Single-ParticleCollision Electrochemical BiosensorDeveloped by a Typical Alkaline Phosphatase-Catalyzed Silver DepositionReaction

Considering the intrinsic importance of alkaline phosphatase (ALP) as a biomarker in disease monitoring and as a mostly widely used biolabel for signal transmission in bioanalysis, the development of a new ALP assay method is highly pursued. Herein, a well-known ALP-catalyzed silver deposition reaction onto gold nanoparticles (Au NPs) was developed into a single-particle-collision-based electrochemical biosensor. ALP-catalyzed dephosphorylation of ascorbic acid 2-phosphate (AA-P) resulted in ascorbic acid (AA), which in turn reduced the silver ion to form a silver nanoshell on the surface of Au NPs (Au@Ag NPs). The generated Au@Ag NPs could stochastically collide with the microelectrode to produce transient current spikes. The collision frequency and charge could concurrently indicate the amount of produced Au@Ag NPs and then the ALP activity. Thus, a new single-particle collision-based electrochemical biosensing platform for ALP was constructed. It operates homogeneously and does not require electrode modification, nanoparticle biofunctionalization, and washing and separation steps. It showed good detection sensitivity toward ALP activity with a quantification limit of 2 mU/mL in 10 μL. The background-free feature endows it with absolute selectivity. It could also be used for inhibitor screening and applied for the ALP assay in the serum. In addition, the proposed collision-based electrochemical strategy was developed for a new enzyme-linked immunosorbent assay. With the human immunoglobulin G (IgG) as a model target, it could effortlessly evaluate 5 ng/mL analytes. It thus opens a new avenue toward the development of single-particle collision-based electrochemical biosensors for a wide range of applications in disease diagnosis and bioanalysis.