A MICROMACHINED THERMAL SENSOR FOR BIOCHEMICAL SENSING AND POLYMER CHARACTERIZTION

Open Access
- Author:
- Zhang, Yuyan
- Graduate Program:
- Electrical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 16, 2005
- Committee Members:
- Srinivas A Tadigadapa, Committee Chair/Co-Chair
Thomas Nelson Jackson, Committee Member
Michael Pishko, Committee Member
Qiming Zhang, Committee Member - Keywords:
- micromachined
thermopile
calorimeter
biochemical
polymer
fluidic - Abstract:
- This thesis presents a micromachined calorimetric sensor for the measurement of the molar enthalpy change of enzymatic reactions and their characterization using high resolution thermal conductivity measurements. A polysilicon heater and a microthermopile sensor have been fabricated on a 2 µm thick, freestanding nitride-oxide-nitride membrane membrane and integrated with glass or polymer microfluidic channels. The p-type polysilicon/gold microthermopiles have a responsivity of 1 V/W, temperature sensitivity of ~4.7 mV/K, and a time constant of less than 100ms. Measurements of the heat of reaction from enzymatic catalysis of glucose, hydrogen peroxide and urea, were performed using glucose oxidase, catalase, and urease respectively in continuous flow configuration using the integrated microfluidic channel. A sensitivity of 53.5µV/M for glucose, 26.5µV/M for hydrogen peroxide and 17µV/M for urea was obtained. Detection limit for glucose measurement in the continuous flow mode is ~ 2 mM (30 pmole). AC calorimetric measurements were performed by introducing a periodic heat signal using the heater and detecting the frequency dependent thermal signal response in the presence of various fluids and polymers. Thermal conductivity of different fluids and five typical polymers used in microfabrication was measured using this device. The results of the predicted thermal conductivity are compared to those available in literature for polyimide (~ 2%) and SU-8® (< 10%) polymers. The device has also been used for monitoring real-time biochemical reactions as the thermal properties change with time due to the changing composition of the test fluid from reactants to products. Real-time enzymatic reaction for (glucose, urea) and antigen-antibody binding reaction (BSA, human fibrinogen) have been observed. This is the first demonstration of monitoring biochemical reactions in real-time using this technique. In summary, a versatile thermal sensor for the study of thermal characteristics of various biochemical samples and reactions has been designed. The integrated microfluidic channel allow for continuous flow testing of various samples. In addition to the determination of the thermal properties of various polymers and biomaterials, the sensor platform can be easily implemented as a thermal fluid flow sensor and a hydrogen sensor.