Near-field microscopy systems such as Scanning Tunneling Microscopy, Atomic Force Microscopy, Scanning Optical Microscopy, and Electron Microscopy can yield highly detailed structural information of biological samples. However, their spectral and operational constraints have limited their use for studying dynamics of biological processes. Alternative single-molecule approaches use various labeling techniques for characterizing structural dynamics of biomolecules. Labeling biomolecules near their active sites can be a major challenge and can affect the natural behavior of molecules in many biological processes. To address these limitations, this project proposes an innovative Scanning Terahertz Nanoscopy system as a powerful label-free biological study tool to advance the research in biophysics. The proposed label-free probing system would allow studying the complex behavior of biomolecules under native conditions, while avoiding exhaustive genetic and biochemical characterization of labeling reactions. The proposed system offers significant flexibility for biological studies in practical settings (flexibility in large area scanning, simultaneous optical excitation, and adding external chemical stimuli) through a fully packaged and fiber-coupled platform. Therefore, the proposed research would benefit the biological research communities conducting research on single-molecule biophysics, cellular structure, nanomedicine, protein folding, etc. As a part of our dissemination, we work closely with the members of the biological research community to utilize and evaluate the developed terahertz spectroscopy system for various biological studies. A special training program is constructed to assimilate graduate students working on this type of interdisciplinary research, undergraduate students and summer interns are recruited for these research activities and special priority is given to recruitment of talented undergraduate and graduate candidates from underrepresented groups.
Terahertz waves offer unprecedented functionalities for label-free characterization of biomolecules and studying the structure, dynamics and operation of biological systems. This is because terahertz photon energies are comparable with the low binding energies of molecules inside heavy biomolecules, offering a platform for differentiating proteins and providing information about their conformation states through terahertz spectroscopy. Additionally, since distinct terahertz signatures of biomolecules are dependent on their intermolecular and intramolecular vibrations and rotations, terahertz spectroscopy enables investigating living cells and their interaction inside various biological systems including cell metabolism and reproduction as well as chemical transfer from the environment to cell through cell membrane and possible conformational changes. Moreover, since terahertz spectroscopy can capture femtosecond-scale dynamic variations, it is very well suited for investigating kinetics of molecular motions during protein rearrangement, folding, and binding to other biomolecules. Despite its great promises, the scope and potential use of terahertz technology for biological studies is still limited by low sensitivity and limited spatial resolution of existing terahertz spectroscopy systems. The proposed nanoscopy system solves both limitations, while offering significantly higher sensitivities and bandwidths compared to the state-of-the-art. The proposed time-domain terahertz spectroscopy system consists of a plasmonic photoconductive terahertz source and an electro-optic crystal for broadband terahertz wave generation and detection, respectively. The plasmonic terahertz source and the electro-optic crystal are integrated with a novel terahertz probe, which consists of a tapered waveguide used for focusing the generated terahertz beam onto the biological sample with nanoscale focus dimensions and coupling the reflected terahertz beam from the sample to the electro-optic crystal for detection. The terahertz probe is designed to allow terahertz spectroscopy at the nanoscale without a considerable impact on the spectral bandwidth.
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.
