Screening for malachite green contamination on live fish skin with chewing gum based viscoelastic SERS sensor

Malachite green (MG), a prohibited but still found antimicrobial in aquafarm and during live fish shipping, is a hot target in food safety screening. Herein, a novel chewing gum based flexible SERS (G-SERS) sensor was proposed for rapid sampling and detection of MG on live fish skin. The whole analysis takes <5 min, while the limit of detection for MG is 0.73 pg. Different from other reports, MG contaminated live fish was monitored daily with the G-SERS sensor, during which the fish was firstly raised in 0.5 ppm MG solution for one day, followed by freshwater for a week. It was found that the SERS signal of residue MG on fish skin could still be seen even on the sixth day, roughly the sale cycle of live fish in a marketplace. Furthermore, the method was also applied for MG screening on the skin of fish purchased from a supermarket and a local street marketplace. MG was found on some fishes from the latter but not from the former, which was cross-validated by LC-MS, suggesting MG risks still exist in smaller marketplaces. This work demonstrated the feasibility of using the flexible SERS sensor for onsite food safety screening.