purified, 20μL is removed and added to each of the two test reagents. The results
can then be obtained by measuring the absorbance of the solution.
As shown in Fig.5.10a, the disc architecture of the Direct bilirubin test
requires a blood separation chamber with a DF valve (DF1). This valve leads
to two metering structures which are also sealed by DF valves (DF2 and DF3); a
waste chamber is included to collect unneeded plasma that overflows from the
metering chamber. Each Metering chamber is connected to an individual reaction
chamber through DF valves. Prior to running the centrifugal platform, the blood
sample must be loaded into the separation chamber through the openings
described as Air Vents in Fig.5.10a, the same procedure is used to load a specific
volume of reagent into each of the reagent chambers. Once each chamber is filled
(Fig.5.10b) it is possible to run the test by increasing the spin rate of the disk
separate the blood sample.
Accelerating the spin rate of the disk to 30 Hz causes the heavier red blood cells
to move towards the edge of the disc without creating enough pressure to burst the
connected DF valve (Fig.5.10c). After the red blood cells have settled further out
then the radial distance of the connecting DF valve (DF1), the disk can be accel-
erated to the burst frequency of DF1. Upon dissolution of the DF film liquid is
released and fills each metering chamber with the excess flowing into the overflow/
waste chamber (Fig.5.10d). This step eventually leaves the required volume of
20 μL for each test ready to be added to the reaction chamber (Fig.5.11).
Once all liquid has settled in the appropriate chambers (Fig.5.10d) the spin rate
of the disk can be increases to the burst frequency of DF valves 2 and 3, this releases
the liquid in the above metering chambers and allows it to pass into the reagent
chambers. At this point the plasma can react with the preloaded reagents to form a
measurable signal which can be measure on disk or if necessary off disk
(Fig.5.10f).
Fig. 5.10 Schematic
Diagram of Liquid
Handling Protocol
5 The Centrifugal Microfluidic: Lab-on-a-Disc Platform 131