Additive-based stability assessment of biologically designed CuO and GSH-CuO nanospheres and their applicability as Nano-biosensors

Uncapped and Glutathione capped Cupric oxide nanospheres were synthesized by the interaction of Berberis lycium (Bl) root extract with corresponding salt solution. CuO nanospheres were best optimized by mixing 2% Bl extract solution with 1 mM CuSO₄·5H₂O (pH 11, 90 °C) Reduced glutathione (0.25 mM) in solution form was added in respective emulsion after 24 h. Synthesis of nanospheres was ensured by distinct surface plasmonic resonance peaks shown by CuO (370-420 nm). Addition of glutathione resulted in sharp blue shift and lowered absorbance values in UV spectra suggesting the decrease in nanoparticles' size and concentration. Average particle sizes as deduced with XRD were found to be 18.52 and 16.57 nm for CuO and GSH-CuO nanospheres respectively. Additive based stability assessment of synthesized nanospheres revealed CuO and GSH-CuO nanospheres to be highly stable in the presence of Catechin hydrate among various tested chemical compounds while ascorbic acid appeared as a strong destabilizing agent. TMB was oxidized by H₂O₂ in the presence of synthesized enzymes likewise horseradish peroxidase; though exhibited moderate results. Glutathione stabilized cupric oxide nanospheres exhibited the potential to be modulated further into efficient nanozymes as these showed better affinity towards chromogenic substrate TMB (K_m value 0.32 mM) and better catalytic efficiency (0.075 mM^-1 s^-1) compared to uncapped CuO nanomimetics (1.6 mM, 0.033 mM^-1 s^-1). All of the tested additives served as inhibitors to the peroxidase mimicking potential of CuO and GSH-CuO nanozymes.