovery rate of 96.1~101.5%, and provided a stable, sensitive, and accurate method for the real-time monitoring of marine environments. [ABSTRACT FROM AUTHOR]

Neglected tropical diseases are those caused by infectious agents or parasites and are considered endemic in low-income populations. These diseases also have unacceptable indicators and low investment in research, drug production, and control. Tropical diseases such as leishmaniasis are some of the main causes of morbidity and mortality around the globe. Electrochemical immunosensors are promising tools for diagnostics against these diseases. One such benefit is the possibility of assisting diagnosis in isolated regions, where laboratory infrastructure is lacking. In this work, different peptides were investigated to detect antibodies against Leishmania in human and canine serum samples. The peptides evaluated (395-KKG and 395-G) have the same recognition site but differ on their solid-binding domains, which ensure affinity to spontaneously bind to either graphene oxide (GO) or graphene quantum dots (GQD). Cyclic voltammetry and differential pulse voltammetry were employed to investigate the electrochemical behavior of each assembly step and the role of each solid-binding domain coupled to its anchoring material. The graphene affinity peptide (395-G) showed better reproducibility and selectivity when coupled to GQD. Under the optimized set of experimental conditions, negative and positive human serum samples responses were distinguished based on a cut-off value of 82.5% at a 95% confidence level. The immunosensor showed selective behavior to antibodies against Mycobacterium leprae and Mycobacterium tuberculosis, which are similar antibodies and potentially sources of false positive tests. Therefore, the use of the graphene affinity peptide as a recognition site achieved outstanding performance for the detection of Leishmania antibodies. [ABSTRACT FROM AUTHOR]

A novel electrochemical immunosensor was developed for highly sensitive detection of brain-derived neurotrophic factor (BDNF), a well-known depression marker. The immunosensor was fabricated by modifying indium tin oxide-coated polyethylene terephthalate (ITO-PET) with N-doped graphene-polyaniline (NG-PANI) and gold nanoparticles (AuNPs) to enhance the conductivity and protein loading capacity. Subsequently, BDNF was immobilized onto the electrode surface via gold-sulfur bonds, followed by the attachment of biotinylated antibody (Biotin-Ab) and horseradish peroxidase-avidin (HRP-Avidin) to create the final immunosensor (HRP-Avidin–Biotin-Ab-BDNF-AuNPs/NG-PANI/ITO-PET). The proposed immunosensor exhibited a linear range of determination (0.781–400 pg/mL) with a low limit of detection (LOD) of 0.261 pg/mL (S/N = 3) and excellent reproducibility (RSD = 1.4%) and stability (92.7%, RSD = 3.1%). Additionally, the immunosensor demonstrated good anti-interference performance and good recovery (98.1–107%). To evaluate the practical utility of the immunosensor, BDNF levels were quantified in the serum of mice with depression induced by chronic unpredictable mild stress (CUMS). The results indicated that the serum BDNF levels were significantly decreased in the depression model group compared with the control group, highlighting the potential of this immunosensor for clinical detection of BDNF in depression diagnosis and treatment. [ABSTRACT FROM AUTHOR]

A sandwich-type electrochemical immunosensor was designed by highly efficient catalytic cycle amplification strategy of CuFe2O4-Pd for sensitive detection of cardiac troponin I. CuFe2O4 with coupled variable valence metal elements exhibited favorable catalytic performance through bidirectional cycling of Fe2+/Fe3+ and Cu+/Cu2+ redox pairs. More importantly, Cu+ acted as the intermediate product of the catalytic reaction, promoted the regeneration of Fe2+ and ensured the continuous recycling occurrence of the double redox pairs, and significantly amplified the current signal response. Pd nanoparticles (Pd NPs) loaded on the surface of amino-functionalized CuFe2O4 (CuFe2O4-NH2) served as electrochemical mediators to capture labeled antibodies (Ab2), and also as co-catalysts of CuFe2O4 to further enhance the catalytic efficiency, thus improving the sensitivity of the electrochemical immunosensor. Under the optimal experimental conditions, the linear range was 0.001 ~ 100 ng/mL, and the detection limit was 1.91 fg/mL. The electrochemical immunosensor has excellent analytical performance, giving a new impetus for the sensitive detection of cTnI. [ABSTRACT FROM AUTHOR]

Neuron-specific enolase (NSE) has gained extensive attention as a reliable target for detecting small cell carcinoma of lungs. In this paper, an electrochemical immunoassay method based on molybdenum disulfide (MoS2) is proposed to detect NSE sensitively. By an in-situ growth method, MoS2 and Au nanoclusters (Au NCs) were composited to form a MoS2@Au nanozyme, and then the secondary antibodies were modified. Primary antibodies were immobilized on amino-reduced graphene oxides to capture NSE. The flower-like MoS2 nanozyme provided abundant sites to load Au NCs and catalyze the decomposition of H2O2, which were beneficial to amplify an amperometric response as well as build up sensitivity. Under optimum conditions, the detection range of this strategy was 0.1 pg·mL−1–10 ng·mL−1 and the limit of detection was 0.05 pg·mL−1. This sensing strategy achieved the prospect of sensitively detecting NSE. Moreover, the prepared electrochemical immunosensor provides a theoretical basis and technical support for the detection of other disease markers. [ABSTRACT FROM AUTHOR]

A novel ultrasensitive nanobody-based electrochemical immunoassay was prepared for assessing human exposure to pyrethroid insecticides. 3-Phenoxybenzoic acid (3-PBA) is a common human urinary metabolite for numerous pyrethroids, which broadly served as a biomarker for following the human exposure to this pesticide group. The 3-PBA detection was via a direct competition for binding to alkaline phosphatase-embedded nanobodies between free 3-PBA and a 3-PBA-bovine serum albumin conjugate covalently immobilized onto citric acid-decorated nylon nanofibers, which were incorporated on a screen-printed electrode (SPE). Electrochemical impedance spectroscopy (EIS) was utilized to support the advantage of the employment of nanofibrous membranes and the success of the immunosensor assembly. The coupling between the nanofiber and nanobody technologies provided an ultrasensitive and selective immunosensor for 3-PBA detection in the range of 0.8 to 1000 pg mL-1 with a detection limit of 0.64 pg mL-1. Moreover, when the test for 3-PBA was applied to real samples, the established immunosensor proved to be a viable alternative to the conventional methods for 3-PBA detection in human urine even without sample cleanup. It showed excellent properties and stability over time.

Abstract Avian influenza virus H9 subtype (AIV H9) has contributed to enormous economic losses. Effective diagnosis is key to controlling the spread of AIV H9. In this study, a nonenzymatic highly electrocatalytic material was prepared using chitosan (Chi)-modified graphene sheet (GS)-functionalized Au/Pt nanoparticles (GS-Chi-Au/Pt), followed by the construction of a novel enzyme-free sandwich electrochemical immunosensor for the detection of AIV H9 using GS-Chi-Au/Pt and graphene–chitosan (GS-Chi) nanocomposites as a nonenzymatic highly electrocatalytic material and a substrate material to immobilize capture antibodies (avian influenza virus H9-monoclonal antibody, AIV H9/MAb), respectively. GS, which has a large specific surface area and many accessible active sites, permitted multiple Au/Pt nanoparticles to be attached to its surface, resulting in substantially improved conductivity and catalytic ability. Au/Pt nanoparticles can provide modified active sites for avian influenza virus H9-polyclonal antibody (AIV H9/PAb) immobilization as signal labels. Upon establishing the electrocatalytic activity of Au/Pt nanoparticles on graphene towards hydrogen peroxide (H2O2) reduction for signal amplification and optimizing the experimental parameters, we developed an AIV H9 electrochemical immunosensor, which showed a wide linear range from 101.37 EID50 mL−1 to 106.37 EID50 mL−1 and a detection limit of 100.82 EID50 mL−1. This sandwich electrochemical immunosensor also exhibited high selectivity, reproducibility and stability.

Herein, an ultra-sensitive and facile electrochemical biosensor for procalcitonin (PCT) detection was developed based on NiCoP/g-C3N4 nanocomposites. Firstly, NiCoP/g-C3N4 nanocomposites were synthesized using hydrothermal methods and then functionalized on the electrode surface by π-π stacking. Afterward, the monoclonal antibody that can specifically capture the PCT was successfully linked onto the surface of the nanocomposites with a 1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and N-Hydroxysuccinimide (NHS) condensation reaction. Finally, the modified sensor was employed for the electrochemical analysis of PCT using differential Pulse Voltammetry(DPV). Notably, the larger surface area of g-C3N4 and the higher electron transfer capacity of NiCoP/g-C3N4 endow this sensor with a wider detection range (1 ag/mL to 10 ng/mL) and an ultra-low limit of detection (0.6 ag/mL, S/N = 3). In addition, this strategy was also successfully applied to the detection of PCT in the diluted human serum sample, demonstrating that the developed immunosensors have the potential for application in clinical testing. [ABSTRACT FROM AUTHOR]

The detection signal of carbohydrate antigen 125 (CA125) can be quantitatively amplified via the dual metal–organic framework (MOF) sandwich strategy. We propose a versatile method for synthesizing uniform MXene and MIL-101(Fe)-NH2 composites that combine the advantages of both materials to build a base layer with superb performance. MXene exhibits excellent electrical conductivity and high surface area. The mesoporous MIL-101(Fe)-NH2 not only increases the loading capacity of the primary antibody but also possesses the catalytic activity of the metal center (Fe). UiO66 loaded with methylene blue (MB) was fabricated as an electrochemical immunosensor signal tag to enable the detection of CA125. The mixture of MXene and MIL-101(Fe)-NH2 prepared as the substrate was fixed by chitosan rich in amino groups. As the signal amplification sector, UiO66@MB enhanced secondary antibody loading capacity and generated a redox signal enabling the detection of antigenic substances. The proposed electrochemical immunosensor demonstrated high sensitivity with a low limit of detection (LOD) of 0.006 U/mL. Therefore, the dual MOF sandwich-based immunosensor provides a novel method for the early diagnosis of CA125. [ABSTRACT FROM AUTHOR]

Electrochemical biosensors are superior technologies that are used to detect or sense biologically and environmentally significant analytes in a laboratory environment, or even in the form of portable handheld or wearable electronics. Recently, imprinted and implantable biosensors are emerging as point-of-care devices, which monitor the target analytes in a continuous environment and alert the intended users to anomalies. The stability and performance of the developed biosensor depend on the nature and properties of the electrode material or the platform on which the biosensor is constructed. Therefore, the biosensor platform plays an integral role in the effectiveness of the developed biosensor. Enormous effort has been dedicated to the rational design of the electrode material and to fabrication strategies for improving the performance of developed biosensors. Every year, in the search for multifarious electrode materials, thousands of new biosensor platforms are reported. Moreover, in order to construct an effectual biosensor, the researcher should familiarize themself with the sensible strategies behind electrode fabrication. Thus, we intend to shed light on various strategies and methodologies utilized in the design and fabrication of electrochemical biosensors that facilitate sensitive and selective detection of significant analytes. Furthermore, this review highlights the advantages of various electrode materials and the correlation between immobilized biomolecules and modified surfaces. [ABSTRACT FROM AUTHOR]

In this study, ZnO nanostructures with different types of morphologies and particle sizes were evaluated and applied for the development of an immunosensor. The first material was composed of spherical, polydisperse nanostructures with a particle size in the range of 10–160 nm. The second was made up of more compact rod-like spherical nanostructures with the diameter of these rods in the range of 50–400 nm, and approximately 98% of the particles were in the range of 20–70 nm. The last sample of ZnO was made up of rod-shaped particles with a diameter of 10–80 nm. These ZnO nanostructures were mixed with Nafion solution and drop-casted onto screen-printed carbon electrodes (SPCE), followed by a further immobilization of the prostate-specific antigen (PSA). The affinity interaction of PSA with monoclonal antibodies against PSA (anti-PSA) was evaluated using the differential pulse voltammetry technique. The limit of detection and limit of quantification of anti-PSA were determined as 1.35 nM and 4.08 nM for compact rod-shaped spherical ZnO nanostructures, and 2.36 nM and 7.15 nM for rod-shaped ZnO nanostructures, respectively. [ABSTRACT FROM AUTHOR]

In this work, a conducting polymer (CP) was obtained through three electrochemical procedures to study its effect on the development of an electrochemical immunosensor for the detection of immunoglobulin G (IgG-Ag) by square wave voltammetry (SWV). The glassy carbon electrode modified with poly indol-6-carboxylic acid (6-PICA) applied the cyclic voltammetry technique presented a more homogeneous size distribution of nanowires with greater adherence allowing the direct immobilization of the antibodies (IgG-Ab) to detect the biomarker IgG-Ag. Additionally, 6-PICA presents the most stable and reproducible electrochemical response used as an analytical signal for developing a label-free electrochemical immunosensor. The different steps in obtaining the electrochemical immunosensor were characterized by FESEM, FTIR, cyclic voltammetry, electrochemical impedance spectroscopy, and SWV. Optimal conditions to improve performance, stability, and reproducibility in the immunosensing platform were achieved. The prepared immunosensor has a linear detection range of 2.0–16.0 ng·mL−1 with a low detection limit of 0.8 ng·mL−1. The immunosensing platform performance depends on the orientation of the IgG-Ab, favoring the formation of the immuno-complex with an affinity constant (Ka) of 4.32 × 109 M−1, which has great potential to be used as point of care testing (POCT) device for the rapid detection of biomarkers. [ABSTRACT FROM AUTHOR]

The evaluation of serological responses to COVID-19 is crucial for population-level surveillance, developing new vaccines, and evaluating the efficacy of different immunization programs. Research and development of point-of-care test technologies remain essential to improving immunity assessment, especially for SARS-CoV-2 variants that partially evade vaccine-induced immune responses. In this work, an impedimetric biosensor based on the immobilization of the recombinant trimeric wild-type spike protein (S protein) on zinc oxide nanorods (ZnONRs) was employed for serological evaluation. We successfully assessed its applicability using serum samples from spike-based COVID-19 vaccines: ChAdOx1-S (Oxford–AstraZeneca) and BNT162b2 (Pfizer–BioNTech). Overall, the ZnONRs/ spike-modified electrode displayed accurate results for both vaccines, showing excellent potential as a tool for assessing and monitoring seroprevalence in the population. A refined outcome of this technology was achieved when the ZnO immunosensor was functionalized with the S protein from the P.1 linage (Gamma variant). Serological responses against samples from vaccinated individuals were acquired with excellent performance. Following studies based on traditional serological tests, the ZnONRs/spike immunosensor data reveal that ChAdOx1-S vaccinated individuals present significantly less antibody-mediated immunity against the Gamma variant than the BNT162b2 vaccine, highlighting the great potential of this point-of-care technology for evaluating vaccine-induced humoral immunity against different SARS-CoV-2 strains. [ABSTRACT FROM AUTHOR]

In this work, two human epidermal growth factor receptors, HER-1 and HER-2, were selected as biomarkers to enable the detection of breast cancer. Therefore, two biosensors were developed using gold sensor chips coupled with amperometric detection of the enzyme label horse radish peroxidase (HRP). The biosensors/immunosensors relied on indirect sandwich enzyme-linked immunosorbent assays with monoclonal antibodies (Ab) against HER-1 and HER-2 attached to the sensors to capture the biomarkers. Detection polyclonal antibodies followed by secondary anti-rabbit (for HER-1) and anti-goat (for HER-2) IgG antibody-HRP were then applied for signal generation. In buffer, the developed sensors showed limits of detections (LOD) of 1.06 ng mL−1 and 0.95 ng mL−1 and limits of quantification (LOQ) of 2.1 ng mL−1 and 1.5 ng mL−1 for HER-1 and HER-2, respectively. In 100% (undiluted) serum, LODs of 1.2 ng mL−1 and 1.47 ng mL−1 and LOQs of 1.5 ng mL−1 and 2.1 ng mL−1 were obtained for HER-1 and HER-2, respectively. Such limits of detections are within the serum clinical range for the two biomarkers. Furthermore, gold nanoparticles (AuNP) labelled with secondary anti-rabbit and anti-goat IgG antibody-HRP were then used to enhance the assay signal and increase the sensitivity. In buffers, LODs of 30 pg mL−1 were seen for both sensors and LOQs of 98 pg mL−1 and 35 pg mL−1 were recorded for HER-1 and HER-2, respectively. For HER-2 the AuNPs biosensor was also tested in 100% serum obtaining a LOD of 50 pg mL−1 and a LOQ of 80 pg mL−1. The HER-2 AuNP electrochemical immunosensor showed high specificity with very low cross-reactivity to HER-1. These findings demonstrate that the two developed sensors can enable early detection as well as monitoring of disease progression with a beneficial impact on patient survival and clinical outcomes. [ABSTRACT FROM AUTHOR]