On-Demand Activatable Peroxidase-like Porous Silicon–Gold Nanozymes for Colorimetric Sensing

Nanozymes have shown promise in a range of applications including food safety, environmental monitoring, clinical diagnostics, and bioimaging. However, more complex applications of nanozymes require better control over their catalytical properties. Herein, we report a peroxidase-like nanozyme that can be activated "on demand". This is based on porous silicon (pSi) particles with nanosized gold inclusion, which are spontaneously generated on their surface by simple addition of a gold solution to a pSi particle suspension. The fast and spontaneous formation of gold nanoparticles (AuNPs) activates peroxidase-like nanozyme features. The nanozymes mimic the enzyme–cofactor relationship of natural enzymes with "on-demand" activation. The Michaelis–Menten constant and maximum velocity parameters were obtained as 1.92 mM and 0.37 × 10–8 MS–1 for tetramethylbenzidine and 0.70 mM and 0.55 × 10–8 MS–1 for H2O2, respectively. The activatable AuNP-pSi nanohybrid exhibited strong nanozyme activity with the ability to detect a thiol group-containing amino acid, homocysteine (Hcy), with a limit of detection of 0.30 μM. Our findings demonstrated that AuNP-pSi nanozymes can detect Hcy in complex solvents such as human serum efficiently. The AuNP-pSi nanozymes offer a robust stability profile without significant activity loss after 12 weeks of a storage period at room temperature. The AuNP-pSi nanozymes have potential in the development of colorimetric sensors and chemical industry processes that require enzymatic activity to switch on at specific parts of the reaction steps.