Development Of Immunosensor Research Articles

Resorc[4]arene Modifiers for Supramolecular Site-Directed Immobilization of Antibodies on Multi-Walled Carbon Nanotubes.

One of the main problems in developing immunosensors featuring carbon nanotubes (CNTs) is immobilizing antibodies (Abs) onto the CNT surface to afford selective binding to target antigens (Ags). In this work, we developed a practical supramolecular Ab conjugation strategy based on resorc[4]arene modifiers. To improve the Ab orientation on the CNTs surface and optimizing the Ab/Ag interaction, we exploited the host-guest approach by synthesizing two newly resorc[4]arene linkers R1 and R2 via well-established procedures. The upper rim was decorated with eight methoxyl groups to promote selective recognition of the fragment crystallizable (Fc ) region of the Ab. Moreover, the lower rim was functionalized with 3-bromopropyloxy or 3-azidopropiloxy substituents to bind the macrocycles on the multi-walled carbon nanotubes (MWCNTs) surface. Accordingly, several chemical modifications of MWCNTs were evaluated. After the morphological and electrochemical characterization of nanomaterials, the resorc[4]arene-modified MWCNTs were deposited onto a glassy carbon electrode surface to evaluate their potential applicability for label-free immunosensor development. The most promising system showed an improved electrode active area (AEL ) of almost 20 % and a site-oriented immobilization of the SARS-CoV-2 spike protein S1 antibody (Ab-SPS1). The developed immunosensor revealed a good sensitivity (23.64 μA mL ng-1 cm-2 ) towards the SPS1 antigen and a limit of detection (LOD) of 1.01 ng mL-1 .

Applying CeO2 nanorods in flexible electrochemical immunosensor to detect C-reactive protein

In this work, we report the development of a flexible electrochemical immunosensor based on CeO2 nanorods (NRs) immobilized with C-reactive protein (CRP) antibody, a biomarker of cardiovascular disease. CeO2 NRs were obtained by microwave-assisted hydrothermal method and characterized by XRD, TEM, and XPS. For the preparation of the working electrode, WE, of the immunosensor, the NRs were dispersed in organic solvent and then functionalized with cystamine and glutaraldehyde, and then modified with CRP antibody. The deposition condition was evaluated for electrode functionalization and immobilization. Functionalization and immobilization were verified by spectroscopic techniques and proved effective repeatability and reproducibility. The developed immunosensor had acceptable reproducibility (coefficient of variation = 4.5 %), allowed detection in the range of 0.3 to 7.0 mg L−1 of CRP with a detection limit of 0.18 mg L−1, and applications that are immediately detectable, easy-to-handle, low-cost and ideal for point-of-care.

Development of Electrochemical Immunosensors for HER-1 and HER-2 Analysis in Serum for Breast Cancer Patients.

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.

Sensitive electrochemical recognition of α-synuclein protein in human plasma samples using bioconjugated gold nanoparticles: An innovative immuno-platform to assist in the early stage identification of Parkinson's disease by biosensor technology.

This research work explains the development of an electrochemical immunosensor for the selective recognition of SNCA in human biofluids. An innovative protocol was proposed for the green synthesis of gold nanoparticle-supported dimethylglyoxime (AuNPs@DMGO) using one-step electrogeneration method. Also, the application of AuNPs@DMGO for the sensitive quantification of α-Synuclein (SNCA) protein and its biomedical analysis. So, an innovative sandwich immunosensor was designed for the sensitive identification of SNCA antigen in an aqueous solution. The gold nanoparticles (AuNPs) were decorated on the surface of the glassy carbon electrode by chronoamperometry technique to provide appropriate immobilization surface with a large number of active sites for immobilization of specific biotinylated antibody (Ab1) and against SNCA protein. Then, the sandwich-type immuno-platform was completed by the attachment of secondary antibody (HRP conjugated Ab [Ab2]) to the primary complexes on the surface of the electrode. For the first time, α-Synuclein protein was measured with an acceptable linear range of 4-64 ng/mL and a lower limit of quantification of 4 ng/mL. Benefiting from the simplicity and high sensitivity, the proposed method shows a potential of employment in clinical applications and high-throughput screening of Parkinson's disease using POC.

Formation of a Conducting Polymer by Different Electrochemical Techniques and Their Effect on Obtaining an Immunosensor for Immunoglobulin G

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.

Resorc[4]arene-Modified Gold-Decorated Magnetic Nanoparticles for Immunosensor Development.

In recent years, several efforts have been made to develop selective, sensitive, fast response, and miniaturized immunosensors with improved performance for the monitoring and screening of analytes in several matrices, significantly expanding the use of this technology in a broad range of applications. However, one of the main technical challenges in developing immunosensors is overcoming the complexity of binding antibodies (Abs) to the sensor surface. Most immobilizing approaches lead to a random orientation of Abs, resulting in lower binding site density and immunoaffinity. In this context, supramolecular chemistry has emerged as a suitable surface modification tool to achieve the preorganization of artificial receptors and to improve the functional properties of self-assembled monolayers. Herein, a supramolecular chemistry/nanotechnology-based platform was conceived to develop sensitive label-free electrochemical immunosensors, by using a resorcarene macrocycle as an artificial linker for the oriented antibody immobilization. To this aim, a water-soluble bifunctional resorc[4]arene architecture (RW) was rationally designed and synthesized to anchor gold-coated magnetic nanoparticles (Au@MNPs) and to maximize the amount of the active immobilized antibody (Ab) in the proper "end-on" orientation. The resulting supramolecular chemistry-modified nanoparticles, RW@Au@MNPs, were deposited onto graphite screen printed electrodes which were then employed to immobilize three different Abs. Furthermore, an immunosensor for atrazine (ATZ) analysis was realized and characterized by the differential pulse voltammetry technique to demonstrate the validity of the developed biosensing platform as a proof of concept for electrochemical immunosensors. The RW-based immunosensor improved AbATZ loading on Au@MNPs and sensitivity toward ATZ by almost 1.5 times compared to the random platform. Particularly, the electrochemical characterization of the developed immunosensor displays a linearity range toward ATZ within 0.05-1.5 ng/mL, a limit of detection of 0.011 ng/ml, and good reproducibility and stability. The immunosensor was tested by analyzing spiked fortified water samples with a mean recovery ranging from 95.7 to 108.4%. The overall good analytical performances of this immunodevice suggest its application for the screening and monitoring of ATZ in real matrices. Therefore, the results highlighted the successful application of the resorc[4]arene-based sensor design strategy for developing sensitive electrochemical immunosensors with improved analytical performance and simplifying the Ab immobilization procedure.

Development of a quartz crystal microbalance-based immunosensor for the early detection of mesothelin in cancer

A robust real-time flow injection assay using Quartz Crystal Microbalance (QCM) biosensor has been developed for the detection of mesothelin, an antigen expressed on various malignant tumors including mesothelioma and ovarian cancers. A QCM sensor chip functionalized with self-assembled monolayer of cysteamine used to fabricate a sensitive immunosensor. Mesothelin specific antibody was immobilized on cysteamine modified gold surface of quartz crystal using N-ethyl-N’-(3-dimethylaminopropyl) carbodiimide and N-hydroxy succinimide coupling. Further, ethanolamine was used as a blocking reagent to prevent the non-specific adsorption on antibody functionalized gold surface. Various concentrations of mesothelin was tested and the resonant frequency variation of the crystal was observed by a quartz crystal microbalance until a stable response is obtained. A good correlation between the frequency changes and concentration of mesothelin tested was observed and the QCM biosensor detects mesothelin in the linear range of 100pg/mLto 50 ng/mL. Thus, QCM assay could be a promising technique for early diagnosis of mesothelioma, ovarian and pancreatic adenocarcinoma.

Disposable Voltammetric Immunosensor for D-Dimer Detection as Early Biomarker of Thromboembolic Disease and of COVID-19 Prognosis

In this work, we report on the development of a simple electrochemical immunosensor for the detection of D-dimer protein in human plasma samples. The immunosensor is built by a simple drop-casting procedure of chitosan nanoparticles (CSNPs) as biocompatible support, Protein A (PrA), to facilitate the proper orientation of the antibody sites to epitopes as a capture biomolecule, and the D-dimer antibody onto a carboxyl functionalized multi-walled carbon nanotubes screen printed electrode (MWCNTs-SPE). The CSNPs have been morphologically characterized by Scanning Electron Microscopy (SEM) and Dynamic Light Scattering (DLS) techniques. Successively, the electrochemical properties of the screen-printed working electrode after each modification step have been characterized by differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). The resulting MWCNTs-CSNPs-PrA-D-dimer Ab immunosensor displays an optimal and promising platform for antibody immobilization and specific D-dimer detection. DPV has been used to investigate the antigen/antibody interaction at different D-dimer concentrations. The proposed voltammetric immunosensor allowed a linear range from 2 to 500 μg L-1 with a LOD of 0.6 μg L-1 and a sensitivity of 1.3 μA L μg-1 cm-2. Good stability and a fast response time (5 s) have been reported. Lastly, the performance of the voltammetric immunosensor has been tested in human plasma samples, showing satisfactory results, thus attesting to the promising feasibility of the proposed platform for detecting D-dimer in physiological samples.

Au nanopartics decorated urchin-like Bi2S3 on graphene wrapped carbon fiber microelectrode: Towards electrochemical immunosensor for sensitive determination of aflatoxin B1

Aflatoxin in food is a significant concern that threatens human health and life and causes a heavy burden on international trade and healthcare. In this work, we developed a new type of label-free electrochemical immunosensor for the high-sensitivity determination of aflatoxin B1 (AFB1) based on Au nanoparticles decorated urchin-like Bi2S3 (Au/Bi2S3) anchored on electrochemically reduced graphene oxide (ERGO) modified carbon fiber (CF) microelectrode (Au/Bi2S3/ERGO/CF). The morphology and characterization of the modified microelectrode were investigated using scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). Under the optimum conditions, the label-free electrochemical immunosensor detected AFB1 within the linear range of 10 pg mL−1 to 20 ng mL−1, with a low detection limit of 8 pg mL−1 and high sensitivity (0.48 μA/ng mL). The immunosensor showed high selectivity, good reproducibility, and acceptable stability. The immunosensor was applied to detecting AFB1 in cornflour samples, offering excellent reliability and accuracy compared with typical detection methods. Finally, this platform provides a superior prospect for the development of a nanohybrid immunosensor.

The Global Research Trend in Electrochemical Microfluidic Technology: A Bibliometric Review

Electrochemical microfluidic technology has been extensively studied in many fields due to its significant advantages. Despite the increasing number of publications on the subject, there are no studies based on bibliometric analysis in this area. In this study, we performed a bibliometric analysis of 457 publications related to electrochemical microfluidic technology during 2012–2021 through the Web of Science core database. Results show that the hot topics include the development of label-free immunosensors, biosensors, microfluidic device performance, and low cost of equipment, and the major contributors to these publications are from China, USA, Spain, India, and Germany. In addition, applications of electrochemical microfluidics in biomedicine, food safety, and environmental monitoring are summarized and analyzed. Finally, the future challenges as well as strategies for future research are discussed. This bibliometric review will be useful for researchers in gaining new insights into the electrochemical microfluidic technology.

Ultrasensitive Determination of Glial-Fibrillary-Acidic-Protein (GFAP) in Human Serum-Matrix with a Label-Free Impedimetric Immunosensor

In this work, immobilizing anti-GFAP antibodies via covalent attachment onto L-cysteine/gold nanoparticles that were modified with screen-printed carbon electrodes (Anti-GFAP/L-cys/AuNps/SPCE) resulted in the development of a sensitive label-free impedance immunosensor for the detection of Glial Fibrillary Acidic Protein (GFAP). The immunosensor's stepwise construction was studied using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). L-cysteine was chosen as the linker between GFAP antibodies and Au NPs/SPCE because it enables the guided and stable immobilization of GFAP antibodies, thus resulting in increased immunosensor sensitivity. As a redox probe, 5 mM of [Fe(CN)6]3-/4- was used to measure the electron-transfer resistance (Ret), which was raised by the binding of antigens to the immobilized anti-GFAP on the surface of the modified electrode. A linear correlation between Rct and GFAP concentration was achieved under optimum conditions in the range of 1.0-1000.0 pg/mL, with an extraordinarily low detection limit of 51.0 fg/mL. The suggested immunosensor was successfully used to detect the presence of GFAP in human blood serum samples, yielding good findings. As a result, the proposed platform may be utilized to monitor central nervous system injuries.

Target-triggered UCNPs/Fe3O4 @PCN-224 assembly for the detection of cadmium ions by upconversion fluorescence and magnetic relaxation switch dual-mode immunosensor

A dual-mode immunosensor based on upconversion fluorescence (UCFL) and magnetic relaxation switch (MRS) was developed for the anti-interference and sensitive detection of cadmium ion (Cd2+). In this strategy, upconversion nanoparticles (UCNPs) and magnetic porous coordination network nanoparticles (Fe3O4 @PCN-224) were employed to form the UCNPs/Fe3O4 @PCN-224 assembly through immune recognition of antigen and antibody. The fluorescence of UCNPs was quenched by the Fe3O4 @PCN-224 due to good adsorption quenching abilities of Fe3O4 @PCN-224. The relaxation performance of the Fe3O4 @PCN-224 was enhanced by the assembling UCNPs on the surface of Fe3O4 @PCN-224, which causing difficulty access of water molecular into the porous structured Fe3O4 @PCN-224. Owing to the anti-background fluorescence interference of UCNPs, the UCFL mode solved the interference of pigment fluorescence in pellucid or colored samples, such as red wine. Due to the quick pre-treament capability of Fe3O4 @PCN-224 at the magnetic field, the MRS mode overcame the disturbance of turbid and opaque samples, such as egg and soymilk. The presence of Cd2+ could affect the assembly process of UCNPs and Fe3O4 @PCN-224. Therefore, the Cd2+ could be detected by UCFL and MRS dual-mode immunosensor. The limits of detection of UCFL and MRS modes for detection of Cd2+ were 0.038 ng/mL and 0.16 ng/mL, respectively. This study provided a valuable information on the development of dual-mode immunosensor for the detection of Cd2+ in foods and had a broad application prospect in rapid detection.

Recent trends in analysis of mycotoxins in food using carbon-based nanomaterials

Mycotoxins (MYTs), a class of low molecular weight secondary metabolites produced by filamentous fungi in food and feed, pose serious global threat to both human health and world economy. Due to their mutagenic, teratogenic, carcinogenic and immunosuppressive effects, the International Agency for Research on Cancer has classified various MYTs under Group 1 to 3 category with aflatoxins being designated under Group 1 category (carcinogenic to humans). Also, the presence of MYTs in trace amounts in diverse food matrices necessitates exploration of highly sensitive methods for onsite analysis. Although conventional chromatographic methods are highly sensitive, they are expensive, tedious and cannot be applied for rapid onsite analysis. In recent years the application of nanomaterials especially carbon-based nanomaterials (CNMs) in the fabrication of low-cost and miniaturized electrochemical and optical sensors has enabled rapid onsite analysis of MYTs with high sensitivity and specificity. Moreover, the CNMs are employed as effective solid phase extraction (SPE) adsorbents possessing high specific surface area for effective enrichment of MYTs to improve the sensitivity of chromatographic methods for MYT analysis in food. This article aims to overview the recent trends in the application of CNMs as SPE adsorbents for sample pretreatment in chromatographic methods as well as in the fabrication of highly sensitive electrochemical and optical sensors for rapid analysis of MYTs in food. Initially, the efficiency of various functionalized CNMs developed recently as adsorbent in packed SPE cartridges and dispersive SPE adsorbent/purification powder is discussed. Then, their application in the development of various electrochemical immunosensors involving functionalized carbon nanotubes/nanofibers, graphene oxide, reduced graphene oxide and graphene quantum dots is summarized. In addition, the recent trends in the use of CNMs for fabrication of electrochemical and fluorescence aptasensors as well as some other colorimetry, fluorometry, surface-enhanced Raman spectroscopy and electrochemical based sensors are compared and tabulated. Collectively, this review article can provide a research update on analysis of MYTs by carbon-based nanomaterials paving a way for identifying future perspectives.

Citrate and glutathione capped gold nanoparticles for electrochemical immunosensing of atrazine: Effect of conjugation chemistry

Recently, the exposure of pesticides/herbicides to the living organisms is increased especially due to agricultural malpractices and industrial processes. In particular, the exposure of pesticides/herbicides (e.g., atrazine) can impart several harsh effects on the human health. The development of efficient detection systems can be crucial in monitoring the atrazine in water and food/plant products, which can be decisive in controlling the deadly exposures of atrazine. Herein, we have developed electrochemical immunosensors for atrazine by employing monoclonal anti-atrazine antibody conjugated gold nanoparticles. Two types of gold nanoparticles (i.e., citrate and glutathione (GSH)-capped AuNPs) were used to modify gold working electrode and utilized for the development of atrazine immunosensors. The conjugation of immunoprobe on working electrode was especially designed to obtain stable and efficient sensing signals. The nanosensing immunoprobes fabricated using citrate-AuNPs and GSH-AuNPs exhibited comparable responses for a wide linear working range of 50 ng/L- 30 μg/L with limit of detection (LOD) values of 0.08 and 0.06 ng/L for atrazine, respectively.

Functionalized Titanium Dioxide Nanoparticle-Based Electrochemical Immunosensor for Detection of SARS-CoV-2 Antibody.

The advancement in biosensors can overcome the challenges faced by conventional diagnostic techniques for the detection of the highly infectious severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Hence, the development of an accurate, rapid, sensitive, and selective diagnostic technique can mitigate adverse health conditions caused by SARS-CoV-2. This work proposes the development of an electrochemical immunosensor based on bio-nanocomposites for the sensitive detection of SARS-CoV-2 antibodies through the differential pulse voltammetry (DPV) electroanalytical method. The facile synthesis of chitosan-functionalized titanium dioxide nanoparticles (TiO2-CS bio-nanocomposites) is performed using the sol-gel method. Characterization of the TiO2-CS bio-nanocomposite is accomplished using UV-vis spectroscopy, Raman spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The electrochemical performance is studied using cyclic voltammetry (CV), DPV, and electrochemical impedance spectroscopy (EIS) for its electroanalytical and biosensing capabilities. The developed immunosensing platform has a high sensitivity with a wide range of detection from 50 ag mL-1 to 1 ng mL-1. The detection limit of the SARS-CoV-2 antibody in buffer media is obtained to be 3.42 ag mL-1 and the limit of quantitation (LOQ) to be 10.38 ag mL-1. The electrochemical immunosensor has high selectivity in different interfering analytes and is stable for 10 days. The results suggest that the developed electrochemical immunosensor can be applicable for real sample analysis and further high-throughput testing.

Precisely designed growth of dual-color quantum dots bilayer nanobeads for ratiometric fluorescent immunoassay

Colloidal quantum dots (QDs) have been widely used as fluorescent labeling materials in the field of in vitro diagnostics (IVD). In spite of the significant development of direct single-signal response fluorescent immunosensors, it is still a challenge to obtain the high accuracy and sensitivity of quantitative results of these sensors due to the influence of several factors unrelated to the analysis. Herein, we present a delicate design and synthesis of dual-color QDs bilayer nanobeads (red and green QDs nanobeads, R&G-QD nanobeads), achieving the precisely control of growth of the silicon layer with different proportions of ammonia, and inhibiting fluorescence resonance energy transfer (FRET) successfully. The dual-color QDs bilayer nanobeads have realized dual-channel detection (the acquisition of two emission wavelengths) of the target, and avoided the problems of low analytical accuracy and imprecise sensitivity of single-signal response. A proof-of-concept demonstration of a fluorescence-linked immunosorbent assay (FLISA) platform is conducted for the quantitative detection of prostate-specific antigen (PSA) with a sensitivity of 49 pg/mL and a linear range of 0.2–800 ng/mL. The dual-color QDs bilayer nanobeads FLISA platform with high sensitivity and accuracy holds great potential for early diagnosis of cancer or other diseases and provides a new approach for IVD.

Graphene-Binding Peptide in Fusion with SARS-CoV-2 Antigen for Electrochemical Immunosensor Construction.

The development of immunosensors to detect antibodies or antigens has stood out in the face of traditional methods for diagnosing emerging diseases such as the one caused by the SARS-CoV-2 virus. The present study reports the construction of a simplified electrochemical immunosensor using a graphene-binding peptide applied as a recognition site to detect SARS-CoV-2 antibodies. A screen-printed electrode was used for sensor preparation by adding a solution of peptide and reduced graphene oxide (rGO). The peptide-rGO suspension was characterized by scanning electron microscopy (SEM), Raman spectroscopy, and Fourier transform infrared spectroscopy (FT-IR). The electrochemical characterization (electrochemical impedance spectroscopy—EIS, cyclic voltammetry—CV and differential pulse voltammetry—DPV) was performed on the modified electrode. The immunosensor response is based on the decrease in the faradaic signal of an electrochemical probe resulting from immunocomplex formation. Using the best set of experimental conditions, the analytic curve obtained showed a good linear regression (r2 = 0.913) and a limit of detection (LOD) of 0.77 μg mL−1 for antibody detection. The CV and EIS results proved the efficiency of device assembly. The high selectivity of the platform, which can be attributed to the peptide, was demonstrated by the decrease in the current percentage for samples with antibody against the SARS-CoV-2 S protein and the increase in the other antibodies tested. Additionally, the DPV measurements showed a clearly distinguishable response in assays against human serum samples, with sera with a response above 95% being considered negative, whereas responses below this value were considered positive. The diagnostic platform developed with specific peptides is promising and has the potential for application in the diagnosis of other infections that lead to high antibody titers.

Synthesis, characterization, and application of gold nanostars for the identification of 2-Arachidonoyl glycerol

Background. The endocannabinoid system (ECS) is a complex of neurotransmitters in the central nervous system (CNS) and plays a key role in regulating cognitive and physiological processes. Also, 2-Arachidonoylglycerol (2-AG) is one of the imperative endocannabinoids with key roles in the CNS. It acts as a signaling lipid and activates the cannabinoid CB1 receptor. In addition, 2-AG is involved in a variety of physiological functions such as energy balance, emotion, pain sensation, cognition, and neuroinflammation. Hence, rapid and specific diagnosis of 2-AG is of great importance in medical neuroscience. Routine methods used in detection of 2-AG are not sensitive and specific. Therefore, the development of new methods in this area has been one of the most important research areas in recent years. Methods. Herein, an innovative immunosensor was developed for quantification of 2-AG. To this end, gold nanostars (GNSs) were synthesized and conjugated with a specific biotinylated antibody activated by EDC/NHS against 2-AG. The resultant bio-conjugate was immobilized on the gold electrode surface and used to detect and analyze 2-arachidonylglycerol antigen by cyclic voltammetry (CV), square wave voltammetry (SWV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy techniques. Results. For the first time, 2-AG protein was measured with an excellent linear range of 0.00048-1 ng/L and lower limit of quantification of 0.00048 ng/L by electroanalysis method. The designed immunosensor showed high sensitivity and specificity in the presence of interfering antigens, which proved its appropriate use in the diagnosis of neurological disorders. Conclusion. The remarkable achievement of the present study is the development of a new immunosensor for the sensitive and accurate detection of 2-AG. The fabricated sensor substrate showed good analytical results for the target analyte. Regardless of the appropriate sensitivity and selectivity of the designed biosensor, the stability of the sensor is low and it is recommended to use it immediately after preparation. Also, the immunosensor engineered in this research was very economical and had a very fast and good performance compared to the usual and traditional methods for detecting 2-AG. Practical Implications. For the first time, 2-AG protein was measured with an excellent linear range of 0.00048-1 ng/L and lower limit of quantification of 0.00048 ng/L by electro analysis method. The designed immunosensor showed high sensitivity and specificity in the presence of interfering antigens, which proved its appropriate use in the diagnosis of neurological disorders.

A quenching electrochemiluminescence immunosensor based on a novel Ag@Ce2Sn2O7 luminophore for the detection of neuron-specific enolase

A quenching electrochemiluminescence (ECL) immunosensor for neuron-specific enolase (NSE) detection was constructed by the resonance energy transfer between Ag@Ce2Sn2O7 (energy donor) and Ag@Cu2O (energy acceptor). The novel luminophore, Ag@Ce2Sn2O7, was synthesized by complexing Ce2Sn2O7 nanocubes with Ag concave-convex nanospheres. It exhibits a stronger ECL emission and a lower potential required for the emissions than pure Ce2Sn2O7. The Ag@Cu2O core-shell structure is composed of a dense Ag core inside and a loose Cu2O shell that provide a large specific surface area and the protection for the independence and integrity of the Ag core. The UV-Vis absorption of Ag@Cu2O overlaps the ECL emission of Ag@Ce2Sn2O7, and thus it can act as a quencher to effectively quench the ECL signal of Ag@Ce2Sn2O7. The great application potentials of the immunosensor in the NSE detection is demonstrated with the good linearity in the wide concentration range of 25 fg/mL - 100 ng/mL, and the low detection limit of 8.6 fg/mL. Our work has provided a reference for the immunosensor development of other biomarkers.

Silver Nanoparticle Labels for Electrochemical Detection of Bioassays

Electrochemistry plays a major role in immunosensor development because of its higher sensitivity, simplicity, portability, and rapidity compared to more common enzymatic, fluorescent and radioactive labelling methods. Silver nanoparticles (AgNPs) have been identified as potential electrochemical labels for such immunoassays. Characterizing the composition, size, shape, and surface modifications of the AgNP is important to achieve expected analytical performance of the bio assay. Here we are interested in studying the effect of nanoparticle shape towards the electrochemical detection of a metallo-immunoassay using Au-Ag galvanic exchange (GE) reaction followed by anodic stripping voltammetry. We observe that during GE between electrogenerated Au3+ and the Ag labels, a thin shell of Au forms on the surface of the NP and prevent further exchange. This shell is more porous when GE proceeds on silver nanocubes (AgNCs) compared to spherical silver nanoparticles (sAgNPs), and therefore, more exchange occurs when using AgNCs. More interestingly, optimizing the ratio of the two types of AgNP labels, we could able to decrease the LOD of a biological assay designed to detect a heart failure biomarker (NT-proBNP) without compromising the dynamic range compared to using either of the two labels independently. This made it possible to achieve the clinically relevant range for NT-proBNP analysis used by physicians for heart failure risk stratification.