R-3 Repository :: Browsing by Author "Colvin, Vicki L."

Browsing by Author "Colvin, Vicki L."

Now showing 1 - 20 of 34

Accessible and green manufacturing of magnetite (ferrous ferric oxide) nanocrystals and their use in magnetic separations
(2008) Yavuz, Cafer Tayyar; Colvin, Vicki L.
This work describes the first size dependent magnetic separation in nanoscale. Magnetite (Fe3O4) nanocrystals of high quality and uniform size were synthesized with monodispersity below 10%. Magnetite nanocrystals of 4 nm to 33 nm (average diameter) were produced. Batch synthesis was shown to go up to 20 grams which is more than 10 times of a standard nanocrystal synthesis, without loosing the quality and monodispersity. Reactor design for mass (1 gram per hour) production of magnetite nanocrystals is reported for the first time. The cost of a kg of lab purity magnetite nanocrystals was shown to be $2600. A green synthesis that utilizes rust and edible oils was developed. The cost of a kg was brought down to $22. Size dependency of magnetism was shown in nanoscale for the first time. Reversible aggregation theory was developed to explain the low field magnetic separation and solution behavior of magnetite nanocrystals. Arsenic was removed from drinking water with magnetite nanocrystals 200 times better than commercial adsorbents. Silica coating was successfully applied to enable the known silica related biotechnologies. Magnetite--silica nanoshells were functionalized with amino groups. For the first time, silver was coated on the magnetite--silica nanoshells to produce triple multishells. Anti-microbial activity of multishells is anticipated.
Biomedical Nanocrystal Agents: Design, Synthesis, and Applications
(2013-09-16) Cho, Minjung; Colvin, Vicki L.; McDevitt, John T.; Wong, Michael S.
In these days, nanomaterials are applied in a variety of biomedical applications including magnetic resonance imaging (MRI), cell imaging, drug delivery, and cell separation. Most MRI contrast agents affect the longitudinal relaxation time (T1) and transverse relaxation time (T2) of water protons in the tissue and result in increased positive or negative contrast. Here, we report the optimization of r1 (1/T1) or r2 (1/T2) relaxivity dynamics with diameter controlled gadolinium oxide nanocrystals (2~22 nm) and iron based magnetic nanocrystals (4 ~33 nm). The r1 and r2 MR relaxivity values of hydrated nanocrystals were optimized and examined depending on their core diameter, surface coating, and compositions; the high r1 value of gadolinium oxide was 40-60 S-1mM-1, which is 10-15 fold higher than that of commercial Gd (III) chelates (4.3~4.6 S-1mM-1). Moreover, in vitro toxicological studies revealed that polymer coated nanocrystals suspensions had no significant effect on human dermal fibroblast (HDF) cells even at high concentration. Towards multimodal imaging or multifunctional ability, we developed the iron oxide/QDs complexes, which consist of cores of iron oxide that act as nucleation sites for fluorescent QDs. The choice of variable QDs helped to visualize and remove large iron oxide materials in a magnetic separation. Additionally, diluted materials concentrated on the magnet could be fluorescently detected even at very low concentration. The designed MRI or multifunctional nanomaterials will give great and powerful uses in biomedical applications.
Biomolecular crystals for material applications and a mechanistic study of an iron oxide nanoparticle synthesis
(2007) Falkner, Joshua Charles; Colvin, Vicki L.
The three projects within this work address the difficulties of controlling biomolecular crystal formats (i.e. size and shape), producing 3-D ordered composite materials from biomolecular crystal templates, and understanding the mechanism of a practical iron oxide synthesis. The unifying thread consistent throughout these three topics is the development of methods to manipulate nanomaterials using a bottom-up approach. Biomolecular crystals are nanometer to millimeter sized crystals that have well ordered mesoporous solvent channels. The overall physical dimensions of these crystals are highly dependent on crystallization conditions. The controlled growth of micro- and nanoprotein crystals was studied to provide new pathways for creating smaller crystalline protein materials. This method produced tetragonal hen egg-white lysozyme crystals (250--100,000 nm) with near monodisperse size distributions (<15%). With this degree of control, existing protein crystal applications such as drug delivery and analytical sensors can reach their full potential. Applications for larger crystals with inherently ubiquitous pore structures could extend to materials used for membranes or templates. In this work, the porous structure of larger cowpea mosaic virus crystals was used to template metal nanoparticle growth within the body centered cubic crystalline network. The final composite material was found to have long range ordering of palladium and platinum nonocrystal aggregates (10nm) with symmetry consistent to the virus template. Nanoparticle synthesis itself is an immense field of study with an array of diverse applications. The final piece of this work investigates the mechanism behind a previously developed iron oxide synthesis to gain more understanding and direction to future synthesis strategies. The particle growth mechanism was found to proceed by the formation of a solvated iron(III)oleate complex followed by a reduction of iron (III) to iron (II). This unstable iron(II) nucleates to form a wustite (FeO) core which serves as an epitaxial surface for the magnetite (Fe3O4) shell growth. This method produces spherical particles (6-60nm) with relative size distributions of less than 15%.
Characterizing Engineered Nanomaterials: From Environmental, Health and Safety Research to the Development of Shaped Nanosphere Lithography for Metamaterials
(2012-09-05) Lewicka, Zuzanna; Colvin, Vicki L.; Tittel, Frank K.; Wong, Michael S.
In this thesis two issues in nanotechnology have been addressed. The first is the comprehensive characterization of engineered nanomaterials prior to their examination in toxicology and environmental studies. The second is the development of a method to produce nanostructure arrays over large areas and for low cost. A major challenge when assessing nanomaterial’s risks is the robust characterization of their physicochemical properties, particularly in commercial products. Such data allows the critical features for biological outcomes to be determined. This work focused on the inorganic oxides that were studied in powdered and dispersed forms as well as directly in consumer sunscreen products. The most important finding was that the commercial sunscreens that listed titania or zinc oxide as ingredients contained nanoscale materials. Cell free photochemical tests revealed that ZnO particles without any surface coating were more active at generating ROS than surface coated TiO2 nanoparticles. These studies make clear the importance of exposure studies that examine the native form of nanomaterials directly in commercial products. The second part of this thesis presents the development of a new method to fabricate gold nanoring and nanocrescent arrays over large areas; such materials have unique optical properties consonant with those described as metamaterials. A new shaped nanosphere lithography approach was used to manipulate the form of silica nanospheres packed onto a surface; the resulting array of mushroom structures provided a mask that after gold evaporation and etching left either golden rings or crescents over the surface. The structures had tunable features, with outer diameters ranging from 200 to 350 nm for rings and crescent gap angles of ten to more than a hundred degrees. The use of a double mask method ensured the uniform coverage of these structured over 1 cm2 areas. Experimental and theoretical investigations of the optical properties of the arrays revealed the optical resonances in the infrared region. Finally, in the course of developing the nanorings, etch conditions were developed to deposit large area arrays of polystyrene nanodoughnuts with diameters from 128 to 242 nm. These non-conductive structures provide an ideal template for further attachment of magnetic of optically emissive nanoparticles.
Chromatographic methods for the separation and analysis of gold nanocrystals
(2006) Al-Somali, Ali M.; Colvin, Vicki L.
With the ever growing applications of nanomaterials, fast, accurate and cost effective characterization methodologies are needed to ensure high quality materials and practical manufacturing. This problem is a challenging one as nanoparticle shape, size and size distribution are all important features which govern properties as diverse as sample melting point and chemical reactivity. New methods that provide key analytical information, along with a means of improving size and shape distributions would have substantial impact on this growing area. Chromatography is a technique which traditionally has been used to both provide analysis as well as separation of high valued added chemicals. Its applications in nanoscience are to date quite limited, and the objective of this thesis is to demonstrate that chromatographic techniques can be used to measure the dimensions of gold nanocrystals in solution as well as provide methods for physically separating complex distributions of particles. Recycling size exclusion chromatography (RSEC) has been employed to effect physical, base-line separation of subpopulations of spherical gold nanocrystals. This method can be easily applied on other nanocrystalline systems and is scalable to large production. Anisotropic gold nanocrystals, such as gold nanorods, exhibit spectacular optical properties that can be utilized in medical and biological fields. An analytical method, based on aqueous SEC that determines the dimensions of gold nanorods has been developed. The method couples the hydrodynamic volume obtained from SEC and aspect ratio from absorption spectra to provide a complete assessment of nanorod ensembles directly in liquid phase media. Additionally, a close analysis of the hydrodynamic values reveals that the nanorods are aligned with the flow, which makes the separation responsive to variations in aspect ratio. Finally, conventional chromatography provides a resolution which is not large enough to sharpen the distributions of the most monodisperse nanoparticles now produced directly in solution. The application of super high-resolution methods, such as critical point chromatography, can substantially improve the separation power and its application to polymer stabilized gold nanocrystals has been demonstrated.
Cisplatin@US-tube Carbon Nanocapsules for Enhanced
(2014-02-28) Guven, Adem; Wilson, Lon J.; Colvin, Vicki L.; Barrera, Enrique V.; Lewis, Michael T.
The use of chemotherapeutic drugs in cancer therapy is often limited by problems with administration such as insolubility, inefficient biodistribution, lack of selectivelty, and inability of the drug to cross cellular barriers. To overcome these limitations, various types of drug delivery systems have been explored, and recently, carbon nanotube (CNT) materials have garnered special attention in the area. This thesis details the preparation, characterization, and in vitro and in vivo testing of a new, ultra-short single-walled carbon nanotube (US-tube)-based drug delivery system for the treatment of cancer. In particular, the encapsulation of cisplatin (CDDP), a widely-used anticancer drug, within US-tubes has been achieved by a loading procedure that is reproducible, and the resulting CDDP@US-tube material characterized by high-resolution transmission electron microscopy (HR-TEM), energy-dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and inductively-coupled optical emission spectroscopy (ICP-OES). Dialysis studies performed in phosphate-buffered saline (PBS) at 37 °C have demonstrated that CDDP release from CDDP@US-tubes can be controlled (retarded) by wrapping the CDDP@US-tubes with Pluronic®-F108 surfactant. The anticancer activity of Pluronic-wrapped CDDP@US-tubes (W-CDDP@US-tubes) has been evaluated against two different breast cancer cell lines, MCF-7 and MDA-MB-231, and found to exhibit enhanced cytotoxicity over free CDDP. Moreover, it has been shown that CDDP release from W-CDDP@US-tubes nanocapsules can be stimulated remotely by a radiofrequency (RF) field which disrupts the Pluronic coating to release CDDP. RF-induced release-dependent cytotoxicity of W-CDDP@US-tubes has been evaluated in vitro against two different liver cancer cell lines, Hep3B and HepG2, and found to exhibit superior cytotoxicity compared to W-CDDP@US-tubes not exposed to RF. Finally, in vivo biodistribution and therapeutic efficacy of the CDDP@US-tube material has been evaluated against three different breast cancer xenograft mouse (SCID/Bg) models, and found to exhibit greater efficacy in suppressing tumor growth than free CDDP for both a MCF-7 cell line xenograft model and a BCM-4272 patient-derived xenograft (PDX) model. The CDDP@US-tubes also demonstrated prolonged circulation time compared to free CDDP which enhances permeability and retention (EPR) effects resulting in significantly more CDDP accumulation in tumors, as determined by Platinum (Pt) analysis via inductively-coupled plasma mass-spectrometry (ICP-MS).
Colloidal crystal approach to the fabrication of photonic band gap materials
(2001) Jiang, Peng; Colvin, Vicki L.
Planar single-crystalline colloidal crystals are fabricated by exploiting the spontaneous crystallization of monodisperse silica spheres into close-packed arrays using a convective self-assembly method. Film thicknesses ranging from single monolayers to over 200 layers can be precisely controlled through varying solution concentration and colloid diameter. These high quality periodic arrays exhibit partial photonic band gaps, whose positions and band width depends on the sphere diameters and the number of layers. Their optical transmission is well described by the scalar wave approximation to Maxwell's equations. The thickness dependence of the photonic band gap has also been studied for the first time. Superlattice colloidal crystals comprised of alternating layers of different sphere sizes can also be formed by the convective self-assembly method. The resulting photonic crystal structures exhibit optical properties which resemble the superposition of the properties of each individual component, with additional structure that suggests the onset of superlattice-type miniband formation. These superlattice structures thus provide a new way to couple light into and out of photonic crystals. These planar colloidal films are then used as scaffolds to make macroporous materials with crystalline arrays of voids. Macroporous polymers are formed by filling the interstitial area with monomer which is subsequently polymerized. The silica templates can be removed by etching with hydrofluoric acid. The large voids defined by the silica colloids are not isolated, but rather interconnected by a network of monodisperse smaller pores whose sizes can be controlled by varying the polymerization temperature. These membranes exhibit striking optical properties and their photonic band gap behavior agrees well with theory. A seeded electroless deposition technique has also been developed for forming macroporous metal membranes. The gold particles attached to the thiol-coated silica colloidal crystals can catalyze the electroless deposition of metals (Ag, Au, Cu, Ni, Co, Pt) inside the arrays and lead to fully dense macroporous metallic films after silica removal. These samples are mechanically robust, electrically active, and possess unusual diffractive optical properties. The macroporous polymers are again used as hosts to grow a wide variety of complex and unusual colloidal structures. This modern "lost-wax" method effectively capitalizes on the perfection of the starting colloids and the resulting template voids to form monodisperse colloids and their colloidal crystals. A wide variety of highly monodisperse inorganic, polymeric and metallic solid and core-shell colloids, as well as hollow colloids with controllable shell thickness and their colloidal crystals can be made. The polymer template can be uniformly deformed to alter colloidal shape and elliptical particles with precisely controlled aspect ratios are formed for the first time. The hollow sphere titania colloidal crystals exhibit partial photonic band gaps, whose spectral position and width depend on the thickness of the shell and on the overlap between adjacent spheres, in a manner consistent with numerical simulations.
Development of iron oxide nano materials-based technology for arsenic remediation
(2016-04-14) Gonzalez Pech, Natalia Isabel; Colvin, Vicki L.
In 2005, the Colvin group proposed the use of magnetite nanoparticles for arsenic adsorption. This would allow the reduction of waste significantly with the additional advantage of magnetic-driven separation at low fields. However, despite the efforts of several groups around the world, the use of arsenic sorbents based in nanomaterials is not yet feasible. Still, the study of new iron-based nanomaterials for arsenic uptake has been increasing over the last years. During my PhD program, I have analyzed the performance of magnetite nanoparticles synthesized by several methodologies with both batch experiments and column tests and varying conditions including groundwater with high silica concentrations (Chapter 4). Silica is one of the most common interferences and dramatically decreases the arsenic removal capabilities. My work included the evaluation of arsenic removal capabilities on site (Salamanca, Mexico) and the comparison with commercially available arsenic sorbents under those difficult conditions− [SiO2] =85ppm and pH=8 (Chapter 3). In spite of the comparable performance of the nanoparticles to other commercial sorbents, their small-scale production and the lack of a simple filtration setup motivated us to design a material that could be used under real-world operation conditions. We proposed the use of clusters of nanoparticles in order to benefit of the properties of both the nanoparticles and the bulk material. The understanding of the mechanism of the synthesis, the effect that synthetic parameters have in the cluster size and unit size, and the corresponding effect in arsenic adsorption are discussed in Chapter 5. Currently, the most pressing needs for groundwater treatment is in developing countries; this forces the use of highly cost-effective strategies. In order to develop a material that can feasibly solve the needs on the field in an inexpensive way, one of the projects was to modify the kitchen synthesis of nanomagnetite previously introduced by our group. Even when in the past a cheap synthesis was achieved, it was a process with several steps and the nanoparticles were not able to absorb arsenic. In this work (Chapter 6), a one-pot synthesis is proposed and studies have shown that the nanoparticles thereby obtained have much better arsenic removal performance than the nanoparticles prepared by thermal decomposition making the material very promising. Even though the work proposed herein will not solve the problem of arsenic contamination, it provides a grasp of the requirements for the implementation of nanomaterials in water treatment technologies and narrows the gap between design of nanomaterials in the lab and their application on the field.
Engineered Metallic Nanostructures: Fabrication, Characterization, and Applications
(2016-04-21) Bohloul, Arash; Colvin, Vicki L.
Metallic nanostructures have garnered a great deal of attention due to their fascinating optical properties, which differ from the bulk metal. They have been proven to exceed expectations in wide variety of applications including chemical and biological sensing. Nevertheless, high-throughput and low cost nanofabrication techniques are required to implant metallic nanostructures in widespread applications. With that vision, this thesis presents a versatile and reliable method for scalable fabrication of gold nanostructures. In this approach, a plasma-treated ordered array of polystyrene nanospheres acts as an initial mask. The key step in this process is the vapor-deposition of nickel as a sacrificial mask. Thereby, gold nanostructures are directly formed on the substrate through the nickel mask. This is an easy, powerful, and straightforward method that offers several degrees of freedom to precisely control the shape and size of nanostructures. We made a library of nanostructures including gold nanocrescents, double crescents, nanorings, and nanodisks with the ability to tune the size in the range of 150 to 650 nm. The fabricated nanostructures are highly packed and uniformly cover the centimeter scale substrate. The optical properties of metallic nanostructures were extensively studied by a combination of UV-Vis-NIR and Fourier transform infrared (FTIR) spectroscopies, and correlation between optical response and geometrical parameters were investigated. In the next part of this thesis, highly sensitive surface enhanced infrared absorption (SEIRA) analysis was demonstrated on gold nanocrescent arrays. Theoretical modeling was confirmed that these substrates provide highly dense and strong hot-spots over the substrate, which is required for surface enhanced spectroscopic studies. Gold nanocrescent arrays exhibit highly tunable plasmon resonance to cover desired molecular vibrational bands. These substrates experimentally illustrated 3 orders of magnitude enhancement of IR signal over the entire substrate and up to 5 orders of magnitude enhancement on hot-spot area. Finally, we showed that fabricated substrates are completely biocompatible for growth, adhesion, and proliferation of human dermal fibroblast cells. Leveraging the capability of gold nanocrescent arrays to enhance IR signals, we developed a real time SEIRA spectroscopic technique for label-free biological cell analysis. The performance of proposed method was assessed by in situ tracking the SEIRA signal of human dermal fibroblast cells cultured on gold nanocrescent arrays.
Engineering Nanoparticle-Protein Associations for Protein Crystal Nucleation and Nanoparticle Arrangement
(2012-09-05) Benoit, Denise; Colvin, Vicki L.; Shamoo, Yousif; Hartgerink, Jeffrey D.
Engineering the nanoparticle - protein association offers a new way to form protein crystals as well as new approaches for arrangement of nanoparticles. Central to this control is the nanoparticle surface. By conjugating polymers on the surface with controlled molecular weights many properties of the nanoparticle can be changed including its size, stability in buffers and the association of proteins with its surface. Large molecular weight poly(ethylene glycol) (PEG) coatings allow for weak associations between proteins and nanoparticles. These interactions can lead to changes in how proteins crystallize. In particular, they decrease the time to nucleation and expand the range of conditions over which protein crystals form. Interestingly, when PEG chain lengths are too short then protein association is minimized and these effects are not observed. One important feature of protein crystals nucleated with nanoparticles is that the nanoparticles are incorporated into the crystals. What results are nanoparticles placed at well-defined distances in composite protein-nanoparticle crystals. Crystals on the size scale of 10 - 100 micrometers exhibit optical absorbance, fluorescence and super paramagnetic behavior derivative from the incorporated nanomaterials. The arrangement of nanoparticles into three dimensional arrays also gives rise to new and interesting physical and chemical properties, such as fluorescence enhancement and varied magnetic response. In addition, anisotropic nanomaterials aligned throughout the composite crystal have polarization dependent optical properties.
Engineering Silver Nanoparticles: Towards a Tunable Antimicrobial
(2014-03-11) Puppala, Hema Lakshmi; Colvin, Vicki L.; Billups, W. Edward; Bennett, George N.
Overwhelming production of commercially available products containing silver nanoparticles (AgNPs) underscores the studies determining their fate in the environment. In order to regulate the use, assess the environmental impact and develop eco-responsible silver products, models that can predict AgNP toxicity based on physicochemical properties are vital. With that vision, this thesis developed well-characterized model libraries of uniform AgNPs stabilized with oleate in the range of 2-45 nm diameter with variable surface coating and investigated the dissolution properties that link AgNP structure to antimicrobial activity. High temperature organic synthesis allowed controlled growth of AgNPs (σ<15%) by an Ostwald ripening mechanism in the first few hours, and followed by size dependent growth rates yielding uniform nanocrystals. Characterization of these materials revealed a crystalline nature, bidentate binding mode of oleate and non-oxidized pristine silver surface. Phase transfer of these AgNPs from organics to water was facilitated by encapsulation and ligand exchange methods using amphiphilic polymers and methoxy poly (ethylene glycol) (mPEGSH) respectively. Among these surface coatings, steric stabilization by mPEGSH not only helped retain their optical properties but also reduced the dissolution (<1(w/w)%) of AgNPs. This enhanced the stability in various environmentally relevant high ionic strength media (such as Hoaglands, EPA hard water and OECD medium), thereby increasing the shelf life. In addition, size, surface coating, pH of the medium and grafting density of the polymer mediated the dissolution of AgNPs. For instance, the rate of dissolution was decreased by 40% when the polymer coating possessed a mushroom conformation and increased with reducing core size. Analogous to dissolution, physicochemical properties also influenced the antimicrobial activity which were studied by minimum inhibitory concentration (MIC) and bactericidal efficacy assays. For example, surface passivation with mPEGSH prevented the oxidation of active silver atoms on the surface, and resulted in reduced toxicity against E. coli. Moreover citrate stabilized AgNPs when surface modified with mPEGSH had reduced toxicity, which was correlated with residual Ag+ in AgNP solution. Therefore this study demonstrates that processes in the environment that increase stability of AgNPs could make them more persistent due to low dissolution. Furthermore, the size and surface chemistry effects of AgNPs studied here make the intrinsic antimicrobial property of silver tunable and hence more versatile. This work also served as a material support for research on investigating toxicity of AgNPs to C. elegans, Daphnia Magna, Populus and Arabidopsis. In the future, this data will be used to develop nanomaterial bioavailability & environmental exposure (nanoBEE) models that predict the environmental impact of AgNPs.
Gadolinium Oxide Nanocrystals: Synthesis, Characterization, and Applications
(2016-04-21) Taheri, Nasim; Colvin, Vicki L.
Of the recent biomedical studies devoted to the development of medical imaging techniques, magnetic resonance imaging (MRI) has been the subject of increased interest. MRI is a powerful diagnostic tool that offers detailed, high-resolution anatomical information by monitoring the relaxation rate of water protons in the presence of a strong magnetic field. However, two objectives that have yet to be fully achieved with MRI include generating efficient contrast and enhancing imaging sensitivity to a level that enables differentiating healthy tissue from malignant tissue. Developing an effective MRI contrast to enhance image quality has therefore become crucial to improving this promising technique. This thesis examines the performance of surface engineered gadolinium oxide nanocrystals as T1 MRI contrast agents. Gadolinium oxide nanocrystals are formed at high temperatures in organic solvents and phase transferred into biological media using a novel sulfonic acid copolymer. The surface engineered gadolinium oxide nanocrystals were designed to exploit the plate-like geometry of nanocrystals to form surfaces that are both accessible to water and effective at preventing particle-particle aggregation. The crystals’ anisotropic shape suggests that the gadolinium surface atoms on the thin plate edges can remain uncoated and thus available to water. The relaxivities of these materials are one order of magnitude (15 times) larger than commercial T1 contrast agents and other gadolinium-containing nanoparticles. The magnetic field dependence of their relaxation rates and the relatively weak size dependence of their relaxivity suggest that inner-sphere water relaxation at the edges of the nanocrystal are responsible for the high relaxation rates. These surfaces have significant potential as T1 MRI contrast agents, offering a non-invasive imaging alternative with numerous applications, including detection and characterization of non-alcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH), and tracking of stem cells in embryos. As part of this thesis, we introduced surface functionalized gadolinium oxide nanocrystals with three different surface coatings—each with unique characteristics. These materials were chosen because they are stable in relevant biological conditions while posing distinct responses in different environments. We examined the effect of surface coating, salt, and protein on the performance of gadolinium oxide nanocrystals as MRI contrast agents. We found that their behavior was altered in plasma, implying that surface coating has an important effect on their interactions with proteins. Moreover, we showed that, unlike other studies in deionized water in which relaxivity has a linear dependency, forming strong protein binding enables relaxivity measurement to be dependent on gadolinium concentration. Finally, we studied the possible cytotoxic effects of gadolinium oxide nanocrystals in vitro and in vivo. Since gadolinium ion is a heavy metal, it is important to ensure that it is shielded with a surface coating and is biocompatible both at the cellular level and in living animals. In vivo, the nanocrystals have a blood circulation lifetime similar to molecular gadolinium agents—sufficient for imaging process duration. Additionally, our biodistribution study showed the crystals’ rapid clearance through the liver, thus confirming its cellular uptake. Collectively, our findings reveal the crystals’ high performance as T1 MRI contrast agents.
High-temperature behavior of nanocrystalline oxides
(2000) Denler, Tiffany Elizabeth; Colvin, Vicki L.
A non-hydrolytic synthetic method has been developed to produce unagglomerated nanocrystalline oxides, particularly titania and zirconia, which do not have hydroxyl groups on the surface. These non-hydrolytic samples display retarded grain growth rates compared to equivalent hydrothermal nanocrystalline titania and zirconia. It is demonstrated that the rate difference can be attributed to both surface chemistry and the level of agglomeration.
Investigating the biological impacts of nanoengineered materials in Caenorhabditis elegans and in vitro
(2013-06-05) Contreras, Elizabeth; Colvin, Vicki L.; Wilson, Lon J.; Zhong, Weiwei
In nematode Caenorhabditis elegans, the chronic and multi-generational toxicological effects of commercially relevant engineered nanoparticles (ENPs), such as quantum dots (QDs) and silver (AgNP) caused significant changes in a number of physiological endpoints. The increased water-solubility of ENPs in commercial products, for example, makes them increasingly bioavailable to terrestrial organisms exposed to pollution and waste in the soil. Since 2008, attention to the toxicology of nanomaterials in C. elegans continues to grow. Quantitative data on multiple physiological endpoints paired with metal analysis show the uptake of QDs and AgNPs, and their effects on nematode fitness. First, C. elegans were exposed for four generations through feeding to amphiphilic polymer coated CdSe/ZnS (core-shell QDs), CdSe (core QDs), and different sizes of AgNPs. These ENPs were readily ingested. QDs were qualitatively imaged in the digestive tract using a fluorescence microscopy and their and AgNP uptake quantitatively measured using ICP-MS. Each generation was analyzed for changes in lifespan, reproduction, growth and motility using an automated computer vision system. Core-shell QDs had little impact on C. elegans due to its metal shell coating. In contrast, core QDs lacked a metal shell coating, which caused significant changes to nematode physiology. In the same way, at high concentrations of 100 ppm, AgNP caused the most adverse effect to lifespan and reproduction related to particle size, but its adverse effect to motility had no correlation to particle size. Using C. elegans as an animal model allowed for a better understanding of the negative impacts of ENPs than with cytotoxicity tests. Lastly, to test the toxicity of water-dispersed fullerene (nanoC60) using human dermal fibroblast cells, this thesis investigated a suite of assays and methods in order to establish a standard set of cytotoxicity tests. Ten assays and methods assessed nanoC60 samples of different purities to show differences in cytotoxic effects. Washed samples of fullerenes, with negligible traces of THF and other impurities, rendered the solution nontoxic. Even when exposed to UV-irradiation, washed nanoC60 were not photosensitized and did not cause cellular death. This work characterizes ENPs and investigates their impact in C. elegans and cells to assess toxicity risks to the environment and to human health.
Iron: From Synthesis, Characterization, and Application of Sulfide Green Rust to Viability in Arsenic Water Treatment
(2013-09-16) Jones, Christopher; Colvin, Vicki L.; Wilson, Lon J.; Alvarez, Pedro J.
Iron chemistry plays an important role in our world. At the nanoscale, iron oxide nanoparticles (nanomagnetite) have many inherent physical or chemical characteristics that drive potential solutions to real-world problems; appropriation of nanomagnetite’s properties as a “scaffold” for chemistry would further enhance its effectiveness in applications. In an effort to make use of nanomagnetite’s physical properties, a new “Sulfide Green Rust” (sGR) has been synthesized from magnetic iron nanoparticles. The material is crystalline, reactive due to high iron(II) content, and dissolves in the aqueous phase. Nanomagnetite’s magnetic properties were also observed to persist after sGR synthesis. X-ray absorption spectroscopy (XAS) confirmed the synthesis of this new FeS2-like material. The crystallinity, composition, and various physical characteristics were examined using a host of techniques including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), Mössbauer spectroscopy, CRYO-TEM, Raman spectroscopy, and ultraviolet-to-visible (UV-Vis) spectroscopy. To demonstrate its use, the material was then subjected to a test of its reactive potential, namely water remediation of an orange dye contaminant. Iron serves a function at the macroscale as well regarding water treatment, since iron coagulation-filtration is the industry standard for arsenic treatment. Determining a technology’s merit as a solution goes beyond technical concern, however, as environmental and economic aspects also play important roles. Life Cycle Analysis, or LCA, methodology works to holistically compare each of these facets from cradle to grave. To address the current arsenic drinking water requirements at a case setting in Hungary, the LCA technique was applied on two example arsenic removal technologies, both coagulation-filtration and adsorption. 9 out of 10 considered impact categories tended to favour coagulation-filtration in this small municipality study, however realistic variations in water chemistry and product characteristics led to some overlap of their environmental impact. Electricity did not have a large direct impact, regeneration of the adsorption technology was very costly, and adsorption’s hazardous waste was not reduced compared to coagulation-filtration. Coagulation-filtration is also the cheaper of the two technologies; its highest cost is that of waste disposal, while the highest single expense modeled is that of adsorption media cost.
Magnetic purification of a sample
(2011-05-10) Colvin, Vicki L.; Yavuz, Cafer Tayyar; Mayo, John Thomas; Yu, Weiyong; Rice University; United States Patent and Trademark Office
Methods for separating magnetic nanoparticles are provided. In certain embodiments, a method is provided for separating magnetic nanoparticles comprising: providing a sample comprising a plurality of magnetic nanoparticles; passing the sample through a first magnetic field; at least partially isolating nanoparticles of the first nanoparticle size desired; altering the strength of the first magnetic field to produce a second magnetic field; and at least partially isolating nanoparticles of the second nanoparticle size desired.
Measuring the Grafting Density of Nanoparticles in Solution by Analytical Ultracentrifugation and Total Organic Carbon Analysis
(American Chemical Society, 2012) Benoit, Denise N.; Zhu, Huiguang; Lilierose, Michael H.; Verm, Raymond A.; Ali, Naushaba; Morrison, Adam N.; Fortner, John D.; Avendano, Carolina; Colvin, Vicki L.
Many of the solution phase properties of nanoparticles, such as their colloidal stability and hydrodynamic diameter, are governed by the number of stabilizing groups bound to the particle surface (i.e., grafting density). Here, we show how two techniques, analytical ultracentrifugation (AUC) and total organic carbon analysis (TOC), can be applied separately to the measurement of this parameter. AUC directly measures the density of nanoparticle–polymer conjugates while TOC provides the total carbon content of its aqueous dispersions. When these techniques are applied to model gold nanoparticles capped with thiolated poly(ethylene glycol), the measured grafting densities across a range of polymer chain lengths, polymer concentrations, and nanoparticle diameters agree to within 20%. Moreover, the measured grafting densities correlate well with the polymer content determined by thermogravimetric analysis of solid conjugate samples. Using these tools, we examine the particle core diameter, polymer chain length, and polymer solution concentration dependence of nanoparticle grafting densities in a gold nanoparticle–poly(ethylene glycol) conjugate system.
Nanocrystalline titania: Controlling physical properties and photocatalytic behavior
(2005) Wahi, Raj; Colvin, Vicki L.
This dissertation describes a hydrothermal method for synthesizing titanium dioxide nanocrystals with controllable physical properties and explores the influence of such properties on the material's photocatalytic efficiency. The preparation of nanoscale titania from an alkoxide precursor in ethanol under mild hydrothermal conditions yields highly crystalline, thermally stable, phase-pure anatase dots whose sizes can be fine-tuned through adjustment of reaction temperature, precursor concentration, and water-to-alkoxide ratio. By optimizing the synthetic conditions, one may obtain grain sizes as small as 5.5 nm and surface areas up to 250 m2 g-1. The importance of various physical properties in determining the photocatalytic performance of nanocrystalline titania is investigated and clarified using photodegradation of an azo dye as a model reaction. Experimental photocatalytic activities, as quantified by dye half-life and Langmuir-Hinshelwood rate constants, confirm that anatase is an inherently superior photocatalyst to rutile and that activity enhancement due to anatase-rutile synergy in mixed-phase catalysts is contingent upon other factors such as the nature of the anatase-rutile interface. Also, it is shown for the first time that the shape of a titania nanocrystal significantly affects its photocatalytic efficiency. Specifically, rodlike anatase nanocrystals with predominantly (1 0 1) surfaces perform poorly as photocatalysts because the non-dissociative adsorption of water to these surfaces prevents efficient generation of the OH• radicals thought to be essential for photocatalytic oxidation.
Polymers having ordered- monodisperse pores and their corresponding ordered- monodisperse colloids
(2005-08-16) Jiang, Peng; Colvin, Vicki L.; Rice University; United States Patent and Trademark Office
Ordered, monodisperse macroporous polymers, their corresponding ordered, monodisperse colloids, and methods of preparing them are disclosed. The methods use an ordered, monodisperse colloidal template to define the polymer pore morphology, which in turn acts as a mold for the growth of a new ordered, monodisperse colloid. The macroporous polymer may be prepared with either spherical or ellipsoidal pores from a wide variety of polymeric systems. The new ordered, monodisperse colloid may be grown from a wide variety of materials including ceramics, semiconductors, metals and polymers. These materials are potentially useful in optical, micro-filtering and drug delivery applications.
Protein crystals as templates for materials chemistry
(2003) Turner, Mary Ellen; Colvin, Vicki L.
This work describes the first use of macromolecular biological crystals as templates for materials synthesis. The macromolecular crystal itself offers unique micro- and mesoporous structure with specific binding sites for molecules. This work utilizes this porous structure for the design of polymer and metal loaded nanocomposites. The crystals are first strengthened with intermolecular covalent cross-links. The sturdy crystals then serve as scaffolds for the infusion of polymers or the growth of metallic nanoparticles. Polymer infused and encased Hen Egg White Lysozyme (HEWL) crystals show reproducible diffraction for many months to a resolution of 4A. Metal nanoparticles can be grown in HEWL crystals using an electroless plating technique in which palladium ions bound to amino acids are subsequently reduced and form a catalytic surface for the deposition of platinum metal. If these nanoparticles are grown in a macromolecular crystal with larger pores, such as Cowpea Mosaic Virus, then the protein structure effectively guides the growth of the nanoparticles resulting in monolithic, highly ordered nanocomposites. These novel patterned materials could find use as x-ray optics, sensors, or x-ray diffraction standards.

Browsing by Author "Colvin, Vicki L."

Results Per Page

Sort Options