CAREER: Multiplexed and Selective Molecular Sensing Based on Raman Enhancement Through 2D Materials

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Nontechnical Description: The sensing of biochemical molecules has growing importance in various fields including Internet of Things (IoT), big data- and machine learning-enabled health monitoring, disease diagnosis, environmental monitoring, and food safety. An ideal molecular sensing platform should be highly sensitive, selective, label-free, generating reproducible signal, and able to detect multiple analytes simultaneously (multiplexity). Nowadays, advanced sensors can achieve high sensitivity and stability using electronic, optical or electrochemical mechanisms. With the assistance of receptors (meaning prior knowledge of the analytes is required), high selectivity of analytes can also be realized. However, high multiplexity within short measurement time and without prior knowledge is still beyond maturity. In this context, Raman spectroscopy, which probes the molecular vibrational modes through the measurement of light scattering, stands out as a promising method to achieve all the above requirements, in particular multiplexity and label-free, due to the multiple, extremely narrow and fingerprinting peaks in Raman spectra. While the main drawback of Raman spectroscopy is the weak signal, surface-enhanced Raman spectroscopy has been developed to mediate this issue with even single-molecule sensitivity using structured metal substrates, yet it has suffered from signal non-uniformity and noise. An alternative, Raman enhancement through two-dimensional materials (RE2D), replaces metallic substrates with 2D materials, a type of material only one atom or a few atoms thick. RE2D has exhibited significantly improved signal uniformity and low noise with the added advantage of tunability. This project will explore the fundamental science and techniques to further enhance the sensitivity and multiplexity of RE2D technology, by fabricating various types of 2D material substrates, combining 2D materials with metallic substrates, and applying electrical voltage to tune the enhancement. The research outcome will also be used as educational tools for research-like undergraduate and graduate courses. In addition, the PI will initiate a mentoring program for female graduate students, which will broadly benefit Penn State female students in their research, study, work-life balance and career development. Technical Description: This project aims to generate new fundamental understanding of the novel phenomenon of Raman enhancement through two-dimensional materials (RE2D), i.e. the enhancement of Raman signals of organic analyte molecules when placed on 2D material surfaces. This new knowledge will pave the way for an entirely new family of sensors that combine a number of desired features: high multiplexity, molecular selectivity, unprecedented signal reliability, and tunability. By further integrating plasmonic structures with 2D materials, high sensitivity will be achieved. The project is organized around two main thrusts: (1) analysis of the effects of 2D material-analyte molecule pairing on RE2D, as well as the tunability of molecular selection in RE2D; and (2) determination of the combined effects of chemical and electromagnetic mechanisms on Raman enhancement in a 2D-plasmonic integrated substrate. The fundamental science revealed and the prototype devices demonstrated will effectively guide the design and fabrication of sensitive and multiplexed RE2D sensors. The research outcomes will be integrated into the education and outreach activities: creating research-like courses and Research Experience for Undergraduate programs on Raman-based nanosensors and 2D material optoelectronics, which cultivate students’ abilities of critical thinking and motivate them to find solutions to societal problems using advanced technologies. The PI will also initiate a women graduate student mentoring program, and pair female Penn State alumnae mentors with female graduate students to support their long-term success.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.