A stable and specific hydrogel-based plasmonic nanosensor for histamine detection

Plasmonic nanosensors have garnered increasing attention due to their naked-eye visibility and facile preparation. However, the inadequate stability and specificity significantly challenged their widespread application. Here, we hypothesized that capping with double-charged acids and loading in the hydrogel should bring gold nanoparticles (AuNPs) more stability and specificity for sensing small molecules. In the plasmonic nanosensor, aspartic acid-capped AuNPs (Asp-AuNPs) served as both the sensing material and colorant. Compared with conventional AuNPs, Asp-AuNPs exhibited a lower Zeta potential and enhanced selectivity for histamine. Moreover, Asp-AuNPs rapidly responded to histamine in less than 2 min, even after seven weeks of storage. The isothermal titration calorimetry analysis further supported the affinity of Asp-AuNPs for histamine. Using the alginate hydrogels as a matrix for Asp-AuNPs, the hydrogel-based plasmonic nanosensor could detect histamine on the surface of and in the atmosphere around expired fish. In summary, we have developed a novel, durable, and stable hydrogel-based plasmonic nanosensor for contact and contactless freshness detection.