Analytica Chimica Acta 590 (2007) 110–117 Multiplexing fibre optic near infrared (NIR) spectroscopy as an emerging technology to monitor industrial bioprocesses Payal Roychoudhury a , Ronan O’Kennedy b , Brian McNeil a,∗ , Linda M. Harvey a a Strathclyde Fermentation Centre, Institute of Pharmacy & Biomedical Science, University of Strathclyde, Glasgow G1 1XW, UK b BioPharmCEDD, GlaxoSmithKline, Beckenham BR3 3BS, Kent, UK Received 15 January 2007; received in revised form 1 March 2007; accepted 4 March 2007 Available online 12 March 2007 Abstract The application of near infrared spectroscopy in bioprocessing has been limited by its dependence on calibrations derived from single bioreactor at a given time. Here, we propose a multiplexed calibration technique which allows calibrations to be built from multiple bioreactors run in parallel. This gives the flexibility to monitor multiple vessels and facilitates calibration model transfer between bioreactors. Models have been developed for the two key analytes: glucose and lactate using Chinese hamster ovary (CHO) cell lines and using analyte specific information obtained from the feasibility studies. We observe slight model degradation for the multiplexed models in comparison to the conventional (single probe) models, decrease in r 2 values from 89.4% to 88% for glucose whereas for lactate from 92% to 91.8% and a simultaneous increase in the number of factors as the model incorporates the inter-probe variability, nevertheless the models were fit for purpose. The results of this particular application of implementing multiplexed-NIRS to monitor multiple bioreactor vessels are very encouraging, as successful models have been built on-line and validated externally, which proffers the prospect of reducing timelines in monitoring the vessels considerably, and in turn, providing improved control. © 2007 Elsevier B.V. All rights reserved. Keywords: Near infrared spectroscopy; Multiplexed calibration; Chinese hamster ovary; On-line 1. Introduction Monoclonal antibodies (MAbs) are key biopharmaceutical products which represent a significant proportion of the current business focus and generate revenues of £3 billion per annum [1]. As with many other biologically derived products, the main production step relies on an engineered cell line being grown in bioreactors with the aim of expressing the required product in large volume. One key characteristic of recombinant derived biopharmaceutical like MAbs is that most product yield and product quality attributes are set during the “manufacturing” within the recombinant cell host [2] and these characteristics are a function of the host cell genetics and physiological response to the large scale culture environment. Existing invasive sensor technologies have a number of disadvantages with respect to implementation in large-scale mammalian cell culture, even though many of the technologies are based on “primary” or direct sensing methods. Existing tech- ∗ Corresponding author. Tel.: +44 141 548 4379; fax: +44 141 553 4124. E-mail address: b.mcneil@strath.ac.uk (B. McNeil). nology, such as automated glucose/metabolite analysers, rely on removal of a clarified sample by filtration. Although these filtra- tion devices are capable of aseptic removal, they are considered as an increased contamination risk, therefore, have restricted application in large scale and commercial mammalian cell cul- ture processes. Moreover, although only small volumes are used for analysis, the process requires considerable volumes to be removed to purge the sample lines; this may not be an issue at pilot scale processes, but in small scale vessels restriction on the maximum volume which can be sampled has limited the sensors utility. Ideally, process monitoring sensors should be suitable for use at all culture volumes: small scale, pilot and commer- cial scale fermentations. The technology should be robust and non-invasive, be dependable and not a potential risk to the pro- cess asepsis. Additionally, the sensor should be multiplexible, enabling multiple bioreactors to be monitored simultaneously (particularly in development). The sensors should also be capa- ble of measuring a number of cell culture parameters, such as cell density, culture viability, glucose, lactate, glutamine, gluta- mate and ammonia, which are critical in making process specific decisions. 0003-2670/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.aca.2007.03.011