A direct heating model to overcome the edge effect in microplates

•Microplates are most widely used in analytical research and diagnostic screening.•No studies to understand or remedy the edge effect by temperature gradients known.•Parameters that cause evaporation rate to increase with temperature identified here.•Heat conduction of the side walls was found responsible for the temperature gradients.•Transparency microplates have inherent immunity to the edge effect problem. Array-based tests in a microplate format are complicated by the regional variation in results of the outer against the inner wells of the plate. Analysis of the evaporation mechanics of sessile drops showed that evaporation rate increase with temperature was due to changes in the heat of vaporization, density and diffusion coefficient. In simulations of direct bottom heating of standard microplates, considerable heat transfer via conduction from the side walls was found to be responsible for lower temperatures in the liquid in wells close to the edge. Applying a two temperature heating mode, 304K at the side compared to 310K at the bottom, allowed for a more uniform temperature distribution. Transparency microplates were found to inherently possess immunity to the edge effect problem due to the presence of air between the liquid and solid wall.