Swellable polymer particles that respond to pH have been prepared by free radical dispersion polymerization using N-isopropylpolyacrylamide (NIPA), methylene-bis acrylamide, 2-dimethoxy-2 phenyl-acetophenone, N-tert-butylacrylamide (NTBA), and methacrylic acid, ethacrylic acid or propacrylic acid.  The polymer particles are incorporated into hydrogel membranes prepared by mixing the pH sensitive polyNIPA particles with aqueous polyvinyl alcohol solutions followed by cross linking using glutaric dialdehyde.  When the polymer particles are dispersed in a hydrogel, there are large changes in the turbidity of the membrane, which can be monitored using visible and near infrared absorbance spectroscopy as the pH of the solution in contact with the membrane is varied.  These polymer particles show a larger response over a narrower pH range than predicted by the Henderson-Hasselbach equation.  Furthermore, the degree of swelling and the apparent pKa of these polymer particles increase with temperature and is independent of the ionic strength of the solution in contact with the membrane.  The pKa of the polymer particles can be tuned to respond sharply in the physiological pH range (5.0 to 7.4) by varying the degree of cross-linking, the amount of NTBA used or the alkyl chain length of the pH sensitive co-monomer. Proposed applications of these polymer particles include gastric pH sensing using magneto-elastic sensing, bioconjugation, and pH monitoring of the progress of open heart surgery using optical fibers where pH serves as a measure of tissue ischemia.

Swellable pH sensitive N-isopropylpolyacrylamide polymer particles for optical sensing

247th National Meeting (2014)

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