Ratiometric optical oxygen sensor based on phosphorescence quenching

Molecular oxygen plays a pivotal role in various biological, chemical and environmental reactions, thus detection of oxygen has attracted much attention. Traditional methods of sensing oxygen including classical Winkler titration, electroanalysis, chemiluminescence and thermoluminescence suffer from limitations such as relatively long response time, oxygen consumption during the sensing process and poor selectivity. The ground state of oxygen is a triplet state, so oxygen can quench the long-lived triplet phosphorescence of luminophores. Optical sensors to detect oxygen through phosphorescence have become a very active research field because of their good sensitivity and selectivity, full reversibility, simplicity, suitability for real-time measurements and minimal consumption of oxygen during measurements. Common detection modalities in optical oxygen sensing include phosphorescence intensity, ratiometric and lifetime measurements. Ratiometric intensity measurements at two different wavelengths allow more reliable detection than at a single wavelength because oxygen responses depend on the ratio of the oxygen sensor and reference luminescent signals. In addition, most ratiometric optical oxygen sensors exhibit a perceivable color change, which is useful for rapid visual sensing. This review focuses on the mechanism of oxygen sensing, material designs for ratiometric sensors and cell imaging. The future development of oxygen sensors is also discussed.