We present the results of acid–base experiments performed at the single ion (H+ or OH−) limit in ∼6 aL volume nanopores incorporating electrochemical zero-mode waveguides (E-ZMWs). At pH 3 each E-ZMW nanopore contains ca. 3600H+ ions, and application of a negative electrochemical potential to the gold working electrode/optical cladding layer reduces H+ to H2, thereby depleting H+ and increasing the local pH within the nanopore. The change in pH was quantified by tracking the intensity of fluorescein, a pH-responsive fluorophore whose intensity increases with pH. This behavior was translated to the single ion limit by changing the initial pH of the electrolyte solution to pH 6, at which the average pore occupancy 〈n〉pore ∼3.6H+/nanopore. Application of an electrochemical potential sufficiently negative to change the local pH to pH 7 reduces the proton nanopore occupancy to 〈n〉pore ∼0.36H+/nanopore, demonstrating that the approach is sensitive to single H+ manipulations, as evidenced by clear potential-dependent changes in fluorescein emission intensity. In addition, at high overpotential, the observed fluorescence intensity exceeded the value predicted from the fluorescence intensity-pH calibration, an observation attributed to the nucleation of H2 nanobubbles as confirmed both by calculations and the behavior of non-pH responsive Alexa 488 fluorophore. Apart from enhancing fundamental understanding, the approach described here opens the door to applications requiring ultrasensitive ion sensing, based on the optical detection of H+ population at the single ion limit.Visualizing dynamic change in the number of protons during electroreduction of protons in attoliter volume zero-mode waveguides.相似文献
Co–Fe bimetallic nanoparticles-affixed polyvinylidene fluoride-co-hexafluoropropylene (PVdF-HFP) nanofiber membrane is fabricated using the electrospinning and chemical reduction techniques. The semicrystalline polymeric backbone decorated with the highly crystalline Co–Fe bimetallic nanoparticles enunciates the mechanical integrity, while the incessant and swift electron mobility is articulated with the consistent dissemination of bimetallic nanoparticles on the intersected and multi-layered polymeric nanofibers. The diffusion and adsorption of glucose are expedited in the extended cavities and porosities of as-formulated polymeric nanofibers, maximizing the glucose utilization efficacy, while the uniformly implanted Co4+/Fe3+ active centers on PVdF-HFP nanofibers maximize the electrocatalytic activity toward glucose oxidation under alkaline regimes. Thus, the combinative sorts including nanofiber and nanocomposite strategies of PVdF-HFP/Co–Fe membrane assimilate the enzyme-less electrochemical glucose detection concerts of high sensitivity (375.01 μA mM?1 cm?2), low limit of detection (0.65 μm), and wide linear range (0.001 to 8 mM), outfitting the erstwhile enzyme-less glucose detection reports. Additionally, the endowments of high selectivity and real sample glucose-sensing analyses of PVdF-HFP/Co–Fe along with the binder-less and free-standing characteristics construct the state-of-the-art paradigm for the evolution of affordable enzyme-less electrochemical glucose sensors.
Trialkoxysilanes (or silanes) have emerged as a very promising alternative for chromates in metal finishing industries. Compared to the conventional chromating processes, the major merits of silane-based surface treatments include: eco-compliance, easy-control processing, comparable corrosion protection of metals as well as paint adhesion to a variety of topcoats. In this overview paper, we report the recent status of silane studies including results of corrosion performance tests, the mechanism of corrosion protection of metals by silanes and the themal stabilities of silane films. We also address the new fields that we are beginning to explore such as nano-structured silane films, “self-healing” silane films, and “super-primers”. 相似文献
Herein we present a new approach for the complete removal of CrVI species, through reduction of CrVI to CrIII, followed by adsorption of CrIII. Reduction of chromium from water is an important challenge, as CrIV is one of the most toxic substances emitted from industrial processes. Chitosan (CS) thin films were developed on plain polysulfone (PSf) and PSf/TiO2 membrane substrates by a temperature-induced technique using polyvinyl alcohol as a binder. Structure property elucidation was carried out by X-ray diffraction, microscopy, spectroscopy, contact angle measurement, and water uptake studies. The increase in hydrophilicity followed the order: PSf < PSf/TiO2 < PSf/TiO2/CS membranes. Use of this thin-film composite membrane for chromium removal was investigated with regards to the effects of light and pH. The observations reveal 100 % reduction of CrVI to CrIII through electrons and protons donated from OH and NH2 groups of the CS layer; the reduced CrIII species are adsorbed onto the CS layer via complexation to give chromium-free water. 相似文献
Circulating nucleic acids, such as short interfering RNA (siRNA), regulate many biological processes; however, the mechanism by which these molecules enter the cell is poorly understood. The role of extracellular‐matrix‐derived polymers in binding siRNAs and trafficking them across the plasma membrane is reported. Thermal melting, dynamic light scattering, scanning electron microscopy, and computational analysis indicate that hyaluronic acid can stabilize siRNA via hydrogen bonding and Van der Waals interactions. This stabilization facilitated HA size‐ and concentration‐dependent gene silencing in a CD44‐positive human osteosarcoma cell line (MG‐63) and in human mesenchymal stromal cells (hMSCs). This native HA‐based siRNA transfection represents the first report on an anionic, non‐viral delivery method that resulted in approximately 60 % gene knockdown in both cell types tested, which correlated with a reduction in translation levels. 相似文献
The cooperative nature of protein substructure and internal motion is a critical aspect of their functional competence about which little is known experimentally. NMR relaxation is used here to monitor the effects of high pressure on fast internal motion in the protein ubiquitin. In contrast to the main chain, the motions of the methyl-bearing side chains have a large and variable pressure dependence. Within the core, this pressure sensitivity correlates with the magnitude of motion at ambient pressure. Spatial clustering of the dynamic response to applied hydrostatic pressure is also seen, indicating localized cooperativity of motion on the sub-nanosecond time scale and suggesting regions of variable compressibility. These and other features indicate that the native ensemble contains a significant fraction of members with characteristics ascribed to the recently postulated "dry molten globule". The accompanying variable side-chain conformational entropy helps complete our view of the thermodynamic architecture underlying protein stability, folding, and function. 相似文献
Transition metal doped ZnS:Ni and ZnS:Cu and co-doped ZnS:Ni, Mn and ZnS:Cu, Cd nanoparticles were synthesized through the chemical precipitation method in an air atmosphere. The XRD analysis of co-doped samples shows the formation of cubic phase. The average size of nanoparticles ranges from 3.6 to 5.5 nm. The formation of co-doped nanoparticles was confirmed by XRD and PL analysis. The PL spectra show that the obtained nanoparticles have good crystal quality. An optimum concentration of transition metals was selected in co-doped ZnS nanoparticles. 相似文献
Chalcones and their analogs have been an area of great interest in recent years. Numerous research papers have been published, and chalcones continue to show promise for new drug investigations. Researchers have explored new approaches for the synthesis of chalcone derivatives, which have revealed an array of pharmacological and biological effects. These chalcone derivatives have shown important antimicrobial, antifungal, anti-mycobacterial, antimalarial, antiviral, anti-inflammatory, antioxidant, antileishmanial anti-tumor, and anticancer properties. This review highlights the synthesis and pharmacological properties of chalcone derivatives. 相似文献