Intrinsic Artefacts in Optical Oxygen Sensors—How Reliable are our Measurements?

Abstract

Optical oxygen sensing is of broad interest in many areas of research, such as medicine, food processing, and micro- and marine biology. The operation principle of optical oxygen sensors is well established and these sensors are routinely employed in lab and field experiments. Ultratrace oxygen sensors, which enable measurements in the sub-nanomolar region (dissolved oxygen), are becoming increasingly important. Such sensors prominently exhibit phenomena that complicate calibration and measurements. However, these phenomena are not constrained to ultratrace sensors; rather, these effects are inherent to the way optical oxygen sensors work and may influence any optical oxygen measurement when certain conditions are met. This scenario is especially true for applications that deal with high-excitation light intensities, such as microscopy and microfluidic applications. Herein, we present various effects that we could observe in our studies with ultratrace oxygen sensors and discuss the reasons for their appearance, the mechanism by which they influence measurements, and how to best reduce their impact. The phenomena discussed are oxygen photoconsumption in the sensor material; depletion of the dye ground state by high-excitation photon-flux values, which can compromise both intensity and ratiometric-based measurements; triplet-triplet annihilation; and singlet-oxygen accumulation, which affects measurements at very low oxygen concentrations.

Luminescent sensing and imaging of oxygen: Fierce competition to the Clark electrode

“…On the other hand, the following aspects should be kept in mind: Sensor membranes usually are made from materials that have high solubility for oxygen. Hence, they will extract O 2 from the sample which may lead to erroneous results in case of small sample volumes and/or very low levels of O 2 ; artifacts may be encountered due to the depletion of the ground state of the indicator under conditions of strong photoexcitation, and – in case of low levels of O 2 – the formation of large fractions of singlet O 2 , in particular when using metalloporphyrin probes . In any instance, the “consumption” rate is much smaller than the chemical consumption of O 2 in Clark electrodes. …”

Fiber-Optic Chemical Sensors and Fiber-Optic Bio-Sensors

“…Optical Luminescence Measuring Oxygen Sensor (LUMOS) measures from 1000 nM down to the detection limit of 0.5 nM and exhibits lower noise, higher resolution and higher sensitivity than the electrochemical STOX sensor [ 220 ]. Various effects that could influence measurements with ultratrace optical oxygen sensors were described by Lehner et al [ 221 ]. Imaging of a space distribution of concentrations as was demonstrated with pH planar optode [ 222 ] might be hardly realized with electrical sensors.…”

Technical note: Measurements and data analysis of sediment-water oxygen flux using a new dual-optode eddy covariance instrument

“…Because they are not sensitive to sulfides, optodes are the superior sensor in hypoxic environments or near anoxic sediment surfaces. Weaknesses of optodes include the bleaching of the sensor dye over time, their non-linear calibration with decreasing resolution at high oxygen concentrations, and interference of strong light with the optical measurements (Lehner et al, 2015). In long-term measurements, the bleaching effect can be reduced through interval measurements.…”