DEVELOPMENT OF CHEMICAL SENSING PLATFORMS BASED ON SOL-GEL-DERIVED THIN-FILMS - ORIGIN OF FILM AGE VS PERFORMANCE TRADE-OFFS

We present a detailed investigation on the evolution and performance o f sol-gel-derived thin films as used for chemical sensing platforms. I n order to develop an understanding of how the sol-gel matrix affects the entrapped recognition chemistry and determine how and whether the analyte interacts with the sensing element, we have chosen to investig ate a simple model probe-analyte system. Specifically, we use static a nd time-resolved fluorescence spectroscopy to report on the photophysi cs and O-2 quenching of pyrene entrapped within sol-gel-derived thin f ilms as a function of precursor form, processing conditions, and stora ge time. The results of this year-long study show that the analytical response of the pyrene-doped film/sensor to O-2 decreases as a functio n of storage time. This response decrease results from two Separate fa ctors. First, the average bimolecular quenching constant decreases fro m (1.3-1.4) x 10(7) to (0.4-0.6) x 10(7) M(-1) s(-1) for fresh and 300 -day-old films, respectively. Second, the average pyrene excited-state fluorescence lifetime, in the absence of quencher, decreases as a fun ction of storage time. The simultaneous decrease in bimolecular quench ing constant and average fluorophore lifetime are directly related to the change in analytical signal (i.e., response). These results demons trate that single-component sol-gel-derived sensing platforms are unst able over time. However, we find that most of the observed instability occurs during the first month following film preparation.