Yen Tony M, Fu Xin, Wei Tao, Nayak Roshan U, Shi Yuesong, Lo Yu-Hwa
Department of Bioengineering, University of California San Diego, La Jolla, CA, 92093-0412, United States.
Chemical Engineering Program, University of California San Diego, La Jolla, California, 92093-0448, United States.
Sci Rep. 2018 Feb 16;8(1):3157. doi: 10.1038/s41598-018-20581-0.
The coffee-ring effect, ubiquitously present in the drying process of aqueous droplets, impedes the performance of a myriad of applications involving precipitation of particle suspensions in evaporating liquids on solid surfaces, such as liquid biopsy combinational analysis, microarray fabrication, and ink-jet printing, to name a few. We invented the methodology of laser-induced differential evaporation to remove the coffee-ring effect. Without any additives to the liquid or any morphology modifications of the solid surface the liquid rests on, we have eliminated the coffee-ring effect by engineering the liquid evaporation profile with a CO laser irradiating the apex of the droplets. The method of laser-induced differential evaporation transitions particle deposition patterns from coffee-ring patterns to central-peak patterns, bringing all particles (e.g. fluorescent double strand DNAs) in the droplet to a designated area of 100 μm diameter without leaving any stains outside. The technique also moves the drying process from the constant contact radius (CCR) mode to the constant contact angle (CCA) mode. Physical mechanisms of this method were experimentally studied by internal flow tracking and surface evaporation flux mapping, and theoretically investigated by development of an analytical model.
咖啡环效应普遍存在于水滴干燥过程中，会影响众多涉及在固体表面上蒸发液体中颗粒悬浮液沉淀的应用性能，比如液体活检组合分析、微阵列制造和喷墨打印等等。我们发明了激光诱导差分蒸发方法来消除咖啡环效应。在不对液体添加任何添加剂或对液体所放置的固体表面进行任何形态修饰的情况下，我们通过用CO激光照射液滴顶部来设计液体蒸发轮廓，从而消除了咖啡环效应。激光诱导差分蒸发方法将颗粒沉积模式从咖啡环模式转变为中心峰模式，使液滴中的所有颗粒（如荧光双链DNA）都聚集到直径为100μm的指定区域，且不会在外部留下任何污渍。该技术还将干燥过程从恒定接触半径（CCR）模式转变为恒定接触角（CCA）模式。通过内部流动跟踪和表面蒸发通量映射对该方法的物理机制进行了实验研究，并通过建立分析模型进行了理论研究。
