A gold-palladium bimetallic nanozyme-based colorimetric sensor for nitrite assay

Bimetallic nanozymes leverage electronic and geometric synergy to overcome single-metal limitations, which may enhance the stability and catalytic efficiency for sensing. We herein synthesize a gold-palladium (Au-Pd) bimetallic nanozyme via a one-step co-reduction method. It exhibits excellent peroxidase-like activity with high substrate affinity and catalytic efficiency. We further construct a colorimetric system for nitrite assay. The AuPd₃ nanozyme catalyzes the oxidation of colorless TMB to blue oxidized TMB (oxTMB) in the presence of H₂O₂. The introduced nitrite could react with oxTMB via diazotization to form yellow products. The recorded absorbance ratio (A₆₅₂/A₄₅₀) thus enables quantitative nitrite detection. This method shows a good linear range from 5 to 500 μM with the limit of detection as low as 0.23 μM. It features simple operation, high sensitivity and favorable accuracy, offering reliable technical support for food safety and environmental monitoring.