Inexpensive inkjet-printed photothermal and colorimetric sensor for real-time monitoring of seafood quality

A cost-effective, user-friendly, and sensitive printed hydrogen sulfide (H2S) sensor with dual colorimetric and photothermal responses was developed. The sensor detects ultra-low H2S concentrations (down to 1 ppm), identifies H2S-producing bacteria (e.g., Shewanella spp., common seafood spoilage bacteria), and enables real-time monitoring of Atlantic cod spoilage during refrigerated storage. It is based on an inkjet-printable sensing ink optimized for printing in terms of particle size, surface tension, and viscosity. The colorimetric and photothermal responses arise from conversion of the sensing film to stable copper sulfide (CuS) upon reaction with volatile biogenic H2S, as confirmed by X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDX). Sensor responses showed a clear correlation with increasing levels of spoilage bacteria in the fish product. As H2S-producing bacteria increased to ∼3 log CFU/mL, the sensor color change (ΔE*) reached 15 (with values ≥ 5 indicating an obvious color change), while the temperature increase (ΔT) reached 6 °C. An additional 1-log increase raised ΔE* to ∼30 and ΔT to 20 °C. This approach provides a non-destructive, low-cost method for sensitive H2S detection, identification of H2S-producing bacteria, and real-time spoilage monitoring in seafood products in which spoilage is predominantly associated with H2S production.