(4ie) Advances in Chemical Sensing: Harnessing Mid-IR Spectroscopy with Microfabricated Devices for Enhanced Sensitivity and Selectivity

The development of advanced chemical sensing strategies is becoming increasingly crucial across diverse fields such as environmental monitoring, plastic recycling, agriculture, defense and safety, mining, food production, bioengineering, and medical diagnostics. Advances in the fabrication of miniaturized mechanical structures for sensing, such as microcantilevers, have dramatically enhanced sensitivities by several orders of magnitude. However, challenges still exist in achieving the required selectivity and response time needed for translation of these sensors for industry. Conventional molecular recognition methods, based on room temperature reversible adsorption on immobilized chemical interfaces (receptors) on sensor surfaces, often suffer from poor selectivity due to the generic nature of weak chemical interactions such as hydrogen bonds or van der Waal forces. Addressing this challenge by integrating Infrared (IR) spectroscopy with nanomechanical devices shows promise in enhancing both sensitivity and selectivity simultaneously. This approach combines the high sensitivity of microfabricated structures with the unique molecular selectivity offered by mid-IR spectroscopy. Using a bimaterial cantilever as a broadband infrared detector at room temperature has been demonstrated to enhance the sensitivity of the sensor platform. The bending of the cantilever beam changes sensitively with absorbed heat energy due to the differential thermal expansion coefficients of the two layers. Plotting the cantilever bending as a function of the scanning wavenumber, the spectroscopic information of the physically adsorbed molecules can be obtained. Different from traditional FTIR which is based on Beer-Lambert law, this method detects the heat from the non-radiative relaxation of IR excited molecules providing a complementary signal to FTIR. By using this method, the photothermal spectrum of physisorbed molecules with pico gram sensitivity has been demonstrated. Moreover, this technique enables non-contact measurement, offering reliable molecular sensitivity and selectivity from a distance. A similar approach was also demonstrated using the resonance response of a commercial quartz tuning fork (QTF). These non-contact methods show the potential of this technique to address societal challenges. For instance, they can significantly enhance molecular recognition of plastic waste for sorting, thereby by addressing a critical issue of increasing the low recycling rates 8% annually at present to higher numbers in the near future. By employing advanced machine learning on spectral databases, these techniques achieved 100% accuracy in identifying plastic waste according to resin identification codes, including challenging materials like black plastics and plastics with contaminates. Furthermore, the techniques are effective in ultra-trace detection of Per- and poly(fluoroalkyl) substances (PFAS), persistent pollutants of environmental concern. The spectroscopic signatures obtained from solutions with trace concentrations of PFAS demonstrate the method's potential in on-site monitoring applications.

Research Interests

Inspired by the quote from Albert Einstein, “Problems cannot be solved at the same level of awareness that created them,” my research interests as an experimentalist focus on understanding basic physics, thinking out of the box, and exploring new concepts for instrumentation to address challenges facing our society today. I believe developing new instrumentation and devices that can provide new information is critical in solving many of the current problems. New information that is not ratiometric is essential for developing new insight and a deeper understanding of the problem. During my PhD, I specialized in developing high-performance standoff sensors based on nano and micro-electro-mechanical systems platforms. These sensors leverage the interaction of molecules with electromagnetic fields to achieve high sensitivity and selectivity. Specifically, my research has demonstrated significant potential in applications related to sustainability, such as rapid identification of plastic waste for efficient sorting and detection of toxic chemicals like PFAS in drinking water. The concept of using miniature devices for standoff sensing represents a fundamental advancement in monitoring capabilities across various environments. This research not only advances fundamental sciences and engineering but also holds promise for economic prosperity.

Thus, the core of my research was listed as:

(1) Innovative Sensing Concepts: Developing novel theoretical frameworks and methodologies for wireless data acquisition and standoff sensors with exceptional performance.

(2) Miniature Integrated Sensors: Fabricating nanomechanical-based sensors integrated with multi-physics approaches for label-free and receptor-free detection of physical, chemical, and biomolecular entities with high sensitivity and selectivity.

(3) Practical Applications: Applying advanced knowledge and techniques to address practical societal challenges, aiming to provide effective solutions through technological innovation.

By advancing these core research areas, I aim to not only unravel the mysteries of nature and enhance our understanding of natural sensory mechanisms but also contribute to solving pressing societal issues and fostering economic growth.

Teaching Interests

Inspired by the teaching philosophy of my teachers, I aim to pass along the wisdom encapsulated in the phrase, “The average teacher explains complexity; the gifted teacher reveals simplicity.” This principle has been a cornerstone throughout my PhD journey. My teaching philosophy is founded on several core principles that guide my approach to education and interaction with students. I believe that teaching is not merely about conveying complex ideas but revealing their inherent simplicity. My goal is to make learning accessible and engaging by distilling intricate concepts into understandable and relatable terms.

• Reciprocal Learning: I view the student-teacher relationship as a dynamic exchange where both parties learn from each other. This fosters an environment of mutual respect and active participation.
• Integration of Theory and Practice: I emphasize the integration of theoretical foundations with practical applications, helping students see the relevance of their learning in real-world scenarios.
• Observation and Critical Thinking: I encourage students to observe nature critically, fostering curiosity and analytical thinking. This approach helps students understand and apply knowledge creatively.
• Individual Strengths: I recognize and nurture each student's unique strengths and talents. My goal is to provide guidance and support to help students build confidence and achieve their goals.
• Diversity and Inclusion: I am committed to creating a diverse and inclusive learning environment where all students feel valued and supported. This enriches the educational experience by incorporating a wide range of perspectives.
• Assessment and Feedback: I use varied evaluation methods, including formative assessments and project-based learning, to provide continuous feedback and promote active engagement.
• Professional Development: I continually pursue professional development through workshops and conferences to stay updated on the latest pedagogical research and innovations.

In addition to my teaching philosophy, I have practical experience that has sharpened my skills as an educator. I organized an after-school touring program in China, where I taught physics to over 20 high school students to prepare them for university entrance exams. During my PhD, I worked as a teaching assistant for several courses, including undergraduate and graduate levels of thermodynamics, CE 509 Transport Phenomena, and CE 407 Separations. These experiences have allowed me to apply my teaching philosophy in diverse educational settings and develop effective strategies to engage and support students.