| February 27, 2013 |
"Enabling and Disrupting Impacts of Interfaces in Energy Systems," by Dawn Bonnell, The University of Pennsylvania, hosted by Chris Fry
Abstract: Recent advances allow us to manipulate, control, and measure local phenomena at nanometer scales. Size dependent behavior of solids has become the hallmark of nanoscale science and nanotechnology. As systems decrease in size, the influence of surfaces and interfaces can dominate the properties. In fact, properties of surfaces and interfaces dictate the behavior of devices ranging from biosensors to solar cells to computer processors. This is particularly true as the size of the constituents decreases.
This talk will present three model examples of behavior at interfaces that have dramatic consequences to energy systems and that also illustrate novel measurements of local properties:
- The first involves size-dependent electronic properties of metal-oxide interfaces, an important issue in device miniaturization.
- The second demonstrates how engineered interfaces in nanoparticle arrays yield new plasmonic interactions useful in energy harvesting.
- The final example illustrates how mechanisms of mass and energy exchange at interfaces in fuel cells can be determined from in situ local probes.
|
| March 13, 2013 |
"Next-Generation Nanocrystals for Cellular Imaging," by Bruce Cohen, Lawrence Berkeley National Laboratory, hostged by Elena Shevchenko
Abstract: Nanocrystals that have unusual or exceptional optical properties have shown promise as transformative probes for biological imaging. Phosphorescent upconverting nanoparticles (UCNPs) have proven to be especially promising as biological labels, and single-particle studies of UCNPs have shown that they exhibit nearly ideal properties as single-molecule imaging probes. UCNPs absorb two or more photons in the near infrared (nIR) and emit one at shorter wavelengths in the visible or nIR, an unusual characteristic that distinguishes them from all luminescent chemicals in the cell, and one that suggests background-free cellular imaging.
We have shown that UCNPs do not blink on and off as most other probes do, and they possess remarkable photostability, resisting photobleaching under continuous irradiation long after organic dyes, proteins, and even quantum dots are extinguished. We have recently developed synthetic methods for control of UCNP size and completed a combinatorial lanthanide scan in order to tune emission wavelengths for multicolor upconverted imaging. We have also developed methods for studying single nanocrystal lifetimes and emission spectra, which has allowed us to understand lanthanide-lanthanide communication within the nanocrystal.
We have also developed luminescent nanocrysta-based thermometers able to detect sub-°C variations within live cells. Temperature is a key parameter in all physiological processes, and probes able to detect small changes in local temperature are necessary for accurate physical descriptions of cellular events. We have conjugated aqueous CdSe-CdS quantum dot-quantum rods conjugated to far-red cyanine dyes, and these probes exhibit a ratiometric 2.4% change per °C over physiological temperatures in aqueous buffers, with a precision of at least 0.2 °C. Within cells, these nanothermometers showed an unexpected enhancement in their temperature response and sensitivity, highlighting the need to calibrate novel probes within the cell. |
