Robert Jeffrey Geddes Carr

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.

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.

Determination of protein size in chromatography column eluants by on-line photon correlation spectroscopy

The dynamic light scattering technique of photon correlation spectroscopy has been used to determine biomacromolecule hydrodynamic radius in solutions flowing at rates similar to those experienced in liquid chromatographic separation systems. Such analyses can be performed rapidly (less than 5 s). The potential of the technique as an on-line noninvasive monitor for liquid chromatography is discussed.

A twin-beam fibre optic laser light scattering system

A simple remote sensing single-particle detection system is described which uses light scattering to determine the size and concentration of scatterers. They report the initial results obtained from the system. A dual wavelength conformation consisting of an inner trigger beam and outer analysis beam is used to eliminate edge effects of the Gaussian profile of the laser beam. This is achieved without the use of complicated optics, by employing an optical fibre and a chromatically dispersive gradient index (GRIN) rod lens to give the correct optical configuration in the scattering volume.

On-line photon correlation spectroscopy using fibre-optic probes

The authors describe the design and construction of a fibre-optic probe for on-line photon correlation spectroscopy measurements. Two such probes, one acting as a launch and the other collecting scattered light, have been used to measure the size of proteins in the eluant of a gel permeation liquid chromatography column. The fibre-optic probe, when compared with conventional bulk optics, has the advantage of small size, ease of alignment and remote operation.

Diffusing wave spectroscopy

A method of measuring the sphere equivalent hydrodynamic radius in highly concentrated suspensions is reported. Results showing the system to be concentration independent are given. The effects of polarization and the use of high birefringence fibers are discussed and shown to be important. The possibility of independence to fluid flow and the monitoring of the enhanced backscatter cone to given information on structure are considered. The equipment allows the use of a dip in probe and laser powers of only 1 mW are required.

Novel biosensor for the real-time study of cell movement

Cell movement is vital to normal tissue growth and regulation. Although not often realized, cells are continually moving relative to each other, and many physically migrating from their original site. Blood and immune cells rely on migrating through other tissues to perform their function. Cell division also needs physical separation of daughter cells, and other cells, e.g. muscle cells have developed their mechanical machinery to perfection. Substrate interactions are complicated. The ability to migrate and stop migrating when needed is a vital part of tissue regeneration. Understanding cell migration and movement is very important to being able to discover how cancer cells are able to continue dividing and why they abnormally migrate. Much other work has established that cells contact substrates through specific attachment points, but it is almost impossible to visualize these in three dimensions since cell cytoplasm is translucent and resolution limited by wavelength of light. We have developed a small senor device of a metalized glass substrate on which we have electron beam lithographically produced arrays of sub-micron circular apertures. A surface plasmon resonance (SPR) wave is set up in the metal by excitation with an incident laser beam. The circular apertures act as discrete centers of optical scattering of the SPR wave and the associated light emanating from these points can be detected and studied using an associated image analysis system. The intensity of the light scattered from each of these apertures is a strong (exponential) function of the changes of local refractive index close to (within 250 nm) the aperture. The contact of the underside of the cell with the aperture bearding surface modulates the intensity pattern of the aperture matrix allowing high resolution of the spatial distribution of the contact points between the cell and the metalized surface.

Submicron optical sources for single macromolecule detection

Nanobit holographic techniques, such as high-energy electron beam lithography, allow apertures of < 50 nm diam. to be fabricated in the metal coating of SPR sensor devices. When the SPR slab waveguide is edge illuminated with a laser, the apertures act as intense scattering centers of the underlying radiation, the scattered light from which is readily detectable by conventional optical microscopy. Given the dimensions of these sub-wavelength optical sources are within an order of magnitude of those of individual biological macromolecules, it should ultimately prove possible to detect interactions between substrate/analyte and individual (labelled) biological macromolecules immobilized in the apertures. The possibility of analyzing the dynamic behavior of single biomacromolecules operating in their natural environment is discussed.