Capacitive liquid level
detection A weak electrical potential is created between the
pipetting channel and the labware carrier. When using conductive tips
(black) and an ionic liquid the capacitance of the circuit is measured.
From this data the software can determine the hieght of the
liquid surface and take appropriate action.
Pressure liquid level
detection A pressure transducer inside the air
displacement channel measures the pressure inside the barrel during
pipetting. The data from this sensor changes as the tip approaches the
liquid surface, touches the surface and drives below. This data can be
used to control pipetting in real-time. Pressure level sensing is the
only way to determine the level of non-ionic liquids.
Key to Claros's device is its ability to perform the test on a small
drop of blood. The surface of the cartridge is covered in narrow
channels, which serve as both storage for the chemicals needed for the
assay and as tiny test tubes in which to carry out the reaction. Each
reagent is lined up sequentially in one long channel and separated by
small air bubbles. Once the cartridge is inserted into the reader, a
vacuum pulls the blood through one channel and delivers the appropriate
sequence of reagents. This approach avoids the pumps used to move
chemicals in other microfluidics chips, enabling a simple and robust
design with no moving parts. The reader itself is simple, using an LED
and photodiode to detect the buildup of silver--the output of the
reaction--on the cartridge. The more silver, the less light passes
through the chip and the higher the PSA level.