Enhanced catalytic efficiency of nanozymes with a V-structured chip for microfluidic biosensing of S. typhimurium

Nanozymes, nanomaterials with enzyme-like characteristics which exhibit lower cost, easier synthesis and functionalization, and better stability compared with natural enzymes, have been widely developed for biosensing, disease therapy and environmental governance. However, the lack of catalytic efficiency of nanozymes compared to natural enzymes makes it difficult for them to completely replace natural enzymes to achieve higher sensitivity and lower detection limits in biosensing. Herein, magnetism-controlled technology was used to form a nanozyme array consisting of stacked Fe₃O₄/Au NPs at the bottom of the microchannel as a spatially confined microreactor for the catalytic reaction. By enhancing the mass transfer process of the substrate towards nanozymes mediated by the corresponding V-structure, a higher local concentration of the substrate and more efficient utilization of active sites of nanozymes were achieved to increase the catalytic efficiency (k_cat/K_M) of the nanozyme array consisting of Fe₃O₄/Au NPs by 95.2%, which was two orders of magnitude higher than that of the open reactor. Based on this, a colorimetric method on an integrated microfluidic platform was proposed for sensitive biosensing of Salmonella typhimurium. The entire detection could be completed within 30 minutes, yielding a linear range from 10² to 10⁷ CFU mL^-1 and a detection limit as low as 5.6 CFU mL^-1.