Abstracts for Publications 1-20

20. S. Asokan, A. R. Carreon, Z. Mu, K. M. Krueger, A. Alkhawaldeh, V. L. Colvin and M.S. Wong,"Synthesis of High-Quality CdSe Nanocrystals in Heat Transfer Fluids", Proceed. of SPIE, Vol. 5705, Photonics West 2005, 60-67 (2005). DOI: 10.1117/12.597272
Abstract:
Fluorescent semiconductor nanoparticles, or quantum dots, have potential uses as an optical material, in which the optoelectronic properties can be tuned precisely by particle size. Advances in chemical synthesis have led to improvements in size and shape control, cost, and safety. A limiting step in large-scale production is identified to be the raw materials cost, in which a common synthesis solvent, octadecene, accounts for most of the materials cost in a batch of CdSe quantum dots. Thus, less expensive solvents are needed. In this paper, we identify heat transfer fluids, a class of organic liquids commonly used in chemical process industries to transport heat between unit operations, as alternative solvents for quantum dot synthesis. We specifically show that two heat transfer fluids can be used successfully in the synthesis of CdSe quantum dots with uniform particle sizes. We observe differences in particle growth using the various solvents.

19. P. Diagaradjane, M. A. Yaseen, J. Yu, M.S. Wong and B. Anvari, "Autofluorescence Characterization of DMBA/TPA Induced Two-Stage Carcinogenesis in Mouse Skin for the Early Detection of Tissue Transformation", Proceed. of SPIE, Vol. 5686, Photonics West 2005, 41-50 (2005). DOI: 10.1117/12.589328
Abstract:
The use of autofluorescence technique in the characterization of the sequential tissue transformation process in 7,12-dimethylbenz(a)anthracene and 12-O-tetradecanoylphorbol-13-acetate (DMBA & TPA) induced two-stage mouse skin carcinogenesis model in conjunction with a suitable statistical method is being explored. The fluorescence excitation emission matrix (EEM) from experimental group (n=40; DMBA/TPA application), control group (n=6; acetone application) and the blank group (n=6; no application of DMBA/TPA or acetone) were measured every week using Fluoromax3 spectrofluorometer coupled with a waveguide fiber optic bundle (JY Horiba, NJ). The EEM was recorded for 19 excitation wavelengths from 280 to 460 nm at 10 nm intervals and the fluorescence emission was scanned from 300 to 750 nm. During the tissue transformation the epithelial tissues underwent biochemical and structural changes that are manifested in the tissue fluorescence. To correlate the tissue morphology with the observed fluorescence differences in the fluorescence emission, animals were sacrificed and the tissue biopsies were subjected to histopathological evaluation. The fluorescence emission corresponding to different fluorophores was extracted from the EEM, and the spectral data were used in multivariate statistical algorithm for the earliest diagnosis of the onset of tissue transformation. The intrinsic fluorescence from tryptophan, NADH and prophyrins showed distinct differences in the spectral signature during the tissue transformation, due to the altered metabolic activities of the cells. The statistical analysis of the spectral data corresponding to each excitation wavelength showed better classification accuracy at 280, 320, 350 and 405 nm excitations, corresponding to tryptophan, collagen, NADH and porphyrins with the classification accuracy of 74.3, 68.1, 64.6 and 74.7 % respectively. The variations in the spectral signature and the results of the statistical analysis suggest that porphyrins, tryptophan and NADH can be targeted as potential tumor markers in the early detection of the tissue transformation process.

18. M. A. Yaseen, P. Diagaradjane, B. M. Pikkula, J. Yu, M. S. Wong and B. Anvari, " "Photothermal and Photochemical Effects of Laser Light Absorption by Indocyanine Green (ICG)", Proceed. of SPIE, Vol. 5695, Photonics West 2005, 27-35 (2005). DOI: 10.1117/12.589702
Abstract:
Indocyanine Green (ICG) is clinically used as a fluorescent dye for imaging purposes. Its rapid circulation kinetics and minimal toxicity has prompted investigation into ICG's utility as a photosentitizer for therapeutic applications. Traditionally, optically mediated tumor therapy has focused on photodynamic therapy, which employs a photochemical mechanism resulting from the absorption of low intensity CW laser light by localized photosensitizers such as Photofrin II, Benzoporphyrin Derivative (BPD), ICG. Treatment of cutaneous vascular malformations such as port-wine stains, on the other hand, is based on a photothermal mechanism resulting from the absorption of high intensity pulsed laser light by hemoglobin. In this study, we compared the effectiveness of combining photochemical and photothermal mechanisms during application of ICG in conjunction with laser irradiation with the intention that the combined approach may lead to a reduction in the threshold dose of pulsed laser light required to treat hypervascular malformations. The blood vessels in rabbit ears were used as an in vivo model for targeted vasculature. Irradiation of the ears with IR light (lambda=785 nm, Deltatau = 3 min, Io = 120 mW) was used to elicit photochemical damage, while photothermal damage was brought about using pulses from a ruby laser (lambda=694 nm, tau = 3 ms) with different fluences. For the combined modality, photochemical damage was induced first and followed by photothermal irradiation. This modality was compared with photothermal irradiation alone. The effectiveness of each irradiation scheme was assessed using histopathological analysis. We present preliminary data that suggests that pretreatment with photodynamic therapy before photothermal coagulation results in more severe vascular damage with lower photothermal fluence levels. The results of this study provide the foundation work for further exploration of the therapeutic potentials of photochemical and photothermal effects during application of ICG in conjunction with laser irradiation.

17. M. O. Nutt, J. B. Hughes and M. S. Wong, "Designing Pd-on-Au Bimetallic Nanoparticle Catalysts for Trichloroethene Hydrodechlorination," Environ. Sci. Technol. 39, 1346 - 1353 (2005). DOI: 10.1021/es048560b
Abstract:
Alumina-supported palladium (Pd) catalysts have previously been shown to hydrodechlorinate trichloroethene (TCE) and other chlorinated compounds in water, at room temperature, and in the presence of hydrogen. The feasibility of this catalytic technology to remediate groundwater of halogenated compounds can be improved by re-designing the Pd material in order to increase catalytic activity. We synthesized and characterized Pd supported on gold nanoparticles (Au NPs) of different Pd loadings. In all cases, we found that these catalysts were considerably more active than Pd NPs, alumina-supported Pd, and Pd-black (62.0, 12.2, and 0.42 L·gPd-1·min-1, respectively). There is a synergistic effect of the Pd-on-Au bimetallic structure, with the material with the highest TCE hydrodechlorination activity (943 L·gPd-1·min-1) comprised of Au NPs partially covered by Pd metal. The Pd-on-Au bimetallic catalyst structure provides a new synthesis approach in improving the catalytic properties of monometallic Pd materials. The resulting nanoparticle-based materials should be highly suitable as hydrodehalogenation and reduction catalysts for the remediation of various organic and inorganic groundwater contaminants.

16. B. Sitharaman, S. Asokan, I. Rusakova, M. S. Wong and L. J. Wilson, "Nanoscale Aggregation Properties of Neuroprotective Carboxyfullerene (C3) in Aqueous Solution," Nano Lett. 4, 1759-1762 (2004). DOI: 10.1021/nl049315t
Abstract:

 

Water-soluble malonic acid derivatives of C60 are known to have potent antioxidant activity with potential medical applications as neuroprotective agents. It is commonly assumed that e,e,e tris-malonic acid-C60 (or C3) exists as discrete molecules solubilized in aqueous solution. In this work, C3 is revealed to aggregate in water. The aggregation properties have been studied as a function of concentration, temperature, and pH by dynamic light scattering (DLS). The C3 aggregates are polydisperse under physiological conditions, do not vary much in size as a function of concentration or temperature, and tend to larger sizes at low pH values. Transmission electron microscopy (TEM) and cryo-TEM have been used to visualize the morphology of the nanocrystalline aggregates. The results suggest that 40−80 nm aggregates of C3, not individual C3 molecules, are responsible for their neuroprotective action in cells.

15. V. S. Murthy, J. N. Cha, G. D. Stucky and M. S. Wong, "Charge-driven Flocculation of Poly-L-Lysine - Gold Nanoparticle Assemblies Leading to Hollow Microspheres," J. Am. Chem. Soc., 126, 5292-5299 (2004). DOI: 10.1021/ja038953v
Abstract:

 

An unusual aggregation phenomenon that involves positively charged poly(l-lysine) (PLL) and negatively charged gold nanoparticles (Au NPs) is reported. Discrete, submicrometer−sized spherical aggregates are found to form immediately upon combining a PLL solution with gold sol (diameter ≈ 14 nm). These PLL−Au NP assemblies grow in size with time, according to light scattering experiments, which indicates a dynamic flocculation process. Water-filled, silica hollow microspheres (outer diameter ≈ microns) are obtained upon the addition of negatively charged SiO2 NPs (diameter ≈ 13 nm) to a suspension of the PLL−Au NP assemblies, around which the SiO2 NPs form a shell. Structural analysis through confocal microscopy indicates the PLL (tagged with a fluorescent dye) is located in the interior of the hollow sphere, and mostly within the silica shell wall. The hollow spheres are theorized to form through flocculation, in which the charge-driven aggregation of Au NPs by PLL provides the critical first step in the two-step synthesis process (“flocculation assembly”). The SiO2 shell can be removed and re-formed by decreasing and increasing the suspension pH about the point-of-zero charge of SiO2, respectively.

14. M. S. Wong and W. V. Knowles, "Surfactant-Templated Mesostructured Materials: Synthesis and Compositional Control," in Nanoporous Materials - Science and Engineering; G. Q. Lu and X. S. Zhao, Eds.; Imperial College Press: London; Chapter 5, pp. 125-164 (2004).
Abstract:
No Abstract.

13. V. S. Murthy, R. K. Rana, J. Yu and M. S. Wong, "Self-assembly of Inorganic Nanoparticles and Polyelectrolytes into Micron-sized Hollow Sphere Structures," PMSE Preprints 90, 632-633 (2004).
Abstract:
The compositional variety in surfactant-templated mesostructured and mesoporous materials widened tremendously since the initial reports on MCM-41 and M41S aluminosilicate mesoporous molecular sieve materials came out. In this chapter the current state of synthesis and compositional control of mesostructured and mesoporous metal oxides is presented. New surfactant templating synthesis routes, especially those that lead to the formation of non-silicates, are described, and a comprehensive update on the available types of such materials is presented. General trends are noted, which could provide insights towards surfactant-templated materials as yet synthesized.

12. J. A. Kloepfer, R. E. Mielke, M. S. Wong, K. H. Nealson, G. Stucky and J. L. Nadeau, "Quantum Dots as Strain- and Metabolism-Specific Microbiological Labels," Appl. Environ. Microbiol. 69, 4205-4213 (2003). DOI: 10.1128/AEM.69.7.4205-4213.2003
Abstract:
Biologically conjugated quantum dots (QDs) have shown great promise as multiwavelength fluorescent labels for on-chip bioassays and eukaryotic cells. However, use of these photoluminescent nanocrystals in bacteria has not previously been reported, and their large size (3 to 10 nm) makes it unclear whether they inhibit bacterial recognition of attached molecules and whether they are able to pass through bacterial cell walls. Here we describe the use of conjugated CdSe QDs for strain- and metabolism-specific microbial labeling in a wide variety of bacteria and fungi, and our analysis was geared toward using receptors for a conjugated biomolecule that are present and active on the organism’s surface. While cell surface molecules, such as glycoproteins, make excellent targets for conjugated QDs, internal labeling is inconsistent and leads to large spectral shifts compared with the original fluorescence, suggesting that there is breakup or dissolution of the QDs. Transmission electron microscopy of whole mounts and thin sections confirmed that bacteria are able to
extract Cd and Se from QDs in a fashion dependent upon the QD surface conjugate.

11. J. N. Cha, M. H. Bartl, M. S. Wong, A. Popitsch, T. J. Deming and G. D. Stucky, "Microcavity Mode Lasing from Block Peptide Hierarchically Assembled Quantum Dot Spherical Resonators," Nano Lett. 3, 907-911 (2003). DOI: 10.1021/nl034206k
Abstract:

 

Quantum dot (QD) resonators for microcavity lasing applications were successfully synthesized by a single system diblock copolypeptide mediated process. Using specifically tailored block peptides and nanoparticles, we present here the cooperative assembly of cadmium selenide (CdSe) QDs and silica nanoparticles into 3-dimensional microcavities with a high QD volume fraction. These hollow QD microspheres are a perfect combination of both quantum and optical confinement, in which the electronic states of the 3-dimensional confined semiconductor nanocrystals are coupled to the photonic states of the spherical microcavity. We show that the specific interaction between the mode properties of the cavity with the emission of its QD building blocks leads to room-temperature microcavity lasing without the use of additional mirrors, substrate spheres, or gratings.

10. J. N. Cha, H. Birkedal, M. H. Bartl, M. S. Wong and G. D. Stucky, "Spontaneous Formation of Nanoparticle Vesicles from Homopolymer Polyelectrolytes," J. Am. Chem. Soc. 125, 8285-8289 (2003). DOI: 10.1021/ja0279601
Abstract:

 

Nanoparticle vesicles were spontaneously assembled from homopolymer polyamine polyelectrolytes and water-soluble, citrate-stabilized quantum dots. The further addition of silica nanoparticles to a solution of quantum dot vesicles generated stable micrometer-sized hollow spheres whose walls were formed of a thick, inner layer of close-packed quantum dots followed by an outer layer of silica. The method employed here to assemble both the nanoparticle vesicles and the hollow spheres is in direct contrast to previous syntheses that use either tailored block copolymers or oil-in-water emulsion templating. We propose that the formation of charge-stabilized hydrogen bonds between the positively charged amines of the homopolymer polyelectrolytes and the negatively charged citrate molecules stabilizing the quantum dots is responsible for the macroscopic phase separation in this completely aqueous system. The ease and processibility of the present approach gives promise for the production of a diverse array of materials ranging in applications from drug delivery to catalysis to micrometer-scale optical devices.

9. M. S. Wong, J. N. Cha, K.-S. Choi, T. J. Deming and G. D. Stucky, "Assembly of Nanoparticles into Hollow Spheres Using Block Copolypeptides," Nano Lett. 2, 583-587 (2002). ACS Hot Article. DOI: 10.1021/nl020244c
Abstract:

 

Various modes are being explored for the construction of functional materials out of nanoparticles. Despite these efforts, the assembly of nanoparticles remains challenging with respect to the requirement of multiple component organization on varying dimensions and length scales. We report here a room-temperature, wet chemical-based synthesis route in which silica and gold nanoparticles (10 nm) are cooperatively assembled with lysine−cysteine diblock copolypeptides into robust hollow spheres (diameter microns). The walls of the hollow spheres are composed of two distinct layers of silica and gold nanoparticles, and the hollow center is created without the use of a sacrificial core, emulsion phase, or hollow preformed substrate. Block copolypeptides designed with specific recognition sites for nanoparticles of various compositions provide a versatile approach for the hierarchical organization of nanoparticles into multidimensional composite arrays.

8. M. S. Wong and G. D. Stucky, "The Facile Synthesis of Nanocrystalline Semiconductor Quantum Dots," Mat. Res. Soc. Symp. Proc.; H. W. Hahn, D. L. Feldheim, C. P. Kubiak, R. Tannenbaum, and R.W. Siegel, Eds.; 2001 MRS Spring Meeting, Vol. 676, Y2.3-2.6 (2002).
Abstract:
Current synthetic techniques to high-quality quantum dots (“QD’s”) involve organometallic precursors that are hazardous and expensive and require they be rapidly injected into an extremely hot solvent to form the QD’s. A new method for synthesizing high-quality CdSe QD’s while circumventing these problems has been developed. Different cadmium salts
were studied as Cd precursors alternative to dimethylcadmium. High-quality CdSe QD’s were found possible with cadmium acetate as the Cd precursor. Changes in solvent temperature and reaction time had a systematic effect on QD particle sizes and the accompanying optical properties. These preliminary results point to a general method for producing high-quality QD’s that is safer and much more versatile.

7. M. S. Wong, H. C. Huang and J. Y. Ying, "Supramolecular-Templated Synthesis of Nanoporous Zirconia-Silica Catalysts," Chem. Mater. 14, 1961-1973 (2002). DOI: 10.1021/cm010076+
Abstract:
Thermally stable, mesoporous, and microporous zirconium-doped silica were prepared via supramolecular templating under low pH conditions. Zirconium loadings of up to 20 wt % were successfully incorporated into the porous silica-based framework, giving materials with very high surface areas, uniform pore sizes, and pore ordering. The zirconium cations were found dispersed throughout the material, and additionally, were preferentially located at the pore wall surface. The extent of Zr incorporation was found to be highly dependent on the synthesis pH and the nature of the Zr salt precursor and could be controlled by modifying the S+X-I+ synthesis route. These Zr-doped materials showed catalytic activity for 1-butene isomerization and cis-cyclooctene oxidation reactions.

6. M. S. Wong, E. S. Jeng and J. Y. Ying, "Supramolecular Templating of Thermally Stable Crystalline Mesoporous Metal Oxides Using Nanoparticulate Precursors," Nano Lett. 1, 637-642 (2001). DOI: 10.1021/nl015594y
Abstract:

 

A supramolecular templating approach to the preparation of crystalline mesoporous metal oxides using inorganic colloidal nanoparticles as building blocks is presented. The nanoparticles are used to form a mesostructured material with a triblock copolymer surfactant as the templating agent and with a tungstate salt as the “binding” agent. Tungstated zirconium oxide produced in this manner was found to be highly thermally stable (in excess of 600 °C) while maintaining mesoporosity and a high surface area. Other mesoporous oxides were produced using zirconium salts, titania nanoparticles, and aluminum polycations, illustrating the flexibility of this “nanoparticle/surfactant templating” route.

5. X. Gao, I. E. Wachs, M. S. Wong and J. Y. Ying, "Structural and Reactivity Properties of Nb-MCM-41: Comparison with That of Highly Dispersed Nb2O5/SiO2 Catalysts", J. Catal. 203, 18-24 (2001). DOI: 10.1006/jcat.2001.3313
Abstract:
The molecular structures of Nb cations in mesoporous material Nb---MCM-41 and the supported Nb2O5/SiO2 catalyst under hydrated and dehydrated conditions were investigated by in-situ Raman and UV-vis-NIR diffuse reflectance spectroscopies. Methanol oxidation was employed as a chemical probe reaction to examine reactivity/selectivity properties of these catalytic materials. The structural characterization techniques demonstrate that similar surface Nb oxide species are present in both Nb---MCM-41 and Nb2O5/SiO2 catalysts, which are sensitive to the environmental conditions (ambient or dehydrated). However, the characterization results also suggest that some Nb atoms in Nb---MCM-41 may be incorporated within the siliceous framework. The spectroscopic results revealed that under dehydrated conditions, the Nb cations in Nb---MCM-41 and 1% Nb2O5/SiO2 are predominantly composed of isolated NbO4 units, while the Nb cations in the supported Nb2O5/SiO2 catalysts possess polymerized NbOx species and/or bulk Nb2O5 with increasing Nb loading. The catalytic results indicate that the dispersed Nb cations in both types of catalysts are active redox sites for methanol oxidation and exhibit similar reactivity and selectivity properties due to the presence of Nb---O---Si bonds in their structures.

4. T. Sun, M. S. Wong and J. Y. Ying, "Synthesis of Amorphous, Microporous Silica with Adamantanamine as a Templating Agent," Chem. Commun., 2057-2058 (2000). DOI: 10.1039/b001079k
Abstract:
Amorphous, microporous silica with a spherical particle morphology has been prepared with adamantanamine, and its unusual structural properties suggest a non-zeolitic
templating synthesis pathway.

3. J. Y. Ying, C. P. Mehnert and M. S. Wong, "Synthesis and Applications of Supramolecular-Templated Mesoporous Materials," Angew. Chem. 111, 58-82 (1999); Angew. Chem. Int. Ed. 38, 56-77 (1999). Review Article. DOI: 10.1002/(SICI)1521-3773(19990115)38:1/2<56::AID-ANIE56>3.0.CO;2-E
Abstract:
The unique structure of MCM-41 silicates (shown in the picture) has provided for extremely attractive properties - uniform pore sizes greater than 20 Å, surface areas exceeding 1000 m2 g-1, and long-range ordering of the pores. Recent research in supramolecular-templated mesoporous materials has led to a wide range of compositions, to uses in a variety of catalytic reactions, and to a better control of bulk morphologies.

2. M. S. Wong and J. Y. Ying, "Amphiphilic Templating of Mesostructured Zirconium Oxide," Chem. Mater. 10, 2067-2077 (1998). DOI: 10.1021/cm970525z
Abstract:
The synthesis of zirconium oxide with a mesostructured framework (Zr-TMS) has been achieved through the use of amphiphilic compounds with a variety of headgroups (anionic and nonionic) and tail group chain lengths (1−18 carbons). Anionic surfactants with phosphate, carboxylate, sulfate, and sulfonate headgroups led to disordered hexagonal and/or layered phases. Mesoporous zirconia with high surface areas could be obtained through calcination of materials templated with phosphate amphiphiles; the phosphate headgroups remained on the pore walls and appeared necessary for thermal stability. Nonionic amine amphiphiles have been found to lead to less ordered zirconia mesostructures, due to the weak interaction with the zirconium n-propoxide precursor. The chain-length-independent templating ability of the amphiphiles and ex situ 31P MAS NMR of dodecyl phosphate (before and after incorporation into Zr-TMS) supported a method of formation involving covalent-bond interactions between the headgroup and the inorganic precursor.

1. M. S. Wong, D. M. Antonelli and J. Y. Ying, "Synthesis and Characterization of Phosphated Mesoporous Zirconium Oxide," Nanostr. Mater. 9, 165-168 (1997). DOI: 10.1016/S0965-9773(97)00044-5
Abstract:
The synthesis of zirconium oxide mesoporous molecular sieves (Zr-TMS1) comprising of hexagonally-packed cylindrical pores was investigated. Sol-gel processing of zirconium n-propoxide ligated with dodecylphosphate surfactants was found to produce a mesostructure similar to MCM-41. Surfactant removal without concomitant pore collapse can be accomplished, yielding mesoporous materials with specific surface areas as high as 560 m2/g. Zr-TMS1 has been found stable to at least 800 °C, retaining surface areas greater than 200 m2/g. Longer-chained alkylphosphates led to larger pore diameters and surface areas. Lewis and Brønsted acidity were found in Zr-TMS1, probably associated with the presence of surface phosphate groups. The extremely high surface area, pore size control, high thermal stability, and surface acidity make this transition metal mesoporous molecular sieve an attractive solid acid catalyst and catalyst support material.