Rapid and Reliable Detection of Alkaline Phosphatase by a Hot Spots Amplification Strategy Based on Well-Controlled Assembly on Single Nanoparticle

The first appeal of clinical assay is always accurate and rapid. For alkaline phosphatase (ALP) monitoring in medical treatment, a rapid, reliable surface-enhanced Raman scattering (SERS) test kit is designed based on a "hot spots" amplification strategy. Consisting of alkyne-tagged Au nanoparticles (NPs), Ag+, and enzyme substrate, the packaged test kit can achieve one-step clinical assay of ALP in human serum within several minutes, while the operation is simple as it directly inputs the sample into the test kit. Here, Ag+ ions are adsorbed onto the surface of Au core due to electrostatic interaction between Ag+ and the negatively charged donor surface, then enzymatic biocatalysis of ALP triggers the reduction of Ag+ and subsequently silver growth occurs on every Au core surface in a controllable manner, forming "hot spots" between the Au core and Ag shell, in which the SERS signal of alkyne Raman reporters would be highly amplified. Meanwhile, ALP mediates a redox reaction of Ag+ as well as the dynamic silver coating process so the increase of SERS intensity is well-controlled and can be recognized with increasing amounts of the targets. Instead of conventional NP aggregation, this leads to a more reproducible result. In particular, the distinct Raman emission from our self-synthesized alkyne reporter is narrow and stable with zero background in the Raman silent region, suffering no optical fluctuation from biosystem inputs and the detection results are therefore reliable with a limit of detection of 0.01 U/L (2.3 pg/mL). Along with ultrahigh stability, this SERS test kit therefore is an important point-of-care candidate for a reliable, efficacious, and highly sensitive detection method for ALP, which potentially decreases the need for time-consuming clinical trials.