Hydrogel diffraction biosensor with mechanical biasing
Abstract
Smart hydrogels are three dimensional cross linked polymers which alter their properties in presence of external stimuli. One such property is reverse volumetric change, in which change in external stimuli causes the hydrogel to swell/shrink. The goal of this research is to develop highly sensitive biochemical sensors using smart hydrogels. This research takes advantage of the reverse swelling ability of hydrogels and the ability of diffraction gratings to detect nanoscale motion. Interferometric analysis of optical diffraction intensity produced by illuminating a laser beam on fabricated hydrogel gratings is used to calibrate the swelling/shrinking of hydrogel. In this study, a biasing technique which can further increase the sensitivity of the system as well as facilitate signal calibration is also introduced. The second chapter describes the details of fabrication of the hydrogel diffraction gratings. Although pH sensitive hydrogel is used as an exemplary model, however, this concept is generic and can be applied to any other volumetric change hydrogels to detect stimuli other than pH. Theory of operation is mentioned in the third chapter. It also describes the experiment setup and introduces the design of the biasing system. The fourth chapter highlights the experimental results and minimum detection limit of around 1.5X10-4 pH is observed. It is also observed that although the translation stage, optical components, electronics and fluidics contribute to the noise, hydrogel is major contributor to the noise in the results. It can also be observed that, since pH sensitive hydrogel is used and number of hydrogen ions in a solution is extremely high and hence the response is larger. But when this setup will be used with other hydrogels to detect far scarcer entities, the mechanical biasing will enhance the sensitivity further to detect low concentrations of these stimuli.
Degree
M.S.M.E.
Advisors
Savran, Purdue University.
Subject Area
Biochemistry|Mechanical engineering
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