Development of Chemical Sensing Platforms Based on Sol−Gel-Derived Thin Films:  Origin of Film Age vs Performance Trade-Offs

Abstract

We present a detailed investigation on the evolution and performance of sol−gel-derived thin films as used for chemical sensing platforms. In 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 investigate a simple model probe−analyte system. Specifically, we use static and time-resolved fluorescence spectroscopy to report on the photophysics and O2 quenching of pyrene entrapped within sol−gel-derived thin films as a function of precursor form, processing conditions, and storage time. The results of this year-long study show that the analytical response of the pyrene-doped film/sensor to O2 decreases as a function of storage time. This response decrease results from two separate factors. First, the average bimolecular quenching constant decreases from (1.3−1.4) × 107 to (0.4−0.6) × 107 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 function of storage time. The simultaneous decrease in bimolecular quenching constant and average fluorophore lifetime are directly related to the change in analytical signal (i.e., response). These results demonstrate that single-component sol−gel-derived sensing platforms are unstable over time. However, we find that most of the observed instability occurs during the first month following film preparation.

Luminescence quenching of tris(2,2′-bipyridine)ruthenium(II) by 2,6-dimethylphenol and 4-bromo-2,6-dimethylphenol in sol–gel-processed silicate thin films

“…Both rates can be attributed to the decay of the photoexcited Ruthenium complex in two different binding sites. This fact, heterogeneity at the molecular level in this type of materials, was reported in previous studies [24][25][26].…”

Luminescent Properties of Tris(2,2′-bipyridine)ruthenium(II) in Sol-Gel-Processed Dip-Coated Thin Films

“…This kinetics result of m = 2 in Eq. [3] for all our luminescence decay measurements may be considered a realistic representation for this work, given the fact that previous studies reported heterogeneity at the molecular level in this type of material (18)(19)(20).…”

Mesostructured Silica Chemically Doped with RuII as a Superior Optical Oxygen Sensor

“…An important point that needs to be pointed out in our system is that careful optimization of the processing conditions is necessary to obtain the mesostructured samples with high quality. This following particular procedure was chosen because it was representative of TEOS-based xerogels reported in the literature [18,[22][23][24]33,36,38,[49][50][51]. A pre-hydrolyzed solution contains TEOS, ethanol, deionized water, and HCl (1:3:5 × 10 -5 :1, molar ratio) was first prepared by refluxing at 90°C for 1 h to form the stock solution [50].…”