Measuring liquid evaporation from micromachined wells

The evaporation process of liquids from sub-nanoliter wells is studied usin g both optical microscopy and electrical impedance measurement utilizing in tegrated electrodes. The wells are manufactured on silicon wafers using con ventional photolithography and etching techniques. The volumes of the wells vary from 15 to 540 pl. The evaporation rate of glycol from wells of vario us sizes is determined to vary from 0.2 (15-pl well) to 1.7 pl/s (540-pl we ll). 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 metho d 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.