A Sensitive Electrochemical Approach for Melamine Detection Using a Disposable Screen Printed Carbon Electrode

We report here a simple and easy electrochemical approach for sensitive detection of non‐electroactive melamine using a disposable screen printed carbon electrode (SPCE) with uric acid as the recognition element. It is based on the competitive adsorptive behavior of melamine at the preanodized SPCE causing suppression in the oxidation current of uric acid. A linear range up to 126 ppb with a detection limit of 1.6 ppb (S/N=3) is achieved at the preanodized SPCE by differential pulse voltammetry. The electrochemical method is successfully applied to detect the melamine content in tainted milk powder and dog food.     

Simulated SERS spectra of 4,4′-bipyridine/gold single molecule junction in different conductance states: ab initio molecular dynamics approach

The SERS spectra of 4,4′-bipyridine/gold single molecule junction in different conductance states at room temperature are calculated by performing ab initio molecular dynamics simulations, in connection with a Fourier transform of the polarizability autocorrelation function, to illustrate that the Raman peaks of the ON state are enhanced by an additional one or two orders of magnitude in comparison with the OFF state. Considering the relative intensities of SERS spectra, the largest enhanced peak for the OFF state is the ring breathing mode due to the simultaneous contribution from structural change, vibrational coupling, and charge transfer. For the ON state, the C–H bending mode has the largest enhancement due to structural change and charge transfer effects. Finally, the SERS spectra of 4,4′-bipyridine junction in the the ON state with perpendicular and tilted orientations are examined to understand the reason why the tilted junction has lower SERS spectrum intensity with doublet feature of the C–C stretching mode.     

The Investigation of Free Radical Intermolecular Addition Following Free Radical SH2′ Cyclization Reactions

The photolytic radical intermolecular addition following S_H2′ cyclization reactions of t‐BuHgCl with 1‐bromo‐4‐(2‐choroallyloxy)‐but‐2‐ene and (E)‐4‐bromobut‐2‐enyl acrylate gave the good yields and the chemoselectivity of the cyclized product. The high stereoselectivity of the reactions is discussed.     

Capillary electrophoresis for analysis of deletion and duplication in exon 44–55 of Duchenne muscular dystrophy gene

In this study, a genotyping CGE method was established for analysis of Duchenne muscular dystrophy (DMD) gene deletions and duplications in exon 44–55. A total of 12 DMD exons (exon 44–55) and 2 internal standard gene fragments were simultaneously amplified by using a universal multiplex PCR (UMPCR) and determined by CGE. The conditions of UMPCR and CGE were optimized, including the kinds of polymerase, temperatures in UMPCR, separation matrix, separation temperature, and voltage. Finally, the separation was performed by 1.2% poly(ethylene oxide) in 1× TBE buffer at ?6 kV and 25°C. After validation, our results showed the peak patterns for differentiation of genetic deletion or duplication in 27 DMD patients and normal subjects, according to the peak height ratios by comparison of two internal standard peaks. Among the 27 subjects, 23 cases are deletion type and four are duplication type. The data of two patients analyzed by this CGE‐PCR method were different from that of multiplex ligation dependent probe amplification method, and the sequencing results demonstrated that our results were correct. This UMPCR‐CGE method was considered better than the multiplex ligation dependent probe amplification method. Furthermore, this method can be used for eugenics in clinical applications.     

Chemical mechanism of surface‐enhanced raman scattering spectrum of pyridine adsorbed on Ag cluster: Ab initio molecular dynamics approach

The surface‐enhanced Raman scattering (SERS) spectrum of pyridine adsorbed on Ag₂₀ cluster (pyridine‐Ag₂₀) at room temperature is calculated by performing ab initio molecular dynamics simulations in connection with a Fourier transform of the polarizability autocorrelation function to investigate the static chemical enhancement behind the SERS spectrum. The five enhanced vibrational modes of pyridine, namely, υ_6a, υ₁, υ₁₂, υ_9a, and υ_8a, can be assigned and identified by using a new analytical scheme, namely, single‐frequency‐pass filter, which is based on a Fourier transform filtering technique. To understand the factors evoking the enhancement in the SERS spectrum, the dynamic properties of molecular structures and charges for both of the free pyridine and adsorbed pyridine are analyzed. The calculated results indicate that the vibrational amplitudes of adsorbed pyridine are enhanced due to both of the electron transfer from pyridine to Ag₂₀ cluster and the softening of pyridine bond. In addition, the N‐Ag stretching within pyridine‐Ag₂₀ will couple with these five vibrational modes of pyridine. Consequently, the electron transfer between pyridine and Ag₂₀ cluster induced by different molecular vibrational modes prompts the redistribution of electron density of pyridine. These factors collectively cause the noticeable change in polarizability during molecular vibrations and hence result in the enhancement of Raman peaks. © 2013 Wiley Periodicals, Inc.     

Synthesis of Nucleobase‐Functionalized Carbon Nanotubes and Their Hybridization with Single‐Stranded DNA

For the first time ssDNA (25‐aptamer of mixed dA, dT, dG, and dC) was wrapped around functionalized single‐walled carbon nanotubes (SWCNTs), whose external surfaces were attached to multiple triazole‐(ethylene glycol)‐dA ligands. This method of hybridization involved the formation of hydrogen bonds between dT of ssDNA and dA of functionalized SWCNTs. It deviates from the reported π–π stacking between the nucleobases of DNA and the external sidewalls of nanotubes. The structural properties of the functionalized SWCNTs and its ssDNA complex were characterized by spectroscopic (including CD and Raman), thermogravimetric, and microscopic (TEM) methods. The results thus obtained establish a new platform of DNA delivery by use of nanotubes as a new vehicle with great potential in biomedical applications and drug development.     

Study of human neutrophil peptides in saliva by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry

Matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) mass spectrometry is used to rapidly characterize the human neutrophil peptides – HNP 1, 2, and 3 – in saliva. The saliva excreted from the parotid and sublingual/submandibular glands of 70 individuals were collected and examined using MALDI‐TOF. The MALDI approach requires no sample pretreatment other than mixing the saliva‐absorbing material with the matrix and drying under ambient conditions. Tissue paper was the best material for collecting the saliva samples because of its strong texture and high absorbance, and sinapinic acid was the best MALDI matrix for the analysis of the HNPs. HNPs were detected in almost all the samples collected from the parotid glands, with no obvious differences among age or gender. In contrast, the distribution of the HNPs in the samples collected from the sublingual/submandibular glands was age‐dependent: no HNPs were detected for those collected from individuals younger than 30, but the HNPs were present in all of the samples collected from those older than 60 years. The increased probability of detecting saliva HNPs with age suggests that HNPs may function as a biomarker for aging. Copyright © 2009 John Wiley & Sons, Ltd.     

Dissipative Particle Dynamics Simulations to Investigate Aggregation of Peptide Amphiphile Nanofibers

Dissipative Particle Dynamics (DPD) method was carried out to investigate the self‐assembly phase behavior of peptide amphiphile (PA) molecules. The simulations showed that these molecules were self‐assembled into three‐dimensional fiber‐like cylindrical aggregates by the assistance of water solvent. The results of DPD simulation are sensitive to various factors including the size of solvent bead, temperature, and the bead ratio of PA to solvent. We found that using 5 to 9 water cluster and solvent bead gives a result of the aggregation of PA molecules into cylindrical fibers. The criteria of forming nanofibers are bead ratios of PA to water larger than 1:6 and temperature above 340 K. The estimated diameter of the cylindrical aggregate agrees well with the experimentally measured value.     

High‐temperature synthesis of Rb2MnP2S6 in molten salt medium

Transparent yellow plates of rubidium manganese hexa­thio­diphosphate, Rb₂MnP₂S₆, were synthesized in molten RbBr. The compound is isotypic to other compounds of the type A₂MP₂Q₆ (A = K, Rb, Cs; M = Mn, Fe; Q = S, Se). Its structure can be viewed as columns of face‐sharing S₆ polyhedra parallel to the a axis, interconnected by Rb⁺. The S₆ polyhedra are centered alternately by Mn (in octahedral coordination) and P₂ units (in trigonal antiprisms). The Mn atom and P₂S₆ group lie on centers of symmetry.     

Homogeneous Platinum‐Deposited Screen‐Printed Edge Band Ultramicroelectrodes for Amperometric Sensing of Carbon Monoxide

We report here the fabrication and application of an electrochemical carbon monoxide (CO) gas sensor based on the deposition of Pt nanoparticles on a screen‐printed edge band ultramicroelectrode (SPUME) with Nafion as the solid polymer electrolyte. Homogeneous size and distribution of Pt nanoparticles is stably deposited on the SPUME without either protective or capped agents. The edge diffusion effect at the SPUME, to even out the generation rate of hydrogen and to speed up the mass transfer of Pt solution, is believed to play a key role in achieving the deposition result. The obvious advantage of the proposed ultramicroelectrode system is that no supporting electrolyte (i.e., internal electrolyte) is required in the sensor scheme. The current–time curve recorded under conditions of +0.45 V vs. pseudo Ag reference electrode and various CO concentrations suggests that current response depends linearly on CO concentration up to 1000 ppm (correlation coefficient=0.994) with a sensitivity of 3.76 nA/(ppm?cm²). This report demonstrates potential application of the disposable CO gas sensor.