Abstracts for Publications 41-60

60. W. Y. L. Ko, H. G. Bagaria, S. Asokan, K.-J. Lin and M. S. Wong, "CdSe Tetrapod Synthesis Using Cetyltrimethylammonium Bromide and Heat Transfer Fluids," J. Mater. Chem. 20(12), 2474-2478 (2010) DOI:10.1039/b922145j


The synthesis of CdSe tetrapod-shaped quantum dots using phenyl-based heat transfer fluids as inexpensive alternatives to octadecene solvent was studied. The CdSe tetrapods were synthesized using the hot-injection method, in which the trioctylphosphine selenide precursor and the shape-inducing cetyltrimethylammonium bromide surfactant were injected into a cadmium oleate-containing solvent at 190 °C. At a synthesis temperature of 160 °C, the resulting quantum dot particles were found to grow more slowly in heat transfer fluids and pure phenyl-type solvents than in octadecene. With synthesis time, the selectivity to tetrapods increased, and the arms grew proportionally in width and length. The use of heat transfer fluids provides a convenient means to control growth of shaped nanoparticles.

59. G. C. Kini, J. Lai, M. S. Wong, and S. L. Biswal, "Microfluidic Formation of Ionically Cross-Linked Polyamine Gels," Langmuir (online) DOI:10.1021/la903983y


In this article, we discuss in situ polymer gelation in microfluidic channels from electrostatically mediated interactions when reactant streams of a linear cationic polymer (poly(allylamine hydrochloride, PAH) and a multivalent anion (sodium citrate) are subjected to shear flow. We find that the polyamine exhibits shear-thickening behavior as it is ionically cross-linked by citrate ions to form viscoelastic gel phases. These gels form at room temperature and remain stable and intact after the cessation of flow. Gelation is found to occur in the polymer stream and not the citrate stream because of an appreciably higher diffusivity of citrate ions when compared to the gel and PAH and because of laminar flow conditions in the microfluidic environment. Gel formation occurred when the pH of the PAH stream was below the PAH pKa value of 8.38 and when citrate was either in a disodium or trisodium state. The formation of aggregates, gels, and droplets was found to depend strongly on the charge ratio and flow conditions. The gelation of PAH begins with the formation of colloidal aggregates of PAH and citrate, which then combine under shear flow to form noncontinuous or continuous gels. Droplets of citrate can form within regions of continuous gels as excess citrate anions diffuse into the gel stream.

58. J. Yu, D. Javier, M. A. Yaseen, N. Nitin, R. Richards-Kortum, B. Anvari and M.S. Wong, "Self-assembly Synthesis, Tumor Cell Targeting, and Photothermal Capabilities of Antibody-coated Indocyanine Green Nanocapsules," J. Am. Chem. Soc., 132(6), 1929-1938 (2010). DOI:10.1021/ja908139y


New colloidal materials that can generate heat upon irradiation are being explored for photothermal therapy as a minimally invasive approach to cancer treatment. The near-infrared dye indocyanine green (ICG) could serve as a basis for such a material, but its encapsulation and subsequent use are difficult to carry out. We report the three-step room-temperature synthesis of 120-nm capsules loaded with ICG within salt-cross-linked polyallylamine aggregates, and coated with antiepidermal growth factor receptor (anti-EGFR) antibodies for tumor cell targeting capability. We studied the synthesis conditions such as temperature and water dilution to control the capsule size and characterized the size distribution via dynamic light scattering and scanning electron microscopy. We further studied the specificity of tumor cell targeting using three carcinoma cell lines with different levels of EGFR expression and investigated the photothermal effects of ICG containing nanocapsules on EGFR-rich tumor cells. Significant thermal toxicity was observed for encapsulated ICG as compared to free ICG at 808 nm laser irradiation with radiant exposure of 6 W/cm2. These results illustrate the ability to design a colloidal material with cell targeting and heat generating capabilities using noncovalent chemistry.

57. W. Zhou, E. I. Ross-Medgaarden, W. V. Knowles, M. S. Wong, I. E. Wachs and C. J. Kiely, "Identification of Active Zr–WOx Clusters on a ZrO2 Support for Solid Acid Catalysts," Nature. Chem 1, 722-728 (2009). DOI:10.1038/NCHEM.433


Tungstated zirconia is a robust solid acid catalyst for light alkane (C4–C8) isomerization. Several structural models for catalytically active sites have been proposed, but the topic remains controversial, partly because of the absence of direct structural imaging information on the various supported WOx species. High-angle annular dark-field imaging of WO3/ZrO2 catalysts in an aberration-corrected analytical electron microscope allows, for the first time, direct imaging of the various species present. Comparison of the relative distribution of these WOx species in materials showing low and high catalytic activities has allowed the deduction of the likely identity of the catalytic active site—namely, subnanometre Zr–WOx clusters. This information has subsequently been used in the design of new catalysts, in which the activity of a poor catalyst has been increased by two orders of magnitude using a synthesis procedure that deliberately increases the number density of catalytically relevant active species.

56. S. E. Plush, M. Woods, Y. Zhou, S. B. Kadali, M. S. Wong and A. D. Sherry, "Nanoassembled Capsules as Delivery Vehicles for Large Payloads of High Relaxivity Gd3+ Agents,"J. Am. Chem. Soc., 131(43), 15918–15923 (2009). DOI:10.1021/ja906981w


Nanoassembled capsules (NACs) that incorporate a polymer aggregate inside a silica shell may be loaded with agents that are of particular interest for therapeutic or diagnostic applications. NACs formed using the MRI contrast agent GdDOTP5− in the internal polymer aggregate are reported herein, the smaller of which show promise as potential MRI contrast agents. Unlike many other nanoencapsulated systems, water access to the inner core of these NACs does not appear to be limited and consequently the water relaxivity per Gd3+ agent can reach as high as 24 mM−1 s−1. Robust, spherical capsules were formed using polyallylamine or poly-l-lysine ranging from 0.2 to 5 μm in diameter. The greatest gains in relaxivity were observed for smaller NACs, for which water accessibility remained high but molecular rotation of the Gd3+ chelate was effectively restricted. Larger NACs did not afford such large gains in relaxivity, the result of poorer water accessibility combined with less-effective rotational restriction.

55. M. A. Yaseen, J. Yu, B. Jung, M. S. Wong, and B. Anvari, "Biodistribution of Encapsulated
Indocyanine Green in Healthy Mice," Mol. Pharmaceutics, online (2009).
DOI: 10.1021/mp800270t


Indocyanine green (ICG) is a fluorescent probe used in various optically mediated diagnostic and therapeutic applications. However, utility of ICG remains limited by its unstable optical properties and nonspecific localization. We have encapsulated ICG within electrostatically assembled mesocapsules (MCs) to explore its potential for targeted optical imaging and therapy. In this study, we investigate how the surface coating and size of the MCs influences ICG’s biodistribution in vivo. ICG was administered intravenously to Swiss Webster mice as a free solution or encapsulated within either 100 nm diameter MCs coated with dextran; 500 nm diameter MCs coated with dextran; or 100 nm diameter MCs coated with 10 nm ferromagnetic iron oxide nanoparticles, themselves coated with polyethylene glycol. ICG was extracted from harvested blood and organs at various times and its amount quantified with fluorescence measurements. MCs containing ICG accumulated in organs of the reticuloendothelial system, namely, the liver and spleen, as well as the lungs. The circulation kinetics of ICG appeared unaffected by encapsulation; however, the deposition within organs other than the liver suggests a different biodistribution mechanism. Results suggest that the capsules’ coating influences their biodistribution to a greater extent than their size. The MC encapsulation system allows for delivery of ICG to organs other than the liver, enabling the potential development of new optical imaging and therapeutic strategies.

54. K. N. Heck, M. O. Nutt, P. Alvarez, and M. S. Wong, "Deactivation Resistance of Pd/Au
Nanoparticle Catalysts for Water-phase Hydrodechlorination," J. Catal. 267, 97-104 (2009) DOI:10.1016/j.jcat.2009.07.015

Catalysts for Water-Phase Hydrodechlorination

Palladium-decorated gold nanoparticles (Pd/Au NPs) have recently been shown to be highly efficient for trichloroethene hydrodechlorination, as a new approach in the treatment of groundwater contaminated with chlorinated solvents. Problematically, natural groundwater can contain chloride and sulfide ions, which are known poisons in Pd-based catalysis. In this study, the effects of chloride and sulfide on the trichloroethene hydrodechlorination catalytic activity were examined for non-supported Pd/Au NPs and Pd NPs, and alumina-supported Pd (Pd/Al2O3). Over the concentration range of 0-0.02 M NaCl, the catalytic activity of Pd/Au NPs was unaffected, while the activities of both the Pd NPs and Pd/Al2O3 catalyst dropped by ~70%. Pd/Au NPs were found to be highly resistant to sulfide poisoning, deactivating completely at a ratio of sulfide to surface Pd atom (S:Pdsurf) of at least 1, compared to Pd NPs deactivating completely at a ratio of 0.5. Pd/Al2O3 retained activity at a ratio of 0.5, pointing to a beneficial role of the Al2O3 support. Sulfide poisoning of Pd/Au NPs with different Pd surface coverages provided a way to assess the nature of active sites. The gold component was found to enhance both Pd catalytic activity and poisoning resistance for room-temperature, water-phase trichloroethene hydrodechlorination.

Graphical Abstract:

The effects of chloride and sulfide on water-phase trichloroethene hydrodechlorination using Pd-on-Au nanoparticles (Pd/Au NPs), Pd NPs, and alumina-supported Pd were studied. Pd/Au NPs were resistant to chloride poisoning unlike monometallic Pd, and they showed greater resistance to sulfide poisoning than monometallic Pd. Lower Pd content surface coverages led to less activity but resistance to sulfide poisoning.

53. S. Leekumjorn and M. S. Wong, "Self-assembly of Nanoparticle Building Blocks," in
Comprehensive Nanoscience and Technology, Volume 3 (Nanoscale Self Assembly), D. Andrews, G. Wiederrecht and G. D. Scholes, Eds., Elsevier: Oxford, 5, 203-224 (2011). DOI: 10.1016/B978-0-12-374396-1.00053-2
Self-Assembly of Nanoparticle Building Blocks

Sukit Leekumjorn and Michael S. Wong

This chapter provides an overview of recent experimental and simulations work in the self-assembly of nanoparticles into structured materials.  The self-assembly of nanoparticle building blocks through substrate assembly, interfacial assembly, and template-assisted assembly is discussed.  Nanoparticle-assembled capsules are highlighted as an example of template-assisted assembly.  The effects of nanoparticle dimensionality, shape, and composition are discussed, with quantum dot tetrapods as a material of interest.  The computational approach to nanoparticle self-assembly is reviewed and assessed.

52. E. Muñoz Tavera, S. B. Kadali, H. G. Bagaria, A. W. Liu,and M. S. Wong ,"Experimental and Modeling Analysis of Diffusive Release from Single-shell Microcapsules," AIChE J. DOI:10.1002/aic.11914
There is much experimental and mathematical work that describes chemical transport from multilayered films of planar geometries. There is less so, however, for chemical transport from multilayered spheres, a common structure for controlled-release materials. Based on the Sturm-Liouville approach of Ramkrishna and Amundson (1974), explicit analytical solutions for the concentration profiles and release kinetics from spherical capsules are presented. Fluorescent dye-release studies using single-shelled microspheres called nanoparticle-assembled capsules were performed to validate the model for uniformly and nonuniformly sized capsules. The combined experiment-modeling approach allows optical microscopy images and release measurements to be readily analyzed for estimating diffusion coefficients in capsule core and shell walls.

51. V.S. Murthy, S.B. Kadali, and M.S. Wong, "Polyamine-Guided Synthesis of Anisotropic, Multicompartment Microparticles," Appl. Mater. Interfac., 1, 590-596 (2009). DOI:10.1021/am8001499

Colloidal particles that have nonuniform bulk or surface compositions are of emerging interest because of their potential applications involving advanced chemical storage and delivery and the self-assembly of novel functional materials. Experimental realization of anisotropic particles is much more difficult than that for particles with uniform bulk and surface composition, however. A new wet-chemical synthesis method to anisotropic microparticles is presented. This approach makes convenient use of the unusual observation of a salt-triggered separation of two water-solubilized polyamines into colloidal aggregates with nonuniform polymer composition. The anisotropic structure of these ionically cross-linked aggregates is explained by the difference in surface tensions of the contained single-polymer domains. Contacting the polymer aggregates with silicic acid or 13-nm silica nanoparticles leads to the charge-driven formation of solid or hollow microspheres, respectively. Depending on the poly(lysine)/poly(allylamine) ratio, the nonuniformity of the polymer aggregates translates to surface patches or internal compartments found in the resultant silica/polymer microparticles. Such hybrid materials with their unique structure could serve as a new basis for targeted chemical delivery and controlled release for potential applications in medicine, food, and cosmetics.

50. E. I. Ross-Medgaarden, I. E. Wachs, W. V. Knowles, A. Burrows, C. J. Kiely, and M. S. Wong, "Tuning the Electronic and Molecular Structure of Catalytic Active Sites with Titania Nanoligands," J. Am. Chem. Soc., 131, 680-687 (2009). DOI:10.1021/ja711456c

A series of supported 1−60% TiO2/SiO2 catalysts were synthesized and subsequently used to anchor surface VOx redox and surface WOx acid sites. The supported TiOx, VOx, and WOx phases were physically characterized with TEM, in situ Raman and UV−vis spectroscopy, and chemically probed with in situ CH3OH-IR, CH3OH-TPSR and steady-state CH3OH dehydration. The CH3OH chemical probe studies revealed that the surface VOx sites are redox in nature and the surface WOx sites contain acidic character. The specific catalytic activity of surface redox (VO4) and acidic (WO5) sites coordinated to the titania nanoligands are extremely sensitive to the degree of electron delocalization of the titania nanoligands. With decreasing titania domain size, <10 nm, acidic activity increases and redox activity decreases due to their inverse electronic requirements. This is the first systematic study to demonstrate the ability of oxide nanoligands to tune the electronic structure and reactivity of surface metal oxide catalytic active sites.

49. M.S. Wong, P. J.J. Alvarez, Y.L. Fang, N. Akcin, M. O. Nutt, J. T. Miller, and K. N. Heck, "Cleaner Water using Bimetallic Nanoparticle Catalysts" J. Chem. Tech. & Biotech, 84, 158-166 (2009). DOI:10.1002/jctb.2002
Groundwater contaminated by hazardous chlorinated compounds, especially chlorinated ethenes, continues to be a significant environmental problem in industrialized nations. The conventional treatment methods of activated carbon adsorption and air-stripping successfully remove these compounds by way of transferring them from the water phase into the solid or gas phase. Catalysis is a promising approach to remove chlorinated compounds completely from the environment, by converting them into safer, non-chlorinated compounds. Palladium-based materials have been shown to be very effective as hydrodechlorination catalysts for the removal of chlorinated ethenes and other related compounds. However, relatively low catalytic activity and a propensity for deactivation are significant issues that prevent their widespread use in groundwater remediation. Palladium-on-gold bimetallic nanoparticles, in contrast, were recently discovered to exhibit superior catalyst activity and improved deactivation resistance. This new type of material is a significant next-step in the development of a viable hydrodechlorination catalysis technology.

48. Q. Li, M. B. Tomson, M. S. Wong, and P. J. J. Alvarez, "Nanotechnology: A Source for
Answers to the Global Clean Water Challenge," Water 21, Magazine of the International
Water Association, August 26-28 (2008)

No abstract yet.

47. M.A. Yaseen, J. Yu, M.S. Wong and B. Anvari, "In-vivo Fluorescence Imaging of Mammalian Organs using Charge-assembled Mesocapsule Constructs Containing Indocyanine Green" Optics Express, 16 (25), 20577-20587 (2008). DOI:10.1364/OE.16.020577
Indocyanine green (ICG) is a fluorescent probe used in clinical imaging. However, its utility remains limited by optical instability, rapid circulation kinetics, and exclusive uptake by the liver. Using mesocapsule (MC) constructs to encapsulate ICG, we have developed a technology to stabilize ICG’s optical properties and alter its biodistribution. We present in vivo fluorescence images of mammalian organs to demonstrate the potential application of our ICG encapsulation technology for optical imaging of specific tissues.

46. K.N. Heck, B.G. Janesko, G.E. Scuseria, N.J. Halas and M.S.Wong, "Observing Metal-Catalyzed Chemical Reactions in Situ Using Surface-Enhanced Raman Spectroscopy on Pd-Au Nanoshells" J. Am. Chem. Soc. , 130 (49), 16592–16600 (2008). DOI:10.1021/ja803556k

Insight into the nature of transient reaction intermediates and mechanistic pathways involved in heterogeneously catalyzed chemical reactions is obtainable from a number of surface spectroscopic techniques. Carrying out these investigations under actual reaction conditions is preferred but remains challenging, especially for catalytic reactions that occur in water. Here, we report the direct spectroscopic study of the catalytic hydrodechlorination of 1,1-dichloroethene in H2O using surface-enhanced Raman spectroscopy (SERS). With Pd islands grown on Au nanoshell films, this reaction can be followed in situ using SERS, exploiting the high enhancements and large active area of Au nanoshell SERS substrates, the transparency of Raman spectroscopy to aqueous solvents, and the catalytic activity enhancement of Pd by the underlying Au metal. The formation and subsequent transformation of several adsorbate species was observed. These results provide the first direct evidence of the room-temperature catalytic hydrodechlorination of a chlorinated solvent, a potentially important pathway for groundwater cleanup, as a sequence of dechlorination and hydrogenation steps. More broadly, the results highlight the exciting prospects of studying catalytic processes in water in situ, like those involved in biomass conversion and proton-exchange membrane fuel cells.

45. M. S. Wong, Book review of Nanoparticles and Catalysis D. Astruc, Ed.; Angew. Chem. 47, 7795-7796 (2008). DOI:10.1002/anie.200785570
No abstract.

44. V. S. Murthy and M. S. Wong, "Enzyme Encapsulation using Nanoparticle-assembled Capsules," in Nanoscale Science and Technology in Biomolecular Catalysis; J. B. Kim, S. H. Kim, and P. Wang, Eds., American Chemical Society: Washington, D.C.; Chapter 13, 214-232 (2008)
We discuss the synthesis and characterization of enzyme-containing nanoparticle-assembled capsules (NACs) using acid phosphatase as the model enzyme. NACs are a new capsular material that can be synthesized rapdily under ambient conditions and mild pH values. Unlike vesiclesand other organic-based hollow sphere structures, NACs can be handled in the absence of water. The hollow forms spontaneously, allowing for non-destructive encapsulation. The enzyme is shown to preserve its activity within the capsules, and a maximum loading and encapsulation efficiency of ~18 wt% and ~70%, respectively, can be achieved. The encapsulated enzymes can be recovered and reused through centrifugation.

43. E. I. Ross-Medgaarden, W. V. Knowles, T. Kim, M. S. Wong, W. Zhou, C. J. Kiely, and I. E. Wachs, "New Insights into the Nature of the Acidic Catalytic Active Sites Present in ZrO2-supported Tungsten Oxide Catalysts," J. Catal. 256, 108-125 (2008) DOI:10.1016/j.jcat.2008.03.003
An extensive series of supported WO3/ZrOx(OH)4−2x catalysts (WZrOH) were synthesized by standard aqueous impregnation of ammonium metatungstate into an amorphous ZrOx(OH)4−2x metastable support, followed by high-temperature calcination (at 773–1173 K). The supported WZrOH catalysts were also compared with well-defined model supported WO3/ZrO2 catalysts (WZrO2) consisting of a thermally stable crystalline m-ZrO2 support. Both series of supported tungsten oxide catalysts were physically characterized (by XRD, XPS, TEM, in situ Raman, and in situ UV–vis spectroscopy) and chemically probed by methanol dehydration (i.e., TPSR spectroscopy and steady-state catalytic studies). Monolayer surface WOx coverage was found to occur at not, vert, similar4.5–5 W-atoms/nm2 for both catalytic systems. Whereas the dehydrated model supported WZrO2 series contained only surface WOx species below monolayer coverage, the dehydrated supported WZrOH series had the same surface WOx species, as well as some Zr-stabilized distorted WO3 nanoparticles (NPs). Above monolayer coverage, the model supported WZrO2 catalysts contained only ordered crystalline WO3 NPs, but the supported WZrOH catalysts had both ordered WO3 NPs and Zr-stabilized distorted WO3 NPs. The comparative methanol dehydration to dimethyl ether acidity study revealed that the Zr-stabilized distorted WO3 NPs were the catalytic active sites in supported WZrOH catalysts. These findings represent a new model for the origin of the enhanced solid acidity of supported WZrOH catalysts.

42. S. B. Kadali, N. Soultanidis, and M. S. Wong, "Assembling Colloidal Silica into Porous Hollow Microspheres," Topic. Catal., 49 (3-4), 251-258 (2008) DOI:10.1007/s11244-008-9079-y
A non-surfactant-based synthesis approach to mesoporous hollow spheres through the use of colloidal silica is presented. Based on nanoparticle assembly chemistry developed previously for silica/polymer hybrid microcapsules, the room-temperature preparation follows a two-step sequence: (1) the electrostatic reaction of cationic polymer with an anionic salt solution, resulting in a suspension of salt-bridged polymer aggregates; and (2) the electrostatic reaction between this suspension and an aqueous suspension of nanoparticles (NPs). As a specific example, 13-nm silica particles, combined with polyallylamine and sodium citrate, gave silica/polymer hollow spheres with a mean diameter of 2.1 μm and a BET surface area of 4 m2/g. After calcination at 600 °C, the resulting silica-only microcapsules had a BET surface area of 259 m2/g, a modal pore size of 4.0 nm, and a pore volume of 0.38 cc/g, values that exceeded those of calcined silica NPs. This colloidal silica-based material is an example of the simultaneous control of pore size (at the nanometer scale) and particle morphology (at the micrometer scale) that is possible through charge-driven NP assembly.

41. M. A. Yaseen, J. Yu, M. S. Wong, and B. Anvari, "Laser-Induced Heating of Dextran-Coated Mesocapsules Containing Indocyanine Green," Biotechnol. Prog., 23 (6), 1431-1440 (2007).
Indocyanine green (ICG) is a photosensitive reagent with clinically relevant diagnostic and therapeutic applications. Recently, ICG has been investigated for its utility as an exogenous chromophore during laser-induced heating. However, ICGapos;s effectiveness remains hindered by its molecular instability, rapid circulation kinetics, and nonspecific systemic distribution. To overcome these limitations, we have encapsulated ICG within dextran-coated mesocapsules (MCs). Our objective in this study was to explore the ability of MCs to induce thermal damage in response to laser irradiation. To simulate tumorous tissue targeted with MCs, cylindrical phantoms were prepared consisting of gelatin, intralipid emulsion, and various concentrations of MCs. The phantoms were embedded within fresh chicken breast tissue representing surrounding normal tissue. The tissue models were irradiated at = 808 nm for 10 min at constant power (P = 4.2 W). Five hypodermic thermocouples were used to record the temperature at various depths below the tissue surface and transverse distances from the laser beam central axis during irradiation. Temperature profiles were processed to remove the baseline temperature and influence of light absorption by the thermocouple and subsequently used to calculate a damage index based on the Arrhenius damage integral. Tissue models containing MCs experienced a maximum temperature change of 18.5 °C. Damage index calculations showed that the heat generation from MCs at these parameters is sufficient to induce thermal damage, while no damage was predicted in the absence of MCs. ICG maintains its heat-generating capabilities in response to NIR laser irradiation when encapsulated within MCs. Such encapsulation provides a potentially useful methodology for laser-induced therapeutic strategies.