Characterization of microfluidic trap and mixer module for rapid fluorescent tagging of microplastics

This study introduces a practical approach utilizing microfluidic trap and mixer modules fabricated with polydimethylsiloxane (PDMS) microfluidic devices. These modules were employed to capture and fluorescently label various randomly shaped microplastics (MPs) like polyethylene (PE), polypropylene (PP), and polystyrene (PS). Within the MPs trap module, grooves were incorporated into a straight-lined channel using SU-8 photolithography. This design induced turbulence effectively trapping and gathering the MPs within aqueous phases at 15 groove spaces, which achieved a trapping efficiency of up to 69% for PS MPs sized at a flow rate of 2 mL/min. Additionally, a mixer module featuring two flow inlets was designed to create a serpentine microfluidic channel, whose design significantly reduced sample and reagent (Nile Red) consumption during MP fluorescence staining at 80 °C. Furthermore, 2 nm gold nanoparticles (Au NPs), conjugated with a PS binding peptide (PSBP), were examined as an alternative fluorescent agent at room temperature. Photoluminescence (PL) and Fourier transform infrared (FT-IR) showcased efficiency of mixer module in labeling 30 mL MP solutions within a short time of 15 min. Moreover, a combined platform integrating trap and mixer devices was devised, incorporating a disposable heating pad and filter paper unit, which offers a simplified and compact MPs staining tool including spherical PE nanoplastics (200 nm–99 μm). This study aims to propose a preliminary concept for a lab-on-a-chip, facilitating the simultaneous collection and fluorescent labeling, which can be instrumentally implemented in future MPs monitoring.