An integrated electronic meniscus sensor for measurement of evaporative flow

Abstract This paper presents an electronic sensor of the meniscus height at the outlet of an open micro-well. It is shown that it can be used to compute the average velocity of the flow induced by evaporation. The sensor is built using a technology for bio-medical micro-devices based on Printed Circuit Board (PCB) manufacturing to allow future integration of it in biochips composed of large arrays of microfluidic channels for parallel bioassays. The sensor consists of two aluminium electrodes located at the top of the micro-well and used to measure the impedance between them. A correlation between the impedance and the meniscus height h is demonstrated. A second correlation between h and the rate of the evaporative flow E R is investigated through optical inspection at different temperatures. Combining these two results we obtained average flow rates from 0.5 to 1 μm/s at room temperature and 33% relative humidity. Such a sensor could find an application in open microfluidics systems where the flow induced by evaporation counteracts the gravitational fall of particles of biological interest.