On-line determination of glucose and lactate concentrations in animal cell culture based on fibre optic detection of oxygen in flow-injection analysis

Investigating flexible feeding effects on the biogas quality in full-scale anaerobic digestion by high resolution, photoacoustic-based NDIR sensing

In future energy systems based on renewable energies, biogas plants can make a significant contribution to stabilizing the electricity grids. However, this requires load-flexible and demand-oriented electricity production by means of flexible feed management. However, these flexible feeding strategies using greatly oscillating, temporally varying high mass loads may lead to critical process failures of the anaerobic digestion process. Currently there is no online, high resolution gas quality measurement technique to detect and prevent biological process failures available. In this contribution, we present a miniaturized, low-cost biogas quality measurement system providing data with high precision and high temporal resolution to overcome this technology gap. To highlight the capabilities of the system we have installed it using a bypass to the main biogas duct after hydrogen sulfide removal at a full-scale research biogas plant. During a three-month field trial, the effect of flexible feeding on the biogas quality has been monitored. The results demonstrate long-term stability of the sensor solution and reveal the effects of changing feeding frequency and composition on gas quantity and quality, which cannot be detected with commercially available state-of-the-art sensing systems.

Indicators for optical oxygen sensors

Continuous monitoring of oxygen concentration is of great importance in many different areas of research which range from medical applications to food packaging. In the last three decades, significant progress has been made in the field of optical sensing technology and this review will highlight the one inherent to the development of oxygen indicators. The first section outlines the bioanalytical fields in which optical oxygen sensors have been applied. The second section gives the reader a comprehensive summary of the existing oxygen indicators with a critical highlight on their photophysical and sensing properties. Altogether, this review is meant to give the potential user a guide to select the most suitable oxygen indicator for the particular application of interest.

Fiber-optic flow-through sensor for online monitoring of glucose

A new microdialysis-based glucose-sensing system with an integrated fiber-optic hybrid sensor is presented. Design and dimensions of the cell are adapted for its coupling with commercially available microdialysis techniques, thereby providing a new system for continuous glucose monitoring. The glucose level is detected via oxygen consumption which occurs as a consequence of enzymatic reaction between immobilized glucose oxidase and glucose. The use of gas-permeable Tygon tubing ensures complete and constant air-saturation of the measuring fluid in the cell. Nevertheless, a reference oxygen optode is used to detect and to compensate response changes caused by events like bacterial growth, temperature fluctuations, or failure of the peristaltic pump. In contrast to widely used electrochemical sensors, the response of the microdialysis-based fiber-optic glucose sensor is highly selective, making this sensor approach particularly advantageous for continuous glucose monitoring of patients in intensive care units. The effects of flow rate, pH, temperature, and common interferences on the sensor response are presented and discussed in detail. The sensor is evaluated in vitro using a 3-day continuous test in glucose-spiked plasma. The ability to measure glucose in humans is demonstrated by coupling the flow-through cell and commercially available microdialysis catheter CMA60. A 24-h monitoring test using this setup is successfully applied to a healthy volunteer.

Multianalyte biosensors on optical imaging bundles

We present an optical biosensor design that expands the utility of enzyme biosensors. These biosensors are fabricated by site-selective photodeposition of analyte-sensitive polymer matrices on optical imaging fibres. These dual-analyte arrays allow for the simultaneous, independent measurement of the analyte of interest and the transducing analyte. The first integrated optical-biosensors using this design have been prepared that allow both the dependent and independent analytes to be measured simultaneously, for example penicillin and pH (Healey & Walt, 1995) or glucose and O2 (Li & Walt, 1995). Independent measurement of the transducing analyte allows penicillin or glucose to be quantitated in the presence of a concurrent pH or O2 change, respectively. Penicillin can be measured in the range 0.25-10.0 mM in the pH range 6.2-7.5. Glucose can be measured in the range 0.6-20.0 mM in the O2 range 20-100%. The utility of the sensor design was demonstrated by using the penicillin-dual-analyte biosensor to quantitate penicillin produced during a Penicillium chrysogenum fermentation.

An in situ electrosynthesized amperometric biosensor based on lactate oxidase immobilized in a poly-o-phenylenediamine film: determination of lactate in serum by flow injection analysis

The electrochemical immobilization of lactate oxidase in a poly-o-phenylenediamine film permits the one-step and all-chemical construction of a lactate amperometric biosensor. The sensor was prepared in situ i.e. in the flow injection analysis (FIA) system by simply injecting a plug of a solution containing the monomer and the enzyme. At a flow rate of 50 microL/min linearity was observed up to 0.2 mM lactate and detection limits of about 2 microM could be easily achieved. Faradaic interferences caused by ascorbate, urate, cysteine and acetaminophen were sufficiently minimized to permit lactate determination in diluted serum by FIA. Results obtained by FIA-amperometric detection compared well (according to a proper t-test at a 95% confidence level) with those obtained by a standard enzymatic colorimetric assay. At a flow rate of 1 ml/min a sample throughput higher than 70 sample h-1 was achieved. After one week of continuous use in the FIA system a 75% decrease in biosensor sensitivity was observed.

Comparison of different biosensor systems suitable for bioprocess monitoring

To achieve effective bioprocess monitoring, sensing systems are required which are suitable for an on-line determination of substrates, inhibitors, nutrients or products. Such devices may utilise biochemical principles, i.e. the specific interaction of biochemical receptors with their surroundings. They can be constructed either as in situ sensors or as flow-through sensors connected to the process via sampling devices. Hence, characteristic features of an in situ glucose electrode are described, e.g. analytical range, sensitivity and stability. The sensor was based on mediated electron transfer from the enzyme glucose oxidase to the graphite electrode, the mediators being tetrathiafulvalene (TTF) or dimethylferrocene (DMF). Additionally, various flow injection analysis (FIA) systems based on oxidases, which were immobilised either on controlled pore glass or in a membrane, were characterised with respect to analytical ranges and sensitivities and applied to glucose, lactate and glutamate determinations in off-line samples taken from an animal cell cultivation.

Biosensors for fermentation control

Over the past year, biosensor development has been an active area of research. The actual application of biosensors in process monitoring and control is limited to a few cases, mainly as a result of difficulties relating to their long-range stability and their sensitivity to interfering compounds. Steam sterilization is no longer a problem though, as the great majority of sensors are part of flow-injection analysis systems.

Applied biosensors

Biosensors are important analytical tools in clinical and environmental monitoring, biotechnological process control, medicine, and in the food and drink industry. This review devotes attention to the most common biosensor in biotechnology, the glucose biosensor, and to recent contributions to the rapidly growing field of optical biosensors. Trends and developments in these areas are discussed.

An automatic dehydrogenase-based flow-injection system: application for the continuous determination of glucose and lactate in mammalian cell-cultures

A concept for the development of an automatic flow-injection analyzer with integrated dehydrogenase columns and its application in the control of industrial processes is presented. The system is based upon a kernel consisting of a nested-loop injection unit, pumps for the filling of the injection loops and the transport of buffer and values for switching on the one hand between sample and standard solutions and on the other hand between different enzyme columns. A Microsoft Windows 3.x application 'WIN-FIA' controls interactively the whole system and can be easily adapted to a specific solution of an analytical problem. As an example, the flow-injection system was used for the continuous determination of glucose and lactate, using glucose dehydrogenase (GDH) and lactate dehydrogenase (LDH) as indicator enzymes, in a mammalian cell-culture fermentation process. The resulting concentration values are in good agreement with those obtained by discontinuously taken standard spectrophotometric enzyme assays.