A single disposable plastic fluidic cell from Carville is replacing difficult to clean steel and glass units in a biological detection system at Porton Down
Improved biological detector A single disposable plastic fluidic
cell is replacing difficult to clean steel and glass units in a
biological detection system at Porton Down 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.
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
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
"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.
"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.
blocks of machined plastic, usually acrylic, are fused together
to produce complex modules, sometimes also containing
encapsulated components, for fluid management applications.
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 given to
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.
Gethin Jones concluded, "Normally improved functionality and
quality come with a cost penalty, but Carville's production
processes actually resulted in a 50% cost saving for these
elements of the instrument." Biotrace International 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
In view of recent world events, that need has never been
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