Thermoresponsive poly-n-isopropylacrylamide gels modified with colloidal gold nanoparticles for electroanalytical applications. 1. Preparation and characterization

Preparation and spectroscopic and electrochemical characterization of thermoresponsive poly-N-isopropylacrylamide (NIPA) hydrogels modified with gold colloidal nanoparticles is described. Gold nanoparticles of various sizes in the range from 2.7 to 18 nanometers in diameter were synthesized and introduced to NIPA polymeric gels during the polymerization process. Dry, ground polymers were reswelled by solutions of well-known and well-controlled composition. Such polymeric gels undergo discontinuous reversible volume phase transition in response to temperature increase; this results in a release of up to 90% of solvent from the polymeric matrix. The potential window was determined in NIPA gels modified with gold nanoparticles and compared to that in pure NIPA gels. Diffusion coefficients of electroactive probes in NITA gels modified with gold and in expelled solutions were determined. It was found that diffusion coefficients of Fc(MeOH)(2) in swollen neat NIPA and NIPA-gel modified with gold nanoparticles are identical within experimental error and they are approximately 10-30% smaller than those in aqueous solutions. Concentration of Fc(MeOH)(2) in expelled solutions was up to 30% smaller than in swollen gel. Mole fractions of electroactive probes in collapsed gels and expelled solutions were also determined.