Abstract
In this paper a new sensor detecting fluidic levels of electrolytes in capillary microfluidic systems is presented. The sensor shown in figure 2 uses two different and independent working principles, that complement one another. On the one hand an array of microelectrodes is used to measure the change in conductance at discrete points during priming. On the other hand a capacitive sensor similar to an electrolytic capacitor measures the analog, continuous position of the meniscus. On account of the difference between and the transient behavior of the two signals, the sensor is also able to detect not simply connected surfaces like liquids afflicted with gaseous bubbles. Due to the special design there is no need to calibrate any of the two working principles for detecting diverse electrolytes and the relative signal deviation is greater than two orders of magnitude for each principle. This high relative signal deviation leads to an outstanding resolution, so that positions of menisci can be resolved with submicron accuracy and in suitable reservoirs the stored volume can be resolved in the subnanoliter range. The appearing capacitances and resistances can easily be evaluated, so that by giving up a part of the high resolution simple and energy optimized drive electronics can be used to read out the sensor. Furthermore it is shown that the sensor can withstand harsh environments (pH 1 to pH 9, particles up to 10μm) for at least ten years.
