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


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

BioPharm International
Volume 22, Issue 6

An important additional advantage of the technology (particularly in fully instrumented systems) is that sensing electronics are extremely stable, requiring only a yearly measurement of electronic offsets (a procedure that takes less than a minute), thus rendering obsolete the time-consuming calibration procedures required for the proper use of conventional probes. By virtually eliminating calibration, the amount of setup labor required to use these sensors is substantially less than with conventional probes. Moreover, because the electronics are never in contact with the process (only the sensing patches are in contact and, although they can be autoclaved, they are cheap enough to be discarded after each use), there is no need for cleaning and sterilization of sensors between experiments. Again, the savings in time (and thus the savings in labor costs) can be quite substantial.

A final advantage of the fluorescence-based sensors is that they can be readily multiplexed so that one sensor is used to measure process parameters in many vessels. For applications in which measurements need be taken only at infrequent intervals, a sensor can be moved from vessel to vessel to measure a given parameter. In such a case, it is only necessary to provide a sensing patch in each vessel. Because the patches cost only a few dollars each, the use of a single sensing head with multiple patches greatly decreases instrumentation costs.

Conversely, another approach to multiplexing uses robotics, X–Y tables, or rotary tables to carry vessels to fixed sensors. For example, the Fluorometrix CellStation HTBR-1 is a 12-reactor system that uses a rotary table to automatically position, at a programmed interval, each of the 12-reactors over a single fluorescence-based module that measures both pH and DO. The same scheme can be used with well plates and other similar devices. The number of vessels or wells that can be monitored with each fixed sensor depends only on the measurement time (which is generally a few seconds) and the maximum time allowed between readings.


As demonstrated above, the use of fluorescence-based sensors during the screening phases of the bioprocess cycle can greatly reduce the elapsed time required to complete these phases and do so with great savings of labor, media, and even facilities costs. However, the greatest value of the technology is that it provides information about the process that might otherwise have to be determined during later phases of the development cycle. For this reason, its use in the screening application is in keeping with the FDA's Process Analytical Technologies initiative (PAT). The FDA encourages a rather broad application of PAT by defining it as:

"Tools and systems that utilize real-time measurements, or rapid measurements during processing, of evolving quality and performance attributes of in-process materials to provide information to ensure optimal processing to produce final product that consistently conforms to established quality and performance standards."

The ultimate goal of PAT is the realization of measurable process conditions that are linked directly to the quality of the product being developed. The ability to measure viable process conditions during the screening phases of the development cycle provides a wealth of information about these cell growth conditions, and therefore, allows an assessment of how closely process-screening devices can be used to replicate large-scale conditions. This data will provide a smoother transition to large-scale processes, requiring fewer experiments to be done in expensive and relatively labor-intensive bioreactors during the laboratory-scale phases. Also, it should be noted that the use of this sensing technology does not require the purchase of novel and costly systems for the screening phases. The sensors are compatible with the well plates, dishes, and flasks that have traditionally been used in small-scale screening operations, and can be readily used to retrofit existing equipment.

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