Stable sensors with tunable sensitivities based on class II xerogels

We report on the analytical figures of merit for O₂-responsive sensor arrays and films formed by sequestering tris(4,7-diphenyl-1,10- phenanthroline)ruthenium(II) within class II organically modified silicates that are composed of tetramethoxysilane or tetraethoxysilane and monoalkylsiloxanes of the form (C_nH_2n+1)-Si-(OR)₃ (n = 1-12, R = Me or Et). These sensors exhibit a reasonably linear response to gaseous and dissolved O₂ (r² > 0.99), and the sensor responses are stable for over 2 years. Sensor sensitivity can be tuned continuously by adjusting n. For gas-phase O₂ detection, changes in the sensor sensitivity depend primarily on the O₂ diffusion coefficient within the xerogel phase. The O₂ solubility coefficient within the xerogel phase is also a factor but to a lesser degree. For dissolved O₂ detection, changes in the sensor sensitivity depend on the O₂ diffusion coefficient and the o₂ solubility coefficient within the xerogel phase. A linear correlation also exists between the sensor sensitivity and the polarity within these xerogels. Finally, the feature size of pin-printed sensor elements was found to depend linearly on pin velocity. The results of these experiments demonstrate a new strategy for creating xerogel-based sensor arrays consisting of diversified sensor elements for the same target analyte.