Enzyme sensor-FIA-system for on-line monitoring of glucose, lactate and glutamine in animal cell cultures

NANOSTRUCTURED Pt–Ir NON-ENZYMATIC GLUCOSE SENSORS

Over the past decade, the development of non-enzymatic electrochemical biosensors had thriven at a considerable rate. Compared with the traditional enzymatic electrochemical biosensors, the non-enzymatic electrochemical biosensors have the advantages of higher sensitivity and stability. Recently, plenty of researches have devoted to synthesizing new materials, such as bimetallic nanoparticles, and also develop specific nanostructures on the sensor surface to solve the problem of poisoning and increase the selectivity. This work develops two non-enzymatic glucose sensors that are based on nanostructured Pt – Ir films which were deposited by electrodeposition. Because of the relatively high deposition current density, bubbles produced vigorously on the working electrode surface. This phenomenon results in leaf-like nanostructure formed naturally on the surface of the working electrode and further increased the catalytic reaction area. Besides, as determined by the sampling analysis method that is developed herein, the presented Pt – Ir sensors mitigate the current drifting problem which is easily observed when a constant potential is applied in an amperometric glucose detection. Furthermore, the presented Pt – Ir sensors show high sensitivity and stability in 1X PBS (0.15 M NaCl ) at 37°C in the glucose concentration range of 1–12 mM. Therefore, the presented non-enzymatic glucose sensors not only provide great potential in biomedical applications, such as homecare products, but can also be adapted for the biological application, such as continuous cell culture monitoring.

Carbon-Nanotube-Enhanced Direct Electron-Transfer Reactivity of Hemoglobin Immobilized on Polyurethane Elastomer Film

In this study, we investigate the direct electron-transfer reactivity of immobilized hemoglobin (Hb) on a polyurethane elastomer (PUE) film for biosensor designs. The PUE film synthesized by an additional polymerization possesses good biocompatibility, uniformity, and conformability and is ready for protein immobilization. Electrochemical and spectroscopic measurements show that the presence of multiwalled carbon nanotubes (MWNTs) increased the protein-PUE interaction, varied polymer morphology, improved the permeability and the conductivity of the PUE film, and thus facilitated the direct electron transfer between the immobilized Hb and the conductivity surface through the conducting tunnels of MWNTs. The immobilized Hb maintains its bioactivities and displays an excellent electrochemical behavior with a formal potential of -(334 +/- 7) mV. The addition of NaNO2 leads to an increase of the electrocatalytic reduction current of nitrite at -0.7 V. This allows us to develop a nitrite sensor with a linear response range from 0.08 to 3.6 mM. The proposed method opens a way to develop biosensors by using nanostructured materials mixed with low electrical conductivity matrixes.

Biosensor for rapid phosphate monitoring in a sequencing batch reactor (SBR) system

A thick-film phosphate biosensor based on hydrogel immobilized pyruvate oxidase (POD) has been developed for rapid phosphate process control monitoring in an experimental sequencing batch reactor (SBR) system. We have employed a phosphate biosensor in an off-line monitoring of phosphate concentrations in a bench scale SBR. Measurements with biosensor show a good correlation (r2=0.98) with those of commercial colorimetric phosphate testing kits. The signal response time was 1 min with a detection limit of 5 microM. The biosensor method showed a good operational stability, needed less experimental procedures and a small sample size (approximately 20 microl). This allows its practical application for rapid phosphate measurements to obtain real time process data in a SBR system.

Continuous glucose monitoring and control in a rotating wall perfused bioreactor

A glucose control system consisting of a single in-line glucose sensor, concentrated glucose solution, and computer hardware and software were developed. The system was applied to continuously control glucose concentrations of a perfusion medium in a rotating wall perfused vessel (RWPV) bioreactor culturing BHK-21 cells. The custom-made glucose sensor was based on a hydrogen peroxide electrode. The sensor continuously and accurately measured the glucose concentration of GTSF-2 medium in the RWPV bioreactor during cell culture. Three sets of two-point calibrations were applied to the glucose sensor during the 55-day cell culture. The system first controlled the glucose concentration in perfusing medium between 4.2 and 5.6 mM for 36 days and then at different glucose levels for 19 days. A stock solution with a high glucose concentration (266 mM) was used as the glucose injection solution. The standard error of prediction (SEP) for glucose measurement by the sensor, compared to measurement by the Beckman glucose analyzer, was +/-0.4 mM for 55 days.

Enzyme-based flow injection analysis system for glutamine and glutamate in mammalian cell culture media

We present the setup of a flow injection analysis system designed for on-line monitoring of glutamate and glutamine. These amino acids represent a major energy source in mammalian cell culture. A cycling assay consisting of glutamate dehydrogenase and aspartate aminotransferase produces NADH proportional to the glutamate concentration in the sample. NADH is then measured spectrophotometrically. Glutamine is determined by conversion to glutamate which is fed into the cycling assay. The conversion of glutamine to glutamate is catalyzed by asparaginase. Asparaginase was used in place of glutaminase due to its relatively high reactivity with glutamine and a pH optimum similar to that of glutamate dehydrogenase. The enzymes were immobilized covalently to activated controlled pore glass beads and integrated into the flow injection analysis system. The application of the immobilized enzymes and the technical setup are presented in this paper.

Methodological aspects of glucose monitoring with a slow continuous subcutaneous and intravenous ultrafiltration system in rats

A method for the continuous ultrafiltration of venous blood or subcutaneous fluid is demonstrated with glucose monitoring in the living rat. Ultrafiltrate was withdrawn at a constant flow rate of approximately 100 nl/min. Glucose content of the ultrafiltrates was electrochemically determined with a flow injection analysis method and a bi-enzyme reactor. After glucose loading, the time course of glucose in the ultrafiltrate from the jugular vein was virtually identical, whereas that from the subcutaneous compartment was attenuated and the peaks blunted as compared to glucose levels in concomitantly assayed arterial blood. Our study demonstrates the potential of low rate ultrafiltration for monitoring metabolism with biosensor technology in vivo.

Glutamine biosensors for biotechnology applications, with suppression of the endogenous glutamate signal

Glutamine membranes for amperometric measurements are described. The interference of the endogenous glutamate is greatly diminished by using a supplementary "anti-glutamate" layer consisting of immobilized glutamate oxidase and catalase on top of the glutamine-sensitive layer having co-immobilized glutaminase and glutamate oxidase. The use of polycarbonate membranes with different permeability characteristics for the control of the substrate's access to the enzyme layers is presented, as well as the effect of the density of the enzyme layer on the sensitivity of these membranes. The fabricated membranes have good operational stability (at least 5 days) and very good linearity (up to 10 mM glutamine). Using an appropriate choice of membranes and cross-linking conditions, membranes with good rejection of glutamate have been fabricated (less than 6% RSD for a 5 mM glutamine sample containing 5 mM glutamate as interferent). These membranes are suitable for monitoring of glutamine levels in mammalian cell cultures without the need of a separate measurement for glutamate.

Determination of glutamine and glutamic acid in mammalian cell cultures using tetrathiafulvalene modified enzyme electrodes

Tetrathiafulvalene (TTF) mediated amperometric enzyme electrodes have been developed for the monitoring of L-glutamine and L-glutamic acid in growing mammalian cell cultures. The detection of glutamine was accomplished by a coupled enzyme system comprised of glutaminase plus glutamate oxidase, while the detection of glutamic acid was carried out by a single enzyme, glutamate oxidase. The appropriate enzyme(s) were immoblized on the Triton-X treated surface of tetrathiafulvalene modified carbon paste electrodes by adsorption, in conjunction with entrapment by an electrochemically deposited copolymer film of 1,3-phenylenediamine and resorcinol. Operating conditions for the glutamine enzyme electrode were optimized with respect to the amount of enzymes immoblized, pH, temperature and mobile phase flow rate for operation in a flow injection (FIA) system. When applied to glutamine and glutamic acid measurements in mammalian cell culture in FIA, the results obtained with enzyme electrodes were in excellent agreement with those determined by enzymatic analysis.

Principles and applications of biosensors for bioprocess monitoring and control

Biosensors are useful analytical devices that can be integrated with on-line process monitoring schemes. In this article, the principles and applications of these devices for bioprocess monitoring are considered. Several different types of biosensors are described, and the applications and limitations of flow injection analysis (FIA) for these applications are discussed. It is hoped that the background provided here can be useful to researchers in this area.

On-line monitoring of an animal cell culture with multi-channel flow injection analysis

A multi-channel flow injection analysis system was used for on-line monitoring of a continuous animal cell culture with high cell density. With this system, the glucose, lactate and glutamine concentration were determined using immobilized dehydrogenases, ammonium using an aqueous o-phthaldialdehyde solution. Glutamine concentration was determined on the basis of the difference between a glutamine and a glutamate measurement. To prevent disturbance of the measurement and pollution of the system, the analytes in the sample were separated from high molecular compounds by on-line dialysis. On-line gas dialysis was used to avoid interference of other amino groups with the ammonium determination. In addition, dialysis was used as a dilution step. The measurement time for all four components was 42 min. This time included a final washing period after the analysis cycle. The system was calibrated once a day. Two continuous cultivations of a hybridoma cell line immobilized in open-porous glass carriers were monitored, using a fluidized bed reactor as cultivation system. The concentration of glutamine, glucose and ammonium determined with the on-line FIA system were in good agreement with the off-line data determined once a day. Only the lactate data showed some deviation. The immobilized enzyme reactors could be used for up to 3000-5000 injections. During the first cultivation, lasting 200 h, the start up period of the reactor was monitored. The on-line measurements described much better the time-course of the concentrations than the off-line data. It was possible to estimate the growth rate of the cells in the micro-carriers by the on-line data. In the course of the second cultivation, which lasted almost 1000 h, the influence of the dissolved oxygen concentration on the cell metabolism was monitored. It was noted that a sudden change of the glutamine concentration in the feed caused a fast change of the consumption and production rate of the measured metabolites.

Determination of ammonium and L-glutamine in hybridoma cell cultures by sequential flow injection analysis

A flow injection analytical system based on a gas diffusion membrane module for ammonia and an ammonium flow-through potentiometric detector has been set up for measurement of L-glutamine and ammonium ions in hybridoma cell cultures. The main feature of the system is that the same basic analytical concept and equipment is used in both measurements, the only difference being for the determination of L-glutamine, in which the sample flows through an immobilized glutaminase cartridge. The conditions to enable the performance of both analysis consecutively, avoiding potential interferences by unwanted deamination of other compounds in the samples, have been determined. Finally, the proposed system has been compared with reference analytical methods for batch hybridoma cell culture experiments.

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.

Mammalian cell culture processes

Over the past year, mammalian cell culture research has been aimed at investigating the influence of culture conditions on viability, productivity and the consistency of post-translational modifications. Studies of the effect of medium conditions and the development of kinetic models are being made in relation to current efforts to develop fed-batch strategies that will optimize recombinant protein production processes. Recent advances have included novel biosensor and bioreactor developments. New technologies have also been applied to investigate high cell density bioreactor and culture conditions.