Electrospray deposition for single nanoparticle studies

Bridging colloidal and electrochemical syntheses of metal nanocrystals with seeded electrodeposition for tracking single nanocrystal growth

Metal nanocrystals (NCs) produced by colloidal synthesis have a variety of structural features, such as different planes, edges, and defects. Even from the best colloidal syntheses, these characteristics are distributed differently in each NC. This inherent heterogeneity can play a significant role in the properties displayed by NCs. This manuscript reports the use of electrochemistry to synthesize Au NCs in a system evaluated to track individual NC growth trajectories as a first step toward rapid identification of NCs with different structural features. Au nanocubes were prepared colloidally and deposited onto a glassy carbon electrode using either electrospray or an airbrush, resulting in well-spaced Au nanocubes. The Au nanocubes then served as seeds as gold salt was reduced to deposit metal at constant potential. Deposition at constant potential facilitates overgrowth on the Au nanocubes to achieve new NC shapes. The effects of applied potential, deposition time, precursor concentration, and capping agents on NC shape evolution were studied. The outcomes are correlated to results from traditional colloidal syntheses, providing a bridge between the two synthetic strategies. Moreover, scanning electron microscopy was used to image the same NCs before and after deposition, linking individual seed features to differences in deposition. This ability is anticipated to enable tracking of individual growth trajectories of NCs to elucidate sources of heterogeneity in NC syntheses.

Controlling morphology in electrosprayed methylcellulose nanowires via nanoparticle addition: coarse-grained modeling and experiments

Electrospray deposition (ESD) has shown great promise for manufacturing micro- and nanostructured coatings at scale on versatile substrates with complex geometries. ESD exhibits a broad spectrum of morphologies depending upon the properties of spray fluids. Among them are nanowire forests or foams obtained via the in-air gelation of electrospray droplets formed from methylcellulose (MC) solutions. In this study, we explored MC ESD loaded with nanoparticles of various shapes and uncovered the effects of particle fillers on morphology evolution using coarse-grained simulations and physical experiments. Utilizing electrostatic dissipative particle dynamics, we modeled the electrohydrodynamic deformation of particle-laden MC droplets undergoing in-flight evaporation. The simulations quantitatively predict the suppression of droplet deformation as the size or concentration of spherical nanoparticles increases. While small particles can be readily encapsulated into the nanowire body, large particles can arrest nanowire formation. The model was extended to nanoparticles with complex topologies, showing MC nanowires emerging from particle edges and vertices due to curvature-enhanced electric stress. In all cases, strong agreements were found between simulation and experimental results. These results demonstrate the efficacy of the coarse-grained model in predicting the morphology evolution of electrosprayed droplets and lay the groundwork for employing MC nanowires for developing nanostructured composites.

Unraveling the Structural Sensitivity of CO2 Electroreduction at Facet-Defined Nanocrystals via Correlative Single-Entity and Macroelectrode Measurements

The conversion of CO₂ into value-added products is a compelling way of storing energy derived from intermittent renewable sources and can bring us closer to a closed-loop anthropogenic carbon cycle. The ability to synthesize nanocrystals of well-defined structure and composition has invigorated catalysis science with the promise of nanocrystals that selectively express the most favorable sites for efficient catalysis. The performance of nanocrystal catalysts for the CO₂ reduction reaction (CO₂RR) is typically evaluated with nanocrystal ensembles, which returns an averaged system-level response of complex catalyst-modified electrodes with each nanocrystal likely contributing a different (unknown) amount. Measurements at single nanocrystals, taken in the context of statistical analysis of a population, and comparison to macroscale measurements are necessary to untangle the complexity of the ever-present heterogeneity in nanocrystal catalysts, achieve true structure-property correlation, and potentially identify nanocrystals with outlier performance. Here, we employ environment-controlled scanning electrochemical cell microscopy to isolate and investigate the electrocatalytic CO₂RR response of individual facet-defined gold nanocrystals. Using correlative microscopy approaches, we conclusively demonstrate that {110}-terminated gold rhombohedra possess superior activity and selectivity for CO₂RR compared with {111}-terminated octahedra and high-index {310}-terminated truncated ditetragonal prisms, especially at low overpotentials where electrode kinetics is anticipated to dominate the current response. The methodology framework described here could inform future studies of complex electrocatalytic processes through correlative single-entity and macroscale measurement techniques.

Cell-membrane-inspired polymers for constructing biointerfaces with efficient molecular recognition

Fabrication of devices that accurately recognize, detect, and separate target molecules from mixtures is a crucial aspect of biotechnology for applications in medical, pharmaceutical, and food sciences. This technology has also been recently applied in solving environmental and energy-related problems. In molecular recognition, biomolecules are typically complexed with a substrate, and specific molecules from a mixture are recognized, captured, and reacted. To increase sensitivity and efficiency, the activity of the biomolecules used for capture should be maintained, and non-specific reactions on the surface should be prevented. This review summarizes polymeric materials that are used for constructing biointerfaces. Precise molecular recognition occurring at the surface of cell membranes is fundamental to sustaining life; therefore, materials that mimic the structure and properties of this particular surface are emphasized in this article. The requirements for biointerfaces to eliminate nonspecific interactions of biomolecules are described. In particular, the major issue of protein adsorption on biointerfaces is discussed by focusing on the structure of water near the interface from a thermodynamic viewpoint; moreover, the structure of polymer molecules that control the water structure is considered. Methodologies enabling stable formation of these interfaces on material surfaces are also presented.