Adam E. Cohen

Department of Chemistry & Chemical Biology
Harvard University
Mallinckrodt Building, Room 115
12 Oxford Street, Cambridge, MA 02138

tel: (617) 496-9466; fax: (617) 495-9131
email: cohen@chemistry.harvard.edu
webpage: http://www.fas.harvard.edu/~aecohen/

Research Interests:

Our effort is split between developing new physical tools to probe wet, squishy molecules and cells, and using our tools to make new measurements. We choose problems by looking in unexplored regimes of time and space; we combine nanofabrication, lasers, microfluidics, electronics, biochemistry, and computers to generate data; and we apply statistics and physical modeling to understand the data.  Research in the lab falls roughly into 3 areas:

Single-molecule Biophysics  We developed a machine called an Anti-Brownian Electrokinetic trap (ABEL trap) that can immobilize a single fluorescent molecule in solution, without any physical tethers.  The ABEL trap works by tracking the Brownian motion of a single molecule using fluorescence microscopy, and then applying feedback voltages to the solution to induce an electrophoretic motion that cancels the Brownian motion.  We are interested in trapping and studying a broad range of molecules, including single organic dye molecules 1 nm in diameter.  Our favorite molecules at the moment are a class of light-driven proton pumps called microbial rhodopsins.

Fundamental Spectroscopy  Can a weak magnetic field affect the outcome of a chemical reaction?  Can light excite chiral molecules of one handedness while leaving the mirror image enantiomers untouched?  We are interested in exploring the basic quantum mechanics of light-matter interactions; particularly in using nanostructures to “sculpt” the electromagnetic field into patterns that interact with molecules in unusual ways.  We hope to develop new kinds of magnetically modulated catalysts; to establish the physical limits on putative magnetic field effects on health; and to perform enantioselective photochemistry.  These projects combine quantum mechanics and electrodynamics with organic synthesis, nanofabrication and precise optical measurements.

Microbial Motion in Mucus Mucus is our new favorite bodily fluid: it coats the respiratory, gastrointestinal, and urogenital tracts and provides a selective barrier, letting in the things we want while keeping out microbial pathogens.  How does it do this, and how to bacteria try to circumvent the mucus barrier?  We are working to relate the microstructure and biochemistry of mucus to its biological functions.  In particular, we are interested in the role that bacterial proteases play in microbial motion in mucus.  Many pathogenic bacteria (e.g. cholera, salmonella, plague) secrete soluble proteases or express proteases on their exterior surface.  Do the proteases merely break down the mucus barrier, or do they play an active role in bacterial motion?  We are testing the hypothesis that asymmetric secretion of proteases can lead to a net force on a bacterium due to an imbalance in the polymer forces.

Selected Publications:

Cohen, A.E. and Moerner, W.E. (2006). Suppressing Brownian motion of individual biomolecules in solution. PNAS 103: 4362-4365.

Cohen, A.E. and Moerner, W.E. (2007). Principal Components Analysis of shape fluctuations of single DNA molecules. PNAS 104: 12622-12627.

Cohen, A.E. and Moerner, W.E. (2007). Internal mechanical response of a polymer in solution. Phys. Rev. Lett. 98: 116001.

Cohen, A.E. and Moerner, W.E. (2008). Controlling Brownian motion of single protein molecules and single fluorophores in aqueous buffer. Opt. Express 16: 6941-6956.

Jain, P., Xiao, Y., Walsworth, R. and Cohen, A.E. (2009). Surface Plasmon Resonance Enhanced Magneto-Optics (SuPREMO): Faraday Rotation Enhancement in Gold-Coated Iron Oxide Nanocrystals. NanoLetters 9: 1644-1650.

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