J. B. Warren

Biological cellular response to carbon nanoparticle toxicity

Recent advances in nanotechnology have increased the development and production of many new nanomaterials with unique characteristics for industrial and biomedical uses. The size of these new nanoparticles (<100?nm) with their high surface area and unusual surface chemistry and reactivity poses unique problems for biological cells and the environment. This paper reviews the current research on the reactivity and interactions of carbon nanoparticles with biological cells in vivo and in vitro, with ultrastructural images demonstrating evidence of human cell cytotoxicity to carbon nanoparticles characteristic of lipid membrane peroxidation, gene down regulation of adhesive proteins, and increased cell death (necrosis, apoptosis), as well as images of nontoxic carbon nanoparticle interactions with human cells. Although it is imperative that nanomaterials be systematically tested for their biocompatibility and safety for industrial and biomedical use, there are now ways to develop and redesign these materials to be less cytotoxic, and even benign to cell systems. With this new opportunity to utilize the unique properties of nanoparticles for research, industry and medicine, there is a responsibility to test and optimize these new nanomaterials early during the development process, to eliminate or ameliorate identified toxic characteristics.

Pauli-limited upper critical field of Fe1+yTe1-xSex

In this work, we investigated the temperature dependence of the upper critical field {mu}{sub 0}H{sub c2}(T) of Fe1.02(3)Te0.61(4)Se0.39(4) and Fe1.05(3)Te0.89(2)Se0.11(2) single crystals by measuring the magnetotransport properties in stable dc magnetic fields up to 35 T. Both crystals show that {mu}{sub 0}H{sub c2}(T) in the ab plane and along the c-axis exhibit saturation at low temperatures. The anisotropy of {mu}{sub 0}H{sub c2}(T) decreases with decreasing temperature, becoming nearly isotropic when the temperature T {yields} 0. Furthermore, {mu}{sub 0}H{sub c2}(0) deviates from the conventional Werthamer-Helfand-Hohenberg theoretical prediction values for both field directions. Our analysis indicates that the spin-paramagnetic pair-breaking effect is responsible for the temperature-dependent behavior of {mu}{sub 0}H{sub c2}(T) in both field directions.

Phase Diagram of KxFe2-ySe2-zSz and the Suppression of its Superconducting State by an Fe2-Se/S Tetrahedron Distortion

We report structurally tuned superconductivity in a K(x)Fe(2-y)Se(2-z)S(z) (0 ≤ z ≤ 2) phase diagram. Superconducting T(c) is suppressed as S is incorporated into the lattice, eventually vanishing at 80% of S. The magnetic and conductivity properties can be related to stoichiometry on a poorly occupied Fe1 site and the local environment of a nearly fully occupied Fe2 site. The decreasing T(c) coincides with the increasing Fe1 occupancy and the overall increase in Fe stoichiometry from z = 0 to z = 2. Our results indicate that the irregularity of the Fe2-Se/S tetrahedron is an important controlling parameter that can be used to tune the ground state in the new superconductor family.

A bubble-powered micro-rotor: conception, manufacturing, assembly and characterization

A steady fluid flow, called microstreaming, can be generated in the vicinity of a micro-bubble excited by ultrasound. In this paper, we use this phenomenon to assemble and power a microfabricated rotor at rotation speeds as high as 625 rpm. The extractible power is estimated to be of the order of a few femtowatts. A first series of experiments with uncontrolled rotor shapes is presented, demonstrating the possibility of this novel actuation scheme. A second series of experiments with 65 µm rotors micromanufactured in SU-8 resin is then presented. Variables controlling the rotation speed and rotor stability are investigated, such as the bubble diameter, the acoustic excitation frequency and amplitude and the rotor geometry. Finally, an outlook is provided on developing this micro-rotor into a MEMS-based motor capable of delivering tunable, infinitesimal rotary power at the microscale. M This article features online multimedia enhancements (Some figures in this article are in colour only in the electronic version)

Diamond kinoform hard X-ray refractive lenses: design, nanofabrication and testing.

Motivated by the anticipated advantageous performance of diamond kinoform refractive lenses for synchrotron X-ray radiation studies, this report focuses on progress in designing, nanofabricating and testing of their focusing performance. The method involves using lift-off and plasma etching to reproduce a planar definition of numerically determined kinoform refractive optics. Tests of the focusing action of a diamond kinoform refractive lens at the APS 8-ID-I beamline demonstrate angular control of the focal spot.

Exosporial membrane plasticity of Clostridium sporogenes and Clostridium difficile

This investigation examines the morphological alterations of the exosporial membranes of Clostridium sporogenes ATCC 3584 and Clostridium difficile ATCC 43594 and 9689 endospores in relation to their possible function during germination in the attachment/colonization process of these pathogenic bacteria. There is no reported function for the exosporial membrane, nor exosporial appendages, of clostridial endospores. Advances in high resolution, scanning electron microscopy (SEM) permit the examination of these delicate, morphological projections on intact spores in the process of attachment. The morphological plasticity of the exosporial membrane projections during activation and germination was examined to determine whether the appearance of these exosporial projections coincided with attachment of the spores to the nutritive substrate, and whether this attachment could be altered by physical agitation, cation competition with Ba2+, chelation with EDTA, or treatment with colchicine. Following incubation, activated spores could not be removed from the agar surface by agitation in water (pH 7.2 or 9.1), nor by agitation in buffer or colchicine, indicating that some form of adherence or attachment to the agar had taken place. When agitated in the presence of Ba2+ or EDTA in phosphate buffered saline or EDTA in water, all activated spores detached from the agar and exhibited decreased exosporial projections and minimal, if any, attachment structures to the agar surface. Activated clostridial spores were found to attach to agar by delicate extensions of the exosporium that could be disrupted by EDTA or Ba2+ exposure, but were unchanged when shaken in buffer or water.

One-dimensional hard x-ray field retrieval using a moveable structure

We present a technique that allows measuring the field of an x-ray line focus using far-field intensity measurements only. One-dimensional phase retrieval with transverse translation diversity is used to recover a hard x-ray beam focused by a compound kinoform lens. The reconstruction is found to be in good agreement with independent knife-edge scan measurements taken at separated planes. The approach avoids the need for measuring the beam profile at focus and allows narrower beams to be measured than the traditional knife-edge scan.

Human epithelial cell processing of carbon and gold nanoparticles

This paper describes some early cellular and intracellular interactions of human polarised lung and colon epithelial cells (representative of two portals of entry, inhalation and ingestion), following exposure to specific carbon and gold engineered nanoparticles in vitro. Cells were incubated with functionalised and non-functionalised carbon nanotube-derived nanoloops (∼28?60 nm diameter), or gold nanoparticles (2 nm and 10 nm Au-core) which were either non-functionalised, or functionalised with biological proteins or ssDNA and analysed using viability staining, transmission electron microscopy (TEM) and field emission scanning (FESEM) electron microscopy. Even with such diverse nanoparticles and functionalisations, we found that the surface properties and size of the nanoparticles determined their cellular binding, incorporation and/or cytotoxicity. However the cells responded to the different types of nanoparticles using various intracellular routes which differed with the cell type, but all of the nanoparticles ultimately were consolidated into aggregates and transported to the basal cell surface. Nanoparticles that were completely covered with biological macromolecules (i.e., recombinant gClq-R protein, non-immune IgGk, monoclonal antibody to gClq-R, or ssDNA) did not cause ultrastructural damage or changes in the cell monolayers. Monoclonal antibody (mAb)-functionalised carbon nanoloops and ssDNA 100% covered Au-nanodots were incorporated and transported within the colon cells using different cellular pathways than those used by the lung cells. Citrate-capped Au-nanoparticles (2 nm and 10 nm) and 20% DNA covered Au-nanoparticles passed into the colon and lung cells through small holes in the apical cell membrane, which could possibly be produced by lipid peroxidation. Serious forms of cell damage were observed with citrate capped 2 nm and 10 nm Au-nanoparticles (i.e., nuclear localisation (2 nm-Au); intracellular membrane damage (10 nm-Au)). Vital staining used to identify cellular necrosis following nanoparticle exposure, was sometimes misleading showing cell necrosis statistics similar to normal controls, when TEM analysis revealed intracellular and organellar damage in identically treated cells.

Imaging unstained proteoglycan aggregates by soft X-ray contact microscopy

Soft X-ray contact microscopy is a relatively new form of ultrastructural imaging, having better than 6 nm resolution and being uniquely well suited for the examination of fragile, unstained biological specimens. The biological specimen placed on a layer of photoresist and exposed to soft X-rays (1-10 nm lambda) of a specific wavelength or broad band. After X-ray exposure, the specimen is removed from the photoresist and the latter chemically developed. When the developed replica is examined by high resolution scanning electron microscopy, the fine structure of the original biological specimen is faithfully reproduced. Since the soft X-ray replica is initially formed due to the differential absorption of the incident X-rays by the biological specimen, the resultant contact replica also reveals information about the elemental composition of the sample. This paper presents our application of this new technique for the study of the proteoglycans, the complex polyanionic macromolecules comprising the gel phase in the matrix of mammalian cartilage.

The Exosporium of B.cereus Contains a Binding Site for gC1qR/p33: Implication in Spore Attachment and/or Entry

B. cereus, is a member of a genus of aerobic, gram-positive, spore-forming rod-like bacilli, which includes the deadly, B. anthracis. Preliminary experiments have shown that gC1qR binds to B. cereus spores that have been attached to microtiter plates. The present studies were therefore undertaken, to examine if cell surface gC1qR plays a role in B. cereus spore attachment and/or entry. Monolayers of human colon carcinoma (Caco-2) and lung cells were grown to confluency on 6 mm coverslips in shell vials with gentle swirling in a shaker incubator. Then, 2 microl of a suspension of strain SB460 B. cereus spores (3x10(8)/ml, in sterile water), were added and incubated (1-4 h; 36 degrees C) in the presence or absence of anti-gC1qR mAb-carbon nanoloops. Examination of these cells by EM revealed that: (1) When B. cereus endospores contacted the apical Caco-2 cell surface, or lung cells, gC1qR was simultaneously detectable, indicating upregulation of the molecule. (2) In areas showing spore contact with the cell surface, gC1qR expression was often adjacent to the spores in association with microvilli (Caco-2 cells) or cytoskeletal projections (lung cells). (3) Furthermore, the exosporia of the activated and germinating spores were often decorated with mAb-nanoloops. These observations were further corroborated by experiments in which B.cereus spores were readily taken up by monocytes and neutrophils, and this uptake was partially inhibited by mAb 60.11, which recognizes the C1q binding site on gC1qR. Taken together, the data suggest a role, for gC1qR at least in the initial stages of spore attachment and/or entry.