Sol-gel-derived sensor materials that yield linear calibration plots, high sensitivity, and long-term stability

Novel O₂-sensing materials based on spin-coated noctyltriethoxysilane (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%).