A microfluidic evaporator with a photothermal porous layer for continuous sample concentration

On microfluidic platform, sample concentration plays a crucial role in on-chip detection, analysis and synthesis, etc. Evaporation-induced solvent removal is frequently applied to various application scenarios due to its simplicity and compatibility. However, the enclosed microfluidic channels often hinder the solvent vapor discharge during the evaporation process due to the formation of two-phase flow and interfacial instability. Herein, we propose a novel microfluidic evaporator incorporated with a photothermal porous layer for continuous sample concentration. By absorbing the sample fluid into the porous structure, the evaporator is capable of achieving volumetric heating of the sample fluid thus enhancing the solvent evaporation while the porous network ensured efficient vapor venting. Moreover, the thermal resistance of porous layer shields the heat transfer towards the bulk fluid therefore prevented the sample solution from overheating during the operation process. The results demonstrate the designed microfluidic evaporator exhibits good sample concentration capability under continuous flow conditions.