In situ microscopy as online tool for detecting microbial contaminations in cell culture.

Microbial contamination in mammalian cell cultures causing rejected batches is costly and highly unwanted. Most methods for detecting a contamination are time-consuming and require extensive off-line sampling. To circumvent these efforts and provide a more convenient alternative, we used an online in situ microscope to estimate the cell diameter of the cellular species in the culture to distinguish mammalian cells from microbial cells depending on their size. A warning system was set up to alert the operator if microbial cells were present in the culture. Hybridoma cells were cultured and infected with either Candida utilis or Pichia stipitis as contaminant. The warning system could successfully detect the introduced contamination and alert the operator. The results suggest that in situ microscopy could be used as an efficient online tool for early detection of contaminations in cell cultures.

Macroporous microcarriers for introducing cells into a microfluidic chip.

Macroporous gelatin beads (CultiSpher™ microcarriers) provide a convenient method for rapidly and reliably introducing cells cultured ex situ into a microfluidic device, where the spheres create a 3D environment for continued cell proliferation. We demonstrate the usefulness of this technique with a proof-of-concept viability analysis of cardiac cells after treatment with doxorubicin.

Searching for process information in the aroma of cell cultures.

Aroma emissions from living cells can provide valuable information about the metabolic and physiological condition of those cells. Electronic noses are chemical gas-sensor arrays that use artificial neural network models to evaluate aromas. They can interpret the complex aroma information emitted from cultures of bacteria, yeast cells and animal cells. Potential applications for electronic noses range from medical diagnosis to industrial bioprocessing.

Analysis of carbohydrates using liquid chromatography--surface plasmon resonance immunosensing systems.

An immunosensing system based on surface plasmon resonance (SPR) was used for on-line detection and characterization of carbohydrate molecules separated by high-performance liquid chromatography. These analytes, with or without serum, were continuously separated and analyzed in the combined liquid chromatography-surface plasmon resonance (LC-SPR) system. By using weak and readily reversible monoclonal antibodies, the SPR system allowed specific on-line monitoring of the substances. To increase the specificity of the immunosensor, nonrelevant antibodies were used as reference in a serial flow cell. The sensitivity of the LC-SPR system was dependent on molecular weight of the carbohydrate, affinity of binding, and design of the sensor.

Monitoring cellular state transitions in a production-scale CHO-cell process using an electronic nose.

An electronic nose is used to monitor the bioreactor off-gas composition in perfused cultivations of a CHO-cell line producing recombinant human blood coagulation factor VIII. The applicability of the electronic nose for monitoring cellular state transitions and process control is explained. It is shown that the instrument can reveal characteristic process states related to product and lactate formation, and detect microbial infections in a very early stage of the infection. The visualization of ideal process conditions is realized by using principal component analysis (PCA) and the on-line applicability of this method is outlined. The results illustrate the potential of the electronic nose as on-line sensor for ensuring product and process quality in production-scale bioprocesses.

Continuous weak-affinity immunosensing.

A multitude of weak biological interactions, either working alone or in concert, occur frequently throughout biological systems. We have used this natural feature of readily reversible interactions as the basis for continuous immunosensing. In a model system, a set of weak monoclonal antibodies directed towards a carbohydrate epitope was studied with the aid of surface plasmon resonance. Because the system requires no regeneration, it can be used as a truly on-line immunosensing device. This principle should have wide application in all areas where there is a need for the continuous evaluation of a molecule.

Porous gold surfaces for biosensor applications.

The sensitivity of optical biosensors where the detection takes place on a planar gold surface can be improved by making the surface porous. The porosity allows a larger number of ligands per surface area resulting in larger optical shifts when interacting with specifically binding analyte molecules. The porous gold was deposited as a thin layer on a planar gold surface by electrochemical deposition in a solution of tetrachloroaurate and lead acetate. A protein, streptavidin, was adsorbed into the formed porous layer and the time course of the adsorption was monitored by in-situ ellipsometry. When the porous layer was 500 nm in thickness a six-fold increase of the ellipsometric response was obtained compared with a planar gold surface. The dependency of porosity and layer thickness was explained with a mathematical model of the gold/porous gold/protein/solution system.

Electronic noses for bioreactor monitoring.

Electronic noses provide new possibilities for monitor the state of a cultivation non-invasively in real-time. The electronic nose uses an array of chemical gas sensors that monitors the off-gas from the bioreactor. By taking advantage of the off-gas components' different affinities towards the sensors in the array it is possible with the help of pattern recognition methods to extract valuable information from the culture in a way similar to the human nose. For example, with artificial neural networks, metabolite and biomass concentration can be predicted, the fermentability of a medium before starting the fermentation estimated, and the growth and production stages of the culture visualized. In this review these and other recent results with electronic noses from monitoring microbial and cell cultures in bioreactors are described.

Monitoring specific interaction of low molecular weight biomolecules on oxidized porous silicon using ellipsometry.

Porous silicon dioxide surfaces have been used for monitoring the specific affinity binding of low molecular weight molecules to streptavidin. Streptavidin was immobilized to the porous silicon dioxide surface by spontaneous adsorption at pH 7.4. Binding of biotin and an oligopeptide synthesized by means of combinatorial chemistry were monitored with an in situ null ellipsometer. Measurements were also done with hydroxy-azobenzene-2-carboxylic acid and DL-6-8-thioctic acid amide. The performance of porous silicon dioxide as a potential surface in biosensor applications was compared with a planar silicon dioxide surface. Porous silicon dioxide showed a 10-fold amplification of the response compared to planar silicon dioxide. It was possible to monitor the binding of biotin and the oligopeptide in the concentration range 2-40 microM. A response time as low as 30 s was obtained for the oligopeptide at 40 microM.

A multisensor array for visualizing continuous state transitions in biopharmaceutical processes using principal component analysis.

An array of sensors with varying sensitivities, a so-called multisensor array, has been used for monitoring the growth and production states of biopharmaceutical processes. The sensor array produced continuous and characteristic response patterns from the processes due to the differences of the sensors. By analysing these patterns with the multivariate method principal component analysis, the state as well as the change of state of the bioprocesses could be visualized. The sensors used in the array were well-known semiconductor and optical gas sensors and the array was connected in an on-line set-up to the bioreactor's headspace effluent. The sensor array was applied to the monitoring of two recombinant bioprocesses, the production of human growth hormone in Escherichia coli and human factor VIII in Chinese ovary hamster cells. The sensor array could clearly visualize the characteristic transitions during the main growth or production phases of these two bioprocesses.

Estimation of biomass and specific growth rate in a recombinant Escherichia coli batch cultivation process using a chemical multisensor array.

A chemical multisensor array is used in combination with an artificial neural network to estimate the biomass concentration and specific growth rate in a recombination Escherichia coli batch cultivation. It is shown that by providing sufficient information to the artificial neural network, an accuracy comparable to that of an established dry weight method can be achieved. The obtained prediction error (1 sigma) of 0.043 g l-1 for biomass compares well with the error of the dry weight method in this low biomass concentration range (0.1-3 g l-1). The prediction for the specific growth rate is accurate during important parts of the cell growth (1 sigma = 0.025 h-1). The results show that this non-invasive method is potentially useful for estimating biomass and specific growth rate on-line in bioprocesses.

Sensor fusion with on-line gas emission multisensor arrays and standard process measuring devices in baker's yeast manufacturing process.

The use of a multisensor array for measuring the emission from a production-scale baker's yeast manufacturing process is reported. The sensor array, containing 14 different gas-sensitive semiconductor devices and an infrared gas sensor, was used to monitor the gas emission from a yeast culture bioreactor during fed-batch operation. The signal pattern from the sensors was evaluated in relation to two key process variables, the cell mass and the ethanol concentrations. Fusion with the on-line sensor signals for reactor weight and aeration rate made it possible to estimate cell mass and ethanol concentration using computation with backpropagating artificial neural nets. Identification of process states with the same fusion of sensor signals was realized using principal component analysis. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 427-438, 1997.

A carbohydrate biosensor surface for the detection of uropathogenic bacteria.

We have developed a new surface for use in biosensors that is based on a gold plate covered with a specific carbohydrate receptor structure. The carbohydrate, Gal alpha 1-4Gal, was bound covalently via a thioalkylcarboxy-spacer, or adsorbed as a neoglycoprotein, to a two-dimensional gold surface. Both types of surfaces showed high specificity in the binding of the uropathogenic bacteria P-fimbriated Escherichia coli compared to the binding of non-infectious bacteria. The signal to noise ratio is sufficiently high to allow specific detection of the bacteria in biosensor applications.

Immobilization of pyranose oxidase (Phanerochaete chrysosporium): characterization of the enzymic properties.

Immobilization of pyranose oxidase (E.C.1.1.3.10) from Phanerochaete chrysosporium is described. The enzyme was bound to a glass-beaded support according to the glutardialdehyde, diazo, and carbodiimide methods with activity yields of 10%-23.3%. Characterization of the enzyme immobilized with the glutardialdehyde showed enhanced operational, storage, and temperature stability. The temperature optimum remained unchanged, but the pH optimum was slightly altered. Kinetic properties and the relative substrate specificities for glucose and xylose showed certain differences.

Ellipsometric studies of plasma protein adsorption on membrane polymers for blood purification.

Description of ellipsometric studies on absorption of the human plasma proteins; albumin (HSA), immunoglobulin G (IgG) and fibrinogen (FGN) to polymer surfaces of polyamide, polysulphone, polyetherpolycarbonate and polyacrylonitrile copolymer. Thin layers of the polymers (20-30 nm) were cast onto silicon dioxide/silicon wafers by a spin-coating procedure. The variations observed in surface concentration and adsorption time of the proteins were significant in all four polymers investigated.

Controlling fermentation of lignocellulose hydrolysates in a continuous hollow-fiber reactor using biosensors.

Fermentation of lignocellulose hydrolysates as spent sulfite liquor or as hydrolysate from sulfur-dioxide-treated wood to ethanol has been controlled by using biosensors for glucose and ethanol. Yield and productivity were studied with respect to concentration level of the metabolites in a continuous hollow-fiber reactor. High constant yield was achieved by controlling the glucose to low concentration levels. Reduced productivity were obtained when fermenting at high ethanol concentrations as an effect of inhibition of the yeast cells. The observations emphasize the advantage of controlling the process to favorable concentrations of monosaccharides and ethanol.

Detection of biospecific interactions using amplified ellipsometry.

Amplified detection of biomolecules and biological interactions using an optical surface technique, ellipsometry, is demonstrated for two biosystems--immunoglobulin G with anti-immunoglobulin G (IgG) and the lectin concanavalin A (Con A) with yeast cells. In order to improve the sensitivity of the ellipsometer signal, an amplifier conjugate is formed by binding the affinity ligand to a 12-nm silica particle which is readily detected by the ellipsometer. Thus by using conjugates of IgG-silica and Con A-silica, amplifications of five to seven times have been obtained enabling detection of less than 20 pg/mm2 of biomolecular material.

Kinetic models for enzymic cellulose degradation in aqueous two-phase systems.

Cellulose materials can readily be degraded into cellobiose and glucose by hydrolysis of the enzymes cellulase and beta-glucosidase in aqueous media. Product inhibition does, however, retard the reaction rate and reduce productivity. This may be avoided by carrying out the degradation of cellulose in an aqueous two-phase system, which permits the enzymes and the substrate to be partitioned to one phase and the products to be extracted into a second phase. In addition, two-phase systems also allow recycling of the enzymes. Here, three models previously developed for "one-phase" enzymic degradation are compared to data from enzymic degradation in an aqueous two-phase system. The models tested agreed relatively well with batch experiments during a period of 200 h. For one of the models tested, continuous degradation also gave accurate agreement.