Using Fluorescence-Based Sensing to Accelerate Process Development - A prove-free system monitors accurately at very small scale - BioPharm International

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Using Fluorescence-Based Sensing to Accelerate Process Development
A prove-free system monitors accurately at very small scale


BioPharm International
Volume 22, Issue 6

Robustness was initially not the only drawback to the technology—equally important was instrument cost. The original prototype instruments used lasers as an excitation source and were consequently financially unsuitable for practical applications. The use of high-intensity LEDs for excitation, which have in the last years dropped in price to a couple of dollars, together with efficient optical and electronic designs, addresses that problem: fluorescence-based sensors are potentially cheaper than conventional probes. Much has been done on the design of a new generation of sensing patches that can be demonstrated to not leach into the culture media or otherwise affect the growing cells.

Even with all of these advances, the technology still has a potential disadvantage in that the sensing patches are subject to photobleaching over time. Because of improved formulations which greatly increase the lifetime of the patches, and the use of phase shift or ratiometric measurements, the sensor's measurements are immune to changes in the patch response caused by photobleaching, except after long-term use. In such a case, the signal to noise ratio drops with time until the measured signals become noisy and less accurate after an excessive number of measurements. Because the effective lifetime of the sensing patch is measured in tens of thousands of readings, this is a problem only with very long processes monitored at frequent intervals (seconds versus minutes or hours). Even in this case, an easy solution exists: a vessel can be equipped with two or more patches in place of a single patch and the sensing head can be moved to a fresh patch whenever the measurements start to become noisy. In this way, processes of arbitrary duration can be monitored with no loss of accuracy and no drift over time.

CONCLUSIONS

As the need for more cost-effective and rapid development of drugs and other bioprocess-related products increases, so does the tolerance for new technologies and approaches in what has been a rather conservative industry. Fluorescence-based sensing technologies, which can greatly decrease overall development time, labor, and costs, become an increasingly useful tool, particularly because their use permits a degree of miniaturization, scalability, and multiplexing previously unavailable. Although there are limitations, particularly in patch development, continued development and maturation in this area holds great promise for the development of a widespread paradigm-shifting technology in the near future.

Joe Qualitz is the president and CEO of Fluorometrix Corporation, Stow, MA, 978.461.2468,

REFERENCES

1. Rao G, Moreira A, Brorson K. Disposable bioprocessing: the future has arrived. Biotechnol Bioeng. 2009 Feb:102(2)348–56.

2. Rao G, et al. Noninvasive sensors as enablers of "smart" disposables. BioProc Int. 2009 Jan;26–9.

3. Kroneis HW, Marsoner HJ. A fluorescence-based sterilizable oxygen probe for use in bioreactor. Sens. Actuators. 1983:(4)587–92.

4. Xudong Ge X, Hanson M, Kostov Y, Moreira AR, Rao G. 2006. Validation of an optical sensor-based high-throughput bioreactor system for mammalian cell culture. J Biotechnol. 2006:122(3):293–306.


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