Eco-friendly one-pot synthesis of gold decorated reduced graphene oxide using beer as a reducing agent

An electrochemical PNA-based sensor for the detection of the SARS-CoV-2 RdRP by using surface-initiated-reversible-addition−fragmentation-chain-transfer polymerization technique

Coronavirus disease 2019 is one of the global health problems. Herein, a highly sensitive electrochemical biosensor has been designed to detect the RNA-dependent RNA polymerase (RdRP) of the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) (SARS-CoV-2 RdRP). Herein, the surface-initiated reversible-addition-fragmentation-chain-transfer polymerization was used to amplify the electrochemical signal. To do that, the thiol-terminated peptide nucleic acid (PNA) probes were first immobilized on the surface of a screen-printed electrode modified with reduced graphene oxide-gold nanocomposite and then the fixed concentration of the SARS-CoV-2 RdRP was added to the electrode surface to interact with PNA probes. Subsequently, the Zr ⁴⁺ ions were added to interact with the phosphate groups of the SARS-CoV-2 RdRP. It allowed us to polymerase the ferrocenylmethyl methacrylate (FcMMA) and 4-cyano-4-(phenylcarbonothioylthio)-pentanoic acid on the SARS-CoV-2 RdRP chain. Since the poly-FcMMA has an electrochemical signal, the response of the PNA-based sensor to SARS-CoV-2 RdRP was increased in the range of 5-500 aM. The limit of detection was calculated to be 0.8 aM which is lower than the previous sensor for SARS-CoV-2 RdRP detection. The proposed PNA-based sensor showed high selectivity to the SARS-CoV-2 RdRP in the presence of the gene fragments of influenza A and Middle East respiratory syndrome coronavirus.

Characteristic analysis of three-ecofriendly reduced graphene oxides (rGOs) and their application in water-ethanol-based fluids with different volume ratios

In this paper, three-ecofriendly reduced graphene oxides (rGOs) were obtained by using three green reducing agents (beer, wine and cocoa) to reduce the graphene oxide (GO), and were labeled as B-rGO, W-rGO and C-rGO. Meanwhile, rGO nanofluids with different water-ethanol volume ratios (25 : 75, 50 : 50, 75 : 25) were prepared based on three-ecofriendly rGOs. The structure properties of the three-ecofriendly rGOs were investigated by XRD, FR-IT, Raman spectroscopy and XPS analysis. Meanwhile, the thermophysical properties of rGO nanofluids were analyzed. Experimental results indicated that the stability and thermophysical properties of rGO nanofluids were slightly different, indicating that the properties of the nanofluids are dependent on the type of base fluids and nanoparticles. When the water-ethanol volume ratio was maintained at 25 : 75, the stability experiment results showed that W-rGO nanofluids presented excellent stability, which indirectly confirmed their excellent thermal conductivity. Furthermore, the contact angle experiment indicated that the contact angles of rGO nanofluids decreased with the increase of temperature. In a word, these three rGOs and their nanofluids exhibited preferable properties that make them promising in the field of heat transfer.

Electroanalysis of isoniazid and rifampicin: Role of nanomaterial electrode modifiers

Thanks to operational simplicity, speediness, possibility of miniaturization and real-time nature, electrochemical sensing is a supreme alternative for non-electrochemical methodologies in drug quantification. This review, highlights different nanotech-based sensory designs for electroanalysis of isoniazid and rifampicin, the most important medicines for patients with tuberculosis. We first, concisely mention analyses with bare electrodes, associated impediments and inspected possible strategies and then critically review the last two decades works with focus on different nano-scaled electrode modifiers. We organized and described the materials engaged in several categories: Surfactants modifiers, polymeric modifiers, metallic nanomaterials, carbon based nano-modifiers (reduced graphene oxide, multi-walled carbon nanotubes, ordered mesoporous carbon) and a large class of multifarious nano composites-based sensors and biosensors. The main drawbacks and superiorities associated with each array as well as the current trend in the areas is attempted to discuss. Summary of 79 employed electrochemical approaches for analysis of isoniazid and rifampicin has also been presented.

A photoelectrochemical sandwich immunoassay for protein S100β, a biomarker for Alzheimer's disease, using an ITO electrode modified with a reduced graphene oxide-gold conjugate and CdS-labeled secondary antibody

A sandwich-type photoelectrochemical immunoassay is described for the protein S100ß which is an Alzheimer's disease biomarker found in the astrocytes of the brain. Antibody against S100ß (anti-S100ß) was labeled with CdS quantum dots and then acted as a secondary antibody. The labeled antibody was characterized by FTIR, ultraviolet-visible and fluorescence spectroscopy. An indium-tin oxide (ITO) electrode was modified with a nanocomposite prepared from reduced graphene oxide and gold nanoparticles. Then, a sol-gel film containing isocyanate functional groups (-N=C=O) was cast on the surface of the electrode. The NCO group reacts with amino groups of the labeled antibody to covalently bind them to the surface. The S100β was bound by the primary immobilized antibody on the rGO-Au/ITO electrode and then sandwiched with the labeled secondary antibody. Cyclic voltammetry and electrochemical impedance spectroscopy were applied to confirm the stepwise changes in the electrochemical properties of the electrode surface. The photoelectrochemical immunoassay, typically operated at a potential of +0.2 V (vs. Ag|AgCl_sat) gives a signal that is related to the logarithm of the S100β concentration in the range from 0.25 to 10 ng·mL^-1 with a lower detection limit of 0.15 pg·mL^-1. The method was successfully applied to the determination of S100β in human serum samples. Graphical abstract Schematic presentation of an immunosensor which is based on an indium tin oxide modified with reduced graphene oxide decorated with gold nanocomposite and antibody. The immunosensor was applied for the determination of S100β biomarker by using in the labeled antibody.