Lasse Jensen
- Assistant Professor of Chemistry
Research Interests
Our research focuses on developing new theoretical and computational tools for addressing fundamental questions relevant to optical spectroscopy of bio- and nano-systems. We are particularly interested in understanding how one can use enhanced Raman spectroscopy to selectively probe a specific subsystem of a more complex system.
Raman Spectroscopy
Raman spectroscopy offers a particularly useful method to assess the secondary structure of proteins because of the structural sensitivity of the amide vibrational bands. These bands can be enhanced by laser excitation in resonance with the p-p* amide electronic transitions, the so-called resonance Raman scattering (RRS) effect. These transitions lie in the deep UV and allow for selective enhancements of the vibrations related to the aromatic side chains and amide bonds in proteins. Furthermore, due to selective enhancements, RRS can be used to study bio-chromophores in-situ, like the green fluorescent protein (GFP, see Fig. 1). GFP has a wide use as a fluorescent marker in many areas of molecular biology and biochemistry. However, interpreting the measured spectra can be highly challenging for such large biomolecules. Theoretical approaches can therefore be extremely useful to interpret and obtain detailed information that is not directly available from experiments. We are interested in developing new methods to simulate the resonance Raman spetra from first-principles and to apply these new methods to gain a microscopic understanding of the relation between the protein structure and its Raman spectrum.
A second area of interest is surface-enhanced Raman scattering (SERS) which plays an increasingly important role in studies of molecules adsorbed onto metal surfaces. In the last few years, SERS enhancements of ~1015have been reported, which has opened up the possibility of using Raman techniques for single molecule detection. Single-molecule SERS is likely to have an enormous impact in nanotechnology, biochemistry, life sciences and sensing technologies. The huge enhancements reported have been attributed to the very high enhanced fields at the surface arising from the plasmon excitations and the chemical interactions between the molecule and the surface. However, the exact nature of the enhancements and the interplay between different enhancement mechanisms are not known. Modeling the normal and enhanced Raman scattering of molecule-metal interfacial structures on the atomic scale, therefore, is crucial in understanding the nature of the observed SERS enhancements. The objective is to construct new theoretical tools for the direct simulation of SERS spectrum. Such tools will be able to give a microscopic description of SERS and thereby provide both mechanistic insights and interpretation of the otherwise complicated experimental results.
In addition to the above areas, we are also interested in exploring other areas of optical spectroscopy such as fluorescense biomarkers, and various types of Raman scattering like Vibrational Raman Optical Activity (VROA) and Hyper-Raman Scattering. VROA is a chiral analog to the normal Raman scattering and thereby particular useful for studying biomolecules. Hyper-Raman scattering is a nonlinear version of normal Raman and provides information about vibrations that are otherwise silent in normal Raman scattering.
