Chemical sensing using semiconductor luminescence: Enhanced selectivity with molecularly imprinted polymer films on cadmium selenium and thermostatic gas detection with LEDs

Chapter 1. An introduction to semiconductor materials and the application of their opto-electronic properties to chemical sensing is provided.; Chapter 2. Molecularly-imprinted films of poly(acrylic acid) (PAA) have been coated onto n-CdSe to enable the band-edge photoluminescence (PL) of the semiconductor to respond selectively to the imprinting analyte. This strategy has been implemented using PAA films deposited in the presence of ammonia and trimethylamine analytes. PAA films have been characterized by IR spectroscopy, which indicates that binding of either analyte nearly reversibly deprotonates the polymer carboxylic acid groups. PL measurements suggest that the imprinted PAA coatings serve as sieves for selective surface binding: In contrast to the bare CdSe surface, which responds both to ammonia and trimethylamine with reversible enhancements in PL intensity, CdSe coated with ammonia-imprinted PAA (AI-PAA) films exhibits reversible PL changes toward ammonia but no response to the more sterically demanding trimethylamine. In contrast, coating the CdSe substrate with trimethylamine-imprinted PAA (TI-PAA) films leads to PL responses to both ammonia and trimethylamine, presumably reflecting larger imprint pores that are less sterically demanding. Implications for chemical sensing using these composite structures are discussed.; Chapter 3. The electro-optical properties of light emitting diodes (LEDs) prepared from III-V semiconductors (In0.5Ga 0.5P compositions) can be altered by the adsorption of gaseous analytes. Changes in electroluminescence (EL) intensity caused by analyte adsorption have served as the signal for chemical sensing applications. This chapter describes attempts to isolate thermal effects from analyte-induced effects, because temperature alters the intensity and wavelength of the emitted luminescence. The utilization of thermostatic conditions for the chemical sensing experiments yielded reversible quenching of EL intensity upon SO2 adsorption and desorption.; Chapter 4. This chapter provides activities for students to investigate structure-property relationships in biological systems. The activities include an investigation of the photoresponse of Wisconsin FastPlants(TM) to LED emission and an experiment to isolate DNA from cells of common foodstuffs.