Analyses of Trace Crystal Violet and Leucocrystal Violet with Gold Nanospheres and Commercial Gold Nanosubstrates for Surface-Enhanced Raman Spectroscopy

Crystal violet (CV) is forbidden but still used in some aquaculture operations due to its low cost and high effectiveness against some fish diseases. Surface-enhanced Raman spectroscopy (SERS) coupled with partial least squares (PLS) regression is applied to analyze trace amounts of CV and its metabolite leucocrystal violet (LCV) in fish fillets. Two different laser sources (633 and 780 nm) and three different gold nanosubstrates (included gold nanospheres and two commercial gold substrates) were used as SERS substrates to achieve optimal analytical results. Gold nanoparticles (diameter 55.4?±?4.5 nm) as synthesized via a reduction method resulted in better sensitivity and accuracy results than the two commercial substrates. The minimum detectable concentration for CV standard solutions was 0.5 ng/mL with the use of gold nanospheres as substrate, compared to 10 and 50 ng/mL with the two commercial substrates. The R ² of actual CV concentrations versus the values predicted (cross-validation) with PLS models ranged from 0.963 to 0.989. For CV contaminated fish muscles, the minimum detectable concentration of CV was 1 ng/g, and the PLS model (n?=?64, 20 for prediction) for total CV and LCV in fish muscles was less satisfied (cross-validation R ²?=?0.889; prediction R ²?=?0.857) compared to those for standard solutions due to the interferences of nontargeted components in fish extract, but the results still indicated the possibility of applying SERS with chemometrics to determine trace amounts of CV and LCV in complex sample systems, such as fish muscles.