Amplification Free Detection of SARS-CoV-2 Using Multi-valent Binding

[Image: see text] We present the development of electrochemical impedance spectroscopy (EIS)-based biosensors for sensitive detection of SARS-CoV-2 RNA using multi-valent binding. By increasing the number of probe–target binding events per target molecule, multi-valent binding is a viable strategy for improving the biosensor performance. As EIS can provide sensitive and label-free measurements of nucleic acid targets during probe–target hybridization, we used multi-valent binding to build EIS biosensors for targeting SARS-CoV-2 RNA. For developing the biosensor, we explored two different approaches including probe combinations that individually bind in a single-valent fashion and the probes that bind in a multi-valent manner on their own. While we found excellent biosensor performance using probe combinations, we also discovered unexpected signal suppression. We explained the signal suppression theoretically using inter- and intra-probe hybridizations which confirmed our experimental findings. With our best probe combination, we achieved a LOD of 182 copies/μL (303 aM) of SARS-CoV-2 RNA and used these for successful evaluation of patient samples for COVID-19 diagnostics. We were also able to show the concept of multi-valent binding with shorter probes in the second approach. Here, a 13-nt-long probe has shown the best performance during SARS-CoV-2 RNA binding. Therefore, multi-valent binding approaches using EIS have high utility for direct detection of nucleic acid targets and for point-of-care diagnostics

Optical and electro-catalytic studies of nanostructured thulium oxide for vitamin C detection

In this report, the nanostructured thulium oxide (Tm2O3) has been prepared using the hydrothermal process without using any template and further heat treatment. The crystalline structure and morphology of prepared sample have been determined by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and Fourier transform infrared (FTIR) spectroscopic techniques. The optical properties of prepared sample have been examined by ultra-violet (UV-Vis), photoluminescence (PL), Raman and X-ray photoelectron spectroscopy (XPS) studies. Furthermore, Tm2O3 nanoparticles have been electrophoretically deposited (EPD) onto indium-tin-oxide (ITO) glass substrate and utilized for electro-oxidation of ascorbic acid (AA). The electro-catalytic behavior of Tm2O3/ITO and bare ITO electrodes for AA electro-oxidation has been studied by cyclic voltammetry. Catalytic oxidation peak current shows a linear dependence on the AA concentration and a linear calibration curve is obtained in the concentration range of 0.2-8 mM of AA. The obtained results indicate that the nanostructured Tm2O3 based electrode offers an efficient strategy and a new promising platform for application of the rare earth metal oxide material in electrochemistry and bioelectronics

A highly efficient rare earth metal oxide nanorods based platform for aflatoxin detection

The nanostructured rare earth metal oxide (samarium oxide, n-Sm2O3) nanorods, prepared using a forced hydrolysis technique, have been electrophoretically deposited (EPD) onto an indium-tin-oxide (ITO) glass substrate. This novel platform has been utilized for co-immobilization of monoclonal antibodies of aflatoxin B-1 (Ab-AFB(1)) and bovine serum albumin (BSA) via electrostatic interactions for food toxin (AFB(1)) detection. Thus prepared n-Sm2O3 nanorods have been characterized by X-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopic techniques. The results of electrochemical response studies of the BSA/Ab-AFB(1)/n-Sm2O3/ITO immunoelectrode obtained as a function of aflatoxin concentration reveal a linearity of 10-700 pg mL(-1), a detection limit of 57.82 pg mL(-1) cm(-2), a response time of 5 s and a sensitivity of 48.39 mu A pg(-1) mL(-1) cm(-2) with a regression coefficient of 0.961. The association constant (K-a) for antigen-antibody interactions obtained is 47.9 pg mL(-1), which indicates high affinity of antibodies towards the antigen (AFB1). The application of n-Sm2O3 modified electrode for immunosensor analysis offers a novel platform and efficient strategy for the application of rare earth metal oxide materials in bioelectronics

A dual enzyme functionalized nanostructured thulium oxide based interface for biomedical application

In this paper, we present results of the studies related to fabrication of a rare earth metal oxide based efficient biosensor using an interface based on hydrothermahy prepared nanostructured thulium oxide (n-Tm2O3). A cohoidal solution of prepared nanorods has been electrophoreticay deposited (EPD) onto an indium-tin-oxide (ITO) glass substrate. The n-Tm2O3 nanorods are found to provide improved sensing characteristics to the electrode interface in terms of electroactive surface area, diffusion coefficient, charge transfer rate constant and electron transfer kinetics. The structural and morphological studies of n-Tm2O3 nanorods have been carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission eLectron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopic techniques. This interfacial platform has been used for fabrication of a total cholesterol biosensor by immobilizing cholesterol esterase (ChEt) and choLesterol oxidase (ChOx) onto a Tm2O3 nanostructured surface. The results of response studies of the fabricated ChEt-ChOx/n-Tm2O3/ITO bioeLectrode show a broad Linear range of 8-400 mg dL(-1), detection Limit of 19.78 mg (dL cm(-2))(-1), and high sensitivity of 0.9245 RA (mg per dL cm(-2))(-1) with a response time of 40 s. Further, this bioeLectrode has been utiLized for estimation of total cholesterol with negligible interference (3%) from analytes present in human serum samples. The utilization of this n-Tm2O3 modified electrode for enzyme-based biosensor analysis offers an efficient strategy and a novel interface for application of the rare earth metal oxide materials in the field of electrochemical sensors and bioelectronic device

Highly Efficient Bienzyme Functionalized Biocompatible Nanostructured Nickel Ferrite-Chitosan Nanocomposite Platform for Biomedical Application

A new hybrid nanocomposite based on hydrothermally synthesized nanostructured NiFe2O4 (n-NiFe2O4) and chitosan (CH) has been explored for bienzyme (cholesterol esterase (ChEt) and cholesterol oxidase (ChOx)) immobilization for application as total cholesterol biosensor. Results of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), Raman spectroscopy (RS) and vibrating sample magnetometer (VSM) studies demonstrate that the ChEt ChOx/n-NiFe2O4 CH composite film is successfully synthesized. The obtained ChEt ChOx/n-NiFe2O4 CH nanocomposite film shows large specific area, high conductivity, good biocompatibility, fast redox properties and improved antimicrobial activity. The fabricated ChEt ChOx/n-NiFe2O4 CH/ITO bioelectrode exhibits largely improved amperometric biosensing performance, i.e., good linearity (5-400 mg/dL), low detection limit (24.46 mg/dL cm(-2)), high sensitivity of 1.73 mu A/(mg/dL cm(-2)), fast response time of 15s, reproducibility of more than 15 times, shelf life of about 90 days and low Michaelis-Menten constant (K-m) value as 7.05 mg/dL (0.1825 mM). Furthermore, this modified bioelectrocle has been utilized for estimation of total cholesterol in human serum samples. This efficient strategy provides new insight into the design of novel flexible electrodes for a wide range of applications in biosensing, bioelectronics, and clinical applications