Byron D. Gates

Monodispersed Colloidal Spheres: Old Materials with New Applications

This article presents an overview of current research activities that center on monodispersed colloidal spheres whose diameter falls anywhere in the range of 10 nm to 1 μm. It is organized into three parts: The first part briefly discusses several useful methods that have been developed for producing monodispersed colloidal spheres with tightly controlled sizes and well-defined properties (both surface and bulk). The second part surveys some techniques that have been demonstrated for organizing these colloidal spheres into two- and three-dimensionally ordered lattices. The third part highlights a number of unique applications of these crystalline assemblies, such as their uses as photonic bandgap (PBG) crystals; as removable templates to fabricate macroporous materials with highly ordered and three-dimensionally interconnected porous structures; as physical masks in lithographic patterning; and as diffractive elements to fabricate new types of optical sensors. Finally, we conclude with some personal perspectives on the directions towards which future research in this area might be directed.

Synthesis and Characterization of Uniform Nanowires of Trigonal Selenium

This article describes a soft, solution-phase approach to the large-scale synthesis of uniform nanowires of trigonal selenium (t-Se) with lateral dimensions controllable in the range of ∼10 to ∼800 nm, and lengths up to hundreds of micrometers. These highly anisotropic, one-dimensional (1D) nanostructures were directly nucleated and grown from aqueous solutions without the help of any physical templates, such as channel-like structures etched in porous materials, or scaffolds assembled from surfactants or block-copolymers. The 1D morphology of the product was solely determined by the linear characteristics of the building blocks—i.e., the extended, helical chains of atoms contained in the crystalline lattice of t-Se. A blue shift was observed for the bandgap and interchain transition of these nanowires when their diameters were reduced from ∼32 to ∼10 nm. The photoconductivity of individual nanowires has also been measured using the four-probe method, and an increase by ∼150 times was found when the sample was taken from the dark and exposed with ∼3 μW μm–2 tungsten light. Since no exotic seeds were involved in this synthetic process, every nanowire (including both ends) should be made entirely of pure selenium, crystallized in the trigonal phase. We believe the protocol described here can be scaled up for the high-volume production of t-Se nanowires that can subsequently serve as the physical or chemical templates to generate 1D nanostructures of various kinds of functional materials. The synthetic strategy itself, may also be extendable to other systems containing chain-like building blocks. The single crystallinity and absence of kinks and other related defects in these nanowires should make them particularly useful in fabricating nanoscale electronic, optical, or mechanical nanodevices.

Self‐Assembly Approaches to Three‐Dimensional Photonic Crystals

A brief review of the historical development of photonic bandgap (PBG) materials is provided and the fabrication methods employed are discussed with emphasis on self-assembly processes. The factors influencing the generation of a complete bandgap, from both an experimental and a calculational standpoint are then presented and discussed. The Figure shows a diamond-like 3D periodic structure.

Directed assembly of nanowires

Nanowires of a diverse range of compositions with tailored physical properties can be produced through synthetic means. These structures have been used as key components in flexible electronics, electronic logic gates, renewable energy technologies, and biological or gas sensing applications. Integrating these nanostructures into device or technology platforms will complement existing nanofabrication procedures by broadening the types of nanostructured materials that are utilized in device fabrication. This integration requires an ability to assemble these nanowires as controllable building blocks. Techniques are being developed that can quickly manipulate large quantities of nanowires through parallel processes.

Photothermal Release of Single-Stranded DNA from the Surface of Gold Nanoparticles Through Controlled Denaturating and Au−S Bond Breaking

Photothermal release of DNA from gold nanoparticles either by thermolysis of the Au-S bonds used to anchor the oligonucleotides to the nanoparticle or by thermal denaturation has great therapeutic potential, however, both processes have limitations (a decreased particle stability for the former process and a prohibitively slow rate of release for the latter). Here we show that these two mechanisms are not mutually exclusive and can be controlled by adjusting laser power and ionic strength. We show this using two different double-stranded (ds)DNA-nanoparticle conjugates, in which either the anchored sense strand or the complementary antisense strand was labeled with a fluorescent marker. The amounts of release due to the two mechanisms were evaluated using fluorescence spectroscopy and capillary electrophoresis, which showed that irradiation of the decorated particles in 200 mM NaOAc containing 10 mM Mg(OAc)(2) with a pulsed 532 nm laser operating at 100 mW favors denaturation over Au-S cleavage to an extent of more than six-to-one. Due to the use of a pulsed laser, the process occurs on the order of minutes rather than hours, which is typical for continuous wave lasers. These findings encourage continued research toward developing photothermal gene therapeutics.

An Efficient Method Based on the Photothermal Effect for the Release of Molecules from Metal Nanoparticle Surfaces

Please release me: The heat generated when metal nanoparticles absorb light results in a significant increase in the temperature of the environment around the particles and is used to selectively break bonds within a molecular system anchored to the nanoparticle surface (see picture). This process represents an advantageous and more universal method to deliver chemicals locally, while avoiding excessive tissue damage.

Development and characterization of oral lipid-based amphotericin B formulations with enhanced drug solubility, stability and antifungal activity in rats infected with Aspergillus fumigatus or Candida albicans.

OBJECTIVE To develop an oral formulation of Amphotericin B (AmpB) with: (A) medium chain triglycerides, fatty acids and nonionic surfactants as a self-emulsifying drug delivery system (SEDDS); or (B) glyceryl mono-oleate (Peceol) with poly(ethylene glycol) (PEG)-phospholipids. METHODS SEDDS formulations were prepared by simple mixing at 40 degrees C. Peceol/DSPE-PEG-lipid formulations were prepared by solvent evaporation. Parameters evaluated included: miscibility, solubility and emulsion droplet size after incubation in simulated gastric fluid (SGF) or simulated intestinal fluid (SIF) via dynamic light scattering. The stability of AmpB in Peceol/DSPE-PEG was evaluated in SGF and SIF. Phase stability of AmpB in Peceol+/-DSPE-PEG following thermal cycling was evaluated by atomic force microscopy (AFM). Aspergillus fumigatus (2.9-3.45 x 10(7) colony forming units per mL [CFU]) or Candida albicans (3-3.65 x 10(6) CFU per mL) were injected via the jugular vein; 48 h later male albino Sprague-Dawley rats (350-400 g) were administered either a single oral gavage of a Peceol-DSPE/PEG2000-based AmpB (10 mg AmpB/kg and 5 mg AmpB/kg for the Candida albicans study only) twice daily for 2 consecutive days, a single intravenous (i.v.) dose of Abelcet (5mg AmpB/kg), or physiologic saline (non-treated controls; n=9) once daily for 2 consecutive days. Antifungal activity was assessed by organ CFU concentrations and plasma galactomannan levels in the case of A. fumigatus and organ CFU concentrations in the case of Candida albicans. Plasma samples were taken from each animal prior to infection, 48 h after initiation of infection but prior to drug treatment and at the end of the study for plasma creatinine determinations as a measure of renal toxicity. RESULTS Mean diameter of SEDDS after 30 min in 150 mM NaCl at 37 degrees C was 200-400 nm. However, the Peceol/DSPE-PEG, where PEG MW was 350, 550, 750 or 2000, showed a greater solubilization of AmpB (5 mg/mL) compared to SEDDS formulations (100-500 microg/mL). Upon dispersion in SIF, Peceol/DSPE-PEG formulations generated submicron emulsion particle sizes varying slightly with PEG MW. Stability of the AmpB in Peceol/DSPE-PEG formulations in SGF or SIF was >80% after 2 h, and best for formulations containing DSPE-PEG 750 or 2000 compared to 350, 550 or Peceol only. Monoglyceride-Peceol-DSPE/PEG2000-based oral AmpB treatment significantly decreased total fungal CFU concentrations recovered in all the organs added together by >80% compared to non-treated controls without significant changes in plasma creatinine levels in the A. fumigatus infected rats. In addition, this formulation significantly decreased kidney fungal CFU concentrations by >75% at the 5 mg/kg dose and by >95% at the 10 mg/kg dose compared to non-treated controls without significant changes in the plasma creatinine levels in the Candida albicans-infected rats. CONCLUSIONS Novel lipid-based AmpB oral formulations were prepared that provide excellent drug solubilization, drug stability in simulated gastric and intestinal fluids and antifungal activity without renal toxicity in rats infected with A. fumigatus and C. albicans.

Hollow Metal Nanorods with Tunable Dimensions, Porosity, and Photonic Properties

An important aspect of synthesizing designer nanostructures is fine-tuning their size, composition, and surface area. These parameters often dictate the unique properties of nanoparticles relative to their bulk counterpart. This paper reports the synthesis of porous metal nanorods with well-controlled dimensions, porosity, and photonic properties. The growth of each nanostructure is directed by a polycrystalline sacrificial template of silver with well-defined, tunable dimensions. This template can be selectively etched to isolate a porous hollow nanostructure. The porosity, composition, and photonic characteristics of this nanostructure are adjustable by controlling the reaction conditions.

Photonic band-gap properties of opaline lattices of spherical colloids doped with various concentrations of smaller colloids

Monodispersed polystyrene beads have been organized into highly ordered, three-dimensional (3D) lattices using a self-assembly procedure recently demonstrated by our group. Such a 3D periodic structure consisting of high and low dielectric regions exhibits a pseudo-band gap (or a stop band) in the optical regime, with the position of this gap mainly determined by the size of the polymer beads. Doping of this 3D crystalline lattice with polymer beads of a smaller size was found to have a profound influence on the order (and thus the photonic band-gap properties) of the lattice. When the concentration of the dopant reached a certain level, phase segregation occurred which led to the formation of samples with relatively smaller domain sizes. In accordance, the attenuation (or rejection ratio) of the stop band also decreased monotonically as the doping level was increased.

Fabrication of three-dimensional photonic crystals for use in the spectral region from ultraviolet to near-infrared

This paper describes a simple and convenient method that allows self-assembly of colloidal particles (50 nm-50 /spl mu/m in diameter) into cubic-close-packed (c.c.p.) lattices over areas larger than 1 cm/sup 2/. These three-dimensional (3D) lattices have a highly ordered structure similar to that of a natural opal, with a packing density of approximately 74%. They strongly diffract light, and each of them exhibits a stop band whose position is mainly determined by the size of the particles. These crystalline assemblies of particles have also been used as templates to fabricate inverse opals, that is, three-dimensionally porous membranes consisting of a c.c.p. lattice of interconnected air balls. Both types of periodic structures are potentially useful as 3D photonic bandgap (PBG) crystals that can be used to control the emission and propagation of light in the spectral region ranging from ultraviolet (UV) to near infrared.