Multicolor and photothermal dual-mode assay of alkaline phosphatase based on the UV light-assisted etching of gold nanorods

A multicolor and photothermal dual-mode assay for sensitive alkaline phosphatase (ALP) determination was realized based on the 3,3′,5,5′-tetramethylbenzidine (TMB)-induced etching of gold nanorods (AuNRs). TMB was oxidized under ultraviolet light irradiation to form TMB + . In the presence of ALP, ascorbic acid phosphate (AAP) is converted to ascorbic acid, which can then reduce the levels of TMB + , resulting in lower concentrations of TMB + . The remaining TMB + was transformed into TMB 2+ after the addition of HCl solution. AuNRs were etched by TMB 2+ to produce a multicolor and photothermal change. Based on the degree of AuNRs etching, this highly sensitive dual-mode assay provided a linear range of 1.0–8.0 mU/mL, with detection limits of 0.34 mU/mL for the multicolor assay and 0.11 mU/mL for the photothermal assay. This method was successfully applied to the determination of ALP in serum samples.