Eco-Corona Formation on Plastics: Adsorption of Dissolved Organic Matter to Pristine and Photochemically Weathered Polymer Surfaces.

Plastic fate in freshwater systems is dependent on particle size, morphology, and physicochemical surface properties (e.g., charge, surface roughness, and hydrophobicity). Environmental aging processes, such as photochemical weathering and eco-corona formation due to dissolved organic matter (DOM) adsorption on plastic surfaces, can alter their physicochemical properties, affecting fate and transport. While plastic aging has been studied from a materials science perspective, its specific implications in environmental contexts remain less understood. Although photochemical weathering and eco-corona formation occur simultaneously in the environment, in this work, we systematically assessed the effects of photochemical weathering on the physicochemical properties of polymers (polyethylene, polypropylene, polyethylene terephthalate, and polystyrene) and how this influences the adsorption of DOMs (Suwannee River humic acid, fulvic acid, and natural organic matter) relative to pristine polymers. Pristine polymers initially had different and distinct physicochemical surface properties, but upon aging, they became more similar in terms of surface properties. Photochemical weathering resulted in a decrease in polymer film thickness, an increase in surface roughness, and hydrophilicity. DOM adlayers on the polymer surfaces resulted in more comparable wettability, effectively masking the initial polymer properties. Collectively, this study explores the physiochemical changes polymers undergo in laboratory studies mimicking environmental conditions. Understanding these changes is the initial step to rationalizing and predicting processes and interactions such as heteroaggregation that dictate the fate of plastics in the environment.

Probing the Separation Distance between Biological Nanoparticles and Cell Membrane Mimics Using Neutron Reflectometry with Sub-Nanometer Accuracy.

Nanoparticle interactions with cellular membranes are controlled by molecular recognition reactions and regulate a multitude of biological processes, including virus infections, biological nanoparticle-mediated cellular communication, and drug delivery applications. Aided by the design of various supported cell membrane mimics, multiple methods have been employed to investigate these types of interactions, revealing information on nanoparticle coverage, interaction kinetics, as well as binding strength; however, precise quantification of the separation distance across which these delicate interactions occur remains elusive. Here, we demonstrate that carefully designed neutron reflectometry (NR) experiments followed by an attentive selection and application of suitable theoretical models offer a means to quantify the distance separating biological nanoparticles from a supported lipid bilayer (SLB) with sub-nanometer precision. The distance between the nanoparticles and SLBs was tuned by exploiting either direct adsorption or specific binding using DNA tethers with different conformations, revealing separation distances of around 1, 3, and 7 nm with nanometric accuracy. We also show that NR provides precise information on nanoparticle coverage, size distribution, material composition, and potential structural changes in the underlying planar SLB induced upon nanoparticle binding. The precision with which these parameters could be quantified should pave an attractive path for investigations of the interactions between nanoparticles and interfaces at length scales and resolutions that were previously inaccessible. This thus makes it possible to, for example, gain an in-depth understanding of the molecular recognition reactions of inorganic and biological nanoparticles with cellular membranes.

Time-Resolved and Label-Free Evanescent Light-Scattering Microscopy for Mass Quantification of Protein Binding to Single Lipid Vesicles.

In-depth understanding of the intricate interactions between biomolecules and nanoparticles is hampered by a lack of analytical methods providing quantitative information about binding kinetics. Herein, we demonstrate how label-free evanescent light-scattering microscopy can be used to temporally resolve specific protein binding to individual surface-bound (∼100 nm) lipid vesicles. A theoretical model is proposed that translates protein-induced changes in light-scattering intensity into bound mass. Since the analysis is centered on individual lipid vesicles, the signal from nonspecific protein binding to the surrounding surface is completely avoided, offering a key advantage over conventional surface-based techniques. Further, by averaging the intensities from less than 2000 lipid vesicles, the sensitivity is shown to increase by orders of magnitude. Taken together, these features provide a new avenue in studies of protein-nanoparticle interaction, in general, and specifically in the context of nanoparticles in medical diagnostics and drug delivery.

Competitive Coadsorption Dynamics of Viruses and Dissolved Organic Matter to Positively Charged Sorbent Surfaces.

Adsorption onto solid-water interfaces is a key process governing the fate and transport of waterborne viruses. Although negatively charged viruses are known to extensively adsorb onto positively charged adsorbent surfaces, virus adsorption in such systems in the presence of negatively charged dissolved organic matter (DOM) as coadsorbate remains poorly studied and understood. This work provides a systematic assessment of the adsorption dynamics of negatively charged viruses (i.e., bacteriophages MS2, fr, GA, and Qß) and polystyrene nanospheres onto a positively charged model sorbent surface in the presence of varying DOM concentrations. In all systems studied, DOM competitively suppressed the adsorption of the viruses and nanospheres onto the model surface. Electrostatic repulsion of the highly negatively charged MS2, fr, and the nanospheres impaired their adsorption onto DOM adlayers that formed during the coadsorption process. In contrast, the effect of competition on overall adsorption was attenuated for less-negatively charged GA and Qß because these viruses also adsorbed onto DOM adlayer surfaces. Competition in MS2-DOM coadsorbate systems were accurately described by a random sequential adsorption model that explicitly accounts for the unfolding of adsorbed DOM. Consistent findings for viruses and nanospheres suggest that the coadsorbate effects described herein generally apply to systems containing negatively charged nanoparticles and DOM.

Viruses at Solid-Water Interfaces: A Systematic Assessment of Interactions Driving Adsorption.

Adsorption to solid-water interfaces is a major process governing the fate of waterborne viruses in natural and engineered systems. The relative contributions of different interaction forces to adsorption and their dependence on the physicochemical properties of the viruses remain, however, only poorly understood. Herein, we systematically studied the adsorption of four bacteriophages (MS2, fr, GA, and Qß) to five model surfaces with varying surface chemistries and to three dissolved organic matter adlayers, as a function of solution pH and ionic strength, using quartz crystal microbalance with dissipation monitoring. The viruses were selected to have similar sizes and shapes but different surface charges, polarities, and topographies, as identified by modeling the distributions of amino acids in the virus capsids. Virus-sorbent interactions were governed by long-ranged electrostatics and favorable contributions from the hydrophobic effect, and shorter-ranged van der Waals interactions were of secondary importance. Steric effects depended on the topographic irregularities on both the virus and sorbent surfaces. Differences in the adsorption characteristics of the tested viruses were successfully linked to differences in their capsid surface properties. Besides identifying the major interaction forces, this work highlights the potential of computable virus surface charge and polarity descriptors to predict virus adsorption to solid-water interfaces.

Dissolved organic matter adsorption to model surfaces: adlayer formation, properties, and dynamics at the nanoscale.

Adlayers of dissolved organic matter (DOM) form on many surfaces in natural and engineered systems and affect a number of important processes in these systems. Yet, the nanoscalar properties and dynamics of DOM adlayers remain poorly investigated. This work provides a systematic analysis of the properties and dynamics of adlayers formed from a diverse set of eight humic and fulvic acids, used as DOM models, on surfaces of self-assembled monolayers (SAMs) of different alkylthiols covalently bound to gold supports. DOM adsorption to positively charged amine-terminated SAMs resulted in the formation of water-rich adlayers with nanometer thicknesses that were relatively rigid, irreversibly adsorbed, and collapsed upon air drying, as demonstrated by combined quartz crystal microbalance and ellipsometry measurements. DOM adlayer thicknesses varied only slightly with solution pH from 5 to 8 but increased markedly with increasing ionic strength. Contact angle measurements revealed that the DOM adlayers were relatively polar, likely due to the high water contents of the adlayers. Comparing DOM adsorption to SAM-coated sensors that systematically differed in surface charge and polarity characteristics showed that electrostatics dominated DOM-surface interactions. Laccase adsorption to DOM adlayers on amine-terminated SAMs served to demonstrate the applicability of the presented experimental approach to study the interactions of (bio)macromolecules and (nano)particles with DOM.

A Roadmap for Building Waterborne Virus Traps.

Outbreaks of waterborne viruses pose a massive threat to human health, claiming the lives of hundreds of thousands of people every year. Adsorption-based filtration offers a promising facile and environmentally friendly approach to help provide safe drinking water to a world population of almost 8 billion people, particularly in communities that lack the infrastructure for large-scale facilities. The search for a material that can effectively trap viruses has been mainly driven by a top-down approach, in which old and new materials have been tested for this purpose. Despite substantial advances, finding a material that achieves this crucial goal and meets all associated challenges remains elusive. We suggest that the road forward should strongly rely on a complementary bottom-up approach based on our fundamental understanding of virus interactions at interfaces. We review the state-of-the-art physicochemical knowledge of the forces that drive the adsorption of viruses at solid-water interfaces. Compared to other nanometric colloids, viruses have heterogeneous surface chemistry and diverse morphologies. We advocate that advancing our understanding of virus interactions would require describing their physicochemical properties using novel descriptors that reflect their heterogeneity and diversity. Several other related topics are also addressed, including the effect of coadsorbates on virus adsorption, virus inactivation at interfaces, and experimental considerations to ensure well-grounded research results. We finally conclude with selected examples of materials that made notable advances in the field.

Time-Resolved Thickness and Shape-Change Quantification using a Dual-Band Nanoplasmonic Ruler with Sub-Nanometer Resolution.

Time-resolved measurements of changes in the size and shape of nanobiological objects and layers are crucial to understand their properties and optimize their performance. Optical sensing is particularly attractive with high throughput and sensitivity, and label-free operation. However, most state-of-the-art solutions require intricate modeling or multiparameter measurements to disentangle conformational or thickness changes of biomolecular layers from complex interfacial refractive index variations. Here, we present a dual-band nanoplasmonic ruler comprising mixed arrays of plasmonic nanoparticles with spectrally separated resonance peaks. As electrodynamic simulations and model experiments show, the ruler enables real-time simultaneous measurements of thickness and refractive index variations in uniform and heterogeneous layers with sub-nanometer resolution. Additionally, nanostructure shape changes can be tracked, as demonstrated by quantifying the degree of lipid vesicle deformation at the critical coverage prior to rupture and supported lipid bilayer formation. In a broader context, the presented nanofabrication approach constitutes a generic route for multimodal nanoplasmonic optical sensing.

An antiviral trap made of protein nanofibrils and iron oxyhydroxide nanoparticles.

Minimizing the spread of viruses in the environment is the first defence line when fighting outbreaks and pandemics, but the current COVID-19 pandemic demonstrates how difficult this is on a global scale, particularly in a sustainable and environmentally friendly way. Here we introduce and develop a sustainable and biodegradable antiviral filtration membrane composed of amyloid nanofibrils made from food-grade milk proteins and iron oxyhydroxide nanoparticles synthesized in situ from iron salts by simple pH tuning. Thus, all the membrane components are made of environmentally friendly, non-toxic and widely available materials. The membrane has outstanding efficacy against a broad range of viruses, which include enveloped, non-enveloped, airborne and waterborne viruses, such as SARS-CoV-2, H1N1 (the influenza A virus strain responsible for the swine flu pandemic in 2009) and enterovirus 71 (a non-enveloped virus resistant to harsh conditions, such as highly acidic pH), which highlights a possible role in fighting the current and future viral outbreaks and pandemics.