Fig 1: Real-time QCM sensor response to 10 ng/mL of AFP in human serum, detected via WO3-conjugated antibody sandwich immunoassay followed by photocatalytic silver staining for signal amplification. The observed decrease in resonance frequency corresponds to the increase in effective mass on the QCM sensor surface. The total frequency shift (Δ frequency) is indicated by the red double-headed arrow in the figure. Δf1 and Δf2 represent the frequency changes induced by the sandwich immunoassay alone and the subsequent photocatalytic silver deposition, respectively.