Self-Assembled Microsphere-Integrated SERS Microneedles for the 3D Mapping of Agrochemicals Penetration in Fresh...

Spatially resolved quantification of agrochemical deposition, penetration, and absorption on and within fresh produce is critical for optimizing efficacy and managing residual risks. This study presents a hydrogel microneedle (MN)-based sensing platform that integrates surface-enhanced Raman scattering (SERS) with silver nanowire (AgNW) arrays. The platform overcomes the inherent limitation of conventional self-assembly methods, which rely on unstable biphasic interfaces, by elucidating a curing mechanism for liquid-liquid interface self-assembled nanostructures. This process enables a controllable transformation of dynamic interfacial assemblies into stable, solid plasmonic microspheres (PMSs). These PMSs function as high-performance SERS units, exhibiting uniform dispersion, long-term stability, and a reproducible electromagnetic hotspot distribution, thereby addressing the signal irreproducibility associated with random nanoparticle encapsulation in MNs. Subsequent integration of the PMSs into a polyethylene glycol diacrylate (PEGDA) hydrogel yields mechanically robust MN arrays with tunable swelling properties. This design confers an integrated pierce-extract-detect functionality, enabling rapid agrochemical screening. For the common pesticide molecules thiram and thiabendazole (TBZ), in the theoretical system, the limits of detection (LODs) are 3.47 × 10^-10 M and 8.81 × 10^-8 M, respectively. When coupled with SERS mapping technology, the platform facilitates two-dimensional and three-dimensional visualization of pesticide distribution on and within fresh produce, revealing spatial patterns governed by multifactor synergy. This work underscores the significant potential of the developed SERS platform in agrochemical residue detection and distribution analysis, opening new avenues for applications in food safety monitoring and sustainable agrochemical development.