High-Throughput All-Optical Determination of Nanorod Size and Orientation.

As a single-particle characterization technique, optical microscopy has transformed our understanding of structure-function relationships of plasmonic nanoparticles, but the need for ex-situ-correlated electron microscopy to obtain structural information handicaps an otherwise exceptional high-throughput technique. Here, we present an all-optical alternative to electron microscopy to accurately and quickly extract structural information about single gold nanorods (Au NRs) using calcite-assisted localization and kinetics (CLocK) microscopy. Color CLocK images of single Au NRs allow scattering from the longitudinal and transverse plasmon modes to be imaged simultaneously, encoding spectral data in CLocK images that can then be extracted to obtain Au NR size and orientation. Moreover, through the use of convolutional neural networks, Au NR length, width, and aspect ratio can be predicted directly from color CLocK images within ∼10% of the true value measured by electron microscopy.

Calcite-Assisted Localization and Kinetics (CLocK) Microscopy.

Localization-based super-resolution imaging techniques have improved the spatial resolution of optical microscopy well below the diffraction limit, yet encoding additional information into super-resolved images, such as anisotropy and orientation, remains a challenge. Here we introduce calcite-assisted localization and kinetics (CLocK) microscopy, a multiparameter super-resolution imaging technique easily integrated into any existing optical microscope setup at low cost and with straightforward analysis. By placing a rotating calcite crystal in the infinity space of an optical microscope, CLocK microscopy provides immediate polarization and orientation information while maintaining the ability to localize an emitter/scatterer with <10 nm resolution. Further, kinetic information an order of magnitude shorter than the integration time of the camera is encoded in the unique point spread function of a CLocK image, allowing for new mechanistic insight into dynamic processes such as single-nanoparticle dissolution and single-molecule surface-enhanced Raman scattering.

Bovine Serum Albumin Enhances Silver Nanoparticle Dissolution Kinetics in a Size- and Concentration-Dependent Manner.

The dissolution of silver nanoparticles (AgNPs) to release Ag(I)(aq) is an important mechanism in potentiating AgNP cytotoxicity and imparting their antibacterial properties. However, AgNPs can undergo other simultaneous biophysicochemical transformations, such as protein adsorption, which can mediate AgNP dissolution behaviors. We report the comprehensive analysis of AgNP dissolution and protein adsorption behaviors with monolayer surface coverage of AgNPs by bovine serum albumin (BSA). AgNP dissolution rate constants, kdissolution, were quantified over several particle sizes (10, 20, and 40 nm) and BSA concentrations (0-2 nM) using linear sweep stripping voltammetry. Across all particle sizes, the dissolution rate constant increased with increasing BSA concentrations. However, protein-enhanced dissolution behaviors were most pronounced for 10 nm AgNPs, which exhibited 3.6-fold and 7.7-fold relative enhancement when compared to 20 and 40 nm AgNPs, respectively. Changes to AgNP surface properties upon interaction with BSA were monitored using dynamic light scattering and zeta potential measurements, while BSA-AgNP complex formation was evaluated using UV-vis spectroscopy and circular dichroism spectroscopy. A subtle increase in the BSA-AgNP association constant was observed with an increase in the AgNP size. Together, these results suggest that the AgNP size dependence of BSA-enhanced dissolution of AgNPs is possibly mediated through both displacement of Ag(I)(aq)-loaded BSA by excess protein in the bulk solution and minimized accessibility of the AgNP surface because of BSA adsorption.

In Situ Quantification of Silver Nanoparticle Dissolution Kinetics in Simulated Sweat Using Linear Sweep Stripping Voltammetry.

Linear sweep stripping voltammetry (LSSV) is demonstrated as a sensitive, rapid, and cost-efficient analytical technique for the quantification of silver nanoparticle (AgNP) dissolution rates in simulated sweat. LSSV does not require the extensive sample preparation (e.g., ultrafiltration or centrifugation) needed by more commonly employed techniques, such as atomic spectroscopy. The limit of detection (LOD) of Ag(I)(aq) was 14 ± 6 µg L-1, and measured dissolution rate constants, kdissolution, varied from 0.0168-0.1524 h-1, depending on solution conditions. These values are comparable and agree well with those determined by others in the literature using atomic spectroscopy. Importantly, LSSV had the necessary sensitivity to distinguish the effects of SSW solution conditions on AgNP dissolution rates. Specifically, enhanced dissolution rates were observed with decreased pH and with increased NaCl concentration. The colloidal stability of AgNPs in SSW solutions was also characterized using dynamic light scattering (DLS), ζ potential, and quantitative UV-vis spectroscopy measurements. An increase in AgNP aggregation rate was observed with increased NaCl concentration in SSW, suggesting that the enhancement in AgNP dissolution is driven by the large Cl/Ag ratio, even as the AgNPs undergo significant aggregation.