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.