David J. Clarke

Development of an On-line Glucose Sensor for Fermentation Monitoring

Abstract A dimethylferrocene-mediated enzyme electrode for glucose (Cass et al., 1984) was evaluated for application to microbial fermentation monitoring and control. The deficiencies revealed - insufficient stability, progressive increase in response time and progressive decrease in linear range - were investigated using electrochemical and radiochemical techniques. The enzyme immobilization was improved with a novel procedure using periodate-oxidized glucose oxidase and an alky lamine electrode coating. An in-situ probe and a computer-controlled analytical system were developed for fermentation monitoring. The glucose concentration of an Escherichia coli batch culture was successfully monitored on line using this analytical system.

The development and application of biosensing devices for bioreactor monitoring and control

Presently, few of the reported (bio)chemical sensor devices have found application in fermentation monitoring and control. Although many devices with desirable selectivities have been reported, few have demonstrated reliability sufficient to encourage significant and widespread application. Chemical sensors (ion-selective electrodes, amperometric detectors, piezoelectric, field-effect transistors, semiconductor, Optrode and optoelectronic sensors), biosensors (based on potentiometric, amperometric, field-effect transistor and conductiometric detectors) and physical detection methods are reviewed with the aim of highlighting the problems of their application in this area. Physical detection principles appear to show promise as reliable and direct monitoring principles. However, even the more reliable discrete (bio)chemical sensor devices require the development of on-line flow sampling and autocalibration methods to demonstrate the necessary reliability. Biosensor devices appear most problematical and it is concluded that continued development of more direct biosensing principles is likely to prove most fruitful.

Monitoring reactor biomass

Abstract Reactor biomass cannot be considered as a single parameter of measurement. The efficacy and analytical information provided by a variety of techniques is considered broadly. The measurement of key parameters (cell concentration, culture viability and contamination) appears best served by physical techniques (acoustic, dielectric and laser light scattering) capable of providing direct, non-invasive monitors.

ESCA investigation of low-temperature ammonia plasma-treated polyethylene substrate for immobilization of protein

A low-temperature radiofrequency plasma excited in anhydrous ammonia was used to modify polyethylene substrate surfaces for covalent immobilization of proteins. Electron spectroscopy for chemical application (ESCA) was used for surface characterization of polyethylene to a depth scale of 7 nm. The data revealed that surface modification is extensive and occurs in seconds at low discharge power. Primary amino functionalities were detected on the polyethylene surface and the level is dependent on plasma parameters. 125I-labelled antibodies covalently attached to amino groups via glutaraldehyde allowed the conditions for optimum level of primary amine to be established. Both ESCA data and protein loadings are in excellent agreement.

Direct monitoring of reactor biomass in fermentation control

Abstract A wide-range, high-resolution method for the determination of microbial mass suitable for real-time monitoring of fermentation systems using the principle of acoustic resonance densitometry is reported. A similar non-invasive technique for the direct analysis of the dielectric properties of high-conductivity microbial suspensions has been made possible by the development of a novel magneto-inductive measurement principle.

Apparatus for the electrical characterisation of conductive fluids

Non-invasive and fully automated conductimetric measurements of electrolyte and bacterial samples were achieved in a closed volume test cell, comprising a magnetic field coil and detector. By monitoring field induced currents in sample electrolytes the magnitude of the sample current was shown to vary as the inverse of the sample impedance. The impedance characteristic was shown to be that of an LCR resonant circuit. This characteristic is primarily a function of the applied frequency and the solution/cell properties being dependent on the solution conductivity and dielectric permittivity at any given concentration. Small changes in sample dielectric permittivity in the presence of a large background conductivity are shown to be significant. The apparatus described can provide fixed or swept frequency conductivity measurements in the range 1 kHz to 2.25 MHz with a lower conductivity sensitivity of 0.9 x 10(-3) Scm-1. Bulk impedimetric characteristics of cell suspensions are derived by a two stage measurement.