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From the Energy and PCET webpages, you have seen that we seek to control the flow of energy to perform useful chemical reactions. We also want to control the energy of excited states to be sensitive to the biological, chemical, and physical world around us. There are two branches to these studies. We synthesize new molecules, supramolecules, and nanomaterials that sense by sending out a unique optical signature. This optical signature can be manipulated in micro- to nanoscale architectures to produce amplified signals. The sensor constructs predominantly rely on a “3R scheme” of recognize, relay, and report. Recognition of a target molecule at the receptor site is communicated to a reporter site that produces a measurable optical signal. The recognition sites can be molecules, supramolecules, or bio-recognition sites (e.g., antibodies, lipid membranes, etc.). The reporter site can be anything from a metal ion encapsulated in a specially designed framework to a quantum dot nanocrystal. The two sites communicate by energy or electron transfer.  As the size of the of sensors moves towards micro- and nano-dimensions, sensitivity with the above active sites is compromised because there are simply too few sensing active sites. To address this, we are interested in converting the signal transduction mechanism from a linear, single photon response to an extremely nonlinear response. To achieve this objective, we are replacing the single ion emission site with a high gain response from a laser. But these are special lasers – they are on the dimensional order of microns to nanons. The laser cavities are: (1) Distributed Feedback (DFB) gratings, (2) spherical resonators exhibiting whisper gallery modes, or (3) microfluidic lasers. By attaching recognition sites to the surface of these cavities, the photon output of the 3R scheme can be replaced with that of a laser.  To give you an idea of the power of our approach, we have begun developing new quantum dot-based optical sensors (in collaboration with the Bawendi group) for the metabolic profiling of growing tumors. Experiments in live animals (in collaboration with the Jain group at MGH) will use our novel quantum dot /dye complexes to image and quantify the physiological parameters of tumor acidosis (pH) and oxygen tension (pO2) in tumor microenvironments and measure the responses of these parameters to antiangiogenic chemotherapy. REFERENCES
We have applied the 3R approach to develop new physical techniques and methods. Physical sensing by 3R is accomplished by our development of the Molecular Tagging Velocimetry (MTV) technique to measure the velocity of highly turbulent 3D flows. Parameters important to the fluid physicist such as turbulence intensities, the Reynolds stress, and vorticity may be calculated. Two phase liquid/solid flows and flows within the cylinders of an internal combustion engine, over airplane wings, in microfluidic channels, and at boundary surfaces under interesting conditions have been quantitatively measured. To see some of the ways the MTV technique has been implemented, visit the web pages of theTurbulence Mixing Lab of Professor Manooch M. Koochesfahani, the MSU Engine Research Lab of Professor Harold Schock, and the turbulent and unsteady flows experiments of Professor Joseph Klewicki. REFERENCES
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