Effect of Hydrophobicity on Nano-Bio Interactions of Zwitterionic Luminescent Gold Nanoparticles at the Cellular Level

Fundamental understanding of how the hydrophobicity impacts cellular interactions of engineered nanoparticles is critical to their future success in healthcare. Herein, we report that inserting hydrophobic octanethiol onto the surface of zwitterionic luminescent glutathione coated gold nanoparticles (GS-AuNPs) of 2 nm enhanced their affinity to the cellular membrane and increased cellular uptake kinetics by more than one order of magnitude, rather than inducing the accumulation of the AuNPs in the bilayer core or enhancing their passive diffusion. These studies highlight the diversity and heterogeneity in the hydrophobicity-induced nano–bio interactions at the cellular level and offer a new pathway to expediting cellular uptake of engineered nanoparticles. In addition, the amphiphilic luminescent AuNPs with high affinity to cell membrane and rapid endocytosis potentially serve as dual-modality imaging probes to correlate fluorescence and electron microscopies at the cellular level

Surface-Chemistry Effect on Cellular Response of Luminescent Plasmonic Silver Nanoparticles

Cellular response of inorganic nanoparticles (NPs) is strongly dependent on their surface chemistry. By taking advantage of robust single-particle fluorescence and giant Raman enhancements of unique polycrystalline silver NPs (AgNPs), we quantitatively investigated effects of two well-known surface chemistries, passive PEGylation and active c-RGD peptide conjugation, on <i>in vitro</i> behaviors of AgNPs at high temporal and spatial resolution as well as chemical level using fluorescence and Raman microscopy. The results show that specific c-RGD peptide−α_vβ₃ integrin interactions not only induced endosome formation more rapidly, enhanced constrained diffusion, but also minimized nonspecific chemical interactions between the NPs and intracellular biomolecules than passive PEGylation chemistry; as a result, surface enhanced Raman scattering (SERS) signals of c-RGD peptides were well resolved inside endosomes in the live cells, while Raman signals of PEGylated AgNPs remained unresolvable due to interference of surrounding biomolecules, opening up an opportunity to investigate specific ligand–receptor interactions in real time at the chemical level

Photoluminescence of a Plasmonic Molecule

Photoluminescent Au nanoparticles are appealing for biosensing and bioimaging applications because of their non-photobleaching and non-photoblinking emission. The mechanism of one-photon photoluminescence from plasmonic nanostructures is still heavily debated though. Here, we report on the one-photon photoluminescence of strongly coupled 50 nm Au nanosphere dimers, the simplest plasmonic molecule. We observe emission from coupled plasmonic modes as revealed by single-particle photoluminescence spectra in comparison to correlated dark-field scattering spectroscopy. The photoluminescence quantum yield of the dimers is found to be surprisingly similar to the constituent monomers, suggesting that the increased local electric field of the dimer plays a minor role, in contradiction to several proposed mechanisms. Aided by electromagnetic simulations of scattering and absorption spectra, we conclude that our data are instead consistent with a multistep mechanism that involves the emission due to radiative decay of surface plasmons generated from excited electron–hole pairs following interband absorption

Optimization of Spectral and Spatial Conditions to Improve Super-Resolution Imaging of Plasmonic Nanoparticles

Interactions between fluorophores and plasmonic nanoparticles modify the fluorescence intensity, shape, and position of the observed emission pattern, thus inhibiting efforts to optically super-resolve plasmonic nanoparticles. Herein, we investigate the accuracy of localizing dye fluorescence as a function of the spectral and spatial separations between fluorophores (Alexa 647) and gold nanorods (NRs). The distance at which Alexa 647 interacts with NRs is varied by layer-by-layer polyelectrolyte deposition while the spectral separation is tuned by using NRs with varying localized surface plasmon resonance (LSPR) maxima. For resonantly coupled Alexa 647 and NRs, emission to the far field through the NR plasmon is highly prominent, resulting in underestimation of NR sizes. However, we demonstrate that it is possible to improve the accuracy of the emission localization when both the spectral and spatial separations between Alexa 647 and the LSPR are optimized