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Langmuir, Vol.29, No.2, 849-855, 2013
Surface-Scribed Transparency-Based Microplates
Transparency sheets, which are normally associated with use on overhead projectors, offer lowered costs and high amenability for optical diagnostics in microplate instrumentation. An alternative microplate design in which circles are scribed on the surface of the transparency to create the boundaries to hold the drop in place is investigated here. The 3D profile of the scribed regions obtained optically showed strong likelihood of affecting three-phase contact line interactions. During dispensation, the contact angle (approximate to 95 degrees) was larger than the drop advancing state (approximate to 80 degrees) due to a period of nonadhesion, where the contact angle later reduced to the drop advancing state followed by increase in the liquid area coverage on the substrate. It was established that 50 mu L was needed to fill the well fully, and the maximum volume retainable before breaching was 190 mu L. While the tilt angle needed for displacement reduced significantly from 50 to 95 mu L, this was markedly better than nonscribed surfaces, where tilt angles always had to be kept to within 30 degrees. It was found that there was greater ability to fill the well with smaller volumes with dispensation at the center. This was attributed to the growing contact line not meeting the scribed edge in parallel if liquid was dispensed closer to it, wherein pinning reduction in some directions permitted liquid travel along the scribed edge to undergo contact angle hysteresis. Fluorescence measurements conducted showed no performance compromise when using scribed transparency microplates over standard microplates.