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 oxygen 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.
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