Oxygen analyzer principle and selection considerations(2)

2. Fluorescence quenching principle

       Fluorescence quenching refers to the process that causes a reduction in the fluorescence intensity (I) and/or decay time (t) of an excited state. Numerous factors can induce quenching; however, the most relevant are oxygen (O2) and temperature. In the presence of a quencher [Q]—in this instance, O2—collisions occur with fluorophores that are returning to the ground state (S0) via fluorescence (F) or phosphorescence (P) pathways, resulting in an increase in non-radiative processes. As the concentration of [Q] increases, this process intensifies, leading to a continuous decline in fluorescence intensity (I) and/or decay time (t); consequently, the concentration of O2 can be quantitatively determined by measuring this reduction in I or t—a relationship described by the Stern-Volmer equation.

This novel optical technology is based on unique oxygen-sensitive REDFLASH indicators, which exhibit exceptional brightness. The underlying measurement principle relies on collisions between oxygen molecules and REDFLASH indicators immobilized on the sensor tip or surface, thereby inducing the quenching of the REDFLASH indicators' luminescence. REDFLASH indicators can be excited by red light (more precisely: orange-red light with a wavelength of 610–630 nm) and exhibit oxygen-dependent luminescence within the near-infrared (NIR) range (760–790 nm).

This optical technology is distinguished by its high precision, high reliability, low power consumption, low cross-sensitivity, and rapid response time. Excitation with red light significantly minimizes interference caused by autofluorescence and places less stress on biological systems.

The luminescence brightness of REDFLASH indicators is substantially higher than that of competing products utilizing blue-light excitation. Consequently, the duration of the red-light flash required for a single oxygen measurement can be reduced from the typical 100 milliseconds to a mere 10 milliseconds, thereby significantly lowering the light dose to which the measurement device is exposed. Furthermore, thanks to the exceptional brightness of the REDFLASH indicators, the actual sensor matrix can be fabricated with a thinner profile, resulting in faster response times for the oxygen sensor.

The measurement principle is based on sinusoidally modulated red excitation light, which generates a phase-shifted, sinusoidally modulated emission signal in the near-infrared region. The optical oxygen sensor measures this phase shift and converts it into oxygen units based on the Stern-Volmer theory.

 The mechanisms responsible for sensor performance degradation are primarily linked to the condition of the optical surface, the integrity of the sensing coating, and the validity of the compensation model—rather than chemical depletion. This characteristic enables the sensor to effectively reduce the frequency of routine maintenance in applications where electrochemical sensors are prone to rapid deterioration.

 Since both temperature and pressure can influence luminescence behavior and oxygen diffusion characteristics, modern optical oxygen sensors typically incorporate temperature and pressure compensation algorithms to maintain measurement accuracy under varying environmental and process conditions.Furthermore, as signal quality can be monitored in real time, this technology possesses significant inherent diagnostic potential.