Microfluidic Size Exclusion Chromatography for Sustainable Nanoplastic Detection

The detection and characterization of nanoplastics in environmental samples pose significant challenges due to their diminutive size and the complex nature of the sample matrices.Size Exclusion Chromatography (SEC) provides a promising approach by separating nanoplastics based on size, enabling precise isolation from other contaminants and macromolecules.This size-based separation is particularly beneficial for obtaining detailed data on the size distribution and concentration of nanoplastics, which is essential for assessing their environmental impact.While traditional SEC commonly utilizes silicon-based microbeads as porous substrates, these do not effectively adsorb small particles.In this study, we employ a novel substrate by mixing chitosan and agarose.This combination not only enhances the capture and retention of nanoplastics but also supports sustainable and costeffective operations.Additionally, the microbeads are compatible with various downstream characterization techniques, including Raman spectroscopy, scanning electron microscopy (SEM), and high-resolution fluorescence imaging, facilitating comprehensive analysis of the nanoplastics.Traditionally, SEC employs silicon-based or agarose-based beads that primarily achieve size-based separation.In this study, we utilize a substrate composed of 1% agarose mixed with 5% v/v chitosan microbeads.Agarose forms a naturally porous network during gelation, while chitosan, with its surface amine groups and positive charge, enhances the adsorption of nanoplastics.This combination not only improves the capture efficiency of nanoplastics but also ensures compatibility with various analytical techniques, including Raman spectroscopy, scanning electron microscopy, UV-Vis spectroscopy, and fluorescence imaging.Furthermore, to enhance Raman spectroscopy capabilities for nanoparticle detection, Surface-Enhanced Raman Spectroscopy (SERS) is implemented by incorporating gold nanoparticles into the gel matrix.The microbeads are packed into a rectangular microfluidic channel.The channel is connected to a porous membrane valve.The valve is closed during sample separation and opened for collecting the microbeads.The system schematic is illustrated in Fig. 1.The nanoplastic water samples are introduced into the channel at varying flow rates, and the system's capture efficiency is subsequently evaluated using a particle size analyzer.After separation, the microbeads are flushed out of the microfluidic channel for fluorescent imaging analysis, and dehydrated for Raman spectroscopy, SEM, and can be scanned using AFM for nanoplastics detection (Fig. 2).In addition, the beads can be remolten for quantitative particle detection using techniques such as UV-Vis (Fig. 3).This work represents a pioneering approach in nanoplastic capture by integrating a system compatible with a wide range of characterization techniques.Notably, this project is one of the few examples that apply Size Exclusion Chromatography (SEC) for detecting and sampling environmental contaminants such as nanoplastics.The innovative approach combines effective size-based separation with flexible, comprehensive analytical integration, offering a sustainable and cost-effective solution.By addressing the limitations of traditional methods, this system advances the field of nanoplastic detection and characterization, providing a significant step forward in environmental monitoring.