Sol−Gel-Derived Sensor Materials That Yield Linear Calibration Plots, High Sensitivity, and Long-Term Stability

Abstract

Novel O2-sensing materials based on spin-coated n-octyltriethoxysilane (Octyl-triEOS)/tetraethylorthosilane (TEOS) composite xerogel films have been synthesized and investigated. These sensors are based on the O2 quenching of tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) ([Ru(dpp)3]2+) sequestered within the xerogels. Scanning electron microscopy and luminescence measurements (steady state and time resolved) have been used to investigate the structure of these films and their analytical figures of merit and determine the underlying reasons for their observed performance. The results show that certain [Ru(dpp)3]2+-doped Octyl-triEOS/TEOS composites form uniform, crack-free xerogel films that can be used to construct high-sensitivity O2 sensors that have linear calibration curves and excellent long-term stability. For example, an 11-month-old sensor based on 50 mol % Octyl-triEOS exhibits more than 4-fold greater sensitivity in comparison to an equivalent sensor based on pure TEOS. Over an 11-month time period, the sensitivity of a pure TEOS-based sensor drops by more than 400% whereas a sensor based on 50 mol % Octyl-triEOS remains stable (RSD = 4%).

Xerogel Optical Sensor Films for Quantitative Detection of Nitroxyl

“…Sol-gel condensation reactions continue to occur after xerogel solidification, and thus long term storage may have detrimental effects on sensor sensitivity as the siloxane network of the gel becomes more densely crosslinked. 37 As such, sensor calibration at the time of nitoxyl detection is important. Calibration of the sensor plate was performed by monitoring the initial rates of Mn II (NO)TPPS formation in the films upon exposure to Angeli's salt and fitting the response to Eq.…”

Antifouling character of ‘active’ hybrid xerogel coatings with sequestered catalysts for the activation of hydrogen peroxide

“…The B5 and B6 xerogels described above were prepared from sols that were doped with the luminescent reporter molecule tris(4,7 0 -diphenyl-1,10 0 -phenanathroline)ruthenium(II) chloride ([Ru(dpp) 3 ] 2þ ) and the resulting xerogels were exposed to various concentrations of dissolved I 7 or O 2 , a quencher for luminescence (Tang et al 2003). In the simplest scenario of a luminophore sequestered within a homogeneous medium, luminophore quenching obeys the Stern-Volmer relationship (Eftink1991; Lakowicz 1999):…”

“…For this ideal case, a plot of I 0 /I Q versus [Q] will be linear with a slope equal to K SV and an intercept of unity. K SV provides a convenient way to assess anion and neutral species transport within the films (Tang et al 2003;Tao et al 2006).…”

“…Transport of small neutral molecules within these types of xerogels has been investigated previously (Tang et al 2003;Tao et al 2006). A screening campaign showed that there was significant I 7 quenching of [Ru(dpp) 3 ] 2þ within the 50% APTES/ 50% TEOS (B5) and the 10% APTES/90% TEOS xerogel (B6) formulations.…”

“…In addition, the properties of the xerogel including porosity, permeability towards various ions and neutral molecules, and the extent of crosslinking can be controlled by the precursors one uses and the processing conditions (Brinker and Scherer 1990;Avnir 1995;Dave et al 1995;Ingersoll and Bright 1997;Jordan et al 1998). Furthermore, other reagents can be sequestered within the xerogel and these reagents can maintain their normal chemical reactivity/function found in solution (Avnir 1995;Dave et al 1995;Pandey et al 2000;Tang et al 2003).…”