AuNRs-MIL-100(Fe) as Surface-Enhanced Raman Spectroscopy Substrates for Rapid and Sensitive Analysis of Malachite Green in Fishpond Water

Malachite green (MG) is a prohibited aquaculture biocide. As its residues in fish can be confirmed only after accumulation in the tissue, early identification of illegal use depends on measuring the rearing water. Here, gold nanorods (AuNRs) were integrated with MIL-100(Fe) to give an anisotropic substrate for the surface-enhanced Raman scattering (SERS) determination of MG in fishpond water. AuNRs of three aspect ratios (2.4, 2.85 and 3.99) were prepared by a seed-mediated route, and the AR 3.99 exhibited the optimal SERS enhancement, giving a signal 56% stronger than the spherical AuNPs-MIL-100(Fe) counterpart at the same Au concentration. The response was linear from 0.1 to 10 μg/L and, in spiked fishpond water, gave R2 = 0.966 and recoveries of 89.6–100.9% (RSD 3.7–9.1%), with no extraction or pre-concentration step. The method is therefore suited to rapid routine monitoring of aquaculture water and to food safety supervision.