Processing of photosensitive PDMS for biosensing
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[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] The processing of photosensitive PDMS for applications in biosensing has been discussed in this thesis. Identification and quantitative analysis of biomolecules are very critical in disease detection and diagnosis. Microcantilever beams have become a widely accepted method to detect biomolecules in a given sample. In terms of antigen-antibody detection, when the antibody is immobilized onto the antigen coated on a cantilever beam, it causes the beam to deflect. This deflection is monitored by a reflected beam of a laser diode using a position sensitive detector. Silicon Nitride or Silicon Oxide is generally used in the fabrication of these cantilever beams. The deflections of these beams are in the nanometer scale and can be reliably detected only using optical beam deflection method. The idea to explore soft polymeric microstructures to replace the relatively brittle silicon structures is in its infancy. Soft polymeric compounds might demonstrate dramatic deflection when used as a material for the cantilever beams. This might increase the sensitivity of the beams to biomolecular binding and open new ideas for other detection approaches, thus driving the need for miniaturized biodetectors for distributed applications. PDMS, generally a material used in IC packaging and medical applications, has been used in MEMS for making disposable 3D structures for DNA analysis. Taking into consideration their biocompatibility, flexibility and commercial availability, the use of PDMS in the cantilever beam fabrication has been discussed. The common approach for PDMS patterning is micromolding which is not suitable for thin film structures. The lack of a clear technique to photo-define PDMS challenges the basis of cantilever beam fabrication using photolithography process. A method to make PDMS photopatternable is discussed. RMS033 from Gelest has been used instead of the commonly used SYLGARD 184 from Dow Corning. We see that PDMS can indeed be photo patternable using basic photolithographic processes. Spin coating can be used to obtain a thickness that lies in the range of 0.1 to 0.5 microns.
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