A click chemistry amplified nanopore assay for ultrasensitive quantification of HIV-1 p24 antigen in clinical samples.

Despite major advances in HIV testing, ultrasensitive detection of early infection remains challenging, especially for the viral capsid protein p24, which is an early virological biomarker of HIV-1 infection. Here, To improve p24 detection in patients missed by immunological tests that dominate the diagnostics market, we show a click chemistry amplified nanopore (CAN) assay for ultrasensitive quantitative detection. This strategy achieves a 20.8 fM (0.5 pg/ml) limit of detection for HIV-1 p24 antigen in human serum, demonstrating 20~100-fold higher analytical sensitivity than nanocluster-based immunoassays and clinically used enzyme-linked immunosorbent assay, respectively. Clinical validation of the CAN assay in a pilot cohort shows p24 quantification at ultra-low concentration range and correlation with CD4 count and viral load. We believe that this strategy can improve the utility of p24 antigen in detecting early infection and monitoring HIV progression and treatment efficacy, and also can be readily modified to detect other infectious diseases.

Cs-RHO Goes from Worst to Best as Water Enhances Equilibrium CO2 Adsorption via Phase Change.

The strong affinity of water to zeolite adsorbents has made adsorption of CO2 from humid gas mixtures such as flue gas nearly impossible under equilibrated conditions. Here, in this manuscript, we describe a unique cooperative adsorption mechanism between H2O and Cs+ cations on Cs-RHO zeolite, which actually facilitates the equilibrium adsorption of CO2 under humid conditions. Our data demonstrate that, at a relative humidity of 5%, Cs-RHO adsorbs 3-fold higher amounts of CO2 relative to dry conditions, at a temperature of 30 °C and CO2 pressure of 1 bar. A comparative investigation of univalent cation-exchanged RHO zeolites with H+, Li+, Na+, K+, Rb+, and Cs+ shows an increase of equilibrium CO2 adsorption under humid versus dry conditions to be unique to Cs-RHO. In situ powder X-ray diffraction indicates the appearance of a new phase with Im3̅m symmetry after H2O saturation of Cs-RHO. A mixed-cation exchanged NaCs-RHO exhibits similar phase transitions after humid CO2 adsorption; however, we found no evidence of cooperativity between Cs+ and Na+ cations in adsorption, in single-component H2O and CO2 adsorption. We hypothesize based on previous Rietveld refinements of CO2 adsorption in Cs-RHO zeolite that the observed phase change is related to solvation of extra-framework Cs+ cations by H2O. In the case of Cs-RHO, molecular modeling results suggest that hydration of these cations favors their migration from an original D8R position to S8R sites. We posit that this movement enables a trapdoor mechanism by which CO2 can interact with Cs+ at S8R sites to access the α-cage.

Synthesis of Highly Active Pd@Cu-Pt/C Methanol Oxidation Electrocatalysts via Continuous, Co-Electroless Deposition.

Controlled deposition of metals is essential for the creation of bimetallic catalysts having predictable composition and character. Continuous co-electroless deposition (co-ED) permits the creation of bimetallic catalysts with predictive control over composition. This method was applied to create a suite of Cu-Pt mixed-metal shell catalysts for use in methanol electrooxidation in direct methanol fuel cell applications (DMFCs). Enhanced performance of Cu-Pt compositions over Pt alone was predicted by existing computational studies in the literature. Experimental evidence from this study supports the bifunctional catalyst explanation for enhanced activity and confirms the optimum Cu:Pt ratio as Cu3Pt for this methanol electrooxidation. This ability to control the composition of a bimetallic shell can be extended to other systems where the ratio of two metals is critical for catalytic performance.

Fabrication of biodegradable particles with tunable morphologies by the addition of resveratrol to oil in water emulsions.

Particles for biomedical applications can be produced by emulsifying biocompatible polymers dissolved in an organic solvent in water. The emulsion is then transferred to an extraction bath that removes the solvent from the dispersed droplets, which leads to polymer precipitation and particle formation. Typically, the particles are smooth and spherical, likely because the droplets remain fluid throughout the solvent extraction process allowing minimization of surface area as the volume decreases. Few modifications to this technique exist that alter the spherical geometry, even though particle performance, from drug delivery to engaging cells of the body, can be tuned with morphology. Here we demonstrate that incorporation of resveratrol, with the aid of ethanol, into the oil phase of an emulsion of poly(lactide-co-glycolide) and dichloromethane in aqueous poly(vinyl alcohol) leads to a crumpled particle morphology. Video microscopy of particle formation revealed that during solvent extraction the droplet crumples in on itself, which does not occur when only ethanol is added to the emulsion. It is unclear why this occurs with resveratrol, but its hydroxyl groups appear to be optimally positioned because removal of the 4' hydroxyl or addition of a 3' hydroxyl resulted in a loss of crumpled particle morphology. We demonstrate that particle morphology can be tuned from that of a crumpled sheet of paper to a deflated sphere by switching out ethanol for a different cosolvent. We quantify the degree of particle deformation with surface area calculated from krypton adsorption isotherms and BET theory and find surface area correlates with resveratrol loading in the particle. Furthermore, spherical particles are achieved when ethyl acetate is used in lieu of dichloromethane and a cosolvent. We propose that during solvent extraction, resveratrol accumulates at the droplet surface where it inhibits polymer chain motion necessary to maintain a spherical geometry and the role of cosolvent is to redistribute resveratrol from the droplet bulk to its surface. This method of producing nonspherical particles extends to polycaprolactone and poly(L-lactic acid) and is compatible with the encapsulation of a hydrophobic fluorescent dye, suggesting hydrophobic bioactive agents could be encapsulated. Taken together, we demonstrate an ability to control morphology of biocompatible polymer particles produced by the widely practiced oil-in-water/solvent extraction protocol via the addition of resveratrol and a cosolvent to the oil phase. The methodology reported is straight forward, and scalable, and expected to be of utility in applications in which a deviation from the default smooth, spherical morphology is desired.

Selective Catalytic Chemistry at Rhodium(II) Nodes in Bimetallic Metal-Organic Frameworks.

We report the first study of a gas-phase reaction catalyzed by highly dispersed sites at the metal nodes of a crystalline metal-organic framework (MOF). Specifically, CuRhBTC (BTC3- =benzenetricarboxylate) exhibited hydrogenation activity, while other isostructural monometallic and bimetallic MOFs did not. Our multi-technique characterization identifies the oxidation state of Rh in CuRhBTC as +2, which is a Rh oxidation state that has not previously been observed for crystalline MOF metal nodes. These Rh2+ sites are active for the catalytic hydrogenation of propylene to propane at room temperature, and the MOF structure stabilizes the Rh2+ oxidation state under reaction conditions. Density functional theory calculations suggest a mechanism in which hydrogen dissociation and propylene adsorption occur at the Rh2+ sites. The ability to tailor the geometry and ensemble size of the metal nodes in MOFs allows for unprecedented control of the active sites and could lead to significant advances in rational catalyst design.

Platinum-ruthenium bimetallic clusters on graphite: a comparison of vapor deposition and electroless deposition methods.

Bimetallic Pt-Ru clusters have been grown on highly ordered pyrolytic graphite (HOPG) surfaces by vapor deposition and by electroless deposition. These studies help to bridge the material gap between well-characterized vapor deposited clusters and electrolessly deposited clusters, which are better suited for industrial catalyst preparation. In the vapor deposition experiments, bimetallic clusters were formed by the sequential deposition of Pt on Ru or Ru on Pt. Seed clusters of the first metal were grown on HOPG surfaces that were sputtered with Ar(+) to introduce defects, which act as nucleation sites for Pt or Ru. On the unmodified HOPG surface, both Pt and Ru clusters preferentially nucleated at the step edges, whereas on the sputtered surface, clusters with relatively uniform sizes and spatial distributions were formed. Low energy ion scattering experiments showed that the surface compositions of the bimetallic clusters are Pt-rich, regardless of the order of deposition, indicating that the interdiffusion of metals within the clusters is facile at room temperature. Bimetallic clusters on sputtered HOPG were prepared by the electroless deposition of Pt on Ru seed clusters from a Pt(+2) solution using dimethylamine borane as the reducing agent at pH 11 and 40 °C. After exposure to the electroless deposition bath, Pt was selectively deposited on Ru, as demonstrated by the detection of Pt on the surface by XPS, and the increase in the average cluster height without an increase in the number of clusters, indicating that Pt atoms are incorporated into the Ru seed clusters. Electroless deposition of Ru on Pt seed clusters was also achieved, but it should be noted that this deposition method is extremely sensitive to the presence of other metal ions in solution that have a higher reduction potential than the metal ion targeted for deposition.

Novel recirculating loop reactor for studies on model catalysts: CO oxidation on Pt/TiO2(110).

A novel recirculating loop microreactor coupled to an ultrahigh vacuum (UHV) chamber has been constructed for the kinetic evaluation of model catalysts, which can be fully characterized by UHV surface science techniques. The challenge for this reactor design is to attain sufficient sensitivity to detect reactions on model single-crystal surfaces, which have a low number of active sites compared to conventional catalysts of equivalent mass. To this end, the total dead volume of the reactor system is minimized (32 cm(3)), and the system is operated in recirculation mode so that product concentrations build up to detectable levels over time. The injection of gas samples into the gas chromatography column and the refilling of the recirculation loop with fresh feed gas are achieved with computer-controlled, automated switching valves. In this manner, product concentrations can be followed over short time intervals (15 min) for extended periods of time (24 h). A proof of principle study in this reactor for CO oxidation at 145-165 °C on Pt clusters supported on a rutile TiO2(110) single crystal yields kinetic parameters that are comparable to those reported in the literature for CO oxidation on Pt clusters on powdered oxide supports, as well as on Pt(100). The calculated activation energy is 16.4 ± 0.7 kcal/mol, the turnover frequency is 0.03-0.06 molecules/(site·s) over the entire temperature range, and the reaction orders in O2 and CO at 160 °C are 0.9 ± 0.2 and -0.82 ± 0.03, respectively.

Preparation and structural analysis of carbon-supported Co core/Pt shell electrocatalysts using electroless deposition methods.

Cobalt core/platinum shell nanoparticles were prepared by the electroless deposition (ED) of Pt on carbon-supported cobalt catalyst (Co/C) and verified by HRTEM images. For a 2.0 wt % Co/C core, the ED technique permitted the Pt loading to be adjusted to obtain a series of bimetallic compositions with varying numbers of monolayers (ML). The tendency for corrosion of Co and the electrochemical (i.e., oxygen reduction reaction (ORR)) activity of the structures were measured. The results from temperature-programmed reduction (TPR) analysis suggest that a single Pt ML coverage is formed at a Pt weight loading between 0.5 and 0.7% on the 2.0% Co/C. HRTEM analysis indicates that the continuity of the Pt shell on the Co core depends on the precursor Co particle size, where "large" Co particles (>10 nm) favor noncontinuous, three-dimensional Pt structures and "small" Co particles (<6 nm) favor layer-by-layer growth. For these larger core-shell particles, Co was observed to quickly corrode in 0.3 M H(2)SO(4). Surface area specific ORR activity, measured by chemisorption techniques, revealed that the Pt-Co/C catalysts performed better than a commercial Pt/C catalyst; however, on a Pt mass basis, only the lower Pt:Co atomic ratio Pt-Co/C catalysts outperformed the Pt/C catalyst.