Gill, Andrew; (1997) The evaluation of an optical biosensor for at-line monitoring and control of a bioprocess. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The evaluation of an optical biosensor to produce real-time data regarding the specific product of interest, which may ultimately permit feed-back control, is discussed. Improvement in the understanding of many bioprocess operations may benefit greatly from the availability of such data. The ability to make control decisions based upon specific product data could lead to increased levels of productivity and sample integrity. The optical biosensor, which utilises a resonant mirror to monitor biomolecular interactions, was configured to permit the monitoring of the recombinant antibody fragment, D1.3 Fv. The Fv fragment is derived from the monoclonal D1.3, which is specific for hen egg lysozyme (HEL) and is able to discriminate turkey egg lysozyme (TEL). During operation both HEL and TEL were immobilised to the surfaces of two biosensor devices, permitting their use to monitor D1.3 Fv during its expression by Escherichia coli. It was demonstrated that HEL provided specific data, whilst TEL provided an appropriate control response. The combined response towards each surface permitted quantification of D1.3 Fv within fermenter broths. Analysis of biosensor data, which had traditionally been performed as an off-line process using either exponential curve fitting or linearisation routines (derivative analysis) to determine the kinetic constants describing the biomolecular interaction under investigation, was shown to be too cumbersome where data was required in real-time. An alternative analytical method based on linear regression of the initial binding curve data was developed, which has been demonstrated off-line, to produce analytical results from biosensor data typically less than 5 seconds after sample addition. Using the routine based upon linear regression the dynamic response of the sensor for purified D1.3 Fv was shown to cover the range 0.2 to 150 μg mL -1, which encompasses the total bioprocess for the production of D 1.3 Fv. The sensor has been demonstrated to provide specific product data during the course of fermentation, indicating the presence of product and permitting the production of a profile depicting the onset of product formation as well the maximum titre. Based upon such data decisions regarding the fate of the fermentation may be taken, for example indicating the optimal point to harvest in order to achieve maximum yields. Preliminary data also indicate the potential of the sensor to monitor the purification of D1.3 Fv by immuno-affinity chromatography. Highlighting such events as column saturation and indicating product location within the eluted fractions.

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