Publications by authors named "Gi-Ra Yi"

110 Publications

Patchy Colloidal Clusters with Broken Symmetry.

J Am Chem Soc 2021 Aug 15;143(33):13175-13183. Epub 2021 Aug 15.

School of Chemical Engineering, Sungkyunkwan University, Suwon, Gyeonggi 16419, Republic of Korea.

Colloidal clusters are prepared by assembling positively charged cross-linked polystyrene (PS) particles onto negatively charged liquid cores of swollen polymer particles. PS particles at the interface of the liquid core are closely packed around the core due to interfacial wetting. Then, by evaporating solvent in the liquid cores, polymers in the cores are solidified and the clusters are cemented. As the swelling ratio of PS cores increases, cores at the center of colloidal clusters are exposed, forming patchy colloidal clusters. Finally, by density gradient centrifugation, high-purity symmetric colloidal clusters are obtained. When silica-PS core-shell particles are swollen and serve as the liquid cores, hybrid colloidal clusters are obtained in which each silica nanoparticle is relocated to the liquid core interface during the swelling-deswelling process breaking symmetry in colloidal clusters as the silica nanoparticle in the core is comparable in size with the PS particle in the shell. The configuration of colloidal clusters is determined once the number of particles around the liquid core is given, which depends on the size ratio of the liquid core and shell particle. Since hybrid clusters are heavier than PS particles, they can be purified using centrifugation.
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http://dx.doi.org/10.1021/jacs.1c05123DOI Listing
August 2021

Large-scale synthesis of colloidal bowl-shaped particles.

Soft Matter 2021 Jun;17(25):6176-6181

Center for Soft Matter Research, Department of Physics, New York University, New York, NY 10003, USA. and Department of Chemical & Biomolecular Engineering, Tandon School of Engineering, New York University, Brooklyn, New York 11201, USA.

We describe a general procedure for the large-scale fabrication of bowl-shaped colloidal particles using an emulsion templating technique. Following this method, single polymeric seed particles become located on individual oil droplet surfaces. The polymer phase is subsequently plasticized using an appropriate solvent. In this critical step, the compliant seed is deformed by surface tension, with the droplet serving as a templating surface. Solvent evaporation freezes the desired particle shape and the oil is subsequently removed by alcohol dissolution. The resulting uniformly-shaped colloidal particles were studied using scanning electron and optical microscopy. By adjusting the droplet size and the seed particle diameter, we demonstrate that the final particle shape can be controlled precisely, from shallow lenses to deep bowls. We also show that the colloid's uniformity and abundant quantity allowed the depletion-mediated assembly of flexible colloidal chains and clusters.
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http://dx.doi.org/10.1039/d0sm00793eDOI Listing
June 2021

Morphologically homogeneous, pH-responsive gold nanoparticles for non-invasive imaging of HeLa cancer.

Nanomedicine 2021 06 13;34:102394. Epub 2021 Apr 13.

Division of Bioconvergence Analysis, Korea Basic Science Institute, Cheongju, Republic of Korea; Bio-Analytical Science, University of Science and Technology, Daejeon, Republic of Korea. Electronic address:

Gold nanoparticles (AuNPs) have been widely used as nanocarriers in drug delivery to improve the efficiency of chemotherapy treatment and enhance early disease detection. The advantages of AuNPs include their excellent biocompatibility, easy modification and functionalization, facile synthesis, low toxicity, and controllable particle size. This study aimed to synthesize a conjugated citraconic anhydride link between morphologically homogeneous AuNPs and doxorubicin (DOX) (DOX-AuNP). The carrier was radiolabeled for tumor diagnosis using positron emission tomography (PET). The systemically designed DOX-AuNP was cleaved at the citraconic anhydride linker site under the mild acidic conditions of a cancer cell, thereby releasing DOX. Subsequently, the AuNPs aggregated via electrostatic attraction. HeLa cancer cells exhibited a high uptake of the radiolabeled DOX-AuNP. Moreover, PET tumor images were obtained using radiolabeled DOX-AuNP in cancer xenograft mouse models. Therefore, DOX-AuNP is expected to provide a valuable insight into the use of radioligands to detect tumors using PET.
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http://dx.doi.org/10.1016/j.nano.2021.102394DOI Listing
June 2021

Molecular Weight Dependent Morphological Transitions of Bottlebrush Block Copolymer Particles: Experiments and Simulations.

ACS Nano 2021 Mar 16;15(3):5513-5522. Epub 2021 Feb 16.

Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea.

The molecular weights and chain rigidities of block copolymers can strongly influence their self-assembly behavior, particularly when the block copolymers are under confinement. We investigate the self-assembly of bottlebrush block copolymers (BBCPs) confined in evaporative emulsions with varying molecular weights. A series of symmetric BBCPs, where polystyrene (PS) and polylactide (PLA) side-chains are grafted onto a polynorbornene (PNB) backbone, are synthesized with varying degrees of polymerization of the PNB () ranging from 100 to 300. Morphological transitions from onion-like concentric particles to striped ellipsoids occur as the of the BBCP increases above 200, which is also predicted from coarse-grained simulations of BBCP-containing droplets by an implicit solvent model. This transition is understood by the combined effects of (i) an elevated entropic penalty associated with bending lamella domains of large molecular weight BBCP particles and (ii) the favorable parallel alignment of the backbone chains at the free surface. Furthermore, the morphological evolutions of onion-like and ellipsoidal particles are compared. Unlike the onion-like BBCP particles, ellipsoidal BBCP particles are formed by the axial development of ring-like lamella domains on the particle surface, followed by the radial propagation into the particle center. Finally, the shape anisotropies of the ellipsoidal BBCP particles are analyzed as a function of particle size. These BBCP particles demonstrate promising potential for various applications that require tunable rheological, optical, and responsive properties.
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http://dx.doi.org/10.1021/acsnano.1c00263DOI Listing
March 2021

Reconfigurable Transitions between One- and Two-Dimensional Structures with Bifunctional DNA-Coated Janus Colloids.

ACS Nano 2020 11 22;14(11):15786-15792. Epub 2020 Oct 22.

Center for Soft Matter Research and Department of Physics, New York University, New York, New York 10003, United States.

Coating colloidal particles with DNA provides one of the most versatile and powerful methods for controlling colloidal self-assembly. Previous studies have shown how combining DNA coatings with DNA strand displacement allows one to design phase transitions between different three-dimensional crystal structures. Here we show that by using DNA coatings with bifunctional colloidal Janus particles, we can realize reconfigurable thermally reversible transitions between one- and two-dimensional self-assembled colloidal structures. We introduce a colloidal system in which DNA-coated asymmetric Janus particles can reversibly switch their Janus balance in response to temperature, resulting in the reconfiguration of assembling structures between colloidal chains and bilayers. Each face of the Janus particles is coated with different self-complementary DNA strands. Toehold strand displacement is employed to selectively activate or deactivate the sticky ends on the smaller face, which enables Janus particles to selectively assemble through either the smaller or larger face. This strategy could be useful for constructing complex systems that could be reconfigured to assemble into different structures in different environments.
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http://dx.doi.org/10.1021/acsnano.0c06846DOI Listing
November 2020

Colloidal diamond.

Nature 2020 09 23;585(7826):524-529. Epub 2020 Sep 23.

Department of Chemical and Biomolecular Engineering, New York University, Brooklyn, NY, USA.

Self-assembling colloidal particles in the cubic diamond crystal structure could potentially be used to make materials with a photonic bandgap. Such materials are beneficial because they suppress spontaneous emission of light and are valued for their applications as optical waveguides, filters and laser resonators, for improving light-harvesting technologies. Cubic diamond is preferred for these applications over more easily self-assembled structures, such as face-centred-cubic structures, because diamond has a much wider bandgap and is less sensitive to imperfections. In addition, the bandgap in diamond crystals appears at a refractive index contrast of about 2, which means that a photonic bandgap could be achieved using known materials at optical frequencies; this does not seem to be possible for face-centred-cubic crystals. However, self-assembly of colloidal diamond is challenging. Because particles in a diamond lattice are tetrahedrally coordinated, one approach has been to self-assemble spherical particles with tetrahedral sticky patches. But this approach lacks a mechanism to ensure that the patchy spheres select the staggered orientation of tetrahedral bonds on nearest-neighbour particles, which is required for cubic diamond. Here we show that by using partially compressed tetrahedral clusters with retracted sticky patches, colloidal cubic diamond can be self-assembled using patch-patch adhesion in combination with a steric interlock mechanism that selects the required staggered bond orientation. Photonic bandstructure calculations reveal that the resulting lattices (direct and inverse) have promising optical properties, including a wide and complete photonic bandgap. The colloidal particles in the self-assembled cubic diamond structure are highly constrained and mechanically stable, which makes it possible to dry the suspension and retain the diamond structure. This makes these structures suitable templates for forming high-dielectric-contrast photonic crystals with cubic diamond symmetry.
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http://dx.doi.org/10.1038/s41586-020-2718-6DOI Listing
September 2020

Cavitation-Inducible Mesoporous Silica-Titania Nanoparticles for Cancer Sonotheranostics.

Adv Healthc Mater 2020 10 7;9(19):e2000877. Epub 2020 Sep 7.

Department of Health Sciences and Technology, SAIHST, Sungkyunkwan University, 81 Irwon-ro, Gangnam-gu, Seoul, 06351, Republic of Korea.

Sonodynamic therapy has received increasing attention for cancer treatments as an alternative to photodynamic therapy. However, its clinical applications have been limited by the lack of a sonosensitizer that is capable of producing sufficient amounts of reactive oxygen species (ROS) in response to ultrasound (US) exposure. Herein, PEGylated mesoporous silica-titania nanoparticles (P-MSTNs) are prepared and used as US-responsive nanocarriers for cancer sonotheranostics. Perfluorohexane (PFH), which is chosen as the gas precursor, is physically encapsulated into P-MSTNs using the oil-in-water emulsion method. Owing to the vaporization of the gas precursor, [email protected] (137 nm in diameter) exhibit a strong photoacoustic signal in vivo for at least 6 h. Compared to P-MSTNs, [email protected] generate significantly higher amounts of ROS due to the nanobubble-induced cavitation in the presence of US. When systemically administered to tumor-bearing mice, [email protected] effectively accumulate in the tumor site due to the passive targeting mechanism. Consequently, [email protected] show much higher antitumor efficacy than P-MSTNs due to the enhanced cavitation-mediated ROS generation in response to US exposure. It is considered that [email protected] may hold significant potential for cancer sonotheranostics.
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http://dx.doi.org/10.1002/adhm.202000877DOI Listing
October 2020

Tunable Photonic Microspheres of Comb-Like Supramolecules.

Small 2020 Jul 22;16(29):e2001315. Epub 2020 Jun 22.

State Key Lab of Materials Processing and Die and Mould Technology and Key Lab of Materials Chemistry for Energy Conversion and Storage of Ministry of Education (HUST), School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology (HUST), Wuhan, 430074, China.

Photonic crystals (PCs) are ideal candidates for reflective color pigments with high color purity and brightness due to tunable optical stop band. Herein, the generation of PC microspheres through 3D confined supramolecular assembly of block copolymers (polystyrene-block-poly(2-vinylpyridine), PS-b-P2VP) and small molecules (3-n-pentadecylphenol, PDP) in emulsion droplets is demonstrated. The intrinsic structural colors of the PC microspheres are effectively regulated by tuning hydrogen-bonding interaction between P2VP blocks and PDP, where reflected color can be readily tuned across the whole visible spectrum range. Also, the effects of both PDP and homopolymer (hPS) on periodic structure and optical properties of the microspheres are investigated. Moreover, the spectral results of finite element method (FEM) simulation agree well with the variation of structural colors by tuning the periodicity in PC microspheres. The supramolecular microspheres with tunable intrinsic structural color can be potentially useful in the various practical applications including display, anti-counterfeit printing and painting.
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http://dx.doi.org/10.1002/smll.202001315DOI Listing
July 2020

Photo-printing of faceted DNA patchy particles.

Proc Natl Acad Sci U S A 2020 05 8;117(20):10645-10653. Epub 2020 May 8.

Department of Physics and Center for Soft Matter Research, New York University, New York, NY 10003;

Patchy particles with shape complementarity can serve as building blocks for assembling colloidal superstructures. Alternatively, encoding information on patches using DNA can direct assembly into a variety of crystalline or other preprogrammed structures. Here, we present a tool where DNA is used both to engineer shape and to encode information on colloidal particles. Two reactive oil emulsions with different but complementary DNA (cDNA) brushes are assembled into CsCl-like crystalline lattices. The DNA brushes are recruited to and ultimately localized at the junctions between neighboring droplets, which gives rise to DNA-encoded faceted patches. The emulsions are then solidified by ultraviolet (UV) polymerization, producing faceted patchy particles. The facet size and DNA distribution are determined by the balance between the DNA binding energy and the elastic deformation energy of droplets. This method leads to a variety of new patchy particles with directional interactions in scalable quantities.
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http://dx.doi.org/10.1073/pnas.1918504117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7245101PMC
May 2020

Strong Coupling of Carbon Quantum Dots in Plasmonic Nanocavities.

ACS Appl Mater Interfaces 2020 Apr 15;12(17):19866-19873. Epub 2020 Apr 15.

School of Mathematics and Physics, Queen's University Belfast, Belfast BT7 1NN, U.K.

Confining light in extremely small cavities is crucial in nanophotonics, central to many applications. Employing a unique nanoparticle-on-mirror plasmonic structure and using a graphene film as a spacer, we create nanoscale cavities with volumes of only a few tens of cubic nanometers. The ultracompact cavity produces extremely strong optical near-fields, which facilitate the formation of single carbon quantum dots in the cavity and simultaneously empower the strong coupling between the excitons of the formed carbon quantum dot and the localized surface plasmons. This is manifested in the optical scattering spectra, showing a magnificent Rabi splitting of up to 200 meV under ambient conditions. In addition, we demonstrate that the strong coupling is tuneable with light irradiation. This opens new paradigms for investigating the fundamental light emission properties of carbon quantum dots in the quantum regime and paves the way for many significant applications.
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http://dx.doi.org/10.1021/acsami.0c03312DOI Listing
April 2020

Reconfigurable Self-Assembly and Kinetic Control of Multiprogrammed DNA-Coated Particles.

ACS Nano 2020 04 25;14(4):4595-4600. Epub 2020 Mar 25.

Center for Soft Matter Research, Department of Physics, New York University, New York, New York 10003, United States.

DNA is a unique molecule for storing information, which is used to provide particular biological instructions. Its function is primarily determined by the sequence of its four nucleobases, which have highly specific base-pairing interactions. This unique feature can be applied to direct the self-assembly of colloids by grafting DNA onto them. Due to the sequence-specific interactions, colloids can be programmed with multiple instructions. Here, we show that particles having multiple DNA strands with different melting profiles can undergo multiple phase transitions and reassemble into different crystalline structures in response to temperature. We include free DNA strands in the medium to selectively switch on and off DNA hybridization depending on temperature. We also demonstrate that DNA hybridization kinetics can be used as a means to achieve targeted assembling structure of colloids. These transitions impart a reconfigurability to colloids in which systems can be transformed an arbitrary number of times using thermal and kinetic control.
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http://dx.doi.org/10.1021/acsnano.0c00164DOI Listing
April 2020

High-Density DNA Coatings on Carboxylated Colloids by DMTMM- and Azide-Mediated Coupling Reactions.

Langmuir 2020 04 30;36(13):3583-3589. Epub 2020 Mar 30.

Center for Soft Matter Research and Department of Physics, New York University, New York, New York 10003, United States.

DNA-mediated colloidal interactions provide a powerful strategy for the self-assembly of ordered superstructures. We report a practical and efficient two-step chemical method to graft DNA brushes onto carboxylated particles, which resolves the previously reported issues such as irreversible aggregation, inhomogeneous coating, and relatively low DNA density that can hinder colloidal crystallization. First, carboxylated particles are functionalized with heterobifunctional poly(ethylene glycol) (NH-PEG-N) by 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM)-activated esterification of carboxylic groups and amide coupling. Then, dibenzocyclooctyne (DBCO)-functionalized DNA strands are grafted onto the pegylated particles through strain-promoted alkyne-azide cycloaddition (SPAAC) on azide groups. The homogeneous PEG brushes provide dispersion stability to the particles and clickable functional groups, resulting in DNA coatings of 1 100 000 DNA per 1 μm particle or 1 DNA per 2.9 nm, about five times higher than previously reported. The DNA-coated particles exhibit a sharp association-dissociation transition and readily self-assemble into colloidal crystals upon annealing. In addition, fluorinated particles and lens-shaped particles with carboxylate groups are successfully grafted with DNA strands in this manner. Janus particles are also functionalized with DNA strands selectively on one of the two faces. Owing to the anisotropic attraction, the DNA-coated Janus particles self-assemble into self-limiting aggregates.
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http://dx.doi.org/10.1021/acs.langmuir.9b03386DOI Listing
April 2020

The effect of blob size in polymer networks on nanoparticle-mediated adhesion of hydrogels.

Soft Matter 2019 Dec;15(48):9942-9948

School of Chemical Engineering, Sungkyunkwan University, Suwon 16419, Republic of Korea.

Silica nanoparticles can be used as an adhesive for hydrogels or biological tissues due to their physical adsorption to polymer chains. Recently, we found that mesoporous nanoparticles were able to enhance the adhesion energy between hydrogels compared with non-porous nanoparticles because of the higher outer surface area of mesoporous silica nanoparticles. However, even in the case that the outer surface areas of mesoporous silica nanoparticles are similar, mesoporous nanoparticles with larger pore diameters showed significantly higher nanoparticle-mediated adhesion energy between hydrogels with a swelling ratio of 400%. Here, we have changed the swelling ratio of hydrogels in the preparation step so that the blob size in the polymer network changed accordingly. In experimental data, we found that the optimum pore size of mesoporous nanoparticles increased as the blob size increased for higher swelling ratio, which is ascribed to the larger blob size of polymer networks in hydrogels.
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http://dx.doi.org/10.1039/c9sm01805kDOI Listing
December 2019

Free-Standing Ion-Conductive Gels Based on Polymerizable Imidazolium Ionic Liquids.

Langmuir 2019 Dec 5;35(50):16624-16629. Epub 2019 Dec 5.

School of Chemical Engineering , Sungkyunkwan University , Suwon 16419 , Republic of Korea.

A free-standing ion-conductive gel is formed by spontaneous self-assembly of the amphiphilic ionic liquid 1-tetradecyl-3-methylimidazolium chloride (CMIm·Cl) and the cross-linkable monomer 6-hexanediol diacrylate (HDODA) in a mixed solvent of 1-octene, 1-butanol, and water. The ionic conductivity of this ion gel is 24 mS cm at 33 °C. To enhance the mechanical strength of the ion gels, the acrylate ionic liquid 1-(2-acryloyloxyundecyl)-3-methylimidazolium bromide (A-CMIm·Br) was added, leading to significant morphological changes of the HDODA phase from spherical, ellipsoid, angular platelets to interconnected with increasing addition of the acrylate ionic liquid and consequent enhancement in the mechanical strength of the resulting ion gels. Small angle X-ray scattering data reveal that the ion gels are composed of bicontinuous phase. The formation of the anisotropic HDODA structures upon introduction of the acrylate ionic liquid was accompanied by a change of the bicontinuous phase to be undulated, which increased the ionic path through the formed film, resulting in reduced ionic conductivity. Such coaxial structured gels may be a promising route for developing highly ion-conductive as well as mechanically stable solid electrolyte systems.
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http://dx.doi.org/10.1021/acs.langmuir.9b03080DOI Listing
December 2019

Synthesis of silver nanoparticles colloids in imidazolium halide ionic liquids and their antibacterial activities for gram-positive and gram-negative bacteria.

Chemosphere 2020 Mar 6;243:125302. Epub 2019 Nov 6.

School of Chemical Engineering, Sungkyunkwan University, Suwon, 16419, Republic of Korea.

Four 1-butyl-3-methylimidazolium halide ionic liquids were synthesized via metathesis and anion exchange reactions. Silver nanoparticles (AgNPs) colloids were synthesized in four ionic liquids in the pressurized reactor by reduction of silver nitrate with hydrogen gas, without adding solvents or stabilizing agents. Antibacterial activities of base ionic liquids and AgNPs colloids in ionic liquids were reviewed by well-diffusion method for gram-positive Bacillus cereus (NCIM-2155) and gram-negative Escherichia coli (NCIM-2931) bacteria. Antibacterial activities of ionic liquids and AgNPs colloids in ionic liquids were observed to be controlled by ionic liquids anions and AgNPs particle size. The 1-butyl-3-methylimidazolium iodide ionic liquid exhibited higher antibacterial activities among the studied ionic liquids. Further, the presence of AgNPs in 1-butyl-3-methylimidazolium iodide, ionic liquid enhanced its antibacterial activity for Bacillus cereus and Escherichia coli bacteria.
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http://dx.doi.org/10.1016/j.chemosphere.2019.125302DOI Listing
March 2020

Enhancing the Wound Healing Effect of Conditioned Medium Collected from Mesenchymal Stem Cells with High Passage Number Using Bioreducible Nanoparticles.

Int J Mol Sci 2019 Sep 28;20(19). Epub 2019 Sep 28.

School of Chemical Engineering, Sungkyunkwan University, Suwon 16419, Korea.

Injecting human mesenchymal stem cells (hMSCs) at wound sites is known to have a therapeutic effect; however, hMSCs have several limitations, such as low viability and poor engraftment after injection, as well as a potential risk of oncogenesis. The use of a conditioned medium (CM) was suggested as an alternative method for treating various wounds instead of direct hMSC administration. In addition to not having the adverse effects associated with hMSCs, a CM can be easily mass produced and can be stored for long-term, thereby making it useful for clinical applications. In general, a CM is collected from hMSCs with low passage number; whereas, the hMSCs with high passage number are usually discarded because of their low therapeutic efficacy as a result of reduced angiogenic factor secretion. Herein, we used a CM collected from high passage number (passage 12, P12) hMSCs treated with gold-iron nanoparticles (AuFe NPs). Our AuFe NPs were designed to release the iron ion intracellularly via endocytosis. Endosomes with low pH can dissolve iron from AuFe NPs, and thus, the intracellularly released iron ions up-regulate the hypoxia-inducible factor 1α and vascular endothelial growth factor (VEGF) expression. Through this mechanism, AuFe NPs improve the amount of VEGF expression from P12 hMSCs so that it is comparable to the amount of VEGF expression from low passage number (passage 6, P6), without treatment. Furthermore, we injected the CM retrieved from P12 MSCs treated with AuFe NPs in the mouse skin wound model (AuFe P12 group). AuFe P12 group revealed significantly enhanced angiogenesis in the mouse skin wound model compared to the high passage hMSC CM-injected group. Moreover, the result from the AuFe P12 group was similar to that of the low passage hMSC CM-injected group. Both the AuFe P12 group and low passage hMSC CM-injected group presented significantly enhanced re-epithelization, angiogenesis, and tissue remodeling compared to the high passage hMSC CM-injected group. This study reveals a new strategy for tissue regeneration based on CM injection without considering the high cell passage count.
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http://dx.doi.org/10.3390/ijms20194835DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6801963PMC
September 2019

Colloidal fibers and rings by cooperative assembly.

Nat Commun 2019 09 2;10(1):3936. Epub 2019 Sep 2.

Center for Soft Matter Research, Department of Physics, New York University, New York, NY, 10003, USA.

Janus colloids with one attractive patch on an otherwise repulsive particle surface serve as model systems to explore structure formation of particles with chemically heterogeneous surfaces such as proteins. While there are numerous computer studies, there are few experimental realizations due to a lack of means to produce such colloids with a well-controlled variable Janus balance. Here, we report a simple scalable method to precisely vary the Janus balance over a wide range and selectively functionalize one patch with DNA. We observe, via experiment and simulation, the dynamic formation of diverse superstructures: colloidal micelles, chains, or bilayers, depending on the Janus balance. Flexible dimer chains form through cooperative polymerization while trimer chains form by a two-stage process, first by cooperative polymerization into disordered aggregates followed by condensation into more ordered stiff trimer chains. Introducing substrate binding through depletion catalyzes dimer chains to form nonequilibrium rings that otherwise do not form.
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http://dx.doi.org/10.1038/s41467-019-11915-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6718632PMC
September 2019

Active Patchy Colloids with Shape-Tunable Dynamics.

J Am Chem Soc 2019 09 5;141(37):14853-14863. Epub 2019 Sep 5.

Department of Chemistry , The University of Hong Kong , Pokfulam Road , Hong Kong SAR , China.

Controlling the complex dynamics of active colloids-the autonomous locomotion of colloidal particles and their spontaneous assembly-is challenging yet crucial for creating functional, out-of-equilibrium colloidal systems potentially useful for nano- and micromachines. Herein, by introducing the synthesis of active "patchy" colloids of various low-symmetry shapes, we demonstrate that the dynamics of such systems can be precisely tuned. The low-symmetry patchy colloids are made in bulk via a cluster-encapsulation-dewetting method. They carry essential information encoded in their shapes (particle geometry, number, size, and configurations of surface patches, etc.) that programs their locomotive and assembling behaviors. Under AC electric field, we show that the velocity of particle propulsion and the ability to brake and steer can be modulated by having two asymmetrical patches with various bending angles. The assembly of monopatch particles leads to the formation of dynamic and reconfigurable structures such as spinners and "cooperative swimmers" depending on the particle's aspect ratios. A particle with two patches of different sizes allows for "directional bonding", a concept popular in static assemblies but rare in dynamic ones. With the capability to make tunable and complex shapes, we anticipate the discovery of a diverse range of new dynamics and structures when other external stimuli (e.g., magnetic, optical, chemical, etc.) are employed and spark synergy with shapes.
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http://dx.doi.org/10.1021/jacs.9b07785DOI Listing
September 2019

DNA functionalization of colloidal particles via physisorption of azide-functionalized diblock copolymers.

Soft Matter 2019 Sep 2;15(35):6930-6933. Epub 2019 Aug 2.

School of Chemical Engineering, Sungkyunkwan University, Suwon 16419, Republic of Korea.

DNA-coated inorganic particles can be prepared simply by physical adsorption of azide-functionalized diblock copolymers (polystyrene-b-poly(ethylene oxide)-azide, PS-b-PEO-N) onto hydrophobically-modified inorganic particles, followed by strain-promoted azide-alkyne cycloaddition (SPAAC, copper-free click chemistry). This approach is applied to organosilica, silica and titania particles. The DNA-coated colloids are successfully crystallized into colloidal superstructures by a thermal annealing process using DNA-mediated assembly.
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http://dx.doi.org/10.1039/c9sm01243eDOI Listing
September 2019

Si nanoparticle clusters in hollow carbon capsules ([email protected]) as lithium battery anodes: toward high initial coulombic efficiency.

Nanoscale 2019 Jul 10;11(28):13650-13658. Epub 2019 Jul 10.

SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University (SKKU), Suwon 16419, Republic of Korea. and School of Chemical Engineering, Sungkyunkwan University (SKKU), Suwon 16419, Republic of Korea.

Large volumetric expansion and structural pulverization have been major problems in Si-based anode materials for Li-ion batteries. To overcome this limitation, yolk-shell structured Si-carbon structures have been proposed to allow for the reversible structural breathing of Si nanoparticles confined inside the carbon shell. However, initial coulombic efficiency (ICE) of the yolk-shell structured anodes is highly decreased mainly due to their extremely high specific surface area (SSA) and the resulting excessive formation of solid electrolyte interphase (SEI) over the carbon shell. Here, instead of using a single Si nanoparticle-containing yolk-shell structure, we propose a novel structure comprising hollow carbon capsules internally encapsulating Si nanoparticle clusters ([email protected]). To implement this structural design, Si nanoparticle clusters are encompassed by a polystyrene matrix ([email protected]) by emulsion polymerization, followed by coating with a polydopamine (PDA) layer ([email protected]@PDA). Then, after annealing them for carbonization, [email protected] are finally prepared, which can decrease the SSA by a factor of one-third compared to the conventional yolk-shell structures. These [email protected] particles have shown remarkably high ICE values of up to 81%. Moreover, the cycling stability could be improved up to 100 cycles because the properly confined Si cluster inside the stable carbon capsule mitigates structural pulverization during repeated lithiation-delithiation processes of Si nanoparticles.
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http://dx.doi.org/10.1039/c9nr04074aDOI Listing
July 2019

Fluorinated Titania Nanoparticle-Induced Piezoelectric Phase Transition of Poly(vinylidene fluoride).

Langmuir 2019 Jul 19;35(26):8816-8822. Epub 2019 Jun 19.

School of Chemical Engineering , Sungkyunkwan University , Suwon 16419 , Republic of Korea.

We prepared F-coated rutile titanium dioxide nanoparticles (r-TiO NPs) via simple thermal annealing of titania NPs in poly(vinylidene fluoride) (PVDF) and demonstrated that the F-coated r-TiO NP-doped composite film could efficiently induce piezoelectric phase transition of non-electroactive PVDF due to highly electronegative F bonds on the surface of these NPs. In the case of a 2.0 wt % composite film, 99.20% of the non-electroactive PVDF was transformed into the electroactive phase. Additionally, utilizing the F-coated r-TiO NPs for a piezoelectric device led to an enhancement of the piezoelectric performance. With the 5.0 wt % composite film, the resulting piezoelectric device exhibited voltage generation of 355 mV, whereas a device with the innate r-TiO NPs exhibited voltage generation of only 137 mV. Furthermore, because of optical inactivity of F-coated r-TiO NPs, the piezoelectric films exhibited high stability under 64 h of photoirradiation at an intensity of 0.1 W/cm. These results indicate that the F-coated r-TiO NP-doped composite films could be useful for various applications, including outdoor energy-harvesting, self-powered wearable devices, and portable sensors.
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http://dx.doi.org/10.1021/acs.langmuir.9b00546DOI Listing
July 2019

Solution-Processable Photonic Inks of Mie-Resonant Hollow Carbon-Silica Nanospheres.

Small 2019 Jun 30;15(23):e1900931. Epub 2019 Apr 30.

School of Chemical Engineering, Sungkyunkwan University, Suwon, 16419, Republic of Korea.

Hollow carbon-silica nanospheres that exhibit angle-independent structural color with high saturation and minimal absorption are made. Through scattering calculations, it is shown that the structural color arises from Mie resonances that are tuned precisely by varying the thickness of the shells. Since the color does not depend on the spatial arrangement of the particles, the coloration is angle independent and vibrant in powders and liquid suspensions. These properties make hollow carbon-silica nanospheres ideal for applications, and their potential in making flexible, angle-independent films and 3D printed films is explored.
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http://dx.doi.org/10.1002/smll.201900931DOI Listing
June 2019

Hypoxia-Responsive Mesoporous Nanoparticles for Doxorubicin Delivery.

Polymers (Basel) 2018 Apr 1;10(4). Epub 2018 Apr 1.

School of Chemical Engineering, Sungkyunkwan University, Suwon 16419, Korea.

Hypoxia, or low oxygen tension, is a common feature of solid tumors. Here, we report hypoxia-responsive mesoporous silica nanoparticles (HR-MSNs) with a 4-nitroimidazole-β-cyclodextrin (NI-CD) complex that is acting as the hypoxia-responsive gatekeeper. When these CD-HR-MSNs encountered a hypoxic environment, the nitroimidazole (NI) gatekeeper portion of CD-HR-MSNs disintegrated through bioreduction of the hydrophobic NI state to the hydrophilic NI state. Under hypoxic conditions, the release rate of doxorubicin (DOX) from DOX-loaded CD-HR-MSNs (DOX-CD-HR-MSNs) increased along with the disintegration of the gatekeeper. Conversely, DOX release was retarded under normoxic conditions. In vitro experiments confirmed that DOX-CD-HR-MSNs exhibit higher toxicity to hypoxic cells when compared to normoxic cells. Confocal microscopy images indicated that DOX-CD-HR-MSNs effectively release DOX into SCC-7 cells under hypoxic conditions. These results demonstrate that CD-HR-MSNs can release drugs in a hypoxia-responsive manner, and thus are promising drug carriers for hypoxia-targeted cancer therapy.
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http://dx.doi.org/10.3390/polym10040390DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6415200PMC
April 2018

Carbon-Based, Ultraelastic, Hierarchically Coated Fiber Strain Sensors with Crack-Controllable Beads.

ACS Appl Mater Interfaces 2019 Apr 9;11(16):15079-15087. Epub 2019 Apr 9.

Fiber-based electronics or textronics are spotlighted as a promising strategy to develop stretchable and wearable devices for conformable machine-human interface and ubiquitous healthcare systems. We have prepared a highly sensitive fiber-type strain sensor (maximum gauge factor (GF) = 863) with a broad range of strain (ε < 400%) by introducing a single active layer onto the fiber. In contrast to other metal-based fiber-type electronics, our hierarchical fiber sensors are based on coating carbon-based nanomaterials with responsive microbeads onto elastic fibers. Utilizing the formation of uniform cracks around the microbeads, the device performance was maximized by adjusting the number of microbeads in the carbon-coating layer. We overcoated the carbon-based coating layer of the elastic fiber with a protective polymeric layer and verified no effects on the GF and the range of strain. Our fiber sensors were repeatedly tested more than 5000 times, exhibiting excellent cyclic responses to on/off switching behaviors. For practical applications, the hierarchical fiber sensors were sewed into electrical fabric bands, which are integrable to a wireless transmitter to monitor waveforms of pulsations, respirations, and various postures of level of bending a spinal cord.
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http://dx.doi.org/10.1021/acsami.9b03204DOI Listing
April 2019

Pyrochlore lattice, self-assembly and photonic band gap optimizations.

Opt Express 2018 Nov;26(23):30052-30060

Non-spherical colloidal building blocks introduce new design principles for self-assembly, making it possible to realize optical structures that could not be assembled previously. With this added complexity, the phase space expands enormously so that computer simulation becomes a valuable tool to design and assemble structures with useful optical properties. We recently demonstrated that tetrahedral clusters and spheres, interacting through a DNA-mediated short-range attractive interaction, self-assemble into a superlattice of interpenetrating diamond and pyrochlore sublattices, but only if the clusters consist of partially overlapping spheres. Here we show how the domain of crystallization can be extended by implementing a longer range potential and consider how the resultant structures affect the photonic band gaps of the underlying pyrochlore sublattice. We show that with the proper design, using clusters of overlapping spheres lead to larger photonic band gaps that open up at lower optical contrast.
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http://dx.doi.org/10.1364/OE.26.030052DOI Listing
November 2018

LDR-Induced miR-30a and miR-30b Target the PAI-1 Pathway to Control Adverse Effects of NSCLC Radiotherapy.

Mol Ther 2019 02 26;27(2):342-354. Epub 2018 Oct 26.

Department of Integrated Biological Science, Pusan National University, Busan 46241, Republic of Korea; Department of Biological Sciences, Pusan National University, Busan 46241, Republic of Korea. Electronic address:

Radiotherapy has been a central part in curing non-small cell lung cancer (NSCLC). However, it is possible that not all of the tumor cells are destroyed by radiation; therefore, it is important to effectively control residual tumor cells that could become aggressive and resistant to radiotherapy. In this study, we aimed to investigate the molecular mechanism of decreased NSCLC radioresistance by low-dose radiation (LDR) pretreatment. The results indicated that miR-30a and miR-30b, which effectively inhibited plasminogen activator inhibitor-1 (PAI-1), were overexpressed by treatment of LDR to NSCLC cells. Phosphorylation of Akt and ERK, the downstream survival signals of PAI-1, was decreased by PAI-1 inhibition. Reduced cell survival and epithelial-mesenchymal transition by PAI-1 inhibition were confirmed in NSCLC cells. Moreover, in vivo orthotopic xenograft mouse models with 7C1 nanoparticles to deliver miRNAs showed that tumor growth and aggressiveness were efficiently decreased by LDR treatment followed by radiotherapy. Taken together, the present study suggested that PAI-1, whose expression is regulated by LDR, was critical for controlling surviving tumor cells after radiotherapy.
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http://dx.doi.org/10.1016/j.ymthe.2018.10.015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6369577PMC
February 2019

Chemically Resistant Perfluoroalkoxy Nanoparticle-Packed Porous Substrates and Their Use in Colorimetric Sensor Arrays.

Langmuir 2018 10 16;34(43):13014-13024. Epub 2018 Oct 16.

iSense LLC , Mountain View , California 94043 , United States.

To create printing substrates for colorimetric sensor arrays, chemically resistant membranes are prepared by coating cellulose filter paper with perfluoroalkoxy (PFA) polymer nanoparticles. A water-based fluorothermoplastic polymer dispersion was diluted with an organic solvent that causes weak aggregation of polymer nanoparticles. The resulting solution improved adhesion between the polymer and the cellulose membrane, providing a more mechanically stable substrate. These PFA polymer-coated substrates demonstrated superior chemical resistance against strong alkalines and had relatively uniform nanoporous structures that substantially improved the printability of a colorimetric sensor array. Finally, colorimetric sensor arrays printed on these substrates were evaluated for the detection of four different toxic industrial chemicals (e.g., ammonia, hydrogen sulfide, nitrogen dioxide, and sulfur dioxide) at or below their permissible exposure limits.
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http://dx.doi.org/10.1021/acs.langmuir.8b02481DOI Listing
October 2018

Roll-to-roll redox-welding and embedding for silver nanowire network electrodes.

Nanoscale 2018 Oct 27;10(39):18627-18634. Epub 2018 Sep 27.

SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon 440-746, Republic of Korea.

We developed a continuous roll-to-roll redox-welding and embedding method for the fabrication of electrodes of silver nanowire (AgNWs) networks. The roll-to-roll welding method involved a sequence of oxidation and reduction reactions in an aqueous solution. The redox-welding significantly decreased the sheet resistance of the AgNW film owing to the strong fusion and interlocking at the nanowire junction, while the optical transmittance was maintained. The first oxidation step using HNO generated ionized silver (Ag) which got re-deposited onto the nanowire junctions via an autocatalytic reaction. The oxide layers, which formed on the nanowire surface by both air exposure and the first step of oxidation, were removed by the second reduction step using NaBH. The redox-welded AgNW electrodes exhibited a sheet resistance of 11.3 Ω sq at the optical transmittance of 90.5% at 550 nm. Furthermore, redox-welding of the AgNWs significantly enhanced their mechanical robustness compared to that of the as-coated AgNWs. The redox-welded AgNWs embedded in a UV curable resin, using a roll-to-roll embedding process, were successfully applied as anode electrodes for large-area and flexible organic light emitting diodes (OLEDs). The device performance is superior to that of a device based on the as-coated AgNW electrode, and is also comparable to that of a device using commercial ITO as the electrode. The redox-welding and embedding processes provide a facile and reliable method for fabricating large-area transparent flexible electrodes for next-generation flexible optoelectronic devices.
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http://dx.doi.org/10.1039/c8nr01040dDOI Listing
October 2018

Transition of Dielectrophoresis-Assembled 2D Crystals to Interlocking Structures under a Magnetic Field.

Langmuir 2018 10 5;34(41):12412-12418. Epub 2018 Oct 5.

Department of Chemical Engineering and Materials Science , Stevens Institute of Technology , Hoboken , New Jersey 07030 , United States.

Aspherical cubic hematite colloids with cylindrical arms protruding from each face, referred to as "hexapods", were assembled via negative dielectrophoresis and then manipulated using an applied magnetic field. Upon application of an ac electric field, the hexapods aligned in close-packed linear chains parallel to the field direction. The chains then aggregated to the center of the device, with adjacent chains separated by distances approximately equal to twice the arm length. The resulting open packing structure exhibited cmm plane group symmetry due to the obstruction of arms, with a high density of incorporated defects. Subsequent application of a magnetic field to the dielectrophoresis (DEP)-assembled structure was found to anneal the colloidal crystal by reorienting the hexapods to align their intrinsic magnetic dipoles with the magnetic field direction. During reorganization, the colloidal packing density was found to decrease by more than 10% at both the center and edges of the crystal, accompanied by a significant loss of ordering, prior to redensification of the 2D lattice with fewer defects. Reorganization at the edge was 1.5 times faster than at the center, consistent with the need for cooperative colloidal motion to remove defects at the centers of the crystals.
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http://dx.doi.org/10.1021/acs.langmuir.8b02706DOI Listing
October 2018

Correction: Compressible colloidal clusters from Pickering emulsions and their DNA functionalization.

Chem Commun (Camb) 2018 09;54(77):10921

School of Chemical Engineering, Sungkyunkwan University, Suwon 16419, Republic of Korea.

Correction for 'Compressible colloidal clusters from Pickering emulsions and their DNA functionalization' by In-Seong Jo et al., Chem. Commun., 2018, 54, 8328-8331.
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http://dx.doi.org/10.1039/c8cc90402bDOI Listing
September 2018
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