Importance and challenges of environmental ligand binding and exchange: Introducing single molecule imaging as a model characterization technique

•Overview of ligand interactions with nanomaterials.•Review of previous assays that have probed polymeric and ligand interactions with synthetic materials.•Knowledge gaps exist in understanding interactions that drive natural organic matter-nanomaterial formation.•Single molecule measurements can probe complex biological systems at the nanoscale interface.•Single molecule fluorescence microscopy can measure polymer ligand adsorption and desorption from single nanoparticles.

Highly surface active nano-scale materials, when released into the natural environment, tend to adsorb geo- and bio-macromolecules and end up presenting a modified interface to biological species. Capped nanocrystals and polymer/surfactant modified nanomaterials also are known to undergo ligand exchange when exposed to natural systems. Thus, nano-bio interactions will primarily be governed by the adsorbed or exchanged natural macromolecules. To-date there has been no established technique determining the kinetics of ligand exchange or characterizing the bound geo-biomacromolecular corona in an environmental setting. Single-molecule imaging utilizing near-infra red spectrometry, and single-molecule imaging of fluorophore-tagged polymeric ligands can enable detailed characterization of biopolymeric corona. This perspective aims to highlight the importance of ligand exchange, identify roles of surface ligands on nano-bio interaction, and present initial evidence of macromolecular characterization on nanotube surfaces using single-molecule techniques. This commentary also aims to outline the challenges facing nano-environmental health and safety community on assessing biological interaction with complex nano-scale heterostructures in a realistic environmental matrix.

Graphical abstractSingle-molecule imaging reveals natural ligand exchange and binding on nanomaterial surfaces in a bio-complex environment.Figure optionsDownload full-size imageDownload high-quality image (367 K)Download as PowerPoint slide