EAGER: Novel photoacoustic sensor using piezoresistive GaN microcantilever

EAGER研究的目的是探索利用真空封闭压阻GaN微悬臂作为高灵敏度超声传感元件开发新型光声化学和生物传感器的可行性。该传感器将用于在空气和液体介质中进行检测，并可能提供：(i)在飞图水平上对表面吸附或沉积的分析物进行高特异性检测，以及（ii）在液体介质中对生物分析物进行独特的无标签检测。该传感器采用真空封闭的谐振GaN微悬臂，集成AlGaN/GaN异质结构场效应晶体管作为高灵敏度偏转传感器，实现了超高灵敏度。为了实现本项目的基本目标，将进行以下工作：(i)通过理论建模和有限元模拟设计光声传感器；（二）压阻式微悬臂梁的制备及微流控通道的集成；传感器的包装和机电特性；压阻式GaN微悬臂梁将采用标准光刻工艺制造，并在高真空中封装，以实现高共振质量因子。对于空气中的检测，在悬臂基座附近表面沉积或吸附的分析物将暴露在红外辐射下进行高灵敏度和选择性的检测，基于固体中产生的光声波。对于液体检测，基于PDMS的分析物储层连接到微流体通道，将在悬臂基座附近进行图案设计，这将允许分析物流动，并结合光谱和多模态检测血细胞。微悬臂传感器的制造将在乔治亚理工学院的纳米制造工厂进行，而传感器的封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，这些概念可以导致高性能和多功能传感器的开发，与空气和液体介质中分析物的最先进传感技术相比，这些传感器具有更优越的特性。首先，由于III-V型氮化物半导体独特的压电特性，与最先进的硅悬臂梁相比，所提出的压阻式微悬臂梁传感器的灵敏度有望提高几个数量级。其次，谐振微悬臂传感器的真空封装与光声传感相结合的创新概念，将由于质量因子的增强而进一步提高灵敏度，同时完全消除悬臂退化，这是利用功能化层进行检测的悬臂传感器的主要挑战。第三，集成微流体通道和功能化层将分析物集中在悬臂基座附近，将最大限度地减少信号损失，并极大地提高信噪比，从而消除了使用宏观单元进行声聚焦和限制的需要，这是目前最先进的光声传感器的一个重大缺点。总的来说，EAGER研究可以对压阻悬臂式传感器和光声传感方法的科学和技术产生变革性影响，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等各个领域具有潜在的应用。作为教育和外联活动的一部分，在整个项目期间，每年至少有一名本科生和一名高中生参与该项目。参与项目活动将为所涉研究生提供广泛的跨学科培训。PI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。

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.