Smartphone-assisted molecularly imprinted fluorescent hydrogel microneedles for on-site screening of patulin on fruit surfaces.

Patulin (PAT) is a hazardous mycotoxin frequently detected in fruits and fruit-derived products, requiring rapid, portable, and visual strategies for on-site food safety screening. Herein, a gelatin methacryloyl (GelMA)/quantum dot-loaded molecularly imprinted polymer (QDs@MIP) hydrogel microneedle platform was developed by integrating molecular imprinting-based recognition, quantum dot fluorescence transduction, and microneedle-assisted surface sampling. QDs@MIP particles, prepared using QDs as fluorescent probes and molecularly imprinted polymers as selective recognition layers, were embedded into GelMA microneedles. Multiscale characterization confirmed successful QDs@MIP construction and preservation of red fluorescence after imprinting and microneedle encapsulation. The obtained microneedles exhibited well-defined arrays, uniform fluorescence distribution, rapid swelling, elastic gel-network behavior, and reliable compressive resistance, enabling conformal attachment and in situ sampling on fruit surfaces. Under optimized conditions, PAT binding and enrichment were accompanied by fluorescence attenuation at approximately 662 nm and a visible color transition under 365 nm UV-vis irradiation. Smartphone-assisted red-green-blue (RGB) analysis converted the fluorescence variation into quantitative signals, with the R/G ratio serving as the analytical parameter for visual PAT determination, achieving a limit of detection (LOD) of 0.009 μg L-1 and a limit of quantification (LOQ) of 0.1 μg L-1. The method provided recoveries of 82.0-112.0% across multiple fruit matrices and showed strong agreement with UPLC-MS/MS analysis. Moreover, the microneedles exhibited enzymatic and soil degradation potential and no obvious in vitro cytotoxicity. This work provides a portable, sustainable, and user-friendly strategy for rapid on-site screening of PAT in fruits.