Analysis of trace methylene blue in fish muscles using ultra-sensitive surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy (SERS) is an emerging technology with great potential for sensitive and rapid analysis of trace methylene blue (MB) in fish muscle. Five different SERS substrates including two commercial nanostructured surface substrates and three types of Au nanoparticles (NPs) with different diameters were compared to optimize enhancement effects. The highest sensitivity with the lowest detection limit of 5 ng/mL for MB standard solutions and 10 ng/g for MB in fish muscles was achieved using the 18 ± 2 nm Au NPs. Partial least squares regression models developed for quantitative analysis showed high linear correlation between the actual and predicted values for MB (R2 cv = 0.958, RPD = 4.84, RMSE = 6.97 ng/g) in fish muscle. Since Au NPs are easy to prepare, stable and affordable, the high sensitivity and predictability of this method has the potential to be widely used for trace analysis of prohibited drug residues in fish and potentially other foods or biological samples.