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
Abstract:
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.