Light-Fueled Beating Coffee-Ring Deposition for Droplet Evaporative Crystallization.

Condensed deposition favors biochemical analysis, bioassays, and clinical diagnosis, but the existing strategies may suffer from low resolution, inaccurate control, cross-contamination, or miscellaneous apparatus. Herein, we propose a noncontact light strategy to enable the condensed deposition for droplet evaporative crystallization, in which the photothermal effect of a focused infrared laser is employed to induce intense evaporation. Due to the localized heating effect, not only can the droplet evaporative crystallization on the hydrophobic substrate be promoted, but also the resultant intensified Marangoni flow enables the movement of the early-formed crystals, preventing the pinning of the triple-phase contact line. Synergy of the Marangoni flow and nonuniform evaporation makes the solutes tend to accumulate near the focused light beam region, which facilitates the condensed deposition. More importantly, this light strategy not only enables condensed deposition on the hydrophobic surface with low hysteresis, but also works successfully on the hydrophilic substrate with high hysteresis via adjusting input laser power. It is demonstrated that the light strategy proposed in the present study has great potential for relevant applications.