Green synthesis, characterization, biological and electrochemical studies of indole pyrazole capped nanomaterials
Authors:   , Majola Senzekile 
Published: January 2022

Green nanomaterial synthesis has become more popular and, with the need for greener approaches to counter higher costs and higher energy usage for chemical and physical processes, scientists are searching for cheaper methods of synthesis. The use of plant extracts has been one of the popular methods because they are known to reduce metal ions from their surface. Green synthesized nanomaterials are relatively unstable compared to chemical and physical methods hence new stabilizing agents (indole pyrazole ligands) have been introduced in this study. The nanomaterials are being applied in electrochemical and biological systems, their behavior may not be as efficient as the new capped nanomaterials. Hence, a comparison of capped and uncapped nanomaterials was studied. Indole pyrazole capped selenium nanoparticles (TRPIDC-CH3 SeNPs), Indole pyrazole capped silver nanoparticles (TRPIDC-CH3 AgNPs), and Indole pyrazole capped cadmium sulphide quantum dots (TRPIDC-CH3 CdSQDs) were successfully synthesized using plant extracts of allium sativum cloves, pelargonium, and moringa leaves, respectively. Green synthesized TRPIDC-CH3 capped nanomaterials were characterized by UV-vis spectrophotometry, HR-TEM, and FTIR analysis. The results revealed no differences in shape, color, functional groups involved, or wavelength, but an increase in average diameter as compared to uncapped nanomaterials. Furthermore, green-fabricated synthesized nanomaterials were tested to evaluate their cytotoxicity against MCF-7, A549, and HEK293 cells. The overall cytotoxicity was low: a dose-dependent increase in cytotoxic activity was observed for each of the nanomaterials, as the concentration increased from 50 μg/ml to 100 μg/ml. Interaction of TRPIDC-CH3 capped and uncapped nanomaterials with human serum albumin (HSA) was investigated under physiological conditions (PBS, pH 7.3) by UV–Vis, and fluorescence. Fluorescence analysis at different temperatures revealed the quenching of HSA. The results showed a single class of binding site and a static ( uncapped) and dynamic (TRPIDC-CH3 capped) quenching mechanism between nanomaterials and HSA. The thermodynamic results indicated van der Waals forces and hydrogen bonds (uncapped) and hydrophobic interactions (TRPIDC-CH3 capped) were dominant. Dual enzyme electrode for the indirect detection of adenosine triphosphate (ATP),using a redox probe as a reference peak, was developed by co-immobilization of the enzymes glucose oxidase (GO) and hexokinase (Hex) and nanomaterials. The implementation of a simple electrochemical technique to co-immobilize enzymes on electrode surfaces demonstrates a significant improvement in the sensitivity, reproducibility and ease of fabrication of ATP biosensors. However, the addition of the TRPIDC-CH3 ligand to QDs affected the surface area and conductive activity of the sensor leading to a decrease in sensitivity and weakening the electrochemical stability of the QDs. The concept proposed provides the technological basis for a new generation of fast, responsive and robust biosensors for the detection of ATP through indirect detection. Keywords: Adenosine triphosphate (ATP); Indole pyrazole ligand (TRPIDC-CH3); Selenium Nanoparticles (SeNPs); Cyclic voltammetry (CV); Square wave voltammetry (SWV); Hexokinase (Hex); Glucose oxidase (GO); Human serum albumin (HSA); MTT assay; MCF-7, A549, and HEK293 cells.