Staff Scientist, Biological Nanostructures Facility
Our research focuses on synthesis of biologically active nanostructures and their applications to biological imaging. A major focus is developing novel nanoparticles with useful and unusual optical properties.
- Caged Quantum Dots
We have developed caged quantum dots, which are nanoparticles that are non-luminescent under typical microscopic illumination but can be activated with stronger pulses of UV light. These nanoparticles are hybrids of hard and soft materials, and their unique optical properties arise from the interaction between a classic organic caging group and a semiconducting quantum dot (QD). We have found that caging is dependent on the emission of the QD but is effective throughout the visible spectrum and even into the nIR, offering a large array of new colors for photoactivatable probes. Caged QDs can be photoactivated within live cells and we are currently studying the physical basis of the interaction between caging group and QD. Learn more
- Lanthanide-doped Upconverting Nanoparticles (UNCPs)
In collaboration with Delia Milliron of the Inorganic Facility and Jim Schuck of the Imaging Facility, we are developing a second type of nanoparticle for single molecule studies—lanthanide-doped upconverting nanoparticles (UCNPs). We have found that UCNPs show nearly ideal optical properties for single molecule imaging, including exceptional photostability, continuous emission, and no spectral overlap with cellular autofluorescence. UCNPs absorb two photons in the nIR and emit one at shorter wavelengths in the visible or nIR; this “anti-Stokes” emission, producing a higher-energy photon from multiple lower-energy photons, is unlike anything found in the cell, so that there is minimal or no background autofluorescence. We have developed a synthesis of monodisperse UCNPs and a simple procedure for transferring them to water and into cells, and we have recorded the first single molecule images of UCNPs. We find that UCNPs do not blink (as QDs and many organic probes do) and that they posses remarkable photostability, resisting photobleaching under continuous irradiation long after organic dyes, proteins, and even QDs are extinguished. Learn more
A.R. Bayles, H.S. Chahal, D.S. Chahal, C.P. Goldbeck, B.E. Cohen, B.A. Helms. Rapid cytosolic delivery of luminescent nanocrystals in live cells with endosome-disrupting polymer colloids. Nano Lett, ASAP.
B.E. Cohen. Biological Imaging: Beyond fluorescence. Nature 467, 407-408 (2010).
S. Wu, G. Han, D.J. Milliron, S. Aloni, V. Altoe, D.V. Talapin, B.E. Cohen, P.J. Schuck. Non-blinking and photostable upconverted luminescence from single lanthanide-doped nanocrystals. PNAS 106 10917-10921 (2009).
G. Han, T. Mokari, C. Ajo-Franklin, B.E. Cohen. Caged quantum dots. J. Am. Chem. Soc. 130, 15811-15813 (2008).
J.S. Salafsky, B.E. Cohen. A second-harmonic-active unnatural amino acid as a structural probe of biomolecules on surfaces. J. Phys. Chem. B 112, 15103–15107 (2008).
A.B., Princeton University
Ph.D., University of California Berkeley, Daniel E. Koshland, Jr.
Postdoctoral Fellowship, University of California San Francisco, Lily Y. Jan