μA Ng Research Articles

N-Graphene Paper Electrodes as Sustainable Electrochemical DNA Sensor

The heteroatom doped graphene structure provides an effective platform for electrochemical sensing of deoxyribonucleic acid (DNA). In this work, we have doped heteroatoms such as nitrogen (N), phosphorus (P), and sulphur (S) to the graphene sheets obtained from biomass. The obtained heteroatom doped graphene was used to prepare electrodes on paper substrate and utilized for electrochemical sensing of calf thymus DNA. The electrochemical sensing response of the electrodes is confirmed from the oxidative peak (0.6 V to 0.8 V) related to guanine (G) sensing for all the electrodes. In addition, N-doped graphene electrode shows effective electrocatalytic oxidation of adenine (A), with high sensing towards guanine and adenine compared to that of other heteroatoms doped printed electrodes. The calculated limit of detection for N-doped graphene electrode is 227 ng ml−1 and 322 ng ml−1 with the sensitivity of 1.35 μA ng−1 cm−2 and 1.33 μA ng−1 cm−2 for guanine and adenine sensing, respectively. The fabricated N-doped graphene electrode has open-up a new pathway to develop an economically and environmentally friendly electrodes for DNA sensing.

Fabrication of a Molecularly Imprinted Nano-Interface-Based Electrochemical Biosensor for the Detection of CagA Virulence Factors of H. pylori.

H. pylori is responsible for several stomach-related diseases including gastric cancer. The main virulence factor responsible for its establishment in human gastric cells is known as CagA. Therefore, in this study, we have fabricated a highly sensitive MIP-based electrochemical biosensor for the detection of CagA. For this, an rGO and gold-coated, screen-printed electrode sensing platform was designed to provide a surface for the immobilization of a CagA-specific, molecularly imprinted polymer; then it was characterized electrochemically. Interestingly, molecular dynamics simulations were studied to optimize the MIP prepolymerization system, resulting in a well-matched, optimized molar ratio within the experiment. A low binding energy upon template removal indicates the capability of MIP to recognize the CagA antigen through a strong binding affinity. Under the optimized electrochemical experimental conditions, the fabricated CagA-MIP/Au/rGO@SPE sensor exhibited high sensitivity (0.275 µA ng-1 mL-1) and a very low limit of detection (0.05 ng mL-1) in a linear range of 0.05-50 ng mL-1. The influence of other possible interferents in analytical response has also been observed with the successful determination of the CagA antigen.

Development of an Electrodeposited Graphene Quantum Dot Electrode for the Electrochemical Detection of C‐Reactive Protein (CRP) Biomarker

AbstractC‐reactive protein (CRP) is a potential cardiac biomarker whose levels fluctuate in response to cardiac diseases. In particular, the severity of cardiovascular disease can be associated with the level of CRP, emphasizing the necessity for a highly sensitive biosensor capable of detecting CRP at ultralow levels in a short period of time. In this study, we used a facile pyrolysis method to synthesize graphene quantum dots (GQDs) with a diameter of 2.2 nm. Then, to fabricate the Au/GQDs/anti‐CRP electrode, GQDs were electrodeposited successfully on the surface of the bare Au electrode to provide a nano‐interfaced matrix platform for effective anti‐CRP immobilization. Cyclic voltammetry was used to investigate the contact between anti‐CRP and CRP in the Fe(CN)63−/4− as a mediator. The recorded current signal from differential pulse voltammetry measurements shows that the associative interaction between the anti‐CRP and CRP is efficiently induced. Furthermore, the Figureure of merits of the developed sensor, including the sensory response of <50 s with a high sensitivity of 58 μA ng−1 mL−1 cm−2 and a low detection capability of 0.104 ng mL−1 (n=3), suggests that it is a potential candidate for point‐of‐care testing. And the fabricated Au/GQDs/anti‐CRP biosensor were used to sense CRP in an artificial serum (ringer lactate) solution.

Amine Functionalized Noble Metal: Metal Oxide Nanohybrid for Efficient Electrochemical Determination of 25-Hydroxy Vitamin-D3 in Human Serum

Quantification of 25-hydroxy vitamin-D3 (25-OHVD3) is important because its deficiency is related to numerous diseases, including osteoporosis, depression, diabetes, heart disease, certain autoimmune conditions, and even Covid-19. In the present study, noble metal-metal oxide nanohybrid based on L-cysteine functionalized gold decorated zirconia nanoparticles (Cys-Au@ZrO2 NPs) were synthesized with the objective of enhanced electrochemical behavior, stability, availability of functional group to covalently bind with biomolecules, and developing an efficient immunosensor for 25-OHVD3 detection. The formation of Au@ZrO2 NPs and further Cys functionalization was validated by various characterizations. Cys-Au@ZrO2 NPs were electrodeposited onto ITO substrate and further modified with antibodies specific to 25-OHVD3 (ab-25VD3) and bovine serum albumin (BSA) to build an immunosensing platform for 25-OHVD3 detection. The fabricated BSA/ab-25VD3/Cys-Au@ZrO2/ITO immunosensor demonstrated an improved sensitivity of 2.01 μA ng−1 ml cm−2, LOD of 3.54 ng ml−1 for the linear detection range of 1–50 ng ml−1 with regression constant of 0.98. Moreover, the analytical performance of the BSA/ab-25VD3/Cys-Au@ZrO2/ITO immunosensor in determining 25-OHVD3 in human serum samples collected from four healthy people yielded satisfactory results that were highly correlated with the conventional enzyme-linked immunosorbent assay (ELISA).

Ultrasensitive early detection of insulin antibody employing novel electrochemical nano-biosensor based on controllable electro-fabrication process

An ultrasensitive novel electrochemical nano-biosensor for rapid detection of insulin antibodies against diabetes antigens was developed in this research. The presence of insulin antibodies has been demonstrated to be a strong predictor for the development of type 1 diabetes in individuals who do not have diabetes but are genetically predisposed. The proposed nano-biosensor fabrication process was based on the optimized sequential electropolymerization of polyaniline and electrodeposition of gold nanoparticles on the surface of the functionalized gold electrode. The morphological and chemical characterization of the modified electrode was studied by field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), and micro Raman spectroscopy. Moreover, the role of each component in the modification of the electrode was studied by electrochemical methods systematically. After immobilizing insulin antigen and blocking with bovine serum albumin, the nano-biosensor was used for determining different concentrations of insulin antibody under the optimal conditions. This nano-biosensor could respond to insulin antibody with a linear calibration range from 0.001 ng ml−1 to 1000 ng ml−1 with the detection limit of 0.017 pg ml−1 and 0.034 pg ml−1 and selectivity of 18.544 μA ng−1 ml.cm−2 and 31.808 μA ng−1 ml.cm−2 via differential pulse voltammetry and square wave voltammetry, respectively. This novel nano-biosensor exhibited a short response time, high sensitivity, and good reproducibility. It was successfully used in determining the insulin antibody in human samples with a standard error of less than 0.178. Therefore, the nano-biosensor has the potential for the application of early detection of type 1 diabetes. To our best knowledge, label-free electrochemical detection of insulin antibody based on immunosensor is developed for the first time.

Studies on carbon-quantum-dot-embedded iron oxide nanoparticles and their electrochemical response

A report on the synthesis of carbon-quantum-dot-embedded iron oxide nanoparticles (CQD@Fe3O4NPs) and their improved electrochemical studies is presented. Fe3O4NPs and CQD@Fe3O4NPs were synthesized by the wet-chemical co-precipitation method. X-ray diffraction measurements exhibited pure cubic phase with Fd3m space group in Fe3O4NPs and CQD@Fe3O4NPs. Fourier-transform infrared spectroscopy measurements confirmed the functionalization of Fe3O4NPs with CQDs. Dynamic light scattering measurements revealed a hydrodynamic radius of 520 nm and 319 nm for Fe3O4NPs and CQD@Fe3O4NPs, respectively. Moreover, zeta potential measurements showed positively charged Fe3O4NPs and negatively charged CQD@Fe3O4NPs. High-resolution transmission electron microscopy measurements showed nearly spherical structure with an average size of around 7 nm for Fe3O4 in both samples, whereas CQDs were nearly 2 nm in size in CQD@Fe3O4NPs. A biocompatibility study showed that CQD@Fe3O4NPs were more biocompatible than the bare Fe3O4NPs. CQD@Fe3O4NPs were then dispersed in chitosan (CHIT) solution, and drop-casted onto an indium tin oxide (ITO) glass substrate for further study. Atomic force microscopy results showed improved surface roughness of the CQD@Fe3O4−CHIT/ITO electrode, providing a better biosensing platform. The electrochemical response studies of CQD@Fe3O4−CHIT/ITO also showed enhanced electrochemical signal compared to Fe3O4−CHIT/ITO electrodes. Thus, a CQD@Fe3O4−CHIT/ITO electrode was used for the detection of vitamin D2 (10–100 ng ml−1) using a differential pulse voltammetry technique. The sensitivity and limit of detection were obtained as 0.069 µA ng−1 ml cm−2 and 2.46 ng ml−1, respectively.

Influence of Quantum Dot Surface on Electrochemical DNA Sensing Mechanism

AbstractOwing to their high surface‐to‐volume ratio, electrocatalytic activity, biocompatibility and novel electron transport properties, quantum dots (QDs) are highly attractive materials for the ultrasensitive detection of biological macromolecules via bioelectronic devices. In this study, a QD‐based genosensor was developed, in which Ga2Te3‐based QDs were synthesized using an aqueous solution approach by mixing 3‐mercaptosuccinic acid (3MSA)‐capped gallium metal precursor with reduced tellurium metal. The results enabled us to reach an original understanding related to the active material involved in the probe DNA sensing mechanism. The morphological and structural characterization of the QDs was performed prior to their utilization in a DNA sensor construction. High‐resolution TEM (HR‐TEM) and atomic force microscopy (AFM) images confirmed the spherical and crystalline nature of the QDs, whereas X‐ray photoelectron spectroscopy (XPS) and X‐ray diffraction (XRD) analyses were able to confirm the oxidation states and formation of the prepared QDs. UV/Vis was capable of finding the optical band gap energy and the photostability of the QDs. The resultant Ga2Te3 QDs together with metal ions confirmed their use for DNA signal detection through their DNA binding mechanism in the genosensor construction. Genosensing in Cs+ and Li+ ions exhibited high sensitivity (2.74–3.69 μA ng−1 mL) and very low detection limits (0.4 pg mL−1) with a linear dynamic range of 0.1–1 ng mL−1.

An efficient electrochemical biosensor for Vitamin-D3 detection based on aspartic acid functionalized gadolinium oxide nanorods

In this study, an efficient electrochemical biosensor for Vitamin-D3 detection using gadolinium oxide nanorods (Gd2O3NRs) has been reported. Gd2O3NRs were hydrothermally synthesized and functionalized with aspartic acid (Asp-Gd2O3NRs). Asp functionalization did not change the phase, shape and structure of Gd2O3NRs. The high-resolution transmission electron microscopy study revealed the diameter of Asp-Gd2O3NRs as 14.26 ± 0.13 nm with enhanced dispersivity. The Gd2O3NRs and Asp-Gd2O3NRs showed zeta potential of +29 and +24 mV, respectively. Asp-Gd2O3NRs exhibited enhanced hydrophilicity and electrochemical property than the bare Gd2O3NRs. A thin film of Asp-Gd2O3NRs was deposited on a glass substrate coated with indium-tin-oxide (ITO) by electrophoretic deposition. The immobilization of Vitamin-D3 monoclonal antibody (Ab-VD) was done on the surface of Asp-Gd2O3NRs/ITO electrode for determination of Vitamin-D3. The study of BSA/Ab-VD/Asp-Gd2O3NRs/ITO immunoelectrode response with different Vitamin-D3 concentration was investigated using differential pulse voltammetry technique. The results of response study exhibited an improved sensitivity value of 0.38 μA ng−1 mL cm−2 with a linear range of 10–100 ng mL−1 for Vitamin-D3 detection while the detection limit of 0.10 ng mL−1 was obtained. This immunosensor showed a satisfactory response to commercially available Vitamin-D3 oral solution. Besides this, in vitro study of Gd2O3NRs and Asp-Gd2O3NRs was performed on RAW 264.7 and MCF-7 cells.

Ceria‐Nanoparticles‐Based Microfluidic Nanobiochip Electrochemical Sensor for the Detection of Ochratoxin‐A

AbstractOchratoxin‐A (OTA) is a fungal mycotoxin that is present in most of the food stuff, and shows adverse effects on human beings. Therefore, the rapid and accurate detection of OTA is necessary. Here, ceria nanoparticles based microfluidic nanobiochip was fabricated for the electrochemical detection of OTA. Ceria nanoparticles were synthesized using a chemical co‐precipitation method and characterized by various techniques. Raman spectroscopy confirmed the formation of fluorite cubic structure. Transmission electron microscopy (TEM) exhibited the formation of very small size (4‐5 nm) with nearly spherical shape nanoparticles. Microfluidic nanobiochip was fabricated using 300 μm microfluidic channel using polydimethylsiloxane (PDMS). Simultaneously, indium tin oxide (ITO) coated Corning glass was used for the fabrication of immunoelectrodes platform using antibodies (anti‐OTA) for the OTA detection. The detection range was achieved from 350 pg ml−1 to 10 ng ml−1 with sensitivity of 7.5 μA ng−1 mL cm−2, without any interference effect using differential pulse voltammetry.

Disposable electrochemical immunosensor for analysis of cystatin C, a CKD biomarker

Specific monitoring of cystatin C (CysC) levels in biological fluids is critical for diagnosis, treatment and mechanistic understanding of a spectrum of diseases, particularly chronic kidney disease (CKD). Despite evidences that CysC correlates with the high risk and/or progression of CKD, its use in clinical practice is still scarce. In this context, we report the development of a simple and sensitive immunosensor for the detection of CysC. The biosensor combines the technology of cost-effective screen-printed electrodes with the high specificity of a sandwich immunoassay. Optimized conditions showed that the sensor operates in a linear range between 10 and 100 ng mL−1, with a detection limit and a sensitivity of 6.0 ng mL−1 and 6.4 ± 0.3 μA ng mL−1 cm−2, respectively. Moreover, the sensor provided precise results (RSD ≤ 6.2%) and the quantification of CysC in CKD serum samples revealed to be in agreement with the values obtained by a particle-enhanced nephelometric immunoassay. In this light, the proposed immunosensor qualifies for clinical application, constituting a step forward in the development of fast, sensitive and cost-effective diagnostic tools that can improve the current medical care settings of CKD patients.

Electrochemically grown polymethylene blue nanofilm on copper-carbon nanofiber nanocomposite: An electrochemical sensor for creatinine

Creatinine is a preferred biomarker for the renal dysfunction, and its selective determination in various biological fluids is useful for the evaluation of renal, muscular and thyroid dysfunctions. Development of a selective and sensitive non-enzymatic electrochemical sensor having a linear response and good stability over a wide range of creatinine concentration is challenging. In this study, a polymeric dye-based metal-carbon nanofiber nanocomposite was successfully fabricated as the electrode of a non-enzymatic electrochemical sensor for creatinine in human biological fluids. Using cyclic voltametry technique, the dendritic poly methylene blue (PMB) nanofibers were electrochemically grown on the surface of the Cu-doped carbon electrode. The PMB molecule acted as a recognition element for creatinine. In virtue of the structural merits and synergistic contribution of the polymer-metal-carbon nanofiber nanocomposites in enhancing the electrocatalytic activity towards creatinine, the fabricated electrode exhibited good sensing performances including a high sensitivity of 0.133 μA ng mL−1, a linear response over 0.5–900 ng mL−1 conentration range and the detection limit of 0.2 ng mL−1 (with a signal-to-noise ratio of 3:1), as well as good selectivity. The proposed electrochemical sensor can be used for the real time detection of creatinine in biological fluids.

Biofunctionalized two-dimensional Ti3C2 MXenes for ultrasensitive detection of cancer biomarker

In this work, ultrathin Ti3C2-MXene nanosheets were synthesized by minimally intensive layer delamination methods, and uniformly functionalized with aminosilane (f-Ti3C2-MXene) to provide a covalent binding for the immobilized bio-receptor (anti-CEA) for label free, ultrasensitive detection of cancer biomarker (carcinoembryonic antigen, CEA). The effect of different redox probes on the electrochemical behavior of f-Ti3C2-MXene was investigated and found that hexaammineruthenium ([Ru(NH3)6]3+) is the preferable redox probe for biosensing. The fabricated biofunctionalized Ti3C2-MXene exhibits a linear detection range of 0.0001–2000 ng mL−1 with sensitivity of 37.9 µA ng−1 mL cm−2 per decade. The wider linear detection range of our f-Ti3C2-MXene is not only higher than previously reported pristine 2D nanomaterials, but is even comparable to other hybrid 2D nanomaterials. We believe that this work opens a new window for development of MXene-based highly sensitive DNA, aptamer, enzyme, antibody, and cell based biosensors, and could be further used in drug delivery application.

Electrochemical immunosensor based on magnetite nanoparticles incorporated electrospun polyacrylonitrile nanofibers for Vitamin-D3 detection

In the present study, magnetite nanoparticles (Fe3O4 NPs) incorporated polyacrylonitrile nanofibers (PANnFs) having diameter of 350–500 nm, were electrospun and directly collected onto indium tin oxide (ITO) coated glass substrate. X-ray diffraction pattern of Fe3O4‑PANnFs confirmed the existence of Fe3O4 NPs within the PANnFs. Nafion was used to make Fe3O4‑PANnFs more adhesive to the ITO surface. Partial hydrolyzation of Fe3O4‑PANnFs/ITO electrode was done using NaOH solution for the partial conversion of nitrile group (C≡N) into carboxyl and amine groups that was confirmed by Fourier transform infrared spectroscopy study. The hydrolyzed Fe3O4‑PANnFs/ITO electrode was used as an immobilization matrix for monoclonal antibody specific to Vitamin-D3 (Anti‑VD) via 1‑ethyl‑3‑(3‑dimethylaminopropyl) carbodiimide and N‑Hydroxysuccinimide chemistry. Bovine serum albumin (BSA) was used as a blocking agent to block the non-specific sites onto Anti‑VD/Fe3O4‑PANnFs/ITO electrode surface. Fabricated BSA/Anti‑VD/Fe3O4‑PANnFs/ITO immunoelectrode showed improved biosensing parameters for Vitamin-D3 detection such as sensitivity of 0.90 μA ng−1 mL cm−2, limit of detection of 0.12 ng mL−1and detection range of 10–100 ng mL−1. The association and dissociation constants were obtained as 74.62 ng mL−1, 4.6 ng mL−1, respectively.

A highly sensitive amperometric immunosensor probe based on gold nanoparticle functionalized poly (3, 4-ethylenedioxythiophene) doped with graphene oxide for efficient detection of aflatoxin B1

In the present work, a platform of Poly (3, 4-ethylenedioxythiophene) (PEDOT) and graphene oxide (GO) composite decorated with spherical gold nanoparticles (AuNPs) has been developed for rapid electrochemical detection of aflatoxin B1 (AFB1). Electrochemical deposition of EDOT onto glassy carbon electrode (GCE) keeping GO as dopant followed by introduction of AuNPs has been achieved resulting in nanohybrid AuNPs/PEDOT-GO electrode. The antibody anti-aflatoxin B1 (anti-AFB1) has been further covalently immobilized onto the surface of AuNPs/PEDOT-GO using EDC/NHS coupling. The morphological and surface characteristics have been studied using Field Emission Scanning Microscopy (FESEM) and contact angle measurements. Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS) studies have been carried out to investigate the electro-catalytic behavior of the modified electrodes. The heterogeneous rate constant (ks) and transfer coefficient (α) have been determined by using Laviron’s method. The proposed immunosensor exhibits a very high sensitivity of 0.989 μA ng mL−1 and 0.397 μA ng mL−1 within two linear range of 0.5–20 ng mL−1 and 20–60 ng mL−1, respectively.

Carbon dots-modified chitosan based electrochemical biosensing platform for detection of vitamin D

Here in, a carbon dots (CDs)-modified chitosan (CH) based biosensing platform was fabricated for vitamin D2 detection. Carbon dots were synthesized through microwave pyrolysis method, and characterized with transmission electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and UV/VIS spectroscopy. Chitosan (1%) solution was prepared in acetic acid (1%) solution and followed by the addition of CDs to prepare the carbon dots-chitosan (CD-CH) composite. A thin film of CD-CH composite was prepared onto ITO glass substrate (CD-CH/ITO) by drop casting method. Surface of the composite film was characterized by atomic force microscopy, static contact angle measurement and cyclic voltammetry. CD-CH/ITO surface was further modified with immobilization of vitamin D2 antibody (Ab-VD2) and bovine serum albumin (BSA) to prepare BSA/Ab-VD2/CD-CH/ITO bioelectrode. Electrochemical response of the bioelectrode towards vitamin D2 antigen (Ag-VD2) was carried out by differential pulse voltammetry. The biosensing electrode showed linearity within the range 10–50 ng mL−1 of Ag-VD2 concentration. The sensitivity was found to be 0.2 μA ng−1 mL cm−2, LOD was 1.35 ng mL−1, and the biosensor had a shelf-life of about 25 days.

PEDOT:PSS/PVA‐Nanofibers‐Decorated Conducting Paper for Cancer Diagnostics

The development of a flexible, label free, low‐cost, and environment friendly biosensor platform is reported for sensitive and rapid detection of cancer biomarker based on poly(3,4‐ethylenedioxythiophene):poly(4‐styrenesulfonate)/polyvinyl alcohol nanofiber decorated conducting paper. This conducting paper based biosensor demonstrates improved sensing performance with linear detection range of 0.2–25 ng mL−1, high sensitivity of 14.2 μA ng−1 mL cm−2, and shelf life of 22 days for a carcinoembryonic antigen (cancer biomarker) detection. This modified conducting paper electrode is a promising alternative over expensive conventional electrodes (indium tin oxide, gold, and glassy carbon) for fabrication of smart point of care devices.

Polyaniline modified flexible conducting paper for cancer detection

We report results of studies relating to the fabrication of a flexible, disposable, and label free biosensing platform for detection of the cancer biomarker (carcinoembryonic antigen, CEA). Polyaniline (PANI) has been electrochemically deposited over gold sputtered paper (Au@paper) for covalent immobilization of monoclonal carcinoembryonic antibodies (anti-CEA). The bovine serum albumin (BSA) has been used for blocking nonspecific binding sites at the anti-CEA conjugated PANI/Au@Paper. The PANI/Au@Paper, anti-CEA/PANI/Au@Paper, and BSA/anti-CEA/PANI/Au@Paper platforms have been characterized using scanning electron microscopy, X-ray diffraction, Fourier transmission infrared spectroscopy, chronoamperometry, and electrochemical impedance techniques. The results of the electrochemical response studies indicate that this BSA/anti-CEA/PANI/Au@paper electrode has sensitivity of 13.9 μA ng−1 ml cm2, shelf life of 22 days, and can be used to estimate CEA in the range of 2–20 ng ml−1. This paper sensor has been validated by detection of CEA in serum samples of cancer patients via immunoassay technique.

Reduced graphene oxide modified smart conducting paper for cancer biosensor.

PSS) and reduced graphene oxide (RGO) composite. The effect of various solvents like methanol, ethylene glycol and H2SO4 on the electrical conductivity of PSS coated Whatman paper has been investigated. The conductivity of this solution processed conducting paper significantly increases from ~1.16×10(-4) S cm(-1) up to ~3.57×10(-2) S cm(-1) (~300 times) on treatment with ethylene glycol. The observed significant increase in electrical conductivity is due to conformational rearrangement in the polymer and is due to strong non-covalent cooperative interaction between PEDOT and the cellulose molecules. Further, incorporation of RGO into the conducting paper results in improved electrochemical performance and signal stability. This paper electrode is a promising alternative over the expensive conventional electrodes (ITO, gold and glassy carbon), that are known to have limited application in smart point-of-care (POC) devices. This low cost, flexible and environment friendly conducting paper based biosensor utilized for cancer biomarker (carcinoembryonic antigen, CEA) detection reveals high sensitivity of 25.8 µA ng(-1) mL cm(-2) in the physiological range, 1-10 ng mL(-1).

Functionalised Au Coated Iron Oxide Nanocomposites Based Reusable Immunosensor for AFB1 Detection

A reusable sandwiched electrochemical piezoelectric immunosensor has been developed for aflatoxin B1 (AFB1) detection using gold coated iron oxide core‐shell (Au‐Fe3O4) nanostructure. The monoclonal anti‐aflatoxin antibody (aAFB1) was immobilized on self‐assembled monolayer of 4‐aminothiophenol on gold coated quartz crystal to fabricate immunoelectrode (BSA/aAFB1/4‐ATP/Au). In addition, secondary rabbit‐immunoglobulin antibodies (r‐IgGs) functionalized with Au‐Fe3O4 NPs via cysteamine (r‐IgG‐Cys‐Au‐Fe3O4) were allowed to interact with AFB1. Both competitive and noncompetitive strategies were employed and a competition between coated AFB1 and free AFB1 was carried out. The competitive mode shows higher linear range (0.05 to 5 ng mL−1) than the noncompetitive one (0.5 to 5 ng mL−1), high sensitivity 335.7 µA ng−1 mL cm−2, and LOD 0.07 ng mL−1. The fabricated immunosensor has been tested using cereal samples spiked with different concentrations of AFB1. The developed competitive immunoelectrode displays good reproducibility, and storage stability and regenerated with negligible loss in activity through removal of the r‐IgG‐Cys‐Au‐Fe3O4 conjugate using a strong external magnet.

A chitosan modified nickel oxide platform for biosensing applications.

We present a highly sensitive and selective electrochemical sandwich immunosensor (the analyte is "sandwiched" between two antibodies) based on chitosan (CH) modified nickel oxide (NiO) nanoparticles for the detection of Vibrio cholerae (Vc). The primary monoclonal antibodies specific to Vibrio cholerae (Ab-Vc) and bovine serum albumin (BSA) were co-immobilized on a CH-NiO surface deposited onto an indium tin oxide (ITO) coated glass electrode. The specific binding of Ab-Vc towards Vc was confirmed by interaction of secondary antibodies conjugated with protein [horse radish peroxidase (HRP)], with varying concentrations of hydrogen peroxide (H2O2), via electrochemical as well as optical techniques. The CH-NiO/ITO and Ab-Vc/CH-NiO/ITO electrodes have been characterized using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy and electrochemical techniques. This immunoelectrode (BSA/Ab-Vc/CH-NiO/ITO) exhibits a detection range of 20-700 ng mL-1 with a sensitivity of 0.644 μA ng mL-1 cm-2 and a low detection range of 0.108 ng mL-1 to Vc concentration. Besides this, the electrochemical response of the sandwich immunosensor (HRP-Ab-Vc/Vc/BSA/Ab-Vc/CH-NiO/ITO) towards H2O2 concentration is found to be linear in the range of 10-50 mM with excellent sensitivity (2.95 mA mM-1 cm-2).