EAGER: Novel photoacoustic sensor using piezoresistive GaN microcantilever

EAGER研究的目的是探索开发一种新型的光声化学和生物传感器的可行性，利用真空封闭的压阻GaN微悬臂梁作为高灵敏度的超声传感元件。该传感器将用于在空气和液体介质中进行检测，并且可以潜在地提供：（i）以高特异性在毫微微克水平检测表面吸附或沉积的分析物，以及（ii）液体介质中生物分析物的独特无标记检测。超高灵敏度的传感器将获得使用谐振GaN微悬臂梁封闭在真空中，集成AlGaN/GaN异质结场效应晶体管作为一个高灵敏度的偏转传感器。为实现本项目的基本目标，将开展以下工作：（一）通过理论建模和有限元模拟设计光声传感器;（二）制作压阻式微悬臂梁和集成微流体通道;（三）传感器的封装和机电特性;（四）传感器的设计和制造;（五）传感器的设计和制造;（六）传感器的设计和制造;（七）传感器的设计和制造;（八）传感器的设计和制造。和（四）用于空气和液体介质中分析物检测的传感器的性能评估压阻GaN微悬臂梁将使用标准的在高真空中进行封装以实现高谐振品质因数。对于在空气中的检测，基于在固体中产生的光声波，悬臂基底附近的表面沉积或吸附的分析物将暴露于IR辐射以执行高度灵敏和选择性的检测。对于液体中的检测，连接到微流体通道的基于PDMS的分析物储存器将在悬臂基底附近图案化，这将允许分析物流动以及血细胞的组合光谱和多模式检测。微悬臂梁传感器的制造将在格鲁吉亚技术纳米工厂进行，而传感器的包装将在南加州大学的PI实验室完成。 智力优势：拟议的EAGER研究将侧重于验证新的传感概念，这些概念可以导致开发高性能和多功能传感器，与最先进的空气和液体介质中分析物的传感技术相比，这些传感器具有更上级的特性。首先，由于III-V族氮化物半导体独特的压电特性，与最先进的Si悬臂梁相比，所提出的压阻式微悬臂梁传感器预计将表现出更高的灵敏度。其次，谐振微悬臂梁传感器的真空外壳与光声传感相结合的创新概念将由于品质因数的提高而进一步提高灵敏度，同时完全消除悬臂梁退化，这是利用功能化层进行检测的悬臂梁传感器的主要挑战。第三，集成微流体通道和功能化层以将分析物集中在悬臂基底附近将使信号损失最小化，并且极大地增加信噪比，从而消除对使用宏观单元的声学聚焦和限制的需要，这是当前最先进的光声传感器的显著缺点。总体而言，EAGER的研究可以对压阻悬臂梁传感器和光声传感方法的科学和技术产生变革性的影响，刺激下一代小型化和高性能光声传感器的积极发展。更广泛的影响：这个高度跨学科的项目预计将导致新型光声传感器的发展，在国防，国土安全，环境监测，药物发现，植入式传感器以及疾病诊断和预后的不同领域具有潜在的应用。作为教育和推广活动的一部分，PI将涉及至少一名本科生和一名高中生在整个项目期间每年从事该项目的工作。参加项目活动将为所涉研究生提供广泛的跨学科培训。研究所将把研究成果纳入研究生课程，并通过参加会议和各种网站传播这些成果。

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.