The objective of the EAGER research is to explore the feasibility of developing a novel photoacoustic chemical and biological sensor utilizing vacuum enclosed piezoresistive GaN microcantilever as a highly sensitive ultrasonic sensing element. The sensor will be utilized to perform detection in both air and liquid media and can potentially offer: (i) detection of surface adsorbed or deposited analytes at femtogram level with high specificity, and (ii) unique label-free detection of bio-analytes in a liquid medium. Ultra high sensitivity of the sensor will be attained using a resonant GaN microcantilever enclosed in vacuum, with integrated AlGaN/GaN heterostructure field effect transistor as a highly sensitive deflection transducer. To attain the basic objective of this project, the following tasks will be performed:(i) Design of the photoacoustic sensor through theoretical modeling and finite element simulations; (ii) Fabrication of the piezoresistive microcantilever and integration of microfluidic channels; (iii) Packaging and electromechanical characterization of the sensor; and (iv) Performance evaluation of the sensor for analyte detection in air and liquid media Piezoresistive GaN microcantilevers will be fabricated using standard photolithographic process and packaged in high vacuum to achieve high resonance quality factor. For detection in air, surface deposited or adsorbed analyte near the cantilever base will be exposed to IR radiation to perform highly sensitive and selective detection, based on photoacoustic waves generated in solid. For detection in liquid, a PDMS based analyte reservoir connected to microfluidic channels will be patterned near the cantilever base, which will allow analyte flow and combined spectroscopic and multimodal detection of blood cells. The fabrication of the microcantilever sensors will be performed at the Georgia Tech Nanofabrication Facility, while the sensor packaging will be done in the PI's lab at USC.
Intellectual Merit: The proposed EAGER research will focus on validating novel sensing concepts that can lead to the development of high-performance and versatile sensors with much superior characteristics compared to the state-of-the-art sensing technologies for analytes in air and liquid media. Firstly, the proposed piezoresistive microcantilever sensors is expected to exhibit orders of magnitude higher sensitivity compared to the state-of-the-art Si cantilevers due to the unique piezoelectric properties of III-V Nitride semiconductors. Secondly, the innovative concept of vacuum enclosure of the resonant microcantilever sensor coupled with photoacosutic sensing, will further enhance the sensitivity by orders of magnitude due to quality factor enhancement, while completely eliminating cantilever degradation, which is a major challenge for cantilever sensors utilizing functionalization layers for detection. Thirdly, integration of microfluidic channels and functionalization layers to concentrate the analytes near the cantilever base will minimize signal loss, and tremendously increases signal-to-noise ratio, thereby eliminating the need for acoustic focusing and confinement using a macroscopic cell, which is a significant drawback for current state-of-the-art photoacoustic sensors. Overall, the EAGER research can have a transformative impact on the science and technology of piezoresistive cantilever sensors and photoacoustic sensing methodologies, spurring aggressive development of next generation of miniaturized and high performance photoacoustic sensors.
Broader Impacts: This highly interdisciplinary project is anticipated to result in the development of novel photoacoustic sensors with potential applications in the diverse fields of defense, homeland security, environmental monitoring, drug discovery, implantable sensors, and disease diagnosis and prognosis. As a part of the educational and outreach activities, the PI would involve at least one undergraduate and one high school student to work on this project every year throughout its duration. Participation of the project activities would provide broad interdisciplinary training of the graduate student involved. The PI would integrate research results in a graduate course, and disseminate them through conference participation and various websites.
