The present invention relates to devices for handling liquid, in particular but not exclusively to distributing and metering liquids, more particularly in a microfluidic device such as a “lab on a disc” device.
Distributing and metering defined volumes of liquid (aliquots) is an essential step in many analytic and diagnostic procedures and constitutes an important unit operation for “lab on a disc” or other microfluidic platforms. In particular for point of care applications, it is desirable for aliquoting to be fast so that the overall processing time of the sample can be kept low.
An example of an aliquoting structure for metering a liquid into a plurality of aliquots is disclosed in U.S. Pat. No. 7,275,858 to Anderson et al. Anderson et al. disclose a centrifugal microfluidic, “lab on a disc”, device with an aliquoting structure. The aliquoting structure has an inlet port, and outlet port and a plurality of aliquoting volumes in between, defined either by a meandering conduit or by a series of microcavities extending from a common continuous microconduit between the inlet and outlet ports. At an extremity of each meander bend or microcavity, an outlet opening is provided with a valve which provides a surface tension barrier to liquid flow. The barrier can be overcome by a centrifugal force due to rotation of the device. The inlet and outlet ports to the microconduit are positioned such that the device is filled by capillary action drawing liquid from the inlet port to the outlet port, filling the meandering bends or microcavities in the process. Devices like those disclosed in Anderson et al have drawbacks, in particular in point of care applications, in that the capillary effect or surface tension driven filling of the aliquoting structure is comparatively slow to the subsequent centrifugally driven distribution of liquid, adding to the overall processing time. Further, since the aliquots are maintained in their respective chamber by a surface tension barrier which is overcome by centrifugal force, the range of rotation speeds achievable with the device while the aliquots are filled and to be maintained within the respective chambers is limited to the burst frequency of the barrier at which the centrifugal force overcomes the surface tension barrier. Thus, the range of operations which can be carried out between filling of the aliquoting structure and dispensing of the aliquots is limited.