Facile Synthesis and Characterization of Ag/Ag₂S Nanoparticles Enzymatically Grown In Situ and their Application to the Colorimetric Detection of Glucose Oxidase

This work describes a simple, fast and reproducible biochemical reaction to modulate the growth of silver/silver sulfide nanoparticles (Ag/Ag₂S NPs) through the enzymatic activity of the glucose oxidase (GOx). This process occurs in aqueous buffered solutions at room temperature under physiological conditions with participation of inexpensive precursors. Oxidation of 1-thio-β-D-glucose is catalyzed by GOx yielding hydrogen sulfide. Direct interaction between silver nitrate and enzymatically produced H₂S in the presence of citric acid as capping agent leads to the generation of Ag/Ag₂S NPs. UV-vis spectroscopy is employed to characterize absorbance spectra of resulting Ag/Ag₂S NPs with the highest signal-to-noise ratio at 385 nm. Enzymatically produced Ag/Ag₂S NPs are characterized by TEM, XPS, DLS and XRD. This new colorimetric method was applied to the detection of enzymatic activity of GOx (LOD 0.557 μg mL-1 and linear range up to 1.5 μg mL-1). The effect of D-glucose on the read-out signal has been studied to confirm the enzymatic mechanism of this process (LOD 176.21 μM and linear range up to 1.25 mM) and was applied to the detection of glucose in human plasma.