Preparation and characterization of graphene oxide encapsulated gold nanoparticles.

We present a simple approach for the fabrication of graphene oxide-encapsulated gold nanoparticles using graphene oxide sheet-wrapping via electrostatic self-assembly. By mixing bovine serum albumin molecule-functionalized gold nanoparticles with graphene oxide dispersion, positively charged bovine serum albumin/gold nanoparticles easily assembled with negatively charged graphene oxide sheets through electrostatic interaction. Transmittance electron microscopy, scanning electron microscopy, atomic force microscopy, and Raman spectroscopy were used to confirm the encapsulation of graphene oxide on gold nanoparticles. Interestingly, graphene oxide sheets wrapping mainly occurs along the main body of single or a few gold nanoparticles. Additionally, by measuring the ultraviolet-visible spectroscopy spectrum, we found that the surface plasmon resonances band of the graphene oxide-encapsulated gold nanoparticles was found to become red-shifted compared to that of pristine gold nanoparticles, whereas similar to that of bovine serum albumin-coated gold nanoparticles. These results indicating that most of graphene oxide-encapsulated gold nanoparticles have good monodispersity and spherical shape. These resulting materials may potentially serve as a platform for plasmon resonance electron transfer spectroscopy or a probe for low level biosensing.

In situ curing of sliding SU-8 droplet over a microcontact printed pattern for tunable fabrication of a polydimethylsiloxane nanoslit.

A tunable process for polydimethylsiloxane (PDMS) nanoslit fabrication is developed for nanofluidic applications. A microcontact printing (µCP) of a laterally spreading self-assembled hexadecanethiol (HDT) layer, combined with in situ curing of a sliding SU-8 droplet, enables precise and independent tuning of a nanoslit-mold width and height using a single µCP master mold. The SU-8 nanoslit-mold is replicated using a hard-soft composite PDMS to prevent channel collapse at low (<0.2) aspect ratio (height over width). The fluidic characteristics as well as dimensions of nanoslits fabricated with various conditions are analyzed using a fluorescein sample and AFM images. Finally, concentration polarization-based sample preconcentration is successfully demonstrated at the nanoslit boundary where an electric double-layer is overlapped.

Thermochemical study for remediation of highly concentrated acid spill: Computational modeling and experimental validation.

The release of concentrated acid solutions by chemical accidents is disastrous to our environmental integrity. Alkaline agents applied to remedy the acid spill catastrophe may lead to secondary damages such as vaporization or spread out of the fumes unless substantial amount of neutralization heat is properly controlled. Using a rigorous thermodynamic formalism proposed by Pitzer to account short-range ion interactions and various subsidiary reactions, we develop a systematic computational model enabling quantitative prediction of reaction heat and the temperature change over neutralization of strongly concentrated acid solutions. We apply this model to four acid solutions (HCl, HNO3, H2SO4, and HF) of each 3 M-equivalent concentration with two neutralizing agents of calcium hydroxide (Ca(OH)2) and sodium bicarbonate (NaHCO3). Predicted reaction heat and temperature are remarkably consistent with the outcomes measured by our own experiments, showing a linear correlation factor R2 greater than 0.98. We apply the model to extremely concentrated acid solutions as high as 50 wt% where an experimental approach is practically restricted. In contrast to the extremely exothermic Ca(OH)2 agent, NaHCO3 even lowers solution temperatures after neutralization reactions. Our model enables us to identify a promising neutralizer NaHCO3 for effectively controlling concentrated acid spills and may be useful for establishment of proper strategy for other chemical accidents.

Characterization of nanoscale recording mark on Ge2Sb2Te5 film.

We have fabricated nanoscale recording marks on Ge(2)Sb(2)Te(5) (GST) films with conductive atomic force microscope (AFM). GST films were deposited on glass or polyimide film with thickness of 150-200 nm by the rf-sputtering method. Through current-voltage (I-V) spectroscopy, good cantilevers for fabrication and characterization of nanoscale marks on GST were selected. A fresh and highly conductive tip showed voltage-switching characteristic in the I-V curve, where the threshold voltage was approximately 1.6 V. Nanoscale dot and wire arrays of crystalline phases were successfully obtained by varying sample bias voltage from -10 to 10 V. With highly conductive tips, nanowires having full-width at half-maximum of approximately 20 nm could be fabricated, whereas nanowires could not be fabricated with bias voltage below -2 V. The width of the nanoscale mark was increased by repetition of AFM lithography even with same applied voltage and lithography speed. For a thicker nanowire, the width measured in current-image (C-image) was observed to be approximately 2 times of that measured in topography-image (T-image). This result supports that current sensing provides an image of phase-changed GST area with higher resolution than topography sensing.

Recent progress of nano-technology with NSOM.

Recent progress of nano-technology with near-field scanning optical microscope (NSOM) is surveyed in this article. We focus mainly on NSOM, nano-scale spectroscopy with NSOM, probe technology of NSOM, and study of nano-structured metallic surface with NSOM. First, we follow developments of aperture NSOM and apertureless NSOM, and then address progress of NSOM-combined spectroscopy which is so sufficiently advanced with apertureless NSOM technology to provide chemical information on length scales of a few nanometers. Recent achievement of nano-scale Raman and IR spectroscopy will be introduced. Finally, research on nano-optic elements using surface plasmon polariton with NSOM is introduced as an example of NSOM applications to nano-structured metallic surfaces.

Simulation study on heat conduction of a nanoscale phase-change random access memory cell.

We have investigated heat transfer characteristics of a nano-scale phase-change random access memory (PRAM) cell using finite element method (FEM) simulation. Our PRAM cell is based on ternary chalcogenide alloy, Ge2Sb2Te5 (GST), which is used as a recording layer. For contact area of 100 x 100 nm2, simulations of crystallization and amorphization processes were carried out. Physical quantities such as electric conductivity, thermal conductivity, and specific heat were treated as temperature-dependent parameters. Through many simulations, it is concluded that one can reduce set current by decreasing both electric conductivities of amorphous GST and crystalline GST, and in addition to these conditions by decreasing electric conductivity of molten GST one can also reduce reset current significantly.

Antibody-based magnetic nanoparticle immunoassay for quantification of Alzheimer's disease pathogenic factor.

Alzheimer's disease (AD) is a neurodegenerative disorder that leads to a decline in cognitive and intellectual abilities and an irreversible mental deterioration. Based on multidisciplinary AD research, the most universally accepted hypotheses on AD pathogenesis are the intracerebral aggregate formation of beta-amyloid (Aß) peptides. According to medical paradigmatic transition from medical treatment to early diagnostic prevention, scientists have considered physiological body fluid as a biomarker medium, in which the promising AD biomarkers could be verified. Recently, use of saliva has been considered as one of the diagnostic fluids over the past decade with meaningful diagnostic potential. We utilized saliva as a biomarker medium to correlate the salivary Aß levels to AD pathological aspects, especially to the mild cognitive impairment group among AD patients, and to verify our detecting system to be sensitive enough for an early diagnostic tool. The identification of the salivary AD biomarkers using a facile microarraying method would motivate this study with the assistance of magnetically assembled antibody-conjugated nanoparticles and a photomultiplier tube as an optical detector. This simple magnetoimmunoassay system measures the photointensity generated by fluorescence, enables the quantification of the Aß peptides from AD salivary samples, and consequently classifies the salivary Aß levels into AD pathological aspects. This method demonstrates a facile approach enabling it to simply detect salivary Aß peptides at a concentration as low as ~20 pg/ml. It is expected that our simple magnetoimmunoassay system may have a potential as a detector for low-level Aß peptides with weak-fluorescence emission.

A 3D scaffold for ultra-sensitive reduced graphene oxide gas sensors.

An ultra-sensitive gas sensor based on a reduced graphene oxide nanofiber mat was successfully fabricated using a combination of an electrospinning method and graphene oxide wrapping through an electrostatic self-assembly, followed by a low-temperature chemical reduction. The sensor showed excellent sensitivity to NO2 gas.

Analysis of beta amyloid peptides employing the small probe molecules.

We herein describe an analytical method employing a small molecule array for the characterization of similar proteins based on ligand binding. In this study, 2 different beta amyloids (Abeta(1-40) and (1-42)) were selected as the model compounds. Their primary structures are identical except for 2 additional C-terminal amino acids. However, many studies have observed different biological and chemical characteristics of these peptides. Thus, the ability to distinguish these 2 peptides is important in the diagnosis and development of treatments for related disorders such as Alzheimer's disease. However, strong non-specific binding is usually observed, even when specific antibodies for each peptide are employed. In this study, Abeta(1-40) and Abeta(1-42) peptides were immobilized on a typical 96-well microplate. Twenty different small probe molecules (modified amino acids conjugated with FITC) were applied to the peptides acting as the secondary antibodies and labeling compounds. The results show that specific binding patterns occurred according to Abeta type and the analysis of the patterns can be used to distinguish these 2 similar peptides.

Measurement of beta-amyloid peptides in specific cells using a photo thin-film transistor.

The existence of beta-amyloid [Aß] peptides in the brain has been regarded as the most archetypal biomarker of Alzheimer's disease [AD]. Recently, an early clinical diagnosis has been considered a great importance in identifying people who are at high risk of AD. However, no microscale electronic sensing devices for the detection of Aß peptides have been developed yet. In this study, we propose an effective method to evaluate a small quantity of Aß peptides labeled with fluorescein isothiocyanate [FITC] using a photosensitive field-effect transistor [p-FET] with an on-chip single-layer optical filter. To accurately evaluate the quantity of Aß peptides within the cells cultured on the p-FET device, we measured the photocurrents which resulted from the FITC-conjugated Aß peptides expressed from the cells and measured the number of photons of the fluorochrome in the cells using a photomultiplier tube. Thus, we evaluated the correlation between the generated photocurrents and the number of emitted photons. We also evaluated the correlation between the number of emitted photons and the amount of FITC by measuring the FITC volume using AFM. Finally, we estimated the quantity of Aß peptides of the cells placed on the p-FET sensing area on the basis of the binding ratio between FITC molecules and Aß peptides.

Assessment of fates of estrogens in wastewater and sludge from various types of wastewater treatment plants.

We measured five estrogens in the wastewater samples from the municipal wastewater treatment plants (M-WWTPs), livestock wastewater treatment plants (L-WWTPs), hospital WWTPs (H-WWTPs) and pharmaceutical manufacture WWTPs (P-WWTPs) in Korea. The L-WWTPs showed the highest total concentration (0.195-10.4 µg L(-1)) of estrogens in the influents, followed by the M-WWTPs (0.028-1.15 µg L(-1)), H-WWTPs (0.068-0.130 µg L(-1)) and P-WWTPs (0.015-0.070 µg L(-1)). Like the influents, the L-WWTPs (0.003-0.729 µg L(-1)) and the M-WWTPs (0.001-0.299µgL(-1)) also showed higher total concentration of estrogens in the effluents than the H-WWTPs (0.002-0.021 µg L(-1)) and P-WWTPs (0.011 µg L(-1) in one sample). The L-WWTPs (37.5-543 µg kg(-1), dry weight) showed higher total concentrations in sludge than the M-WWTPs (3.16-444 µg kg(-1), dry weight) like the wastewater. The distribution of estrogens in the WWTPs may be affected by their metabolism in the human body, their transition through biological treatment processes, and their usage for livestock growth. Unlike the concentration results, the daily loads of estrogens from the M-WWTPs were the highest, which is related to the high capacities of WWTPs.

Detection of two different influenza A viruses using a nitrocellulose membrane and a magnetic biosensor.

Here we describe a new analytical method for the detection of two influenza A viruses by nitrocellulose membrane and magnetic sensors that employ a special frequency mixing technique. The combination of the nitrocellulose membrane and magnetic bead detection permits a rapid assay procedure and excludes two steps (the development of color and the stop reaction) required for usual immunochemical detection methods such as ELISA. Quantitative virus detection was performed using magnetic beads conjugated with secondary antibody. The results were compared with conventional assay methods and with a dot-blot assay with fluorescence compound (FITC). Under optimum conditions, our new assay procedure is capable of detecting picograms of virus per well. This new method combining the nitrocellulose membrane and magnetic bead detection reduces analytical time and allows stable and repeatable analyses of samples in point-of-care applications.

Complete Binocular Blindness as the First Manifestation of HIV-Related Cryptococcal Meningitis.

Ocular complications of HIV-related cryptococcal meningitis are reasonably common, but complete binocular blindness as the first manifestation of HIV is extremely rare. A 58-year-old man presented with binocular blindness. He experienced blurred vision for 3 days before the blindness. Mild pleocytosis was present in the cerebrospinal fluid, from which Cryptococcus neoformans was cultured. Serology revealed positivity for HIV antibody. He was treated with antifungal and antiretroviral therapy. This case indicates that HIV-related cryptococcal meningitis should be taken into consideration when determining the cause of unexpected sudden binocular blindness.