Imprinted poly(acrylic acid) films on cadmium selenide. A composite sensorstructure that couples selective amine binding with semiconductor substrate photoluminescence

Molecularly imprinted films of poly(acrylic acid) (PAA) have been coated on to n-CdSe in order to make the band-edge photoluminescence (PL) of the semi conductor respond selectively to the imprinting analyte. This strategy has been implemented using PAA films deposited in the presence of ammonia and t rimethylamine analytes. PAA films have been characterized by IR spectroscop y, which indicates that binding of either analyte nearly reversibly deproto nates the polymer carboxylic acid groups. PL measurements suggest that the imprinted PAA coatings serve as sieves for selective surface binding: In. c ontrast to the bare CdSe surface, which responds both to ammonia and trimet hylamine with reversible enhancements in PL intensity, CdSe coated with amm onia-imprinted PAA (AI-PAA) films exhibits reversible PL changes toward amm onia but no response to trimethylamine. The PL changes for the AI-PAA films can be fit to a dead-layer model that indicates that ammonia binding reduc es the CdSe depletion width by similar to 100 Angstrom an effect comparable to that seen for the bare surface. Binding constants of similar to 10(3) M -1, estimated using the Langmuir adsorption isotherm model, are similar for adsorption of ammonia onto bare and AI-PAA-coated CdSe surfaces. Coating t he CdSe substrate with trimethylamine-imprinted PAA (TI-PAA) Rims leads to PL responses to both ammonia and trimethylamine, presumably reflecting larg er imprint pores that are less sterically demanding. Implications for chemi cal sensing using these composite structures are discussed.