A gold-based nanobeacon probe for fluorescence sensing of organophosphorus pesticides

A nanomaterials-based novel molecular beacon has attracted growing attentions in fluorescent assays as many nanomaterials possess excellent quenching efficiency. In this work, a gold-based nanobeacon probe was established to detect organophosphorus pesticides for the first time. The constructed gold-based nanobeacon acted as a signal indicator and could display the decreasing of the intensity in the presence of targets, which competitively bound to single strand DNA. To achieve a high sensitive probe, some parameters including solution pH, temperature and reaction time were investigated and optimized. The gold-based nanobeacon probe assay was proved to be rapid and sensitive to achieve a detection limit of 0.035 μM for isocarbophos, 0.134 μM for profenofos, 0.384 μM for phorate and 2.35 μM for omethoate, respectively. The prepared nanobeacon effectively reduced the background and improved the detection sensitivity and selectivity. The probe is stable, easy to operate and does not need sophisticated instruments. These features makes the probe feasible for screening trace organophosphorus pesticides in real samples.     

Rank 2 Ample Vector Bundles on Some Smooth Rational Surfaces

Several classification results for ample vector bundles of rank 2 on Hirzebruch surfaces, and on Del Pezzo surfaces, are obtained. In particular, we classify rank 2 ample vector bundles with _c2 less than seven on Hirzebruch surfaces, and with _c2 less than four on Del Pezzo surfaces.     

Spectroscopic characterization of core and shell regions in monolayer protected gold nanoparticles

We report studies on the structure of the metallic core and the alkyl cap layer in monolayer protected gold nanoparticles having sizes down to 1.6 nm. These particles are obtained by laser ablating gold targets in alkane-thiol solutions at different concentrations. The electronic structure of gold core and the vibrational properties of the capping hydrocarbon chains reveal effects connected with the nanosized nature of the particles.     

Electrical behavior of the Au/MoS2 interface studied by light emission induced by scanning tunneling microscopy

Light emitted in the tunneling junction of a scanning tunneling microscope has been used to establish the electrical characteristics of nanojunctions made of Au islands deposited on flat MoS₂ surfaces. It is shown that these characteristics are those of rectifying contacts when the gold islands are isolated and that they evolve toward those of ohmic contacts when the island density increases. It is observed that the rectifying behavior also evolves over time as on infinite metal/semiconductor contacts. Using the STM tip, single gold islands can be manipulated on the MoS₂ surface so that their electrical behavior can be changed depending on their position with regard to the other islands.     

An AFM, XPS and electrochemical study of molecular electroactive monolayers formed by wet chemistry functionalization of H-terminated Si(1 0 0) with vinylferrocene

Molecular electroactive monolayers have been produced from vinylferrocene (VFC) via light-assisted surface anchoring to H-terminated n- and p-Si(1 0 0) wafers prepared via wet chemistry, in a controlled atmosphere. The resulting Si-C bound hybrids have been characterized by means of XPS and AFM. Their performance as semiconductor functionalized electrodes and their surface composition have been followed by combining electrochemical and XPS measurements on the same samples, before and after use in an electrochemical cell. White-light photoactivated anchoring at short (1 h) exposure times has resulted in a mild route, with a very limited impact on the initial quality of the silicon substrate. In fact, the functionalized Si surface results negligibly oxidized, and the C/Fe atomic ratio is close to the value expected for the pure molecular species. The VFC/Si hybrids can be described as (η⁵-C₅H₅)Fe²⁺(η⁵-C₅H₄)-CH₂-CH₂-Si species, on the basis of XPS results. Electrochemical methods have been applied in order to investigate the role played by a robust, covalent Si-C anchoring mode towards substrate-molecule electronic communication, a crucial issue for a perspective development of molecular electronics devices. The response found from cyclic voltammograms for p-Si(1 0 0) functionalized electrodes, run in the dark and under illumination, has shown that the electron transfer is not limited by the number of charge carriers, confirming the occurrence of electron transfer via the Si valence band. The hybrids have shown a noticeable electrochemical stability and reversibility under cyclic voltammetry (cv), and the trend in peak current intensity vs. the scan rate was linear. The molecule-Si bond is preserved even after thousands of voltammetric cycles, although the surface coverage, evaluated from cv and XPS, decreases in the same sequence. An increasingly larger surface concentration of Fe³⁺ at the expenses of Fe²⁺ redox centers has been found at increasing number of cv’s, experimentally associated with the growth of silicon oxide. Surface SiO⁻ groups from deprotonated silanol termination, induced by the electrochemical treatments, are proposed as the associated counterions for the Fe³⁺ species. They could be responsible for the observed decrease in the electron transfer rate constant with electrode ageing.     

A novel approach to the acoustic characterisation of porous road surfaces

Porous road surfaces offer an effective means of reducing the generation and propagation of noise from road traffic. However, the porosity of these surfaces can deteriorate over time, leading to a reduction in their noise reducing properties. Efficient methods are therefore required for monitoring this performance. Existing techniques for performing in-situ measurements of acoustic absorption are unsuitable for use within the traffic stream. Static measurements using time domain Maximum Length Sequence (MLS) based techniques have been demonstrated to offer advantages over traditional techniques, presenting the opportunity for measurements under dynamic conditions. This paper describes the design of a system for carrying out dynamic MLS-based measurements. Results are presented which demonstrate that stable dynamic measurements can be carried out at speeds of up to 30 km/h.     

Eu- and Yb-induced reconstructions on a vicinal Si(1 0 0) surface

Early stages of rare-earth metal (Yb and Eu) growth on a vicinal, single-domain Si(1 0 0)2 × 1 surface have been studied in the coverage range of 0.1-0.3 monolayer (ML) by low energy electron diffraction, scanning tunneling microscopy, and synchrotron radiation photoemission spectroscopy. We show that Yb induces the 2 × 3 periodicity in the whole range of coverage studied. The 2 × 3 reconstruction coexists with the local 3 × 2/4 × 2 structure at about 0.2 ML of Yb. In contrast, Eu forms the 3 × 2 periodicity at 0.1-0.2 ML, whereas this structure is converted into the 2 × 3 phase at about 0.3 ML. The atomic arrangement and electronic properties of these reconstructions and the adsorbate-mediated modification of surface morphology are investigated.