Disposable plastic flowcell keeps maintenance easy

Edited by the Engineeringtalk editorial team Oct 18, 2001

A major upgrade of the biological detection system manufactured by Biotrace International features a single, disposable plastic flowcell manufactured under contract by Carville

A major upgrade of the biological detection system manufactured by Biotrace International for the Chemical and Biological Defence Establishment, Porton Down, has resulted in a drastic reduction in instrument cleaning time from several hours to a couple of minutes, so minimising system downtime.

For military applications the frequency of cleaning can be as often as once a day, so labour savings are considerable.

The system, a joint MOD/Biotrace development, has now been adapted for commercial applications, mainly in the food and health industries.

Key to the success of the new design was the replacement of the previous fixed fluidics module comprising a stainless steel block sealed at either side by glass plates, a construction that was time consuming to strip down for cleaning.

In its place is a single, disposable plastic flowcell manufactured under contract by Carville, Dorking.

The principle of operation, before and now, is to extract a liquid sample from the test site and combine it with an enzyme that reacts with adenosine tri-phosphate, a substance present in all living organisms, to generate light.

Photomultiplier tubes detect the light and warn of the presence of biological matter in the sample.

The input to the flowcell may originate either from a liquid sample or from a large, on-line flow of ambient air, the latter being the variant developed for military use.

"We knew that to make the flowcell a one-piece unit was going to be challenging," said Gethin Jones, Instrument Design Manager at the Biotrace production facility in Bridgend.

"The 26mm diameter unit needed to be optically clear, chemically inert and water tight, and the internal zigzag pipework had to be bonded to microbore Teflon tubing at the two inlets and single outlet.

We initially experimented with moulded plastic parts, but it soon became apparent that we needed something more specialised." Contact was made with Carville, a company which pioneered diffusion bonding of plastics in 1983 and continues to be the leading practitioner worldwide.

Multiple blocks of machined plastic, usually acrylic, are fused together to produce complex modules, sometimes also containing encapsulated components, for fluid management applications.

With this technique there is no use of adhesives or cement which could corrupt the samples under analysis.

Biotrace and Carville worked together on the flowcell design, which not only uses the diffusion bonding process but also a newly developed technique for bonding the Teflon tubing into the acrylic cell body.

"Prototypes were then produced which worked exceptionally well", continued Mr Jones.

An order was then placed on Carville to manufacture several hundred complete sets of machined parts for the new Biotrace Biological Detection System, including not only the flowcells but also micro-flow pump assemblies, the manufacturing standard of which was also excellent, according to Mr Jones.

He concluded, "Normally improved functionality and quality come with a cost penalty, but Carville's production processes actually resulted in a 50 per cent cost saving for these elements of the instrument." Biotrace International Plc is a world leader in the development, manufacture and supply of equipment for hygiene testing and microbial detection in food, industrial and environmental markets.

Its Civil Defence and Military Division started supplying the original design of biological detection system to Porton Down during the Gulf War in 1991, since which time sales have steadily increased, reflecting the growing need to safeguard against the threat of biological warfare.

In view of recent world events, that need has never been greater and sales are likely to rise substantially in the coming years.

In parallel, the commercial applications are set to grow rapidly as well.

Biotrace is currently negotiating with the Department of Health to apply the on-line version of the instrument to minimise secondary infections by checking the sanitisation level of the air in hospital operating theatres.

This could be achieved by continuously sampling the flow from the air conditioning system outlets.

Another commercial application of the on-line instrument in the food industry is to check in real time the biological loading of flushing water from cleaning-in-place systems so that the optimum amount of cleaning takes place.