Escherichia coli -polydopamine coated stir bar sorptive extraction combing with portable mass spectrometer for rapid and simultaneous detection of triphenylmethane residues in fishes

Rapid, accurate, and simultaneous detection of triphenylmethane (TPM) residues and their metabolites in aquaculture products is vital to ensure the safety of aquatic products. In this study, a novel Escherichia coli ( E. coli ) engineering bacteria-polydopamine (PDMS@PDA@ E. coli ) coated stir bar was prepared for the extraction and enrichment of malachite green (MG), leucomalachite green (LMG), crystal violet (CV), and leucocrystal violet (LCV), which are typical TPM drugs utilised in aquaculture. A PDMS stir bar was first modulated to show hydrophilic properties via plasma treatment to enhance the evenness and stability of PDA coating. Subsequently, the PDMS@PDA stir bar was adsorbed with E. coli to form PDMS@PDA@ E. coli coating, which showed enhanced extraction capacity and selectivity towards TPMs. These characteristics were due to the specific adsorption properties of TPM dyes by Gram -negative bacteria. A hand -held stirring device was installed with the stir bar for on-site extraction. To directly detect the eluted targets without separation, a portable mass spectrometer was utilised. Under the optimal conditions, the samples can be rapidly pretreated (within 30 min) and used for the analysis of 4 TPMs with a recovery of 77.8 %-97.0 % together with the detection limits of 0.13 -0.38 mu g/kg. These findings prove that the assay has potential application value and broad prospects for the on-site detection of TPM residues in fish.