Long-wavelength fluorescent indicators for the determination of oxygen partial pressures

Optical methods for sensing and imaging oxygen: materials, spectroscopies and applications

We review the current state of optical methods for sensing oxygen. These have become powerful alternatives to electrochemical detection and in the process of replacing the Clark electrode in many fields. The article (with 694 references) is divided into main sections on direct spectroscopic sensing of oxygen, on absorptiometric and luminescent probes, on polymeric matrices and supports, on additives and related materials, on spectroscopic schemes for read-out and imaging, and on sensing formats (such as waveguide sensing, sensor arrays, multiple sensors and nanosensors). We finally discuss future trends and applications and summarize the properties of the most often used indicator probes and polymers. The ESI† (with 385 references) gives a selection of specific applications of such sensors in medicine, biology, marine and geosciences, intracellular sensing, aerodynamics, industry and biotechnology, among others.

Integrated optical sensing of dissolved oxygen in microtiter plates: a novel tool for microbial cultivation

Microtiter plates with integrated optical sensing of dissolved oxygen were developed by immobilization of two fluorophores at the bottom of 96-well polystyrene microtiter plates. The oxygen-sensitive fluorophore responded to dissolved oxygen concentration, whereas the oxygen-insensitive one served as an internal reference. The sensor measured dissolved oxygen accurately in optically well-defined media. Oxygen transfer coefficients, k(L)a, were determined by a dynamic method in a commercial microtiter plate reader with an integrated shaker. For this purpose, the dissolved oxygen was initially depleted by the addition of sodium dithionite and, by oxygen transfer from air, it increased again after complete oxidation of dithionite. k(L)a values in one commercial reader were about 10 to 40 h(-1). k(L)a values were inversely proportional to the filling volume and increased with increasing shaking intensity. Dissolved oxygen was monitored during cultivation of Corynebacterium glutamicum in another reader that allowed much higher shaking intensity. Growth rates determined from optical density measurement were identical to those observed in shaking flasks and in a stirred fermentor. Oxygen uptake rates measured in the stirred fermentor and dissolved oxygen concentrations measured during cultivation in the microtiter plate were used to estimate k(L)a values in a 96-well microtiter plate. The resulting values were about 130 h(-1), which is in the lower range of typical stirred fermentors. The resulting maximum oxygen transfer rate was 26 mM h(-1). Simulations showed that the errors caused by the intermittent measurement method were insignificant under the prevailing conditions.

Electroluminescent lamp-based phase fluorometer and oxygen sensor

We have tested 454-nm violet-emitting solid state electroluminescent lamps (ELLs) as inexpensive intensity-modulated excitation light sources for phase fluorometric oxygen sensors. Compared with blue-emitting silicon carbide LEDs, planar surface ELLs can be produced in various shapes and in large sizes. Accordingly, the overall optical output power emitted by ELLs is much higher than that of blue LEDs. By arranging a large-size ELL close to a large-size fluorescent chemical sensor, we obtained a large number of fluorescence photons allowing for the use of a pin photodiode instead of a photomultiplier tube as the detector. For a sinusoidal driving voltage at a frequency f, the ELL output light is modulated at 2f and at harmonics of 2f. Because of this nonlinear modulation characteristic, we used a square wave driving signal, resulting in a pulsed light output at a repetition rate twice the square wave frequency. The shortest light pulses obtained had a FWHM close to about 1 microsecond. This means that the violet ELLs used in our tests provide modulation frequencies at twice the square wave driving frequency and at all harmonics thereof up to about 1 MHz. This would allow the use of fluorescent chemical sensors with decay times as short as 30 ns, assuming that a phase shift of 10 degrees is adequate for the application. Due to the high ELL driving voltage, effective shielding is required to avoid electromagnetic interference between the modulated light source and the photodetector. Depending on the driving frequency and voltage applied, the ELLs showed a decrease in the optical output power to 50 or even 10% during the first 100 h of operation.

Development of a medical fiber-optic oxygen sensor based on optical absorption change

A new fiber-optic oxygen sensor has been developed for use in medical applications. The sensor's viologen indicator becomes strongly absorbent after brief UV stimulation, and then returns to the transparent state. The rate of indicator return to transparency is proportional to the local oxygen concentration. Indicator absorbance is monitored with a red LED and receiving photodiode, and absorbance data are processed by a dedicated cpu. The solid-state sensor system has performance comparable to existing oxygen measurement techniques, and may be applicable for both in vitro and in vivo oxygen measurements.