Novel hybrid optical sensor materials for in-breath O2 analysis

Abstract

This study focuses on the optimisation and characterisation of novel, ORganically MOdified SILicate (ORMOSIL)-based, hybrid sensor films for use in the detection of O₂ on a breath-by-breath basis in human health monitoring applications. The sensing principle is based on the luminescence quenching of the O₂-sensitive ruthenium complex [Ru(II)-tris(4,7-diphenyl-1,10-phenanthroline)], which has been entrapped in a porous sol–gel film. The detection method employed is that of phase fluorometry using blue LED excitation and photodiode detection. Candidate sensor films include those based on the organosilicon precursors, methyltriethoxysilane, ethyltriethoxysilane, n-propyltriethoxysilane and phenyltriethoxysilane. While it has been established previously by the authors that these films exhibit a stable, highly sensitive response to O₂, this study focuses on selecting the material most suited for use in a breath monitor, based on the sensitivity, response time and humidity sensitivity of these films. Key parameters to be optimised include the O₂ sensitivity of the film and the film polarity, i.e. the degree of hydrophobicity. These parameters are directly linked to the precursors used. In this study a n-propyltriethoxysilane-derived O₂ sensor platform was selected as the optimum material for in-breath O₂ analysis due to its short response time, negligible humidity interference and suitable O₂ sensitivity in the relevant range in addition to its compatibility with a single-point calibration strategy.