Microfluidic devices have been wide applied in biochemical detection, medical analysis and material synthesis, etc. In these on-chip operations, sample concentration is essential for improving reaction efficiency and reducing reaction time. Evaporation induced concentration is simple and efficient for various types of samples. However, the closed microfluidic chambers severely hinder the vapor discharge therefore limit the on-chip application scenario of the evaporation-based concentration. Moreover, the instability of the gas-liquid interface during the evaporation process strongly disturbs the flow and fluid control in the microfluidic structures. Here we designed a microfluidic evaporator with porous photothermal evaporation layer for sample concentration. By utilizing a porous structure with photothermal conversion ability, high-efficient evaporation can be achieved and the disturbance of the flow stability can be minimized during the phase change process. Effects of the hydrophilicity of porous layer, light intensity and solution flow rate were investigated. The concentration rate could be regulated by changing the light intensity and the solution flow rate. The designed microfluidic evaporator exhibited efficient concentration performance with low selectivity for different sample types. We believe this design has a great potential to be applied in other microfluidic platforms as integrated front-end unit or directly end-use purpose.

microfluidics,photothermal,evaporation,porous layer,two phase flow