Response characteristics of optical sensors for oxygen: a model based on a distribution in τoand kq

Abstract

The typical response characteristics of most optical oxygen sensors include downward curving Stern–Volmer plots and often multi-exponential luminescence decay profiles in the absence and presence of oxygen. The wide range of different response features exhibited by optical oxygen sensors is usually attributed to different degrees of heterogeneity in the sensor films. This heterogeneity is described in this paper by a log-Gaussian distribution in the natural luminescent lifetime of the oxygen-quenchable lumophore, τ_o, and the quenching rate constant, k_q. A ‘log-Gaussian distribution in τ_o and k_q’ model is used to generate theoretical response profiles which exhibit the same disparate range of features as real optical oxygen sensors. However, unlike other models, such as the ‘two-site’ model, the ‘log-Gaussian distribution in τ_o and k_q’ model generates model parameter values which are physically plausible and consistent at all partial pressures of oxygen, pO₂. The model is used to fit successfully the Stern–Volmer plots and luminescent decay profiles reported for a number of different optical oxygen sensors. For each of the real sensors examined, the values of the model parameters K_SV,mdl, ρ₁, ρ₂ and τ_o,mdl which give the best fit to the observed data are reported. The latter data allows prediction of the response features of the associated optical oxygen sensor at any value of pO₂