Enzyme–free uric acid electrochemical sensors using β–cyclodextrin modified carboxylic acid functionalized carbon nanotubes

Carboxylic acid-functionalized multi-walled carbon nanotubes (COOH-MWCNT) were modified via ultrasonication with β-cyclodextrin (β-CD) to obtain a COOH-MWCNT:β-CD nanocomposite material for the purpose of developing an enzyme-free electrochemical sensor for uric acid—a clinically relevant molecule implemented in pregnancy-induced hypertension diagnosis. The nanocomposite material is deposited onto glassy carbon electrodes and subsequently capped with layers of Nafion and Hydrothane polyurethane. The surface morphology and electronic structure of the nanocomposite material were characterized using UV–Vis, TEM, and FTIR. The performance of the electrochemical sensor was measured through direct injection of UA during amperometry. With the high surface area of the COOH-MWCNT in concert with the selectivity provided by β-CD, the composite system outperforms similar COOH-MWCNT systems, displaying enhanced UA sensitivity versus films with only COOH-MWCNT. With the improved sensitivity (4.28 ± 0.11 µA mM−1) and fast response time (4.0 ± 0.5 s), the sensors offer wide detection of UA across clinically relevant ranges (100–700 μM) as well as demonstrated selectivity against various interferents

Stable Aqueous Nanoparticle Film Assemblies with Covalent and Charged Polymer Linking Networks

The construction of highly stable and efficiently assembled multilayer films of purely water soluble gold nanoparticles is reported. Citrate-stabilized nanoparticles (CS-NPs) of average core diameter of 10 nm are used as templates for stabilization-based exchange reactions with thioctic acid to form more robust aqueous NPs that can be assembled into multilayer films. The thioctic acid stabilized nanoparticles (TAS-NPs) are networked via covalent and electrostatic linking systems, employing dithiols and the cationic polymer poly(l-lysine), respectively. Multilayer films of up to 150 nm in thickness are successfully grown at biological pH with no observable degradation of the NPs within the film. The characteristic surface plasmon band, an optical feature of certain NP film assemblies that can be used to report the local environment and core spacing within the film, is preserved. Growth dynamics and film stability in solution and in the air are examined, with poly(l-lysine) linked films showing no evidence of aggregation for at least 50 days. We believe these films represent a pivotal step toward exploring the potential of aqueous NP film assemblies as a sensing apparatus

Monolayer-Protected Nanoparticle Film Assemblies as Platforms for Controlling Interfacial and Adsorption Properties in Protein Monolayer Electrochemistry

Assembled films of nonaqueous nanoparticles, known as monolayer-protected clusters (MPCs), are investigated as adsorption platforms in protein monolayer electrochemistry (PME), a strategy for studying the electron transfer (ET) of redox proteins. Modified electrodes featuring MPC films assembled with various linking methods, including both electrostatic and covalent mechanisms, are employed to immobilize cytochrome c (cyt c) for electrochemical analysis. The background signal (non-Faradaic current) of these systems is directly related to the structure and composition of the MPC films, including nanoparticle core size, protecting ligand properties, as well as the linking mechanism utilized during assembly. Dithiol-linked films of Au225(C6)75 are identified as optimal films for PME by sufficiently discriminating against detrimental background current and exhibiting interfacial properties that are readily engineered for cyt c adsorption and electroactivity (Faradaic current). Surface concentrations and denaturation rates of adsorbed cyt c are dictated by specific manipulation of the individual MPCs composing the outer layer of the film. The use of specially designed, hydrophilic MPCs as a terminal film layer results in near-ideal cyt c voltammetry, attributed to a high degree of molecular level control of the necessary interfacial interactions and flexibility needed to create a uniform and effective binding of protein across large areas of a substrate. The electrochemical properties of cyt c at MPC films, including ET rate constants that are unaffected by the large ET distance introduced by MPC assemblies, are compared to traditional strategies employing self-assembled monolayers to immobilize cyt c. The incorporation of nanoparticles as protein adsorption platforms has implications for biosensor engineering as well as fundamental biological ET studies

Gold Nanoparticle Colorants as Traditional Ceramic Glaze Alternatives

Historically, Roman stained glass has been a standard for high‐temperature color stability since biblical times but was not properly characterized as emission from nanoparticle plasmon resonance until the 1990s. The methods under which it was created have been lost, but some efforts have recently been made to recreate these properties using gold nanoparticle inks on glassy surfaces. This body of work employs gold nanoparticle systems ranging from 0.015% to 0.100% (wt/wt), suspended in a clear glaze body. The glazes are fired with traditional ceramic methods—in both gas reduction and electric oxidation kilns—in which nanoparticles are retained and can be imaged via TEM. Various colors intensities are reported in addition to changes in nanoparticle size after application and firing. The nanoparticle glazes are compared to traditional red glazes, highlighting the significantly lower metal loading required (5%‐10% for traditional glazes vs 0.100% for gold (wt/wt)), therein. Finally, proof of concept is provided with a functional gold nanoparticle mug, fired in reduction, that costs roughly 0.98$ USD in gold used

Pengenalan Alat Navigasi, Keselamatan dan Kesehatan pada Kapal Penangkap Ikan Enterprise di Perairan Selat Makassar

On voyage fishing vessel should be equipped with proper navigation equipment. Cadets who will be working onboard of a  fishing vessel should understanding and aware of navigational equipment, safety equipment and healthy equipment. Because ,it could cause accident and awareness on navigational equipment. One of the ways for cadets to understand about navigation equipment are Maps, Campasses, Global Positioning System, Radia and Automatic Identification System. Each of these navigation equipment are hhaving their own function and operating system. So, it is a mandatory for every cadets to understand and aware in operating sthes navigation and know about  safety equipment and healthy equipment on Enterprise fishing vessel

How native state topology affects the folding of Dihydrofolate Reductase and Interleukin-1beta

The overall structure of the transition state and intermediate ensembles experimentally observed for Dihydrofolate Reductase and Interleukin-1beta can be obtained utilizing simplified models which have almost no energetic frustration. The predictive power of these models suggest that, even for these very large proteins with completely different folding mechanisms and functions, real protein sequences are sufficiently well designed and much of the structural heterogeneity observed in the intermediates and the transition state ensembles is determined by topological effects.Comment: Proc. Natl. Acad. Sci. USA, in press (11 pages, 4 color PS figures) Higher resolution PS files can be found at http://www-physics.ucsd.edu/~cecilia/pub_list.htm

Polyelectrolyte-Linked Film Assemblies of Nanoparticles and Nanoshells: Growth, Stability, and Optical Properties

Multi-layer films of nanoparticles and nanoshells featuring various polymeric linkage molecules have been assembled and their optical properties characterized. The growth dynamics, including molecular weight effects, and stability of the various nanoparticle film constructions, using both single polymer as well as combinations of alternating charge polyelectrolytes as linking mechanisms, are presented. The polymeric linkers studied include poly-L-lysine, poly-L-arginine, poly(allylamine hydrochloride), and polyamidoamine dendrimers. Significantly air stable films were achieved with the use of multi-layered polymeric bridges between the nanoparticles and nanoshells. Optical sensitivity normally observed with these nanomaterials in solution was observed for their corresponding film geometries, with the nanoshell films exhibiting a markedly higher ability to report their local dielectric environment

Electropolymerized Layersas Selective Membranesin First Generation Uric Acid Biosensors

Electropolymerized films that can serve as semi-permeable membranes and provide selectivity within a xerogel-based, 1stgeneration biosensor assembly are explored in this study. Layered biosensing schemes of this nature rely primarily upon an electropolymerized ad-layer to supplement the xerogel and provide effective selectivity for detection of a targeted analyte. While effective electropolymers have been established for glucose sensing, the adaptation of the strategy to other analytes of clinical importance hinges upon the systematic evaluation of electropolymerized films to identify a selective film. Uric acid is a key species in the diagnosis/monitoring of a number of diseases and conditions. An effective uric acid biosensor, exhibiting high selectivity against common interferent species while maintaining uric acid sensitivity across physiologically relevant concentrations, would represent significant sensor development. Cyclic voltammetry allows for initial electropolymerization as well as the verification of polymer-modified electrodes. By forming electropolymerized films at glassy carbon electrodes, the sensitivity and permeability index toward uric acid and other interferents is readily measured via amperometric current responses. Of the significant number of polymer films examined in the study, only those films formed from luminol/aniline and luminol/Nafion mixtures showed positive selectivity coefficients for uric acid when incorporated into the layered xerogel schemes. The use of these specific mixed polymer films within the biosensing scheme resulted in well-defined amperometric responses to uric acid, linear calibration curves across clinically relevant uric acid concentrations, and effective selectivity for uric acid with discrimination against all major interferents except acetaminophen. The demonstrated and systematic evaluation of a specifically selective electropolymerized film is an important advancement for uric acid biosensor development as well as further adaptation of biosensing strategies involving polymer interfaces to other targeted analytes

Adaptable Xerogel-Layered Amperometric Biosensor Platforms on Wire Electrodes for Clinically Relevant Measurements

Biosensing strategies that employ readily adaptable materials for different analytes, can be miniaturized into needle electrode form, and function in bodily fluids represent a significant step toward the development of clinically relevant in vitro and in vivo sensors. In this work, a general scheme for 1st generation amperometric biosensors involving layer-by-layer electrode modification with enzyme-doped xerogels, electrochemically-deposited polymer, and polyurethane semi-permeable membranes is shown to achieve these goals. With minor modifications to these materials, sensors representing potential point-of-care medical tools are demonstrated to be sensitive and selective for a number of conditions. The potential for bedside measurements or continuous monitoring of analytes may offer faster and more accurate clinical diagnoses for diseases such as diabetes (glucose), preeclampsia (uric acid), galactosemia (galactose), xanthinuria (xanthine), and sepsis (lactate). For the specific diagnostic application, the sensing schemes have been miniaturized to wire electrodes and/or demonstrated as functional in synthetic urine or blood serum. Signal enhancement through the incorporation of platinum nanoparticle film in the scheme offers additional design control within the sensing scheme. The presented sensing strategy has the potential to be applied to any disease that has a related biomolecule and corresponding oxidase enzyme and represents rare, adaptable, sensing capabilities

Reply to Comment on "Criterion that Determines the Foldability of Proteins"

We point out that the correlation between folding times and $\sigma = (T_{\theta } - T_{f})/T_{\theta }$ in protein-like heteropolymer models where $T_{\theta }$ and $T_{f}$ are the collapse and folding transition temperatures was already established in 1993 before the other presumed equivalent criterion (folding times correlating with $T_{f}$ alone) was suggested. We argue that the folding times for these models show no useful correlation with the energy gap even if restricted to the ensemble of compact structures as suggested by Karplus and Shakhnovich (cond-mat/9606037).Comment: 6 pages, Latex, 2 Postscript figures. Plots explicitly showing the lack of correlation between folding time and energy gap are adde