Vedant Sumaria’s PhD Dissertation Defense

“Exploring Micro-Machined Glass Shell Resonators For Sensor Application”

Abstract:

This work presents the exploration of the chip-scale glass blowing technique for novel sensing methods. On-chip microspherical glass shells (MSG) of hundreds of micrometers in diameter with ultra-smooth surfaces and sub-micrometer wall thicknesses have been fabricated and have been shown to sustain optical whispering gallery mode resonance with high Q-factors of greater than 25 million. These resonators exhibit a temperature sensitivity of 1.17 GHz K−1 and can be configured as ultra-high-sensitivity thermal sensors for a wide range of applications.

We demonstrate a thermal infrared (IR) detector based on a high-quality factor (Q) whispering gallery mode (WGM) borosilicate glass microspherical shell resonator and investigate its performance in detecting IR radiation in the wavelength range of 1 –20 μ m. The resonator exhibits a temperature sensitivity of 1.17 GHz/K with a Q-factor of 3 million and can be configured as a high-sensitivity infrared sensor. The microspherical shell IR sensor achieved a noise-equivalent power (NEP) of 944.89 pW/√Hz experimentally. A laser Doppler vibrometer (LDV) is used to measure the physical expansion of the microspherical glass resonator when IR radiation is absorbed. A dimensional change of ≈100 fm is shown to be resolved.

A comparison of two calorimetric biosensing systems with relatively high-throughput sample analysis is also reported. The calorimetric biosensor system compared are a thin (20 μm) micro-machined Y-cut quartz crystal resonator (QCR) and a MSG (6 μm thick) Whispering Gallery Mode (WGM) resonator as a temperature sensor placed close to a chemical reaction chamber with the immobilized enzyme. The enzymes (urease and glucose oxidase) were immobilized on superparamagnetic nanoparticles using covalent bonding. This configuration enables a sensing system where the reaction chamber is physically separated from the analyte solution of interest and thereby free from fouling effects typically associated with biochemical reactions occurring on the sensor surface. The performance of this biosensing system is compared by the detection of 0-250 mM urea and glucose in phosphate buffer.

Further, we present MSG WGM resonator-based thermal sensor array which is configured with a 3D printed reaction chamber that utilizes the backside silicon of the resonator for sensitive calorimetric biosensing applications. The coupling of heat from the reaction chamber to the WGM resonator is achieved via conduction from the analyte medium. The sensor was aligned to the opening of the 3D-printed reaction chamber, and the device was mounted using a thermo-elastic epoxy. This sensor configuration allows for a very robust sensing platform with no fouling of the sensor surface or degradation in its performance metrics. Resonance frequency tracking using the Pound-Drever- Hall locking method was used for enzymatic activity measurements. Results of the catalytic reaction of glucose with glucose oxidase and the hydrolysis reaction of urea by urease are reported. In addition, body fluids such as blood plasma, serum, and blister fluid are tested, which match very well with the experimental results. From the analysis of the signal-to-noise ratio of the glucose sensor, a resolution of 100 nM could be obtained, improving the detection limit by a factor of 10,000 compared to QCR sensors.

Committee:

Prof. Srinivas Tadigadapa (Advisor)

Prof. Matteo Rinaldi

Prof. Yongmin Liu

Prof. Rosemary Smith