Rapid detection of trace methylene blue and malachite green in four fish tissues by ultra-sensitive surface-enhanced Raman spectroscopy coated with gold nanorods

The residue of fishery drugs in aquatic food products has not diminished and has caused worldwide attention. This study aimed to develop a surface-enhanced Raman spectroscopy (SERS) method coupled with gold nanorods (AuNRs) substrates to rapidly detect methylene blue (MB) and malachite green (MG) in fish tissues. Three different aspect ratios (AR) of AuNRs were synthesized by a seed-mediated growth method based on adjusting the amount of 0.1 M of sliver nitrate solution. The 3.5 AR of AuNRs was selected as the optimal substrate because it showed the highest enhancement effect on the probe molecule. MB and MG standard solutions were detected at levels as low as 0.5 and 0.1 ng/mL, respectively. After processing the four fish tissues through a simplified sample preparation method, we compared matrix interference for SERS detection. For the four fish species, the lowest detectable concentration of MB was 5 ng/g for snakehead fish, and 1 ng/g for yellow catfish, black carp, and tilapia fillets. The lowest detectable concentration of MG was 1 ng/g for snakehead fish, 0.5 ng/g for yellow catfish and black carp, and 0.3 ng/g for tilapia fillets. This study shows that SERS coupled with AuNRs could be used for the analysis of trace amounts of contaminants in intricate food matrices as an active, fast and sensitive approach.