Collaborative Research: IDBR: Metamaterial Enhanced Spectrometer for Hyperspectral Terahertz Imaging of Biological Specimens
The objective of the proposed research is the development of novel instrumentation to facilitate highly sensitive, hyperspectral imaging of biological specimens, in the minimally explored yet information-rich electromagnetic spectrum of terahertz frequencies. This spectrum is broad in spectroscopic possibilities due to presence of the intermolecular vibrational, rotational and torsional modes, providing a distinct broadband molecular fingerprint and intrinsic contrast for biomolecular identification. However existing terahertz imaging approaches have limited sensitivity due to (1) Lack of efficient coupling of terahertz radiation in and out of the biological sample, (2) Higher level of signal loss due to unwanted scattering at sample/spectrometer interface, and (3) Lack of efficient detectors in the terahertz frequency range, thus limiting their performance. Moreover the detectors are typically single pixel detectors that require scanning to obtain a 2D image and they fail to capture the spatiotemporal evolution of biomolecular dynamics.
To solve these issues, the proposed instrument brings two emergent technologies ¨C (1) Metamaterials (MMs) and (2) Plasma wave operation of GaAs pHEMT device. Metamaterials are artificial structures with subwavelength metallic inclusions that can be designed to exhibit exotic electromagnetic response such as negative permittivity and permeability, negative index, and ideal absorption or transmittance. Plasma wave operation of GaAs pHEMT device facilitates resonant detection of terahertz radiation with unparalleled sensitivity.
Intellectual Merit: The proposed program will result in the development of a Metamaterial Enhanced Reflectance (or Transmittance) Imaging Terahertz (MERIT/METIT) spectrometer as an ultrasensitive platform for terahertz imaging of cells and tissues. These spectrometers will shed new light on ultra-fast conformational protein dynamics (protein folding) and other biomolecular processes responsible for pathogenesis in many human diseases, primarily cancer. Key technical innovations of the proposed spectrometer are (1) Realization of perfect impedance matched spectral conjugate layers to eliminate spurious reflections and to mitigate effects of water absorption, and (2) Realization of a high speed (>106 frames/sec), large 2D terahertz focal plane array (TFPA) based on resonant plasma wave detection of terahertz radiation by a GaAs pHEMT device. An interdisciplinary collaboration between PIs at multiple institutions (Boston College and Tufts University) with records of achievement in metamaterials theory, simulation and experiment, HEMT transistor device modeling and fabrication, and practical knowledge in imaging, evince the potential for carrying out a successful research and educational program.
Broader Impact: Beyond providing rich spectroscopic images of biological cells and tissues for fundamental studies, the instrument has potential in medical diagnostics and drug discovery. The PIs plan to reach out to the biology community through articles in print and online magazines frequented by biologists. The instrument will be made accessible to Boston area researchers for evaluation purposes. The instrument development project will establish a research and teaching laboratory at Boston College and Tufts University in the area of metamaterials and THz imaging devices. It will train the future generation of science and engineering majors in experimental techniques, such as extremely broadband frequency domain spectroscopy, fabrication of metamaterials, GaAs III-V technology as well as computer simulation techniques. The PIs have a strong commitment to undergraduate research through involvement in (1) summer scholars and BEND program for undergraduate research, and (2) the McNair scholarship program, a graduate school preparation program for students from underrepresented groups. Activities aimed at K©12 outreach is made possible through the ongoing Student Teacher Outreach Mentor Program (STOMP). The PIs plan to share the excitement of their research and discovery through lectures at local high©schools and development of web-based tutorials.
, in the minimally explored yet information-rich electromagnetic spectrum of terahertz frequencies. The project effort resulted in several impactful outcomes such as making metamaterial based absorbers as impedance matched layers, terahertz detectors in CMOS and GaAs HEMT process and also a biological platform for cell trapping and lysis using graphene as transparent conducting electrodes. Detailed outcome summary: 1) Metamaterials enable realization of single, dual and multi-band absorbers on flexible substrate that can be applied to any sample as impedance matched layers for terahertz imaging 2) CMOS and GaAs processes that are conventionally used for electronics and RF applications can also be used for realization of terahertz detectors and imagers. 3) The platform cell trapping and lysis allows one to capture selected cells and lyse them in high throughput manner using an arrray of microwells sandwiched between graphene electrodes. Such a platform enables transparent terahertz and far-infrared analysis of cellular contents using the proposed (or any other) terahertz spectrometer. It is also a valuable stand-alone instrumentation for routine biological investigations. Broader Impact Outcome: These technological advances can be utilized in assembling a state of the art terahertz spectrometer for biological studies. The project effort led to the training and mentoring of graduate and undergraduate students, including members from under-represented groups. It also led to publications of several journal articles and conference proceedings, and public dissemination of the technical efforts through lectures and workshops.
