Monitoring the Stimulated Uncapping Process of Gold-Capped Mesoporous Silica Nanoparticles.

To establish a new method for tracking the interaction of nanoparticles with chemical cleaving agents, we exploited the optical effects caused by attaching 5-10 nm gold nanoparticles with molecular linkers to large mesoporous silica nanoparticles (MSN). At low levels of gold loading onto MSN, the optical spectra resemble colloidal suspensions of gold. As the gold is removed, by cleaving agents, the MSN revert to the optical spectra typical of bare silica. Time-lapse images of gold-capped MSN stationed in microchannels reveal that the rate of gold release is dependent on the concentration of the cleaving agent. The uncapping process was also monitored successfully for MSN endocytosed by A549 cancer cells, which produce the cleaving agent glutathione. These experiments demonstrate that the optical properties of MSN can be used to directly monitor cleaving kinetics, even in complex cellular settings.

Detecting plasmon resonance energy transfer with differential interference contrast microscopy.

Gold nanoparticles are ideal probes for studying intracellular environments and energy transfer mechanisms due to their plasmonic properties. Plasmon resonance energy transfer (PRET) relies on a plasmonic nanoparticle to donate energy to a nearby resonant acceptor molecule, a process which can be observed due to the plasmonic quenching of the donor nanoparticle. In this study, a gold nanosphere was used as the plasmonic donor, while the metalloprotein cytochrome c was used as the acceptor molecule. Differential interference contrast (DIC) microscopy allows for simultaneous monitoring of complex environments and noble metal nanoparticles in real time. Using DIC and specially designed microfluidic channels, we were able to monitor PRET at the single gold particle level and observe the reversibility of PRET upon the introduction of phosphate-buffered saline to the channel. In an additional experiment, single gold particles were internalized by HeLa cells and were subsequently observed undergoing PRET as the cell hosts underwent morphological changes brought about by ethanol-induced apoptosis.

Single Particle Orientation and Rotational Tracking (SPORT) in biophysical studies.

The single particle orientation and rotational tracking (SPORT) techniques have seen rapid development in the past 5 years. Recent technical advances have greatly expanded the applicability of SPORT in biophysical studies. In this feature article, we survey the current development of SPORT and discuss its potential applications in biophysics, including cellular membrane processes and intracellular transport.

Influence of polarization setting on gold nanorod signal at nonplasmonic wavelengths under differential interference contrast microscopy.

Researchers rely on a variety of microscopic techniques for observing and tracking anisotropic nanoparticles in real time experiments. This technical note focuses on the optical behavior exhibited by gold nanorods at nonplasmonic wavelengths under differential interference contrast microscopy (DIC). Intense diffraction patterns appear at nonplasmonic wavelengths, and the behavior of these patterns can be altered by adjusting the surrounding medium or the polarizer setting. Such patterns are absent when linear and crossed polarizations are utilized. Making polarization adjustments is important in DIC microscopy, because it affects bias retardation and image contrast. The nonplasmonic diffraction bands that were observed could potentially be exploited for rotational tracking, but more importantly, researchers should exhibit care in selecting a nanorod sample and the polarization setting when working with DIC microscopy.