Determining Alkaline Phosphatase Based on Core–Shell Gold@silver Nanocubes by Single-Particle Dark-Field Images

We develop a rapid and ultrasensitive colorimetric method for alkaline phosphatase (ALP) activity based on dark-field microscopy. In the presence of ALP, l-ascorbic acid 2-phosphate (AA2P) was hydrolyzed by ALP into ascorbic acid (AA), which acted as a reductant to reduce KIO₃ into I₂ which subsequently etched core–shell Au@Ag nanocubes. The change in morphology of the Au@Ag nanocubes led to a significant color variation (blue → yellow/green) in dark-field imaging. A linear range of 1.5 μU/mL–150 U/mL (R² = 0.98) and limit of detection (LOD) of 0.183 μU/mL for ALP were obtained. What’s more, the successful detection of ALP in serum samples demonstrated that this sensing strategy is suitable for the ALP determination in complex biological samples.