Colorimetric nanozyme sensor based on chain-like PtNi nanoparticles for nitrite ion detection in food samples

Here, we combine the peroxidase-like activity of chain-like PtNi nanoparticles (PtNi CNPs) and diazotization reaction to construct a dual-signal ratiometric colorimetric platform for nitrite ion detection. Compared to Pt NPs, PtNi CNPs exhibit better peroxidase-like activities with Michaelis constant (K_m) of 0.15 mM and maximum reaction rate (V_max) of 8.09 × 10^-8 Ms.^-1 towards 3, 3', 5, 5'-tetramethylbenzidine (TMB) and K_m of 5.08 mM and V_max of 16.07 × 10^-8 Ms.^-1 towards H₂O₂. After adding nitrite ion, diazotization reaction between oxidized TMB and nitrite ion occurs, resulting in an attenuated absorption peak signal at 652 nm and an enhanced absorption peak signal at 450 nm, accompanied by a color change (blue-yellow green). This dual-signal ratiometric (A_{652 nm}/A_{450 nm}) method shows a good linear relationship ranging from 20 to 350 μM and 0.3237 μM of detection limit. Importantly, the method shows great potential in detecting nitrite ion in real food samples.