A colorimetric POCT mediated by poly(tannic acid)-capped AgNPs for the detection of hazardous H₂S: Applications in meat spoilage monitoring and halitosis diagnosis.

This study proposes a novel hydrophilic point-of-care testing (POCT) integrated with poly(tannic acid)-capped silver nanoparticles (PTA-AgNPs) designed to facilitate the naked-eye detection of hydrogen sulfide (H₂S) in food and human breath. We synthesize PTA-AgNPs using a handheld syringe filter by combining tannic acid, which serves as both a reducing and capping agent, with silver nitrate as the source of metal ions. Herein, a cellulose acetate syringe filter served as the substrate, facilitating the on-site surface dispersion of PTA-AgNPs. The PTA-AgNPs exhibit high stability, optical sensitivity, and selectivity, making them an effective probe for the spectrophotometric, colorimetric, and naked-eye detection of H₂S in both aqueous and gaseous media. Upon exposure to H₂S, the PTA-AgNPs underwent a visible color change from brownish-yellow to brownish-gray, attributed to the aggregation of PTA-AgNPs and the formation of silver sulfide nanoparticles. The calculated limit of detection is approximately 24.2 nM, while the limit of quantitation is 125 nM. Furthermore, we employ the POCT kits to monitor bacterial spoilage in protein-rich foods, such as fish, pork, and chicken, as well as for halitosis diagnosis by detecting H₂S in human breath. The POCT integrated with PTA-AgNPs shows potential as a convenient tool for developing practical biosensors to monitor bacterial growth in clinical, food industry, and environmental applications.