Development of a Binary Digestion System for Extraction Microplastics in Fish and Detection Method by Optical Photothermal Infrared

Accumulating evidence indicates that aquatic organisms ingest microplastics (MPs), which may be a threat to essentially the entire global ecosystem. In current detection methods, even in cutting-edge nanoplastic technology, a major challenge for detecting microplastics (MPs) in aquatic organisms is removing complex biological matrices, such as fat. Herein we report combining HNO3 and H2O2 to form a binary digestive reagent system to determine MPs in biological tissue. With insights obtained from a Gaussian model, the adding manners of two reagents were discussed. Thus, in the final protocol, we mixed MPs and tissue with 20 mL of 30% (v/v) aqueous H2O2, 10 mL 0.5 M NaOH,1 mL 5 mM Fe2+, and 40 mL 11.5% (v/v) aqueous HNO3, in sequence at different time intervals. What's more, sodium dodecyl sulfate (SDS) and ultrasound-alone or together-were explored to solve the problem of removing fat residues and thus membrane blockage during filtration. In this paper, we used the O-PTIR microscope to verify the feasibility of the protocol. Compared with traditional detection methods, the O-PTIR spectroscopy can significantly improve the lateral resolution, down to sub and super-micrometer, and the ability to quickly obtain high spatial resolution far-field non-contact infrared spectra, which provide a novel method for qualitative analysis of MPs. In field applications, in our attempt, the fixed wavenumber image by O-PTIR can realize sub and super-micrometer MPs in situ, far-field measurements. The present method is highly efficient, and facilitates the identification of plastic particles.