Design, Microfabrication And Characterization Of A Microheater Platform For Studying DNA-surface Interactions

Abstract

The past few decades have witnessed significant research towards developing DNA biosensors and gene chips. These devices obtain sequence-specific DNA information in a faster, simpler and cheaper manner compared to traditional hybridization assays. Miniaturization of DNA handling and processing devices has contributed significantly towards this effort. Despite the large amount of work in this research direction, much more needs to be understood about the fundamental interactions of DNA and other biological macromolecules with their microenvironment, particularly with inorganic surfaces. For example, a basic understanding of thermal interactions of DNA with surfaces may help develop novel strategies for probing, purifying and manipulating DNA.This thesis describes the design, microfabrication and characterization of a microheater device on glass. This device is capable of producing large temperature rise through electrical heating in a thin microheater deposited on the glass substrate. Thermal-electrical design principles behind the design of the microheater device are described. Microfabrication of the device was carried outusing photolithography and metal deposition. Microheaters fabricated on glass slides and glass coverslips were thermally characterized and compared with each other. Experimental data showed a linear dependence oftemperature rise on electrical power, which is along expected lines. Data indicates that a temperature rise of over 100 C may be obtained by passing a relatively small amount of current. Experimental data was found to be in excellent agreement with finite-element simulation results. Simulations were also carried out to understand the transient thermal behavior of the microheater device. In order to demonstrate the microheater device, experiments were carried out to detach DNA immobilized on the microheater surface through a Streptavidin-Biotin bond, SAM modified glass surface can be functionalized with NHS biotin as a linker to streptavidin which can immobilize any biotinylated molecule like biotinylated DNA. It has previously been reported that biotin-stretavidin bond can be broken at 70 °C using a non-ionic aqueous solution. Following thermal calibration, DNA was immobilized on the microheater surface, and then experiments were carried out to detach it using the microheater. Fluorescence imaging results show that the fluorescent intensity after heating is considerably lower than before heating, thereby confirming the breaking of biotin -streptavidin bond and hence specifically detaching DNA.The microheater device described in this work may find applications in several other areas of bioengineering interest. While this work investigated a single microheater line, it would be interesting to study the effect of several strategically placed microheater for producing a desired temperature field. This may aid in DNA analysis chips where controlled attachment, detachment and manipulation of DNA is desirable. Further, the microheater platform may provide a novel thermal interface for studying thermal effects on cells.