3.2.2 Electromechanical Pumping
Clime et al. created a microfluidic disk with integrated microelectronics responsible
for on-disk pneumatic pumping of liquid through specific chambers [ 25 ]. This
programmable valving system allows the accurate displacement of fluid by
pressurising individual as well as multiple ports of the microfluidic disk. This
system has the advantage of being able to pump liquid towards the centre of
rotation, thereby giving it a clear advantage over conventional microfluidic designs
however its greatest disadvantage is its extensive complexity. The design requires
integrated electronics as well as slip-rings for power transfer to the device, this
novel technology is currently in its infancy however there is need for this degree of
fluid control in the future of centrifugal microfluidics.
4 Valving Design
When developing a new Lab-on-a-disk liquid handling protocol it is necessary to
achieve the simplest and most accurate disk design possible, this requires an
understanding of the proposed assay or biochemical test to be implemented. Timing
of reagent delivery, reagent volumes, incubation times, washes and reagent routing
must be taken into account whilst designing the disk architecture, can these unit
operations be accomplished using passive valving schemes or do they require more
complex integrations. Using passive valving schemes, can the operation be accom-
plished using frequency dependant valving (Siphon, Capillary, Centrifugo-
pneumatic etc.) or should each LUO be triggered by the previous thereby being
independent of the rotational frequency (Paper imbibition, Event Triggered). These
questions will help in making the simplist architecture possible whilst developing a
highly accurate and cost affective Lab-on-a-disk platform.
5 Spin Stand
5.1 Operation
Due to the rapid rate of rotation of microfluidic discs during operation, a special
experimental test rig is used to visualise flow. In particular, this development tool
provides critical feedback to determine if failures occur (due to manufacturing
flaws) and for optimising the fluidic design. This rig is typically referred to as a
‘spin stand’[ 26 ].
Generally, spin stands use a stroboscopic system to visualise a disc during
rotation. Here, a camera and strobe are synchronised such that, as the motor spindle
passes through a particular angular location, a pulse is generated which triggers the
126 B. Henderson et al.