Biosensors are used for the detection of molecules in biological samples, for instance proteins or DNA for diagnostic applications. It is also desired to detect drugs, therapeutic or abuse, in blood, urine or saliva. Such tests are developed to be used in many different settings and surroundings, e.g. at the point of care for medical applications, or at any desired place for drugs of abuse, e.g. at the roadside. In all cases a robust, reliable and sensitive device is required, which must also be low cost since it needs to be disposed after the measurement.
Carrying out such a biochemical assay requires a certain degree of fluid handling, at least the sample fluid must be introduced in the sensing device in order to allow binding of the target molecules to the sensor surface. Depending on the kind of assay more or less complicated microfluidic systems are designed. Since the sample is contaminating it must not get in contact with the instrument and must be stored safely inside the cartridge during and after the measurement.
Recently fully integrated micro fluidic on chip biochemical systems or lab on a chip systems have been developed. An issue in these micro fluidic systems is the manipulation of the fluids from and to the different reaction chambers, for which micro actuators such as pumps and valves are needed. Pumping and valving can be done in numerous ways. Depending on the application, for example type of assay, performance requirements, and cost requirements, the actuation of the fluid for dissolution of reagents, incubation, binding and washing, as an example, is implemented in different ways. There is a trade-off between the degree of control and simplicity, wherein simplicity can be identified with low costs. Either the fluid is actuated directly by mechanical metering with pistons or the fluid is not actuated but driven by capillary forces, so-called passive driving.
The latter is a cost-effective solution but does not allow for flow reversal, the flow rate is limited and not constant with distance and most importantly depending on the viscosity and surface tension of the fluid. A change in the required flow characteristics needs to be implemented in ‘hardware’ on the disposable which makes the system less flexible. Mechanical driving on the other hand is very flexible but requires physical contact which creates problems with operational lifetime of the instrument and contamination i.e. cleaning problems.
Therefore there may be a need for an alternative low-cost fluid actuation technology in microfluidic systems in particular for medical disposables, like biosensors.