# US 2019/0314872 A1 · Reversing coffee-ring effect by laser-induced differential evaporation > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2019/0314872 A1 - Document ID: US20190314872A1 - Status: Published application - Kind: A1 - Application number: 16/383,059 - Filed: 2019-04-12 - Published: 2019-10-17 - Earliest claimed: 2018-04-12 - Assignees: The Regents of the University of California - Applicants: The Regents of the University of California - Inventors: Yu-Hwa Lo; Tony Minghung Yen - Web page: https://patentgrep.com/patent/US20190314872A1 ## CPC - B08B 7/0042: {by laser} - B01D 1/0029: {Use of radiation} - B01D 1/0082: {Regulation; Control} - B01D 1/18: to obtain dry solids (B01D1/24 takes precedence) - B01D 1/20: Sprayers (in general B05B) - F26B 3/20: the heat source being a heated surface {, e.g. a moving belt or conveyor}(F26B3/22 takes precedence) - F26B 3/28: by radiation, e.g. from the sun - F26B 3/347: Electromagnetic heating, e.g. induction heating or heating using microwave energy - H01S 3/2232: {Carbon dioxide (CO2) or monoxide [CO]} - B08B: CLEANING IN GENERAL; PREVENTION OF FOULING IN GENERAL - B01D: SEPARATION (separating solids from solids by wet methods B03B, B03D; by pneumatic jigs or tables B03B; by other dry methods B07; magnetic or electrostatic separation of solid materials from solid materials or fluids, separation by high-voltage electric fields B03C; centrifuges, vortex apparatus B04; presses per se for squeezing-out liquid from liquid-containing material B30B9/02; treatment of water C02F, e.g. softening by ion-exchange C02F1/42; {arrangements of air intake cleaners in gas turbine plants F02C7/05} ; arrangements or mounting of filters in air-conditioning, air-humidification or ventilation F24F13/28) - F26B: DRYING SOLID MATERIALS OR OBJECTS BY REMOVING LIQUID THEREFROM (drying devices for combines A01D41/133; racks for drying fruit or vegetables A01F25/12; drying foodstuffs A23; drying hair A45D20/00; body-drying implements A47K10/00; drying household articles A47L; drying gases or vapours B01D; chemical or physical processes for dewatering or like separating liquids from solids B01D43/00; centrifugal apparatus B04; drying ceramics C04B33/30; drying yarns or fabrics in association with some other form of treatment D06C; drying frames for laundry without heating or positive air circulation, domestic laundry-or spin-driers, wringing or hot pressing laundry D06F; furnaces, kilns, ovens F27) - H01S: DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL ## Abstract Disclosed are methods, devices and systems to cause differential evaporation of micro-droplets in a scalable fashion. In some embodiments, an attenuated laser is used to focus an attenuated laser power to the center of an aqueous solution droplet, producing a differential evaporative flux profile that is peaked at the droplet apex. The laser-induced differential evaporation described herein is a breakthrough in the enrichment and focused deposition of water-soluble molecules such as nucleic acids, proteins, inks, and other small molecules. Disclosed is a general solution to remove the “coffee-ring effect”, ubiquitous in the drying process of aqueous droplets that causes many adverse outcomes. The disclosed techniques enable new paradigms in liquid biopsy combinational analysis, microarray fabrication, and ink-jet printing. ## Claims ### Claim 1 A microdroplet evaporation apparatus, comprising: a light source; a substrate to hold a microdroplet at a location; and a focusing module configured to focus the light source at an apex of the microdroplet, such that a beam waist of the focused light source has a diameter less than a diameter of the microdroplet. ### Claim 2 (depends on 1) The microdroplet evaporation apparatus of claim 1, wherein the focusing module causes illumination by the light source of a plurality of wells including the well at the same time or nearly the same time. ### Claim 3 (depends on 1) The microdroplet evaporation apparatus of claim 1, further comprising: an x-y mechanical translation apparatus configured to selectively translate the substrate to one of a plurality of wells with corresponding microdroplets including the well. ### Claim 4 (depends on 1) The microdroplet evaporation apparatus of claim 1, wherein the microdroplet evaporation apparatus causes a drying of the microdroplet leaving a deposition of solids that were previously dissolved in the microdroplet before the microdroplet was dried. ### Claim 5 (depends on 4) The microdroplet evaporation apparatus of claim 4, wherein the deposition of solids is uniform or nearly uniform across the dried microdroplet. ### Claim 6 (depends on 4) The microdroplet evaporation apparatus of claim 4, wherein the deposition of solids is approximately the same size as the microdroplet. ### Claim 7 (depends on 4) The microdroplet evaporation apparatus of claim 4, wherein the deposition of solids includes deposition of water-soluble molecules including one or more of nucleic acids, proteins, inks, and other small molecules. ### Claim 8 (depends on 1) The microdroplet evaporation apparatus of claim 1, wherein the light source is a laser. ### Claim 9 (depends on 1) The microdroplet evaporation apparatus of claim 1, wherein the laser is a CO2 laser. ### Claim 10 (depends on 9) The microdroplet evaporation apparatus of claim 9, wherein the beam waist of the CO2 laser is approximately 25-35 microns. ### Claim 11 (depends on 9) The microdroplet evaporation apparatus of claim 9, wherein a beam of the CO2 laser is focused on the apex of the microdroplet to generate a differential evaporation. ### Claim 12 (depends on 11) The microdroplet evaporation apparatus of claim 11, wherein a differential evaporative flux profile has a maximum at the apex of the microdroplet. ### Claim 13 (depends on 12) The microdroplet evaporation apparatus of claim 12, wherein the beam focused at the apex of the microdroplet causes a uniform or nearly uniform deposition of solids when the microdroplet is dried. ### Claim 14 (depends on 1) The microdroplet evaporation apparatus of claim 1, wherein the microdroplet is an aqueous solution droplet with a droplet diameter of between 100 μm and 1.5 mm. ### Claim 15 (depends on 1) The microdroplet evaporation apparatus of claim 1, wherein the well is approximately 100 μm in diameter. ### Claim 16 (depends on 1) The microdroplet evaporation apparatus of claim 1, wherein the microdroplet has a volume between 1-10 microliters. ### Claim 17 A method of evaporating a microdroplet, comprising: holding, by a substrate, a microdroplet at a location; illuminating, by a light source, the microdroplet; and focusing the light source at an apex of the microdroplet to cause a drying of the microdroplet, wherein a beam waist of the focused light source has a diameter less than a diameter of the microdroplet. ### Claim 18 (depends on 17) The method of evaporating a microdroplet of claim 17, wherein the drying of the microdroplet leaves a deposition of solids that were previously dissolved in the microdroplet before the microdroplet was dried. ### Claim 19 (depends on 18) The method of evaporating a microdroplet of claim 18, wherein the deposition of solids is uniform or nearly uniform across the dried microdroplet. ### Claim 20 (depends on 18) The method of evaporating a microdroplet of claim 18, wherein the deposition of solids includes deposition of water-soluble molecules including one or more of nucleic acids, proteins, inks, and other small molecules.