Core-shell inverse opal photonic crystal hydrogel microneedle patch integrating pH and histamine sensing for salmon freshness monitoring.

Abstract

Food freshness monitoring remains a significant challenge owing to the complex and diverse nature of spoilage-related biomarkers. Here, we report a core-shell inverse opal photonic crystal hydrogel microneedle patch that enables dual-parameter (pH and histamine) sensing for minimally invasive food freshness assessment. The microneedles are reinforced with a transient polyvinyl alcohol coating to provide sufficient mechanical strength for tissue penetration. This coating rapidly dissolves to expose the sensing hydrogel. The inverse opal structure offers a large specific surface area and facilitates rapid analyte diffusion, enabling fast and sensitive responses. Histamine detection, based on molecular imprinting, achieves a limit of detection of 0.011 mM with a maximum reflection peak shift of 116 nm. The pH-responsive microneedles exhibit a broad detection range (pH 3-10), a maximum wavelength shift of 224 nm, and a rapid response time of 50 s. The sensing signals are readily visualized as structural color changes and quantified via reflection peak shifts. The platform exhibits excellent selectivity and reproducibility. In situ detection in salmon samples shows strong correlation with high-performance liquid chromatography results, confirming its practical applicability. This work presents a versatile microneedle-based platform for real-time, multi-biomarker monitoring of food freshness.