An efficient way to pattern biomarkers on glass surfaces for bioassays is to deposit colloidal drops and evaporate them. The remaining deposits, however are not always homogeneous and sometimes exhibit ring-like patterns. In this work, the process of ring-like patterns investigated numerically and experimentally. The numerical modeling accounts for the evaporation of a colloidal nanoliter drop on a solid, non-isothermal substrate. The equations governing fluid, heat and mass transport are expressed in a Lagrangian framework. The diffusion of vapor in the gas surrounding the drop is solved numerically and depends on the drop-substrate geometry and thermodynamic conditions. Numerical results predict a radial flow pattern, as well as the formation of multiple rings. Experimental results are presented for the evaporation of nanoliter water drops with a low concentration of polymer microspheres on glass and PDMS substrates. Different deposit patterns are observed, such as a peripheral ring on glass and a uniform deposit on PDMS, which is modeled and explained by the influence of wetting angle on evaporation and by the attraction forces [1] between the particles and PDMS substrate.

[1] L. V. Andreeva, A. V. Koshkin, P. V. Lebedev-Stepanov, A N Petrov, and M. V. Alfimov, "Driving forces of the solute self-organization in an evaporating liquid droplet," Colloids and Surfaces A: Physicochem. Eng. Aspects, vol. 300, pp. 300-306, 2007.