Aaron M. Keller

Plasmonic giant semiconductor nanocrystals with enhanced light output and suppressed blinking for biomedical applications

Hybrid semiconductor-metal nanoparticles are of both fundamental and practical interest. CdSe semiconductor nanocrystal quantum dots (NQDs) are emissive following direct absorption of photons, while nanosized metal structures exhibit plasmonic absorption and light scattering. In a hybrid nanoscale architecture, both optical phenomena can be integrated as metal-semiconductor coupling via non-radiative energy transfer and modifications of the radiative decay rates through Purcell effect, alter the emission mechanism resulting in a range of effects from photoluminescence (PL) quenching to enhancement.

Note: Time-gated 3D single quantum dot tracking with simultaneous spinning disk imaging.

We describe recent upgrades to a 3D tracking microscope to include simultaneous Nipkow spinning disk imaging and time-gated single-particle tracking (SPT). Simultaneous 3D molecular tracking and spinning disk imaging enable the visualization of cellular structures and proteins around a given fluorescently labeled target molecule. The addition of photon time-gating to the SPT hardware improves signal to noise by discriminating against Raman scattering and short-lived fluorescence. In contrast to camera-based SPT, single-photon arrival times are recorded, enabling time-resolved spectroscopy (e.g., measurement of fluorescence lifetimes and photon correlations) to be performed during single molecule/particle tracking experiments.

Three dimensional time-gated tracking of non-blinking quantum dots in live cells

Single particle tracking has provided a wealth of information about biophysical processes such as motor protein transport and diffusion in cell membranes. However, motion out of the plane of the microscope or blinking of the fluorescent probe used as a label generally limits observation times to several seconds. Here, we overcome these limitations by using novel non-blinking quantum dots as probes and employing a custom 3D tracking microscope to actively follow motion in three dimensions (3D) in live cells. Signal-to-noise is improved in the cellular milieu through the use of pulsed excitation and time-gated detection.