title: Open-atmosphere sustenance of highly volatile attoliter-size droplets on surfaces.
abstract: The controlled formation and handling of minute liquid volumes on surfaces is essential to the success of microfluidics in biology, chemistry, and materials applications. Even though current methods have demonstrated their potential in a variety of experimental assays, there remain significant difficulties concerning breadth of applicability, standardization, throughput, and economics. Here we introduce a unique microfluidic paradigm in which microscopic volatile droplets are formed, sustained, and manipulated in size and content at any desired spot on unpatterned substrates. Their sustainability is warranted by continuous replacement of the rapidly vaporizing sessile fluid through controlled equivalent volume deposition of smaller discrete liquid entities by an electrohydrodynamic nanodripping process. Using nanoparticle inks we show that the concentration of solutes in so-stabilized droplets can be linearly increased at isochoric conditions and user-defined rates. An intriguing insensitivity of the droplet shape toward surface heterogeneities ensures robustness and experimental reproducibility, even when handling attoliter quantities. The unique capabilities and technical simplicity of the presented method introduce a high degree of flexibility and make it pertinent to a diverse range of applications.
authors.affiliation: Laboratory of Thermodynamics in Emerging Technologies, Department of Mechanical and Process Engineering, Eidgenössische Technische Hochschule Zürich (ETH Zurich), CH-8092 Zurich, Switzerland.
authors.forename: Patrick
authors.initials: P
authors.lastname: Galliker
authors.forename: Julian
authors.initials: J
authors.lastname: Schneider
authors.forename: Lukas
authors.initials: L
authors.lastname: Rüthemann
authors.forename: Dimos
authors.initials: D
authors.lastname: Poulikakos
mesh_terms: D007368:Interferometry; D046210:Microfluidic Analytical Techniques; D044085:Microfluidics / Q000379:methods*; D018625:Microscopy, Atomic Force; D008855:Microscopy, Electron, Scanning; D008956:Models, Chemical; D049329:Nanostructures; D013499:Surface Properties; D014835:Volatilization
keywords: digital microfluidics; noncontact printing; sessile droplets
references.citation: J Phys Chem B. 2007 May 17;111(19):5277-83
references.pmid: 17455971
references.citation: Proc Natl Acad Sci U S A. 2012 Oct 9;109(41):16455-8
references.pmid: 23010925
references.citation: Anal Chem. 2012 Nov 20;84(22):10012-8
references.pmid: 23072614
references.citation: Lab Chip. 2004 Aug;4(4):292-8
references.pmid: 15269794
references.citation: Nat Commun. 2012 Jun 12;3:890
references.pmid: 22692533
references.citation: Langmuir. 2006 Jan 3;22(1):116-26
references.pmid: 16378409
references.citation: Nat Nanotechnol. 2010 Jan;5(1):15-25
references.pmid: 20032986
references.citation: Chem Soc Rev. 2010 Mar;39(3):1153-82
references.pmid: 20179830
references.citation: Langmuir. 2008 Feb 19;24(4):1371-80
references.pmid: 18020467
references.citation: Lab Chip. 2005 Oct;5(10):1161-7
references.pmid: 16175274
references.citation: Lab Chip. 2012 Feb 7;12(3):422-33
references.pmid: 22011791
references.citation: Lab Chip. 2008 Feb;8(2):198-220
references.pmid: 18231657
references.citation: Lab Chip. 2012 Jun 21;12(12):2146-55
references.pmid: 22318506
references.citation: Angew Chem Int Ed Engl. 2003 Feb 17;42(7):768-72
references.pmid: 12596195
references.citation: J Colloid Interface Sci. 2003 Jul 1;263(1):237-43
references.pmid: 12804908
references.citation: Proc Natl Acad Sci U S A. 2009 Aug 25;106(34):14195-200
references.pmid: 19617544
references.citation: Nat Rev Drug Discov. 2006 Mar;5(3):210-8
references.pmid: 16518374
references.citation: Angew Chem Int Ed Engl. 2007;46(30):5670-703
references.pmid: 17585397
references.citation: Lab Chip. 2008 Oct;8(10):1632-9
references.pmid: 18813384