Strategy for In Situ Imaging of Cellular Alkaline Phosphatase Activity Using Gold Nanoflower Probe and Localized Surface Plasmon Resonance Technique

In this work, a simple and ultrasensitive localized surface plasmon resonance (LSPR) method that use Au nanoflowers (AuNFs) as a probe was designed for in situ monitoring of alkaline phosphatase (ALP) activity. The AuNFs were fabricated by hydrogen tetrechloroaurate-induced oxidative disruption of polydopamine-coated Au nanoparticles (AuNPs), and subsequently, growth of Au nanopetals on AuNPs occurred. The as-prepared AuNFs showed a much higher LSPR capability and stronger scattering color change than AuNPs. The strategy for in situ cellular ALP activity detection relied on the deposition of Ag on the AuNFs surface, which changed the morphology of AuNFs and led to a tremendous LSPR response and scattering color change. The deposition of Ag shell on AuNFs was related to ALP activity, where ALP catalyzed the hydrolysis of l-ascorbic acid 2-phosphate sesquimagnesium salt hydrate to form l-ascorbic acid (AA), and then AA reduced Ag+ to Ag and deposited onto AuNFs. With this concept, the ALP activity could be monitored with a detection limit of 0.03 μU L–1. Meanwhile, the ALP activity of single HepG2 cells and HEK 293 cells was tracked with a proposed approach, which indicated the trace expression level of ALP in HEK 293T cell and overexpressed level of ALP in HepG2 cells. After treatment with drugs, the cellular ALP activity of HepG2 cells was decreased with the treating time and dose increasing. Therefore, the proposed strategy could be used for tracking the cellular ALP activity, which paved a new avenue for cell studies and held great potential for discovering novel ALP-based drugs applications.