Franz Reininger

Miniaturized luminescence lifetime-based oxygen sensor instrumentation utilizing a phase modulation technique

Optical oxygen sensors are mainly based on the principle of luminescence quenching. In contrast to already existing intensity-based systems, the measurement of the luminescence lifetime provides certain advantages, such as insensitivity to photobleaching or leaching of the dye or changes in the intensity of excitation light. This facilitates the use of simple optical systems or optical fibers. Phase measurement techniques have shown to be a powerful tool for indirect measurement of luminescence lifetimes. Here, dyes with luminescence decay times in the order of tens or hundreds of microseconds allow the use of simple opto-electronic circuitry and low-cost processing electronics. An optical oxygen sensor module has been developed with the dimensions of only 120 X 60 X 30 mm. The instrument is based on the measurement of the decay time of the luminophore by measuring the phase shift between the square-wave excitation and the detected square-wave of the emission coming from the sensor. The instrument is based on semiconductor devices (light-emitting diodes, photodiodes) and may be used for the detection of oxygen in gaseous or liquid samples. Platinum(II) octaethylporphyrin-ketone, which is incorporated in an oxygen-permeable polymer and which has an unquenched lifetime of approximately 60μs, is used as the oxygen-sensitive dye. The typical measurement range of the device is from 0 to 200 hPa oxygen partial pressure with a resolution of <I hPa over the whole measurement range. Measurement accuracy of <±1 hPa has been obtained for periods of 24 h of continuous measurement. The sensor response times t 90 are typically <1 s for gases and 1-5 min for liquid samples.

Recent progress in optical oxygen sensor instrumentation

Optical methods for the determination of dissolved or gaseous oxygen are mainly based on the principle of fluorescence quenching. Measurement schemes have been reported which employ various oxygen-sensitive dyes and bulky instrumentation. Typically, expensive fluorescence spectrometers or fibre-optic photometers have been used, and the applicability of such instruments is rather limited. A system based on low-cost semiconductor devices (light-emitting diodes (LEDS), photodiodes, low-cost analogue and digital components) and new LED-compatible oxygen-sensitive membranes has been developed at our institute. The instrument is capable of determining dissolved or gaseous oxygen and may be calibrated, for example, by a simple two-point calibration procedure with air-saturated and oxygen-free water. Thermostatization of the flow-through cell results in higher measurement accuracy and in a reduced influence of the ambient temperature on the instrument. The overall performance of the oxygen sensor has been investigated, e.g. measurement stability, effectivity of thermostatization, calibration, oxygen diffusion into the measuring cell and excitation feed-through.

Fiber-optic remote detection of pesticides and related inhibitors of the enzyme acetylcholine esterase

Abstract We present a novel method for the remote detection of inhibitors (e.g., pesticides) of the enzyme acetylcholine esterase (AChE) with a fiber-optic photometer based exclusively on the use of solid-state opto-electronic components including light-emitting diodes and photodiodes. The method employs a yellow synthetic enzyme substrate which is hydrolyzed by the enzyme to give a blue product. In the presence of an inhibitor, the rate of formation of this blue product is reduced. The resulting signal change is detected via fiber optics and may serve as an alarm.

Study of the performance of an optochemical sensor for ammonia

An optical sensor for ammonia based on ion pairing has been investigated. A pH-sensitive dye (bromophenol blue) was immobilized as an ion pair with cetyltrimethylammonium in a silicone matrix. The colour of the dye changes reversibly from yellow to blue with increasing concentration of ammonia in the sample. The concentration of ammonia can be determined by measuring the transmittance at a given wavelength. All measurements were performed with a dual-beam, solid state photometer. The measurement range is from 6 × 10−7 to 1 × 10−3 M (0.01 to 17 μg ml−1) in 0.1 M sodium phosphate buffer, pH 8. The 90% and 100% response times at a flow rate of 2.5 ml min−1 are 4 min and 10 min, respectively, for a change from 41.9 to 82.5 μM ammonia, or 12 min and 48 min, respectively, for change from 160 to 0 μM ammonia. A continuous drift in signal baseline and ammonia sensitivity limited the measurement stability. The sensor was useful over a period of a few days. The storage stability is more than 10 months (dry). No interference due to pH was observed in the range from pH 5 to pH 9. Sensor performance is seriously affected by amines and cationic detergents. The sensor could be sterilized with 3% hydrogen peroxide or dry heat (90 °C).

Fast optochemical sensor for continuous monitoring of oxygen in breath-gas analysis

An application of an optochemical oxygen sensor to respiratory gas monitoring is presented. A new prototype module has been developed, which is suitable for the determination of oxygen concentration in mainstream breath-gas flow, directly at the patients mouth. The sensor is based on the measurement of the quenching of the intensity of photoluminescence of the dye platinum(II)-octaethylporphyrin-ketone by molecular oxygen. The dye has been immobilized in various polymers with and without plasticizer. The characteristics of the resulting oxygen-sensitive membranes have been determined with emphasis mainly on their oxygen response characteristics, such as calibration graphs, oxygen sensitivities, oxygen resolution and response times. The suitability of the optochemical oxygen sensors for clinical use in respiratory gas-exchange measurements has been demonstrated in combination with a prototype instrument.

Optical oxygen sensor instrumentation based on the detection of luminescence lifetime

Optical oxygen sensors are mainly based on the principle of luminescence quenching. In contrast to arready existing intensity-based systems, the measurement of the luminescence lifetime provides certain advantages, such as insensitivity to photobleaching or leaching of the dye, or changes in the intensity of excitation light. This facilitates the use of simple optical systems or optical fibres. A new family of oxygen-sensitive dyes, the porphyrin-ketones, has been introduced, which exhibits favorable spectral properties and decay times in the order of tens and hundreds of microseconds. This allows the use of simple optoelectronic circuitry and low-cost processing electronics. An optical oxygen sensor module has been developed with the dimensions of only 120 x 60 x 30 mm. The prototype is based on the measurement of the decay time of the luminophore by measuring the phase shift between the square-wave excitation and the detected square-wave of the emission coming from the sensor. The instrument is based on semiconductor devices (light-emitting diodes, photodiodes) and may be used for the detection of oxygen in gaseous or liquid samples. The measurement range of the device is from 0 to 200 hPa oxygen partial pressure with a resolution of < 1 hPa over the whole measurement range. The overall measurement accuracy of < +/- 1 hPa has been obtained for periods of 24 h of continuous measurement in a thermostatted environment. The sensor response times t90 are typically < 1 s for gases and 0.5 to 5 min for liquid samples.

New instrumentation for optical measuring of oxygen in gas or dissolved in liquids.

The optical oxygen sensor is a novel device for the determination of oxygen in gases or dissolved in liquids. It is based on the measurement principle of fluorescence quenching, which is completely different from that of polarographic oxygen sensors (today the most widespread devices of oxygen detection). The new instrument offers features and advantages, which render it not only a realistic alternative, but, for specific applications, make it superior to existing electrochemical methods. The system is based on low-cost semiconductor devices (light-emitting diodes, photodiodes, low-cost analogue and digital components) and new LED-compatible oxygen-sensitive membranes. The flow cell of the instrument may be thermostatted and the sensor can be calibrated by a simple two-point calibration procedure. The optical oxygen sensor is particularly suitable for measuring dissolved oxygen in respirometry, since no oxygen is consumed by the device and the signal is independent of sample flowrate or stirring speed. Typical fields of application are monitoring of oxygen in ground and drinking water, in process control in bioreactors and in breath gas and blood gas analysis.

Optochemical Sensor for Ammonia Based on a Lipophilized pH Indicator in a Hydrophobic Matrix

Abstract An optical sensor for the determination of ammonia in water based on ion pairing has been investigated. A pH-sensitive dye is immobilized as an ion pair in a silicone matrix. The colour of the dye changes from yellow to blue depending on the concentration of ammonia in the sample solution. This change is reversible. The concentration of ammonia can be determined by measuring the transmittance at a given wavelength. All measurements were performed with a dual-beam optical meter. The measurement range was from 5.9 × 10−7 to 1 × 10−3 M (0.01 to 17 mg/l) in 0.1 M phosphate buffer of pH 8. The detection limit was 10 μg/l. The response times at a flow rate of 2.5 ml/min were 4 min for t90 and 10 min for t100 at a change from 41.9 to 82.5 μM ammonia and 12 min for t90 and 48 min for t100 at a change from 160 to 0 μM ammonia. The operational lifetime of the ammonia sensor was limited to a period of a few days only. A continuous decrease in baseline signal and relative signal change was observed over the ...