Electrokinetic particle translocation through a nanopore

Nanoparticle electrophoretic translocation through a single nanopore induces a detectable change in the ionic current, which enables the nanopore-based sensing for various bio-analytical applications. In this study, a transient continuum-based model is developed for the first time to investigate the electrokinetic particle translocation through a nanopore by solving the Nernst-Planck equations for the ionic concentrations, the Poisson equation for the electric potential and the Navier-Stokes equations for the flow field using an arbitrary Lagrangian-Eulerian (ALE) method. When the applied electric field is relatively low, a current blockade is expected. In addition, the particle could be trapped at the entrance of the nanopore when the electrical double layer (EDL) adjacent to the charged particle is relatively thick. When the electric field imposed is relatively high, the particle can always pass through the nanopore by electrophoresis. However, a current enhancement is predicted if the EDL of the particle is relatively thick. The obtained numerical results qualitatively agree with the existing experimental results. It is also found that the initial orientation of the particle could significantly affect the particle translocation and the ionic current through a nanopore. Furthermore, a relatively high electric field tends to align the particle with its longest axis parallel to the local electric field. However, the particle's initial lateral offset from the centerline of the nanopore acts as a minor effect.     

Design and synthesis of amidine-type peptide bond isosteres: application of nitrile oxide derivatives as active ester equivalents in peptide and peptidomimetics synthesis

Amidine-type peptide bond isosteres were designed based on the substitution of the peptide bond carbonyl (C=O) group with an imino (C=NH) group. The positively-charged property of the isosteric part resembles a reduced amide-type peptidomimetic. The peptidyl amidine units were synthesized by the reduction of a key amidoxime (N-hydroxyamidine) precursor, which was prepared from nitrile oxide components as an aminoacyl or peptidyl equivalent. This nitrile oxide-mediated C-N bond formation was also used for peptide macrocyclization, in which the amidoxime group was converted to peptide bonds under mild acidic conditions. Syntheses of the cyclic RGD peptide and a peptidomimetic using both approaches, and their inhibitory activity against integrin-mediated cell attachment, are presented.     

Direct numerical simulation of electrokinetic translocation of a cylindrical particle through a nanopore using a Poisson-Boltzmann approach

Nanopore-based sensing of single molecules is based on a detectable change in the ionic current arising from the electrokinetic translocation of individual nanoparticles through a nanopore. In this study, we propose a continuum-based model to investigate the dynamic electrokinetic translocation of a cylindrical nanoparticle through a nanopore and the corresponding ionic current response. It is the first time to simultaneously solve the Poisson-Boltzmann equation for the ionic concentrations and the electric field contributed by the surface charges of the nanopore and the nanoparticle, the Laplace equation for the externally applied electric field, and the modified Stokes equations for the flow field using an arbitrary Lagrangian-Eulerian method. Current blockade due to the particle translocation is predicted when the electric double layers (EDLs) of the particle and the nanopore are not overlapped, which is in qualitative agreement with existing experimental observations. Effects due to the electric field intensity imposed, the EDL thickness, the nanopore's surface charge, the particle's initial orientation and lateral offset from the nanopore's centerline on the particle translocation including both translation and rotation, and the ionic current response are comprehensively investigated. Under a relatively low electric field imposed, the particle experiences a significant rotation and a lateral movement. However, the particle is aligned with its longest axis parallel to the local electric field very quickly due to the dielectrophoretic effect when the external electric field is relatively high.     

Asymmetric synthesis of α-amino-1,3-dithianes via chiral N-phosphonyl imine-based Umpolung reaction without using chromatography and recrystallization

A series of α-amino-1,3-dithianes have been synthesized via the asymmetric Umpolung reaction of 2-lithio-1,3-dithianes with chiral N-phosphonyl imines in good chemical yields (up to 82%) and good to excellent diastereoselectivities (>99:1). The manner by which chiral N-phosphonyl imines are slowly added into the solution of 2-lithio-1,3-dithiane was found to be crucial for achieving excellent diastereoselectivity. The current synthesis was proven to follow the GAP chemistry (group-assistant-purification chemistry) process, which avoids traditional purification techniques of chromatography or recrystallization, i.e., the pure chiral α-amino-1,3-dithianes attached with the chiral N-phosphonyl group were readily obtained by washing the solid crude products with hexane or a mixture of hexane-ethyl acetate.     

A glassy carbon electrode modified with graphene and tyrosinase immobilized on platinum nanoparticles for sensing organophosphorus pesticides

An amperometric biosensor is described for the detection of organophosphorus pesticides. It is based on the enzyme tyrosinase immobilized on platinum nanoparticles and the use of a glassy carbon electrode modified with graphene. Tyrosinase was immobilized on the electrode surface via electrostatic interaction between a monolayer of cysteamine and the enzyme. In the presence of catechol as a substrate, the pesticides chlorpyrifos, profenofos and malathion can be determined as a result of their inhibition of the enzyme which catalyzes the oxidation of catechol to o-quinone. Platinum nanoparticles and graphene effectively enhance the efficiency of the electrochemical reduction of o-quinone, thus improving sensitivity. Under optimum experimental conditions, the inhibition effect of the pesticides investigated is proportional to their concentrations in the lower ppb-range. The detection limits are 0.2, 0.8 and 3?ppb for chlorpyrifos, profenofos and malathion, respectively. The biosensor displays good repeatability and acceptable stability.

Electrochemical determination of NADH using a glassy carbon electrode modified with Fe3O4 nanoparticles and poly-2,6-pyridinedicarboxylic acid, and its application to the determination of antioxidant capacity

We have prepared a glassy carbon electrode modified with poly-2,6-pyridinedicarboxylic acid and with magnetic Fe₃O₄ nanoparticles. This modification enhances the effective surface area and the electrocatalytic oxidation of nicotinamide adenine dinucleotide (NADH) in addition to providing positively charged groups for electrostatic assembly of the phosphate group of NADH. The modified electrode responds linearly to NADH in the range from 5?×?10^?8 to 2.5?×?10^?5?M and gives a lower detection limit of 1?×?10^?8?M. It displays satisfactory selectivity and reproducibility. The sensor was applied to rapid screening of plant extracts for their antioxidant properties.

广义Weyl型李代数Wgl_n(F)上的2-上同调群

设F是一特征为零的域,W是F上的广义Weyl代数,gl_n(F)为F上的一般线性李代教,则结合代数Wgl_n(F)上具有一个诱导的李代数结构,本文讨论了李代数Wgl_n(F)的2-上同调群的结构.     

Optical refractometer based on an asymmetrical twin-core fiber Michelson interferometer

We report and demonstrate an optical refractometer based on a compact fiber Michelson interferometer. The Michelson interferometer is composed of an asymmetrical twin-core fiber containing a central core and a side core. By chemically etching a segment of the twin-core fiber until the side core is exposed, the effective index of the side core in the etched region is sensitive to the environmental refractive index, which leads to a shift of the transmission spectrum of the Michelson interferometer. The experimental results show that such a device has a refractive index resolution of more than 800 nm/refractive index unit in the range of 1.34-1.37.     

Fabrication, structure and luminescence properties of polycrystalline Tb-doped Lu2SiO5 films by Pechini sol–gel method

Tb³⁺-doped lutetium oxyorthosilicate (Tb:Lu₂SiO₅, LSO) films have been successfully fabricated on carefully cleaned silicon (1 1 1) substrates by Pechini sol–gel method combined with the spin-coating technique. X-ray diffraction (XRD), photoluminescence (PL) spectra and atomic force microscopy (AFM) were employed to characterize the resultant films. XRD patterns indicated that the films were crystallized into A-type LSO phase at 1000 °C, followed by a phase transition from A-type LSO to B-type LSO occurred at 1100 °C. The AFM observation revealed that the phosphor films were uniform and crack-free, consisting of closely packed grains with an average size of 200–300 nm. The PL spectra showed the characteristic emission ⁵D₄ → ⁷F_J (J = 3–6) for Tb³⁺, The lifetime of Tb³⁺ in Tb:LSO films was 2.33 ms. The effect of heat-treatment temperature on the luminescent properties was also investigated.     

Design,synthesis and biological evaluation of 1,4-dihydrothieno[3′,2′:5,6]thiopyrano[4,3-c]pyrazole-3-carboxylic amide derivatives as potential estrogen receptor antagonists

The estrogen receptor is a target for therapeutic agents for hormone replacement in menopausal women,osteoporosis, reproductive cancers such as breast cancer,uterine cancer and prostate cancer.1,4-Dihydrothieno[3’,2’:5,6]thiopyrano[4,3- c]pyrazole-3-carboxylic amide derivatives were designed,synthesized and biological evaluated as potential estrogen receptor antagonists.