• Regular copy paper converted into low-cost spoilage sensors • No pre-synthesized sensing material - sensors printed simply and rapidly • Printed sensors showed dual-mode detection capabilities • Sensor response increased rapidly with higher levels of spoilage bacteria • Spoilage sensors tested on packed Atlantic cod stored under realistic conditions A cost-effective, user-friendly, and sensitive printed hydrogen sulfide (H 2 S) sensor with dual colorimetric and photothermal responses was developed. The sensor detects ultra-low H 2 S concentrations (down to 1 ppm), identifies H 2 S-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 H 2 S, 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 H 2 S-producing bacteria increased to ∼3 log CFU/mL, the sensor color change (Δ E *) reached 15 (with values ≥ 5 indicating an obvious color change), while the temperature increase (Δ T ) reached 6°C. An additional 1-log increase raised Δ E * to ∼30 and Δ T to 20°C. This approach provides a non-destructive, low-cost method for sensitive H 2 S detection, identification of H 2 S-producing bacteria, and real-time spoilage monitoring in seafood products in which spoilage is predominantly associated with H 2 S production.
Gulin-Sarfraz et al. (Wed,) studied this question.