Affinity capture of nanoplastics and their thermogravimetric quantification on plasma polymer coated filters

Abstract

Nanoplastics (NPs) are an emerging pollutant of concern due to their potential environmental and health impacts. Yet their detection and quantification remain analytically challenging. Conventional filtration methods often fail to effectively capture particles below 100 nm, and existing analytical techniques are limited by high cost, low throughput, or extensive sample preparation. This study presents a proof-of-concept approach for the passive capture and thermogravimetric quantification of nanoplastics using plasma polymer-coated mixed cellulose ester (MCE) filters. Plasma polymer films of acrylic acid (AAc), 2-methyl-2-oxazoline (POx), 1,7-octadiene (OD), and perfluorooctane (PFO) were used to modify the surface chemistry of the filters. Coated filters were characterised by ellipsometry, X-ray photoelectron spectroscopy, and contact angle measurements, confirming the desired physicochemical properties. Thermogravimetric analysis (TGA) demonstrated polymer-specific degradation peaks for polystyrene (PS), poly(methyl methacrylate) (PMMA), and polycaprolactone (PCL) NPs, with detection limits as low as 5 μg in the presence of filter material. Affinity-based capture was evaluated by filtering NP suspensions through coated and uncoated filters, with quantification by TGA and visual assessment via SEM. Results showed improved retention of PS on hydrophobic (PFO) filters and PMMA on hydrophilic (POx) filters, consistent with expected surface interaction mechanisms. While overall recovery was low, TGA proved to be a sensitive and reliable method for quantifying retained NPs above a threshold mass. This work demonstrates the potential of combining surface-engineered filters with TGA as a simple, low-cost screening method for nanoplastics, and highlights the importance of surface chemistry in improving capture efficiency for nanoscale contaminants.