With support from the Chemical Measurement and Imaging Program in the Division of Chemistry, Professor Wei Min of Columbia University is developing new measurement methods that have the potential to provide chemical information on individual molecules, the ultimate capability in measurement science. Raman spectroscopy and microscopy are popular tools for measuring chemical properties of molecules, as these tools enable research discoveries and chemical assessments, which are of value to industry, health care, materials and biological research, and environmental monitoring. However, conventional Raman methods are restricted, in that many molecules are required to generate a Raman signal sufficiently different from the background, which is referred to as the detection limit. Professor Min is improving the detection limit of Raman microscopy through an unprecedented approach, such that individual molecules can be chemically characterized on a routine basis, while present in a variety of chemical and biological environments. Professor Min and his team use this new form of Raman microscopy to simultaneously obtain images of many species found inside biological cells, as well as study the behavior of individual enzymes, thereby facilitating our understanding of the complex biological world. The Min group is leveraging their expertise in spectroscopy and microscopy to develop demonstrations and educational laboratory experiments that engage underrepresented minority students in local high schools and community colleges, with the goal being enhancement of student physical science skills and interest in future careers in science and engineering. The impact of these new instruments and labs is amplified by online dissemination through high-impact, internet-based instructional videos.
Raman spectroscopy provides exquisite chemical information about molecular structure and dynamics resulting from interactions with the environment. Unfortunately, Raman signals are intrinsically weak in the optical far field. Although established near-field methods of surface-enhanced Raman spectroscopy can offer superb limits of detection, the strict reliance of near-field approaches on close interaction of target molecules with metallic nanostructures limits their application to a select group of chemical and biological systems. The project addresses the urgent need for ultra-low-limit-of-detection Raman microscopy, without relying on nanostructures. Professor Min and his team combine resonance Raman spectroscopy with stimulated Raman scattering microscopy to achieve ultra-low-limit-of-detection vibrational imaging. This enabling technology results from enhancement of the Raman scattering cross section by several orders of magnitude, due to the joint action of electronic resonant amplification and stimulated Raman amplification, making possible single-molecule limits of detection. Professor Min and his team employ the new ultra-low-limit-of-detection Raman microscopy method in multi-wavelength imaging of the interior of biological cells, as well as in mechanistic studies of single-molecule, enzyme-catalyzed biochemical reactions.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
