Single‐Step Fabrication of High‐Density Microdroplet Arrays of Low‐Surface‐Tension Liquids

Abstract

Discontinuous dewetting is a powerful method enabling the generation of thousands of microdroplets with a specific geometry, volume and at predefined locations on a patterned substrate. [1][2][3][4] During the discontinuous dewetting process, liquid is moved along a surface possessing strong dewettability with a pattern of highly wettable spots to create an array of pinned droplets from picoliter up to microliter volumes. [5] The advantages of this procedure are that it is a single-step method, permits massive parallelization, is compatible with highthroughput screening (HTS) experiments [6,7] but does not depend on expensive robotics and automation, thereby minimizing experimental costs. These advantages make this method attractive for HTS of cells including single cell screenings, diagnostic or personalized medicine applications. 2Recently several biological applications requiring both miniaturization and multiplexing have been realized via discontinuous dewetting. Driven by surface tension, cell-laden hydrogels were assembled on a glass surface patterned with hydrophobic and hydrophilic regions. [8] Superhydrophobic-superhydrophilic microarrays were used to create dropletmicroarrays for high-throughput screening of living cells [7,[9][10][11] , to create arrays of hydrogel micropads [2] and for single cell screening. [12] However, most of the patterns developed thus far only apply to fabricating microdroplet arrays of high surface tension liquids such as water (surface tension γ lv =72.2 mN m -1 ), while the method often fails when most of the organic solvents with lower surface tensions (e.g., ethanol, γ lv =22.1 mN m -1 or n-hexane, γ lv =18.4 mN m -1 ) are involved.There are very few methods compatible with low surface tension liquids. Thus, Whitesides and co-workers utilized a two-phase system consisting of water and an immiscible hydrocarbon fluid to generate microdroplet arrays of hydrocarbons on patterned SAMs. [13] However, their approach is incompatible with water-miscible organic solvents. Dropletmicroarrays were also generated using discontinuous dewetting on arrays of microwells produced in poly(dimethylsiloxane) (PDMS These superomniphobic surfaces have been applied to form microdroplets of organic liquids by discontinuous dewetting. To fabricate superoleophobic surfaces, however, special designs of surface topography such as overhang [15,16] or pinecone-like structures [14] are needed, and in many cases the surfaces obtain this complex topography at the expense of their laborious preparation, sacrificing mechanical strength and transparency. [17,18] 3Here we describe a straightforward two-step approach for surface patterning that enables the fabrication of high-density arrays of microdroplets by discontinuous dewetting compatible with organic liquids with surface tension as low as γ lv =18.4 mN m -1 . The method is based on the chemical modification of a chloro(dimethyl)vinylsilane-coated flat glass surface with 1H,1H,2H,2H-perfluorodecanethiol (PFDT) via the UV-induced thiol-ene click reac...

Micro‐/Nanostructured Interface for Liquid Manipulation and Its Applications

“…The modification procedure begun with the silanization reaction of chloro(dimethyl)vinylsilane on the glass slide, which endowed vinyl groups on the substrates for subsequent UV‐induced thiol–ene click reaction. So 1H,1H,2H,2H ‐perfluorodecanethiol (PFDT) was modified on the substrates with UV irradiation through a quartz photomask leading to a nonwettable surface, and the remaining vinyl groups reacted with cysteamine …”

“…For example, the volume of microdroplet had been reported to be as low as picoliter and femtoliter, and the geometry of the (micro)reservoir can be tuned for the synthesis of materials with specific shapes, such as hydrogel particles, biofilm microcluster, metal organic framework microsheet, and nanoparticle assembly . 3) (Micro)reservoirs can be spatially close to each other because droplet coalesce is avoided, which paves the way for miniaturization and point‐of‐care application of the SPW . 4) SPW can be obtained by fabricating micro‐/nanostructures on various substrates, which can promote the wider applications of SPW based on the functions of different substrates …”

“…So 1H,1H,2H,2H-perfluorodecanethiol (PFDT) was modified on the substrates with UV irradiation through a quartz photomask leading to a nonwettable surface, and the remaining vinyl groups reacted with cysteamine. [127] Chemical modification by polymerization reaction is also an important surface modification method, which includes radical polymerization, copolymerization, and grafted polymerization. For example, Sui et al reported a switchable, CO 2 -responsive oil-water separation material based on aerogels of cellulose nanofibers.…”

“…[268] 3) (Micro)reservoirs can be spatially close to each other because droplet coalesce is avoided, which paves the way for miniaturization and point-of-care application of the SPW. [127,258,259,269,270] 4) SPW can be obtained by fabricating micro-/nanostructures on various substrates, which can promote the wider applications of SPW based on the functions of different substrates. [271][272][273] Until now, SPW had been extensively explored as an effective high-throughput platform for bioassay and biosensing.…”

A Photocatalytically Active Lubricant‐Impregnated Surface

“…The field of liquid repelling surface has rapidly expanded from the classical self-cleaning applications [1] to more specialized issues such as anti-biofouling, [2] oil-water separation, [3] patterning, [4] gas separation, [5] and particle synthesis. [6] Among various kinds of liquid repelling surfaces,l ubricant impregnated surfaces (LISs) exhibit alow lateral adhesion for liquid drops;d rops easily slide on al ubricant layer.…”