Measuring liquid evaporation from micromachined wells

The evaporation process of liquids from sub-nanoliter wells is studied using both optical microscopy and electrical impedance measurement utilizing integrated electrodes. The wells are manufactured on silicon wafers using conventional photolithography and etching techniques. The volumes of the wells vary from 15 to 540 pl. The evaporation rate of glycol from wells of various sizes is determined to vary from 0.2 (15-pl well) to 1.7 pl/s (540-pl well). Measurements show that the evaporation rate of glycol depends linearly on the weil width. not on the well surface area. The impedance measurement between two integrated electrodes located in the well is an accurate method for monitoring the liquid evaporation in sub-nanoliter wells, and can be applied in automated high-speed screening (HSS) systems. (C) 2000 Elsevier Science S.A. All rights reserved.