the above layers to those below as well as creating access points for the fluid to come
in contact with the dissolvable tabs contained within the DF support layer.
7.5 DF Support (PSA)
This layer contains the dissolvable film tabs which restrict the movement of fluid by
creating a build-up of pressure as the fluid approaches the tab, this resistance to fluid
movement can be overcome by increasing the spin rate of the disc thereby allowing
release of connected fluid reservoirs. Through cuts were also created to allow the
passage of fluid back towards the upper microchannels once valves were burst.
7.6 Mid-Layer (PMMA)
Through channels were cut in a layer of PMMA to allow the movement of fluid
between layers in both directions, this layer also forms a support structure and seal
for the layers above and below.
7.7 Lower Channels (PSA)
Similar to the microchannel layer the final layer of PSA allows fluid movement
connecting the above valves to further microchannels.
7.8 Base Layer (PMMA)
A final PMMA seal is used to complete the structure.
7.9 Testing
Once fabrication and assembly are complete the Lab-on-a-disk design requires
testing to ensure that all unit operations (Valving, Metering, routing, etc.) work
correctly, this is done using the custom spin stand described above in Fig.5.7.To
test the Lab-on-a-disk design, the reagents intended for use are replaced with water
coloured with food dye so that the movement of fluid around the disk can be more
easily visualised against the white background of the disk. The spin rate of the disk
can be controlled manually to assess the specific burst frequency’s required, if the
140 B. Henderson et al.