CEE Seminar -Fate of nanoplastics in biofilms

Microplastics, particularly nanoplastics, are widespread contaminants, virtually present in all engineering and environmental systems. Also abundant in these systems are biofilms, or bacteria surrounded with extracellular polymeric substances (EPS) to form a three-dimensional matrix structure. There is compelling evidence indicating nanoparticle (NP) ubiquity, accumulation, and interaction with environmental biofilms. However, the fundamental understanding of the exact mechanisms governing the interaction between nanoparticles and biofilms is still unclear. Herein, we present a study to explore the effect of crosslinking density on the diffusive behavior of NPs in heterogeneous matrices like alginate. With advanced analysis of fluorescence microscopy data, we characterized and map the heterogeneous diffusion of 20, 100, and 200 nm carboxylated-polystyrene nanoparticles in a calcium cross-linked alginate model matrix of varying concentrations. Our findings showed that an increase in cross-linking concentration decreases NP diffusion and pore accessibility in a size-dependent manner. In addition, all sizes of particles experienced a degree of confinement and partial confinement, leading to the conclusion that NP diffusion in heterogeneous matrices, like alginate and the extracellular polymeric substances (EPS) matrix of a biofilm, is anisotropic due to the spatial heterogeneities and micro-domains present in the EPS structure.