High Resolution Level Sensors for Harsh Environments

In this paper a new sensor detecting fluidic levels of electrolytes in capillary microfluidic systems is presented. The sensor uses two different and independent working principles. 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 measures the analog, continuous position of the meniscus. Due to the design there is no need to calibrate any of the two working principles for detecting diverse electrolytes and the relative signal level swing is greater than two orders of magnitude for each principle. This high relative signal level swing makes it possible to resolve positions of menisci with submicron accuracy and in suitable reservoirs the stored volume can be resolved in the subnanoliter range. The sensor can withstand harsh environments (pH 1 to pH 9) for at least ten years.