A lateral nanoflow assay reveals nanoplastic fluorescence heterogeneity

Abstract

Colloidal nanoplastics present technological opportunities, environmental concerns, and measurement challenges. To meet these challenges, we develop a lateral nanoflow assay from sample-in to answer-out. Our measurement system integrates complex nanofluidic replicas, super-resolution optical microscopy, and comprehensive statistical analyses to measure polystyrene nanoparticles that sorb and carry hydrophobic fluorophores. An elegant scaling of surface forces within our silicone devices hydrodynamically automates the advection and dominates the diffusion of the nanoparticles. Through steric interaction with the replica structure, the particle size distribution reciprocally probes the unknown limits of replica function. Multiple innovations in the integration and calibration of device and microscope improve the accuracy of identifying single nanoparticles and quantifying their diameters and fluorescence intensities. A statistical model of the measurement approaches the information limit of the system, discriminates size exclusion from surface adsorption, and reduces nonideal data to return the particle size distribution with nanometer resolution. A Bayesian statistical analysis of the dimensional and optical properties of single nanoparticles reveals their fundamental structure-property relationship. Fluorescence intensity shows a super-volumetric dependence, scaling with nanoparticle diameter to nearly the fourth power and confounding basic concepts of chemical sorption. Distributions of fluorescivity - the product of the number density, absorption cross section, and quantum yield of an ensemble of fluorophores - are ultrabroad and asymmetric, limiting ensemble analysis and dimensional or chemical inference from fluorescence intensity. These results reset expectations for optimizing nanoplastic products, understanding nanoplastic byproducts, and applying nanoplastic standards