Silver ion-regulated reliable and rapid detection technique for alkaline phosphatase based on surface-enhanced Raman...

The primary characteristics of a clinical assay are its accuracy and speed. For alkaline phosphatase (ALP) monitoring in medical treatment, a rapid, reliable surface-enhanced Raman scattering (SERS) detection technique was designed based on the controlled "hot spot" effect caused by the mediation of silver ions (Ag⁺). Consisting of functionalized Au nanoparticles (NPs), Ag⁺, and the enzyme substrate 2-phospho-L-ascorbic acid triso-dium salt (AAP), the fabricated detection technique can achieve a reliable clinical assay for ALP detection in human serum within several minutes. Herein, due to the coordination interaction of Ag⁺ and the cyano group (-CN), Ag⁺ can coordinate with p-mercaptobenzonitrile (MBN) modified on the surface of Au NPs, leading to the connection of adjacent Au NPs in a controllable manner to form a chain structure, in which the SERS signal of MBN at 2228 cm^-1 in the Raman silent region would be highly amplified. Under the enzymatic biocatalysis of ALP, AAP was converted into ascorbic acid (AA). AA triggered the reduction of Ag⁺ into Ag⁰, resulting in a decrease in the concentration of Ag⁺. Meanwhile, the decrease in the SERS intensity of MBN was well-controlled and was recognized with the increased amounts of ALP. Based on this, the SERS detection technique for ALP was established. The limit of detection (LOD) for the detection of ALP was as low as 1.23 pg mL^-1 (0.005 U L^-1). Because of all these characteristics and its ultrahigh stability, this SERS detection technique is an important point-of-care candidate for the reliable, efficacious, and highly sensitive detection of ALP.