液滴流微反应器的基础研究及其应用

doi:10.16085/j.issn.1000-6613.2015.03.001

摘要/Abstract

摘要： 综述了近些年来快速发展的液滴微流控技术, 回顾了微流控系统中液滴的基本行为, 如液滴的生成、运动、聚并和分裂等研究进展, 重点探讨微液滴作为反应器其内部的流动、传质和反应过程, 以及液滴流微反应器已有的和潜在的重要应用价值。通过精确调控液滴在微尺度上的行为(产生、聚并与分裂、内部的混合与反应等), 使单个液滴成为新型受限空间内的微型间歇反应器, 而微通道内的液滴流进而形成了若干间歇反应器构成的连续流反应器新型式。除了微流控技术普遍具有的微小尺寸效应带来传质传热强化、易于放大等优势外, 液滴流微反应器还具有诸如避免试剂交叉污染、液滴内部可控混合、易于独立调控、便于高通量筛选或者制备等独特特点, 使得其在功能材料制备、化学合成以及生物化工方面有着广泛的应用。

关键词: 多相流, 微反应器, 液滴流, 微通道, 流体力学

Abstract: This review aims to introduce the droplet-based microfluidics which has been growing rapidly in recent years. Some of the basic droplet operations are summarized focusing on fluid flow pattern, mass transfer and reaction both inside droplets and at interface of droplets. Some of typical examples of existing as well as potential applications of droplet-based microreactors in various fields are also discussed. The developed technologies and techniques provide means to precisely control droplet volumes and accurately manipulate behavior of individual droplet(e.g., generation of droplets, coalescence and fission, mixing and reactions inside the droplets). As a result, each individual droplet acts as a small batch reactor under confined conditions. Accordingly, these small flowing batch reactors together form a new type of novel continuous-flow reactors. Besides the usual advantages brought by microfluidics, e.g., intensified mass and heat transfer and easy scale-up, droplet-based microfluidics have unique features, such as ability to avoid cross contamination, rapid mixing of fluids inside the droplets, independent control of each droplet and high throughput. These features allow them to be widely used in many fields, such as preparation of functional materials, chemical synthesis, biochemical engineering, and so on.

Key words: multiphase flow, microreactor, droplet flow, micro-channel, fluid mechanics

中图分类号:

TQ052

赵述芳, 白琳, 付宇航, 金涌, 程易. 液滴流微反应器的基础研究及其应用[J]. 化工进展, 2015, 34(3): 593-607,616.

ZHAO Shufang, BAI Lin, FU Yuhang, JIN Yong, CHENG Yi. Fundamental research and applications of droplet-based microreactor[J]. Chemical Industry and Engineering Progree, 2015, 34(3): 593-607,616.

参考文献

[1] Whitesides G M.The origins and the future of microfluidics[J].Nature, 2006, 442:368-373.

[2] Manz A, Graber N, Widmer H M.Miniaturized total chemical-analysis systems-A novel concept for chemical sensing[J].Sensors and Actuators B:Chemical, 1990, 1:244-248.

[3] Mitchell P.Microfluidics-downsizing large-scale biology[J].Nature Biotechnology, 2001, 19:717-721.

[4] Squires T M, Quake S R.Microfluidics:Fluid physics at the nanoliter scale[J].Reviews of Modern Physics, 2005, 77:977-1026.

[5] Pamme N.Continuous flow separations in microfluidic devices[J].Lab Chip, 2007, 7:1644-1659.

[6] Makgwane P R, Ray S S.Synthesis of nanomaterials by continuous-flow microfluidics:A review[J].Journal of Nanoscience and Nanotechnology, 2014, 14:1338-1363.

[7] Song H, Chen D L, Ismagilov R F.Reactions in droplets in microflulidic channels[J].Angewandte Chemie-International Edition, 2006, 45:7336-7356.

[8] Teh S Y, Lin R, Hung L H, et al.Droplet microfluidics[J].Lab Chip, 2008, 8:198-220.

[9] Seemann R, Brinkmann M, Pfohl T, et al.Droplet based microfluidics[J].Reports on Progress in Physics, 2012, 75:016601.

[10] Solvas X C I, deMello A.Droplet microfluidics:Recent developments and future applications[J].Chemical Communications, 2011, 47:1936-1942.

[11] Fouillet Y, Jary D, Chabrol C, et al.Digital microfluidic design and optimization of classic and new fluidic functions for lab on a chip systems[J].Microfluidics and Nanofluidics, 2008, 4:159-165.

[12] Abdelgawad M, Wheeler A R.The digital revolution:A new paradigm for microfluidics[J].Advanced Materials, 2009, 21:920-925.

[13] 郑利, 张正, 李丹, 等.基于声表面波技术的微流体混合及仿真[J].传感技术学报, 2011:1098-1101.

[14] Shui L, Eijkel J C T, van den Berg A.Multiphase flow in microfluidic systems-control and applications of droplets and interfaces[J].Adv.Colloid Interface Sci., 2007, 133:35-49.

[15] Martin-Banderas L, Rodriguez-Gil A, Cebolla A, et al.Towards high-throughput production of uniformly encoded microparticles[J].Advanced Materials, 2006, 18:559.

[16] Duraiswamy S, Khan S A.Droplet-based microfluidic synthesis of anisotropic metal nanocrystals[J].Small, 2009, 5:2828-2834.

[17] Huebner A, Sharma S, Srisa-Art M, et al.Microdroplets:A sea of applications?[J].Lab Chip, 2008, 8:1244-1254.

[18] Pollack M G, Parnula V K, Srinivasan V, et al.Applications of electrowetting-based digital microfluidics in clinical diagnostics[J].Expert Review of Molecular Diagnostics, 2011, 11:393-407.

[19] Okochi H, Nakano M.Comparative study of two preparation methods of W/O/W emulsions:Stirring and membrane emulsification[J].Chemical & Pharmaceutical Bulletin, 1997, 45:1323-1326.

[20] Sugiura S, Nakajima M, Iwamoto S, et al.Interfacial tension driven monodispersed droplet formation from microfabricated channel array[J].Langmuir, 2001, 17:5562-5566.

[21] Kobayashi I, Mukataka S, Nakajima M.Novel asymmetric through-hole array microfabricated on a silicon plate for formulating monodisperse emulsions[J].Langmuir, 2005, 21:7629-7632.

[22] Gijsbertsen-Abrahamse A J, van der Padt A, Boom R M.Status of cross-flow membrane emulsification and outlook for industrial application[J].Journal of Membrane Science, 2004, 230:149-159.

[23] Lambrich U, Schubert H.Emulsification using microporous systems[J].Journal of Membrane Science, 2005, 257:76-84.

[24] Christopher G F, Anna S L.Microfluidic methods for generating continuous droplet streams[J].Journal of Physics D:Applied Physics, 2007, 40:R319-R336.

[25] Kashid M N, Agar D W.Hydrodynamics of liquid-liquid slug flow capillary microreactor:Flow regimes, slug size and pressure drop[J].Chemical Engineering Journal, 2007, 131:1-13.

[26] Serizawa A, Feng Z P, Kawara Z.Two-phase flow in microchannels[J].Experimental Thermal and Fluid Science, 2002, 26:703-714.

[27] Kawahara A, Chung P M Y, Kawaji M.Investigation of two-phase flow pattern, void fraction and pressure drop in a microchannel[J].International Journal of Multiphase Flow, 2002, 28:1411-1435.

[28] Wang W T, Liu Z, Jin Y, et al.Lbm simulation of droplet formation in micro-channels[J].Chemical Engineering Journal, 2011, 173:828-836.

[29] Cristini V, Tan Y C.Theory and numerical simulation of droplet dynamics in complex flows-A review[J].Lab Chip, 2004, 4:257-264.

[30] Ben-Tzvi P, Rone W.Microdroplet generation in gaseous and liquid environments[J].Microsystem Technologies-Micro-and Nanosystems-Information Storage and Processing Systems, 2010, 16:333-356.

[31] Niu X, Gulati S, Edel J B, et al.Pillar-induced droplet merging in microfluidic circuits[J].Lab Chip, 2008, 8:1837-1841.

[32] Christopher G F, Bergstein J, End N B, et al.Coalescence and splitting of confined droplets at microfluidic junctions[J].Lab Chip, 2009, 9:1102-1109.

[33] Jin B J, Kim Y W, Lee Y, et al.Droplet merging in a straight microchannel using droplet size or viscosity difference[J].Journal of Micromechanics and Microengineering, 2010, 20(3):035003.

[34] Fidalgo L M, Abell C, Huck W T S.Surface-induced droplet fusion in microfluidic devices[J].Lab Chip, 2007, 7:984-986.

[35] Berge B, Konovalov O, Lajzerowicz J, et al.Melting of short 1-Alcohol monolayers on water-thermodynamics and X-ray-scattering studies[J].Physical Review Letters, 1994, 73:1652-1655.

[36] Cordero M L, Burnham D R, Baroud C N, et al.Thermocapillary manipulation of droplets using holographic beam shaping:Microfluidic pin ball[J].Appl.Phys.Lett., 2008, 93.

[37] Chabert M, Dorfman K D, Viovy J L.Droplet fusion by alternating current (Ac) field electrocoalescence in microchannels[J].Electrophoresis, 2005, 26:3706-3715.

[38] Ahn K, Agresti J, Chong H, et al.Electrocoalescence of drops synchronized by size-dependent flow in microfluidic channels[J].Appl.Phys.Lett., 2006, 88.

[39] Niu X Z, Gielen F, deMello A J, et al.Electro-coalescence of digitally controlled droplets[J].Analytical Chemistry, 2009, 81:7321-7325.

[40] Leshansky A M, Pismen L M.Breakup of drops in a microfluidic T junction[J].Physics of Fluids, 2009, 21:023303.

[41] Menetrier-Deremble L, Tabeling P.Droplet breakup in microfluidic junctions of arbitrary angles[J].Physical Review E, 2006, 74:035303.

[42] Jullien M C, Ching M J T M, Cohen C, et al.Droplet breakup in microfluidic t-junctions at small capillary numbers[J].Physics of Fluids, 2009, 21:072001.

[43] Link D R, Anna S L, Weitz D A, et al.Geometrically mediated breakup of drops in microfluidic devices[J].Physical Review Letters, 2004, 92:054503.

[44] Bedram A, Moosavi A.Droplet breakup in an asymmetric microfluidic T junction[J].European Physical Journal E, 2011, 34(8):78.

[45] Samie M, Salari A, Shafii M B.Breakup of microdroplets in asymmetric T junctions[J].Physical Review E, 2013, 87(5):053003.

[46] Gunther A, Jhunjhunwala M, Thalmann M, et al.Micromixing of miscible liquids in segmented gas-liquid flow[J].Langmuir, 2005, 21:1547-1555.

[47] Hodges S R, Jensen O E, Rallison J M.The motion of a viscous drop through a cylindrical tube[J].Journal of Fluid Mechanics, 2004, 501:279-301.

[48] Kinoshita H, Kaneda S, Fujii T, et al.Three-dimensional measurement and visualization of internal flow of a moving droplet using confocal micro-piv[J].Lab Chip, 2007, 7:338-346.

[49] Sarrazin F, Loubiere K, Prat L, et al.Experimental and numerical study of droplets hydrodynamics in microchannels[J].AIChE Journal, 2006, 52:4061-4070.

[50] van Steijn V, Kreutzer M T, Kleijn C R.Mu-piv study of the formation of segmented flow in microfluidic T-junctions[J].Chemical Engineering Science, 2007, 62:7505-7514.

[51] Wang C, Nguyen N T, Wong T N.Optical measurement of flow field and concentration field inside a moving nanoliter droplet[J].Sensors and Actuators A:Physical, 2007, 133:317-322.

[52] Harries N, Burns J R, Barrow D A, et al.A numerical model for segmented flow in a microreactor[J].International Journal of Heat and Mass Transfer, 2003, 46:3313-3322.

[53] Kashid M N, Gerlach I, Goetz S, et al.Internal circulation within the liquid slugs of a liquid-liquid slug-flow capillary microreactor[J].Industrial & Engineering Chemistry Research, 2005, 44:5003-5010.

[54] Wang W T, Shao T, Zhao S F, et al.Experimental and numerical study of mixing behavior inside droplets in microchannels[J].AIChE Journal, 2013, 59:1801-1813.

[55] Jahnisch K, Baerns M, Hessel V, et al.Direct fluorination of toluene using elemental fluorine in gas/liquid microreactors[J].Journal of Fluorine Chemistry, 2000, 105:117-128.

[56] Losey M W, Jackman R J, Firebaugh S L, et al.Design and fabrication of microfluidic devices for multiphase mixing and reaction[J].Journal of Microelectromechanical Systems, 2002, 11:709-717.

[57] Ahmed-Omer B, Barrow D, Wirth T.Effect of segmented fluid flow, sonication and phase transfer catalysis on biphasic reactions in capillary microreactors[J].Chemical Engineering Journal, 2008, 135:S280-S283.

[58] Burns J R, Ramshaw C.The intensification of rapid reactions in multiphase systems using slug flow in capillaries[J].Lab Chip, 2001, 1:10-15.

[59] Zhang H, Tumarkin E, Peerani R, et al.Microfluidic production of biopolymer microcapsules with controlled morphology[J].J.Am.Chem.Soc., 2006, 128:12205-12210.

[60] Li S W, Xu H H, Wang Y J, et al.Controllable preparation of nanoparticles by drops and plugs flow in a microchannel device[J].Langmuir, 2008, 24:4194-4199.

[61] Shah R K, Kim J W, Weitz D A.Monodisperse stimuli-responsive colloidosomes by self-assembly of microgels in droplets[J].Langmuir, 2010, 26:1561-1565.

[62] Song H, Tice J D, Ismagilov R F.A microfluidic system for controlling reaction networks in time[J].Angewandte Chemie-International Edition, 2003, 42:768-772.

[63] Tice J D, Song H, Lyon A D, et al.Formation of droplets and mixing in multiphase microfluidics at low values of the reynolds and the capillary numbers[J].Langmuir, 2003, 19:9127-9133.

[64] Song H, Bringer M R, Tice J D, et al.Experimental test of scaling of mixing by chaotic advection in droplets moving through microfluidic channels[J].Appl.Phys.Lett., 2003, 83:4664-4666.

[65] Bringer M R, Gerdts C J, Song H, et al.Microfluidic systems for chemical kinetics that rely on chaotic mixing in droplets[J].Philosophical Transactions of the Royal Society of London Series A:Mathematical Physical and Engineering Sciences, 2004, 362:1087-1104.

[66] Zhao S F, Wang W T, Zhang M X, et al.Three-dimensional simulation of mixing performance inside droplets in micro-channels by lattice boltzmann method[J].Chemical Engineering Journal, 2012, 207:267-277.

[67] Liu Z, Cheng Y, Jin Y.Experimental study of reactive mixing in a mini-scale mixer by laser-induced fluorescence technique[J].Chemical Engineering Journal, 2009, 150:536-543.

[68] Gas J, Poddar P, Almand J, et al.Superparamagnetic polymer nanocomposites with uniform fe₃O₄ nanoparticle dispersions[J].Advanced Functional Materials, 2006, 16:71-75.

[69] Dittrich P S, Manz A.Lab-on-a-chip:Microfluidics in drug discovery[J].Nature Reviews Drug Discovery, 2006, 5:210-218.

[70] Nisisako T, Okushima S, Torii T.Controlled formulation of monodisperse double emulsions in a multiple-phase microfluidic system[J].Soft Matter., 2005, 1:23-27.

[71] Nie Z H, Xu S Q, Seo M, et al.Polymer particles with various shapes and morphologies produced in continuous microfluidic reactors[J].J.Am.Chem.Soc., 2005, 127:8058-8063.

[72] Abate A R, Kutsovsky M, Seiffert S, et al.Synthesis of monodisperse microparticles from non-newtonian polymer solutions with microfluidic devices[J].Advanced Materials, 2011, 23:1757.

[73] Utada A S, Lorenceau E, Link D R, et al.Monodisperse double emulsions generated from a microcapillary device[J].Science, 2005, 308:537-541.

[74] Chu L Y, Utada A S, Shah R K, et al.Controllable monodisperse multiple emulsions[J].Angewandte Chemie-International Edition, 2007, 46:8970-8974.

[75] Wang W, Xie R, Ju X J, et al.Controllable microfluidic production of multicomponent multiple emulsions[J].Lab Chip, 2011, 11:1587-1592.

[76] Guillot P, Colin A, Utada A S, et al.Stability of a jet in confined pressure-driven biphasic flows at low reynolds numbers[J].Physical Review Letters, 2007, 99:104502.

[77] Utada A S, Chu L Y, Fernandez-Nieves A, et al.Dripping, jetting, drops, and wetting:The magic of microfluidics[J].MRS Bulletin, 2007, 32:702-708.

[78] Park J M, Anderson P D.A Ternary model for double-emulsion formation in a capillary microfluidic device[J].Lab Chip, 2012, 12:2672-2677.

[79] Shum H C, Sauret A, Fernandez-Nieves A, et al.Corrugated interfaces in multiphase core-annular flow[J].Physics of Fluids, 2010, 22:082002.

[80] Shao T, Feng X L, Jin Y, et al.Controlled production of double emulsions in dual-coaxial capillaries device for millimeter-scale hollow polymer spheres[J].Chemical Engineering Science, 2013, 104:55-63.

[81] Tao J, Song X Y, Liu J X, et al.Microfluidic rheology of the multiple-emulsion globule transiting in a contraction tube through a boundary element method[J].Chemical Engineering Science, 2013, 97:328-336.

[82] Wang J T, Liu J X, Han J J, et al.Rheology investigation of the globule of multiple emulsions with complex internal structures through a boundary element method[J].Chemical Engineering Science, 2013, 96:87-97.

[83] Wang J T, Liu J X, Han J J, et al.Effects of complex internal structures on rheology of multiple emulsions particles in 2d from a boundary integral method[J].Physical Review Letters, 2013, 110:066001.

[84] Zhao S F, Wang W T, Shao T, et al.Mixing performance and drug nano-particle preparation inside slugs in a gas-liquid microchannel reactor[J].Chemical Engineering Science, 2013, 100:456-463.

[85] Yen B K H, Gunther A, Schmidt M A, et al.A microfabricated gas-liquid segmented flow reactor for high-temperature synthesis:The case of cdse quantum dots[J].Angewandte Chemie-International Edition, 2005, 44:5447-5451.

[86] Shestopalov I, Tice J D, Ismagilov R F.Multi-step synthesis of nanoparticles performed on millisecond time scale in a microfluidic droplet-based system[J].Lab Chip, 2004, 4:316-321.

[87] Sugiura S, Nakajima M, Itou H, et al.Synthesis of polymeric microspheres with narrow size distributions employing microchannel emulsification[J].Macromol.Rapid Commun., 2001, 22:773-778.

[88] Nisisako T, Torii T, Higuchi T.Novel microreactors for functional polymer beads[J].Chemical Engineering Journal, 2004, 101:23-29.

[89] Sugiura S, Nakajima M, Tong J H, et al.Preparation of monodispersed solid lipid microspheres using a microchannel emulsification technique[J].J.Colloid Interface Sci., 2000, 227:95-103.

[90] Chang J Y, Yang C H, Huang K S.Microfluidic assisted preparation of cdse/zns nanocrystals encapsulated into poly(Dl-Lactide- Co-Glycolide) microcapsules[J].Nanotechnology, 2007, 18(30):305305.

[91] Budhlall B M, Marquez M, Velev O D.Microwave, photo- and thermally responsive pnipam-gold nanoparticle microgels[J].Langmuir, 2008, 24:11959-11966.

[92] Yang C H, Huang K S, Lin Y S, et al.Microfluidic assisted synthesis of multi-functional polycaprolactone microcapsules:Incorporation of Cdte quantum dots, Fe₃O₄ superparamagnetic nanoparticles and tamoxifen anticancer drugs[J].Lab Chip, 2009, 9:961-965.

[93] Ji X H, Cheng W, Guo F, et al.On-demand preparation of quantum dot-encoded microparticles using a droplet microfluidic system[J].Lab Chip, 2011, 11:2561-2568.

[94] Gong X Q, Peng S L, Wen W J, et al.Design and fabrication of magnetically functionalized core/shell microspheres for smart drug delivery[J].Advanced Functional Materials, 2009, 19:292-297.

[95] Nie Z H, Li W, Seo M, et al.Janus and ternary particles generated by microfluidic synthesis:Design, synthesis, and self-assembly[J].J.Am.Chem.Soc., 2006, 128:9408-9412.

[96] Walther A, Muller A H E.Janus particles[J].Soft Matter., 2008, 4:663-668.

[97] Burns J R, Ramshaw C.A microreactor for the nitration of benzene and toluene[J].Chemical Engineering Communications, 2002, 189:1611-1628.

[98] Cygan Z T, Cabral J T, Beers K L, et al.Microfluidic platform for the generation of organic-phase microreactors[J].Langmuir, 2005, 21:3629-3634.

[99] Wu T, Mei Y, Cabral J T, et al.A new synthetic method for controlled polymerization using a microfluidic system[J].J.Am.Chem.Soc., 2004, 126:9880-9881.

[100] Harrison C, Cabral J T, Stafford C M, et al.A rapid prototyping technique for the fabrication of solvent-resistant structures[J].Journal of Micromechanics and Microengineering, 2004, 14:153-158.

[101] Jovanovic J, Rebrov E V, Nijhuis T A, et al.Phase-transfer catalysis in segmented flow in a microchannel:Fluidic control of selectivity and productivity[J].Industrial & Engineering Chemistry Research, 2010, 49:2681-2687.

[102] Al-Rawashdeh M, Zalucky J, Muller C, et al.Phenylacetylene hydrogenation over [Rh(NBD)(PPh3)₂] BF₄ catalyst in a numbered-up microchannels reactor[J].Industrial & Engineering Chemistry Research, 2013, 52:11516-11526.

[103] Dencic I, Meuldijk J, de Croon M, et al.From a review of noble metal versus enzyme catalysts for glucose oxidation under conventional conditions towards a process design analysis for continuous-flow operation[J].Journal of Flow Chemistry, 2011, 1:13-23.

[104] Illg T, Hessel V, Lob P, et al.Novel process window for the safe and continuous synthesis of tert.-butyl peroxy pivalate in a micro-reactor[J].Chemical Engineering Journal, 2011, 167:504-509.

[105] Onal Y, Lucas M, Claus P.Application of a capillary microreactor for selective hydrogenation of Alpha, Beta-Unsaturated aldehydes in aqueous multiphase catalysis[J].Chemical Engineering & Technology, 2005, 28:972-978.

[106] Zhu Y G, Power B E.Lab-on-a-chip in vitro compartmentalization technologies for protein studies[J].Protein-Protein Interaction, 2008, 110:81-114.

[107] Wu N, Oakeshott J, Brown S, et al.Microfluidic droplet technique for in vitro directed evolution[J].Australian Journal of Chemistry, 2010, 63:1313-1325.

[108] Theberge A B, Courtois F, Schaerli Y, et al.Microdroplets in microfluidics:An evolving platform for discoveries in chemistry and biology[J].Angewandte Chemie-International Edition, 2010, 49:5846-5868.

[109] Vyawahare S, Griffiths A D, Merten C A.Miniaturization and parallelization of biological and chemical assays in microfluidic devices[J].Chemistry & Biology, 2010, 17:1052-1065.

[110] Kelly B T, Baret J C, Taly V, et al.Miniaturizing chemistry and biology in microdroplets[J].Chemical Communications, 2007:1773-1788.

[111] Huebner A, Srisa-Art M, Holt D, et al.Quantitative detection of protein expression in single cells using droplet microfluidics[J].Chemical Communications, 2007:1218-1220.

[112] Koster S, Angile F E, Duan H, et al.Drop-based microfluidic devices for encapsulation of single cells[J].Lab Chip, 2008, 8:1110-1115.

[113] He M Y, Edgar J S, Jeffries G D M, et al.Selective encapsulation of single cells and subcellular organelles into picoliter- and femtoliter-volume droplets[J].Analytical Chemistry, 2005, 77:1539-1544.

[114] Edd J F, Di Carlo D, Humphry K J, et al.Controlled encapsulation of single-cells into monodisperse picolitre drops[J].Lab Chip, 2008, 8:1262-1264.

[115] Chabert M, Viovy J L.Microfluidic high-throughput encapsulation and hydrodynamic self-sorting of single cells[J].Proceedings of the National Academy of Sciences of the United States of America, 2008, 105:3191-3196.

[116] McPherson A.Introduction to protein crystallization[J].Methods, 2004, 34:254-265.

[117] Wang J T, Wang J, Han J J.Fabrication of advanced particles and particle-based materials assisted by droplet-based microfluidics[J].Small, 2011, 7:1728-1754.

[118] Hansen C, Quake S R.Microfluidics in structural biology:Smaller, faster...better[J].Current Opinion in Structural Biology, 2003, 13:538-544.

[119] Zheng B, Gerdts C J, Ismagilov R F.Using nanoliter plugs in microfluidics to facilitate and understand protein crystallization[J].Current Opinion in Structural Biology, 2005, 15:548-555.

[120] Zheng B, Roach L S, Ismagilov R F.Screening of protein crystallization conditions on a microfluidic chip using nanoliter-size droplets[J].J.Am.Chem.Soc., 2003, 125:11170-11171.

[121] Zheng B, Tice J D, Roach L S, et al.A droplet-based, composite Pdms/Glass capillary microfluidic system for evaluating protein crystallization conditions by microbatch and vapor-diffusion methods with on-chip X-ray diffraction[J].Angewandte Chemie-International Edition, 2004, 43:2508-2511.

[122] Zheng B, Tice J D, Ismagilov R F.Formation of arrayed droplets of soft lithography and two-phase fluid flow, and application in protein crystallization[J].Advanced Materials, 2004, 16:1365-1368.

[123] Zheng B, Ismagilov R F.A microfluidic approach for screening submicroliter volumes against multiple reagents by using preformed arrays of nanoliter plugs in a three-phase liquid/liquid/gas flow[J].Angewandte Chemie-International Edition, 2005, 44:2520-2523.

[124] Evans H M, Surenjav E, Priest C, et al.In situ formation, manipulation, and imaging of droplet-encapsulated fibrin networks[J].Lab Chip, 2009, 9:1933-1941.