Zhihong Nie

Publications of Zhihong Nie

• Temperature mediated generation of armoured bubbles.

  Authors: Ethan Tumarkin, Jai Il Park, Zhihong Nie, Eugenia Kumacheva

  Chemical communications (Cambridge, England). 12/2011; 47(47):12712-4.

  This communication describes a novel strategy for the continuous microfluidic generation of highly monodispersed particle-coated microbubbles using temperature-dependent dissolution of carbon dioxide.

• Temperature-controlled 'breathing' of carbon dioxide bubbles.

  Authors: Ethan Tumarkin, Zhihong Nie, Jai Il Park, Milad Abolhasani, Jesse Greener, Barbara Sherwood-Lollar, Axel Günther, Eugenia Kumacheva

  Lab on a chip. 08/2011; 11(20):3545-50.

  We report a microfluidic (MF) approach to studies of temperature mediated carbon dioxide (CO(2)) transfer between the gas and the liquid phases. Micrometre-diameter CO(2) bubbles with a narrow sizeWe report a microfluidic (MF) approach to studies of temperature mediated carbon dioxide (CO(2)) transfer between the gas and the liquid phases. Micrometre-diameter CO(2) bubbles with a narrow size distribution were generated in an aqueous or organic liquid and subsequently were subjected to temperature changes in the downstream channel. In response to the cooling-heating-cooling cycle the bubbles underwent corresponding contraction-expansion-contraction transitions, which we term 'bubble breathing'. We examined temperature-controlled dissolution of CO(2) in four exemplary liquid systems: deionized water, a 0.7 M aqueous solution of NaCl, ocean water extracted from Bermuda coastal waters, and dimethyl ether of poly(ethylene glycol), a solvent used in industry for absorption of CO(2). The MF approach can be extended to studies of other gases with a distinct, temperature-dependent solubility in liquids.

• Programmable diagnostic devices made from paper and tape.

  Authors: Andres W Martinez, Scott T Phillips, Zhihong Nie, Chao-Min Cheng, Emanuel Carrilho, Benjamin J Wiley, George M Whitesides

  Lab on a chip. 10/2010; 10(19):2499-504.

  This paper describes three-dimensional microfluidic paper-based analytical devices (3-D microPADs) that can be programmed (postfabrication) by the user to generate multiple patterns of flow throughThis paper describes three-dimensional microfluidic paper-based analytical devices (3-D microPADs) that can be programmed (postfabrication) by the user to generate multiple patterns of flow through them. These devices are programmed by pressing single-use 'on' buttons, using a stylus or a ballpoint pen. Pressing a button closes a small space (gap) between two vertically aligned microfluidic channels, and allows fluids to wick from one channel to the other. These devices are simple to fabricate, and are made entirely out of paper and double-sided adhesive tape. Programmable devices expand the capabilities of microPADs and provide a simple method for controlling the movement of fluids in paper-based channels. They are the conceptual equivalent of field-programmable gate arrays (FPGAs) widely used in electronics.

• Integration of paper-based microfluidic devices with commercial electrochemical readers.

  Authors: Zhihong Nie, Frédérique Deiss, Xinyu Liu, Ozge Akbulut, George M Whitesides

  Lab on a chip. 10/2010; 10(22):3163-9.

  The combination of simple Electrochemical Micro-Paper-based Analytical Devices (EµPADs) with commercially available glucometers allows rapid, quantitative electrochemical analysis of a number ofThe combination of simple Electrochemical Micro-Paper-based Analytical Devices (EµPADs) with commercially available glucometers allows rapid, quantitative electrochemical analysis of a number of compounds relevant to human health (e.g., glucose, cholesterol, lactate, and alcohol) in blood or urine.

• Micro- and nanopatterning of inorganic and polymeric substrates by indentation lithography.

  Authors: Jinlong Gong, Darren J Lipomi, Jiangdong Deng, Zhihong Nie, Xin Chen, Nicholas X Randall, Rahul Nair, George M Whitesides

  Nano letters. 07/2010; 10(7):2702-8.

  This paper describes the use of a nanoindenter, equipped with a diamond tip, to form patterns of indentations on planar substrates (epoxy, silicon, and SiO(2)). The process is called "IndentationThis paper describes the use of a nanoindenter, equipped with a diamond tip, to form patterns of indentations on planar substrates (epoxy, silicon, and SiO(2)). The process is called "Indentation Lithography" (IndL). The indentations have the form of pits and furrows, whose cross-sectional profiles are determined by the shapes of the diamond indenters, and whose dimensions are determined by the applied load and hardness of the substrate. IndL makes it possible to indent hard materials, to produce patterns with multiple levels of relief by changing the loading force, and to control the profiles of the indentations by using indenters with different shapes. This paper also demonstrates the transfer of indented patterns to elastomeric PDMS stamps for soft lithography, and to thin films of evaporated gold or silver. Stripping an evaporated film from an indented template produces patterns of gold or silver pyramids, whose tips concentrate electric fields. Patterns produced by IndL can thus be used as substrates for surface-enhanced Raman scattering (SERS) and for other plasmonic applications.

• Step-growth polymerization of inorganic nanoparticles.

  Authors: Kun Liu, Zhihong Nie, Nana Zhao, Wei Li, Michael Rubinstein, Eugenia Kumacheva

  Science (New York, N.Y.). 07/2010; 329(5988):197-200.

  Self-organization of nanoparticles is an efficient strategy for producing nanostructures with complex, hierarchical architectures. The past decade has witnessed great progress in nanoparticleSelf-organization of nanoparticles is an efficient strategy for producing nanostructures with complex, hierarchical architectures. The past decade has witnessed great progress in nanoparticle self-assembly, yet the quantitative prediction of the architecture of nanoparticle ensembles and of the kinetics of their formation remains a challenge. We report on the marked similarity between the self-assembly of metal nanoparticles and reaction-controlled step-growth polymerization. The nanoparticles act as multifunctional monomer units, which form reversible, noncovalent bonds at specific bond angles and organize themselves into a colloidal polymer. We show that the kinetics and statistics of step-growth polymerization enable a quantitative prediction of the architecture of linear, branched, and cyclic self-assembled nanostructures; their aggregation numbers and size distribution; and the formation of structural isomers.

• Electrochemical sensing in paper-based microfluidic devices.

  Authors: Zhihong Nie, Christian A Nijhuis, Jinlong Gong, Xin Chen, Alexander Kumachev, Andres W Martinez, Max Narovlyansky, George M Whitesides

  Lab on a chip. 02/2010; 10(4):477-83.

  This paper describes the fabrication and the performance of microfluidic paper-based electrochemical sensing devices (we call the microfluidic paper-based electrochemical devices, microPEDs). TheThis paper describes the fabrication and the performance of microfluidic paper-based electrochemical sensing devices (we call the microfluidic paper-based electrochemical devices, microPEDs). The microPEDs comprise paper-based microfluidic channels patterned by photolithography or wax printing, and electrodes screen-printed from conducting inks (e.g., carbon or Ag/AgCl). We demonstrated that the microPEDs are capable of quantifying the concentrations of various analytes (e.g., heavy-metal ions and glucose) in aqueous solutions. This low-cost analytical device should be useful for applications in public health, environmental monitoring, and the developing world.

• Properties and emerging applications of self-assembled structures made from inorganic nanoparticles.

  Authors: Zhihong Nie, Alla Petukhova, Eugenia Kumacheva

  Nature nanotechnology. 01/2010; 5(1):15-25.

  Just as nanoparticles display properties that differ from those of bulk samples of the same material, ensembles of nanoparticles can have collective properties that are different to those displayedJust as nanoparticles display properties that differ from those of bulk samples of the same material, ensembles of nanoparticles can have collective properties that are different to those displayed by individual nanoparticles and bulk samples. Self-assembly has emerged as a powerful technique for controlling the structure and properties of ensembles of inorganic nanoparticles. Here we review different strategies for nanoparticle self-assembly, the properties of self-assembled structures of nanoparticles, and potential applications of such structures. Many of these properties and possible applications rely on our ability to control the interactions between the electronic, magnetic and optical properties of the individual nanoparticles.

• Close-Packed Superlattices of Side-by-Side Assembled Au-CdSe Nanorods.

  Authors: Nana Zhao, Kun Liu, Jesse Greener, Zhihong Nie, Eugenia Kumacheva

  Nano letters. 08/2009;

  We report solution-based side-by-side self-assembly of Au-tipped CdSe nanorods (NRs) in large two-dimensional superlattices and the deposition of these lattices on a substrate with NRs alignedWe report solution-based side-by-side self-assembly of Au-tipped CdSe nanorods (NRs) in large two-dimensional superlattices and the deposition of these lattices on a substrate with NRs aligned perpendicular to the surface. The side-by-side assembly of the NRs was triggered by changing the solvent quality for the ligands coating the long side of the nanorods. The stability of the self-assembled superlattices was enhanced due to the hydrogen bonding between the ligands attached to the Au tips of the nanorods. The reported approach can further facilitate the hierarchical integration of multicomponent NRs into functional devices.

• A Microfluidic Approach to Chemically Driven Assembly of Colloidal Particles at Gas-Liquid Interfaces.

  Authors: Jai Il Park, Zhihong Nie, Alexander Kumachev, Ahmed I Abdelrahman, Bernard P Binks, Howard A Stone, Eugenia Kumacheva

  Angewandte Chemie (International ed. in English). 04/2009;

• An "inside-out" microfluidic approach to monodisperse emulsions stabilized by solid particles.

  Authors: Zhihong Nie, Jai Il Park, Wei Li, Stefan A F Bon, Eugenia Kumacheva

  Journal of the American Chemical Society. 01/2009; 130(49):16508-9.

• Multi-Step Microfluidic Polymerization Reactions Conducted in Droplets: The Internal Trigger Approach.

  Authors: Wei Li, Hung Pham, Zhihong Nie, Brendan Macdonald, Axel Güenther, Eugenia Kumacheva

  Journal of the American Chemical Society. 08/2008;

  We report the application of the "internal trigger" approach to multistep microfluidic polymerization reactions conducted in droplets, namely, polyaddition and polycondensation. We hypothesized andWe report the application of the "internal trigger" approach to multistep microfluidic polymerization reactions conducted in droplets, namely, polyaddition and polycondensation. We hypothesized and experimentally established that heat generated in an exothermic free radical polymerization of an acrylate monomer (Reaction 1) triggers the polycondensation of the urethane oligomer (Reaction 2). Completion of two microfluidic polymerization reactions led to the continuous synthesis of polymer particles with an interpenetrating polymer network (IPN) structure. Use of this microfluidic synthesis allowed us (i) to conduct efficient screening of the compositions of the monomer mixtures; (ii) to achieve control of the stoichiometric ratios of reactants in Reaction 2 by varying the flow rates of liquids; (iii) to reach control over the morphology of the resulting particles; and (iv) to produce polymer particles with a narrow size distribution and a predetermined size.

• Patterning surfaces with functional polymers.

  Authors: Zhihong Nie, Eugenia Kumacheva

  Nature materials. 05/2008; 7(4):277-90.

  The ability to pattern functional polymers at different length scales is important for research fields including cell biology, tissue engineering and medicinal science and the development of opticsThe ability to pattern functional polymers at different length scales is important for research fields including cell biology, tissue engineering and medicinal science and the development of optics and electronics. The interest and capabilities of polymer patterning have originated from the abundance of functionalities of polymers and a wide range of applications of the patterns. This paper reviews recent advances in top-down and bottom-up patterning of polymers using photolithography, printing techniques, self-assembly of block copolymers and instability-induced patterning. Finally, challenges and future directions are discussed from the point of view of both applicability and strategies for the surface patterning of polymers.

• Microfluidic synthesis of macroporous copolymer particles

  Authors: Stanislav Dubinsky, Hong Zhang, Zhihong Nie, Ilya, Gourevich, Dan Voicu, Martin Deetz, Eugenia Kumacheva

  MACROMOLECULES. 05/2008; 41(10):3555.

  Macroporous copolymer particles have a broad range of applications such as ion exchange resins and sorbents, catalyst supports, and carriers of biologically active species. Many of these applicationsMacroporous copolymer particles have a broad range of applications such as ion exchange resins and sorbents, catalyst supports, and carriers of biologically active species. Many of these applications require precise control of the dimensions of microbeads in the range from 50 to 100 mu m and predetermined size of pores. IN This paper reports semicontinuous photoinitiated microfluidic synthesis of macroporous polymer particles with the designated dimensions and a range of internal structures. Comparison with microspheres synthesized by conventional suspension polymerization shows,that microfluidic synthesis provides better control over the porous structure of the microbeads.

• "Supramolecular" assembly of gold nanorods end-terminated with polymer "pom-poms": effect of pom-pom structure on the association modes.

  Authors: Zhihong Nie, Daniele Fava, Michael Rubinstein, Eugenia Kumacheva

  Journal of the American Chemical Society. 04/2008; 130(11):3683-9.

  We report a predefined self-organization of gold nanorods (NRs) end-terminated with multiple polymer arms ("pom-poms") in higher-order structures. The assembly of polymer-tethered NRs was controlledWe report a predefined self-organization of gold nanorods (NRs) end-terminated with multiple polymer arms ("pom-poms") in higher-order structures. The assembly of polymer-tethered NRs was controlled by changing the structure of the polymer pom-poms. We show that the variation in the molecular weight of the polymer molecules and their relative location with respect to the long side of the NRs resulted in two competing association modes of the nanorods, that is, their side-by-side and end-to-end assembly, and produced bundles, chains, rings, and bundled chains of the NRs. The superposition of the two variables controlling the organization of NRs allowed us to create a map showing the variation in the longitudinal plasmonic bands of the NRs achieved by their self-assembly.

• Self-assembly of metal-polymer analogues of amphiphilic triblock copolymers.

  Authors: Zhihong Nie, Daniele Fava, Eugenia Kumacheva, Shan Zou, Gilbert C Walker, Michael Rubinstein

  Nature materials. 09/2007; 6(8):609-14.

  Organized arrays of anisotropic nanoparticles show electronic and optical properties that originate from the coupling of shape-dependent properties of the individual nanorods. The organization ofOrganized arrays of anisotropic nanoparticles show electronic and optical properties that originate from the coupling of shape-dependent properties of the individual nanorods. The organization of nanorods in a controllable and predictable way provides a route to the fabrication of new materials and functional devices. So far, significant progress has been achieved in the self-assembly of nanorod arrays, yet the realization of a range of different structures requires changing the surface chemistry of the nanoparticles. We organized metal nanorods in structures with varying geometries by using a striking analogy between amphiphilic ABA triblock copolymers and the hydrophilic nanorods tethered with hydrophobic polymer chains at both ends. The self-assembly was tuneable and reversible and it was achieved solely by changing the solvent quality for the constituent blocks. This approach provides a new route to the organization of anisotropic nanoparticles by using the strategies that are established for the self-assembly of block copolymers.

• Screening of the effect of surface energy of microchannels on microfluidic emulsification.

  Authors: Wei Li, Zhihong Nie, Hong Zhang, Chantal Paquet, Minseok Seo, Piotr Garstecki, Eugenia Kumacheva

  Langmuir : the ACS journal of surfaces and colloids. 08/2007; 23(15):8010-4.

  We report the results of a systematic study of the effect of the surface energy of the walls of microchannels on emulsification in parallel flow-focusing microfluidic devices. We investigated theWe report the results of a systematic study of the effect of the surface energy of the walls of microchannels on emulsification in parallel flow-focusing microfluidic devices. We investigated the formation of water-in-oil (W/O) and oil-in-water (O/W) emulsions and found that the stability of microfluidic emulsification depends critically on the preferential wetting of the walls of the microfluidic device by the continuous phase. The condition for stable operation of the device is, however, different than that of complete wetting of the walls by the continuous phase at equilibrium. We found that W/O emulsions form when the advancing contact angle of water on the channel wall exceeds theta approximately 92 degrees. This result is unexpected because at equilibrium even for theta < 92 degrees the microchannels would be completely wet by the organic phase. The criterion for the formation of W/O emulsions (theta > 92 degrees) is thus more stringent than the equilibrium conditions. Conversely, we observed the stable formation of O/W emulsions for theta < 92 degrees, that is, when the nonequilibrium transition to complete wetting by oil takes place. These results underlie the importance of pinning and the kinetic wetting effects in microfluidic emulsification. The results suggest that the use of parallel devices can facilitate fast screening of physicochemical conditions for emulsification.

• Microfluidic production of biopolymer microcapsules with controlled morphology.

  Authors: Hong Zhang, Ethan Tumarkin, Raheem Peerani, Zhihong Nie, Ruby May A Sullan, Gilbert C Walker, Eugenia Kumacheva

  Journal of the American Chemical Society. 10/2006; 128(37):12205-10.

  We report a microfluidic approach to generating capsules of biopolymer hydrogels. Droplets of an aqueous solution of a biopolymer were emulsified in an organic phase comprising a cross-linking agent.We report a microfluidic approach to generating capsules of biopolymer hydrogels. Droplets of an aqueous solution of a biopolymer were emulsified in an organic phase comprising a cross-linking agent. Polymer gelation was achieved in situ (on a microfluidic chip) by diffusion-controlled ionic cross-linking of the biopolymer, following the transfer of the cross-linking agent from the continuous phase to the droplets. Gelation was quenched by collecting particles in a large pool of cross-linking agent-free liquid. The structure of microgels (from capsules to gradient microgels to particles with a uniform structure) was controlled by varying the time of residence of droplets on the microfluidic chip and the concentration of the cross-linking agent in the continuous phase. We demonstrated the encapsulation of a controlled number of polystyrene beads in the microgel capsules. The described approach was applied to the preparation of capsules of several polysaccharides such as alginate, kappa-carrageenan, and carboxymethylcellulose.

• Janus and ternary particles generated by microfluidic synthesis: design, synthesis, and self-assembly.

  Authors: Zhihong Nie, Wei Li, Minseok Seo, Shengqing Xu, Eugenia Kumacheva

  Journal of the American Chemical Society. 08/2006; 128(29):9408-12.

  This paper reports a microfluidic method for fast continuous synthesis of Janus particles and three-phase particles with narrow size distribution. Synthesis of particles included emulsification ofThis paper reports a microfluidic method for fast continuous synthesis of Janus particles and three-phase particles with narrow size distribution. Synthesis of particles included emulsification of monomer liquids and in-situ photoinitiated polymerization of multiphase droplets. We show the strategy for precise control over the structure of Janus particles and their structure-dependent assembly in clusters. We demonstrate an asymmetric chemical modification of the surface of JPs by conjugating them with protein molecules. The Janus and ternary particles were synthesized from largely immiscible liquids and had a sharp interface between the constituent phases.

• Continuous microfluidic reactors for polymer particles.

  Authors: Minseok Seo, Zhihong Nie, Shengqing Xu, Michelle Mok, Patrick C Lewis, Robert Graham, Eugenia Kumacheva

  Langmuir : the ACS journal of surfaces and colloids. 01/2006; 21(25):11614-22.

  This article provides an overview of our work in the area of the synthesis of polymer particles in continuous microfluidic reactors. The method includes (a) the generation of highly monodisperseThis article provides an overview of our work in the area of the synthesis of polymer particles in continuous microfluidic reactors. The method includes (a) the generation of highly monodisperse monomer droplets in a microfluidic flow-focusing device and (b) in-situ solidification of these droplets by means of photopolymerization. We discuss the effect of monomer properties on the emulsification process, the effect of the polymerization rate on the production of high-quality particles, the role of the material of the microfluidic device in droplet formation, and the synthesis of particles with different shapes and compositions. We also demonstrate the production of highly ordered arrays of polymer particles achieved by photopolymerization of the dynamic lattices of monomer droplets in microfluidic channels. The article is concluded with a summary of future research directions in the production of polymer colloids in microfluidic reactors.