Anal. Chem. 2002, 74, 1343 -1348.

Diffusion and Concentration of Molecular Probes in Thermoresponsive Poly(N-isopropylacrylamide) Hydrogels: Effect of the Volume Phase Transition

Weimin Zhang, Irina Gaberman, and Malgorzata Ciszkowska*
Department of Chemistry, Brooklyn College and the Graduate Center, City University of New York, Brooklyn, New York 11210-2889


Poly(N-isopropylacrylamide), NIPA, thermoresponsive hydrogels with well-defined concentrations of an electroactive probe, 1,1'-ferrocenedimethanol, Fc(MeOH)2, were prepared. The discontinuous reversible volume phase transition of such gels occurs at 32 ± 1 C and results in a release of ~93% of the solution from the polymeric network. Transport of Fc(MeOH)2 in both swollen and collapsed gels was studied using steady-state voltammetry and chronoamperometry at platinum microelectrodes. The diffusion coefficient of Fc(MeOH)2 in collapsed gels was ~2 orders of magnitude smaller than that in swollen gels. UV/vis spectroscopic studies showed that for 3.0% NIPA gel, the concentration of Fc(MeOH)2 in the collapsed phase was ~6 times higher than that in released solution and 4.5 times higher than in the original swollen gel.