Uniform PtCoRuRhFe high-entropy alloy nanoflowers: Multi-site synergistic signal amplification for colorimetric assay of captopril

Uniform PtCoRuRhFe high-entropy alloy nanoflowers (HEANFs) were fabricated by a simple wet-chemical co-reduction method in oleylamine for quantitative colorimetric determination of captopril (CAP) based on multi-site synergistic signal amplification. Specifically, the peroxidase mimetic activity of the PtCoRuRhFe HEANFs was examined through catalysis of 3,3′,5,5′-tetramethylbenzidine (TMB) oxidation, whose catalytic mechanism was investigated by electron paramagnetic resonance (EPR) spectroscopy. The role of the ·O₂⁻ was figured out during the catalytic procedure. Further, the oxidation of TMB (oxTMB) can be effectively reduced by CAP, accompanied by quickly transforming the solution color from blue to colorless. More importantly, the absorbance at 652 nm is linearly related to the CAP concentration in a range 5.0–50.0 mM with a low detection limit of 2.82 mM. The method has been applied to the determination of CAP in human urine samples. It offers a simple and high-efficiency method for facile and visual detection of CAP in hospitals.