2012-2013 Seminar Series

2012 - 2013
Sept 27

Julie Biteen, University of Michigan hosted by Domenico Pacifici, Engineering

Barus & Holley Room 190, 4PM

Peering into Cells One Molecule at a Time:Single-molecule and plasmon-enhanced fluorescence forsuper-resolution imaging of living bacteria

Abstract:  Single-molecule fluorescence brings the resolution of opticalmicroscopy down to the nanometer scale, allowing us to unlock themysteries of how biomolecules work together to achieve the complexitythat is a cell. This high-resolution, non-destructive method for examiningsubcellular events has opened up an exciting new frontier: the study ofmacromolecular localization and dynamics in living cells. We havedeveloped methods for single-molecule investigations of live bacterialcells, and have used these techniques to investigate three importantprokaryotic systems: membrane-bound transcription activation in Vibriocholerae, carbohydrate catabolism in Bacteroides thetaiotaomicron, and DNA mismatch repair inBacillus subtilis. Each system presents unique challenges, and we will discuss the importantmethods developed for each system, in particular, a comparison of membrane-bound and solubleproteins, extensions to two-color and 3D imaging, and adaptations for studying live anaerobiccells. Furthermore, we use the plasmon modes of bio-compatible metal nanoparticles to enhancethe emissivity of single-molecule fluorophores. The resolution of single-molecule imaging in cellsis generally limited to 20-40 nm, far worse than the 1.5-nm localization accuracies which havebeen attained in vitro. We therefore use plasmonics to improve the brightness and stability ofsingle-molecule probes, and in particular fluorescent proteins, which are widely used for bioimaging.We find that gold-coupled fluorophores demonstrate brighter, longer-lived emission,yielding an overall enhancement in total photons detected. Ultimately, this results in increasedlocalization accuracy for single-molecule imaging. Furthermore, since fluorescence intensity isproportional to local electromagnetic field intensity, these changes in decay intensity and rateserve as a nm-scale read-out of the field intensity. Our work indicates that plasmonic substrates areuniquely advantageous for super-resolution imaging, and that plasmon-enhanced imaging is apromising technique for improving live cell single-molecule microscopy.

Feb 22

Shayla Sawyer, Rensselaer Polytechnic Institute, hosted by Domenico Pacifici, Engineering

Barus & Holley Room 190, 4PM

Hybrid nanostructures for enhanced optoelectronics

Abstract: Performance enhancement is enabled by the use of lowcost, hybrid inorganic/organic nanostructured materials. For much ofthis research, the inorganic materials are nanostructured metaloxides. Advantages due to a high surface to volume ratio for betterlight absorption and an inherent large internal gain are typicallyhindered by surface defects and slow carrier transport mechanisms.Our research explores processes and the development of noveldevices with strategic use of inorganic/organic core shell structureswhich provide surface passivation, better light absorption, andimproved carrier transport. The combination provides markedly improved detectorperformance such as high responsivities on the order of 100s of A/W and improved transientresponses by orders of magnitude. Furthermore, the nature of these materials leads to itsdeposition on various substrates, extending its potential sensing applications.

May 2 

Emilia Morosan, Rice University 

Barus & Holley Room 190, 4PM

The interplay between magnetism and superconductivity – the “water” and “oil”of condensed matter physics

MacMillan Hall 317, 12PM 

Abstract: Conventional wisdom teaches us that magnetism and superconductivity areincompatible. However several examples are now known, which not only contradictthis long-held belief, but support the idea that magnetic instabilities are necessaryfor high temperature superconductivity. In this talk, I will discuss our understandingof the interplay between crystal structure, magnetism and superconductivityas a route for designing practical superconductors. Some specific examples willinclude a newly discovered transition metal pnictides superconductor, 2D and 3Dtransition metal pnictides, and a unique magnetic structure in a layered transitionmetal oxychalcogenide.