Fluorescence polarization-based detection of phosphate moisturizers using a pepsin NPs/ZIF - L sensing platform

Conventional methods for detecting phosphate-based moisture, such as ion chromatography and molybdenum blue spectrophotometry, often involve time - consuming sample pretreatment or fall short when it comes to rapid, on-site analysis. To address this limitation, we report here a fluorescence polarization (FP) sensing platform built on pepsin nanoparticles (Pepsin NPs) loaded onto a two-dimensional zeolitic imidazolate framework ZIF - L (Pepsin NPs/ZIF - L). This platform enables sensitive detection of common phosphate moisturizers, including sodium hexametaphosphate, sodium tripolyphosphate, and sodium pyrophosphate. In this design, ZIF - L serves as an effective FP signal amplifier. By adsorbing Pepsin NPs onto its surface, it restricts their rotational freedom, thereby elevating the FP value. When polyphosphates are introduced, they competitively coordinate with Zn²⁺ sites within the ZIF - L framework, causing its disruption. This releases the Pepsin NPs and reduces the FP signal. The sensor shows linear responses across the following concentration ranges: 0-305.9 mg/L for sodium hexametaphosphate, 0-183.9 mg/L for sodium tripolyphosphate, and 0-133.0 mg/L for sodium pyrophosphate.