Optimization in Enhanced Raman Spectroscopy

Conjugated metallic nanoparticles are a promising means to achieve ultrasensitive and multiplexed sensing in intact 3D samples, especially for biological applications, via surface enhanced Raman scattering (SERS). We show that enhancement and extinction are linked and compete in a collection of metallic nanoparticles. In a solution of nanospheres, the Raman signal vanishes when nanoparticles are excited at their plasmon resonance, while increasing nanoparticle concentrations at off-resonance excitation sometimes leads to decreased signal. The Raman signal from aggregates is also examined and the connection between the extinction and the enhancement is described. We develop an effective medium theory that explains both phenomena. Optimal choices of excitation wavelength, individual particle enhancement factor, and concentrations are indicated.

Thomas van Dijk is expected to complete his Ph.D. in physics at Vrije University in Amsterdam in April. His dissertation has a focus on theoretical and experimental studies in optical coherence theory, while his main areas of research include computed imaging, inverse problems, statistical optics, and plasmonics. van Dijk is interested in exploring the theoretical frontiers in bio-optics, which uses light to study, manipulate, and treat biological samples, toward advancing the design of experimental methods and analysis of results. He plans to concentrate his work on problems in the imaging and diagnosis of disease in order to meet both clinical and research needs.  

Biosensors, Protocells, and Beyond

We have developed a fluorescence resonance energy transfer (FRET)-based biosensor to study the structure and function of Src Homology 2 domain containing phosphatase 2 (Shp2) both in vitro and in mammalian cells. We found that one form of intramolecular interaction resulted in FRET increase of Shp2 biosensor in vitro upon kinase activation while a different intramolecular interaction of the biosensor occurs in cells. We have teased out some factors that contribute to the distinctive forms of intramolecular interactions, such as the presence of other binding partners in cells. However, there is still a large gap between the results in vitro and in cells. This discrepancy is a common problem as the source of the inconsistency is the dramatically different environments of in vitro and in cell assays. To bridge the gap, we propose to build an intermediate platform, which has some cellular features and more complexity than in vitro but still preserves the advantage of the in vitro system with controlled building blocks and environment. We utilize mesoporous silica cell replica templated from real cells as the core to load proteins and coat it with a lipid bilayer to form a “protocell.” We show that simple biochemical reactions can be reconstituted in this protocell platform, which can be further developed to reconstitute more complicated cellular functions.

Jie Sun is currently a Beckman Postdoctoral Fellow. She is working with Eric Jakobsson, Yingxiao Wang, and Jeff Brinker on bottom-up synthesis biology using protocells as a synthetic platform to reconstitute cellular functions. She was formerly a postdoctoral research associate and a Ph.D. student in the Wang group at the University of Illinois, where she did research on the development and application of fluorescence resonance energy transfer-based sensors and actuators. She received her B.S. in animal and plant biotechnology from the University of Hong Kong and her M.S. and Ph.D. in molecular and integrative physiology from U of I.