Sensitive and reproducible gold nanostar@metal-organic framework-based SERS membranes for the online monitoring of the freshness of shrimps.

Given the prevalence of food safety, online monitoring of food quality is essential. Surface-enhanced Raman scattering (SERS) has excellent sensitivity and molecular fingerprinting capabilities in analytical fields, but its accuracy in food safety monitoring is severely constrained, particularly for gaseous molecules. To further develop the SERS technique in food sensing, in this work, a slippery liquid-infused porous surface (SLIPS) platform was developed for the real-time monitoring of the change in gaseous molecules in shrimp spoilage processes. In order to monitor the change in pH and gaseous biogenic amine molecules (BAs), 4-mercaptopyridine (4-Mpy) and 4-mercaptobenzaldehyde (4-MBA)-functionalized ZIF-8-encapsulated gold nanostars (AuNS@ZIF-8) were utilized as response probes, respectively. Due to the superior gaseous molecule trapping ability of ZIF-8 and the excellent enrichment effect of SLIPS substrates, the use of 4-Mpy and 4-MBA-functionalized AuNS@ZIF-8-SLIPS substrates exhibited excellent online SERS sensing performance for pH and gaseous putrescine molecules. The detection ranges for pH and gaseous BAs were 4.0-9.0 and 10-10 (v/v) with RSDs of 4.1% and 4.2%, respectively. Furthermore, the SERS monitoring platform was used to monitor shrimp spoilage at 25 °C and 4 °C in real time. Hence, the AuNS@ZIF-8-SLIPS membrane strategy can serve as a promising alternative to ensure accurate, real-time, and non-destructive monitoring of gaseous molecules for food freshness.