Facile and controllable one-step fabrication of selenium nanoparticles assisted by l-cysteine

A simple and solution-phase approach for large-scale synthesis of selenium nanoparticles (Nano-Se) by reducing sodium selenite (Na₂SeO₃) with l-cysteine has been demonstrated in this study. l-cysteine was used as both the reducing agent and surface modifier to control the formation of Nano-Se. The effects of reactant concentrations and ratios, and reaction time on the size and stability of Nano-Se were also investigated. The morphology and chemical composition of Nano-Se were characterized using various spectroscopic and microscopic methods. The results showed that varying the concentration ratio of l-cysteine to Na₂SeO₃ could control the diameter and morphology of Nano-Se, but not affecting their crystalline phases and chemical compositions. Monodisperse and homogeneous spherical Nano-Se with an average diameter of about 100 nm could be synthesized with the concentration ratio of l-cysteine to Na₂SeO₃ at 4:1. A striking feature of the as-synthesized Nano-Se was their good stability when dispersed in the reaction solutions, which indicates their potential in medical applications.     

Facile, one-step controlled synthesis of Se nanocrystals in the presence of l-tyrosine

Se with different morphologies was synthesized using l-tyrosine as reducing agent and soft template by means of hydrothermal method. The method was simple and convenient to handle. The reaction process was monitored using ultraviolet-visible spectroscopy (UV-vis) and Fourier-transform infrared spectroscopy (FTIR). The morphology and crystalline phase were determined by transmission electron microscopy (TEM), scanning electronic microscopy (SEM) and X-ray diffraction (XRD) pattern. The results show that the morphologies and the crystalline phases of Se can be easily controlled. By varying the concentration ratio of l-tyrosine to selenious acid, the morphologies and crystalline phases of Se were not changed, but the diameter of Se was different. Se nano-rods are obtained in the lower temperature, and there is a transformation of microspheres into nanorods of Se with the increase of reaction time or reaction temperature. In addition, we discuss the possible mechanism of the reduction of SeO₃²⁻ ions by l-tyrosine. The eco-friendly, biogenic synthesis strategy could be widely used for preparing inorganic/organic biocomposites.     

Crystal growth and characterization of new nonlinear optical single crystals of l-alaninium fumarate

Amino acid based crystals exhibit excellent nonlinear and electro optical properties. A new nonlinear optical single crystal l-alaninium fumarate (LAF) belonging to the amino acid group was grown by slow evaporation solution growth technique. Single crystal X-ray diffraction study showed that LAF belongs to orthorhombic crystal system. The UV-Vis-NIR spectrum of LAF showed very good transparency in the region from 300 nm to 1100 nm. Fourier transform infrared is used to confirm the presence of various functional groups in the grown crystal. Thermal properties of the LAF crystal were carried out by thermogravimetric analysis (TGA) and differential thermal analysis (DTA) techniques, which indicate that the material does not decompose before melting. The melting point of grown crystal was observed as 267.5 °C by melting point apparatus. The existence of nonlinear optical (NLO) property of LAF was confirmed by second harmonic generation test using Nd:YAG laser fundamental wavelength of 1064 nm.     

Ellipsometric determination of optical properties of carbazole-containing poly(l-glutamate) thin films prepared from different solvents

In this study, the refractive indices (n) and thicknesses of carbazole-containing hole-transport materials such as poly(γ-carbazolylethyl l-glutamate) (PCELG) and poly(N-vinyl carbazole) (PVCz) films were determined by carrying out ellipsometric measurements. The thicknesses of PCELG and PVCz films determined by ellipsometric analysis were in good agreement with those determined by surface profilometry. The dependence of the refractive indices of the PCELG films on film thickness was classified into two types on the basis of the solvent from which the films were prepared: the refractive indices either increased with increasing film thickness, as in the case of PCELG films prepared from 1,2-dichloroethane (DCE) and monochlorobenzene (?-Cl), or were independent of the film thickness, as in the case of films prepared from 1,1,2,2-tetrachloroethane (TCE). A comparison of these results with the structures of the polymers, as determined by ¹H NMR, reveals that the two types of dependences of the refractive indices of the PCELG thin film on the film thickness can be attributed to the two types of aggregation structures and/or orientational characteristics corresponding to the helical conformation of the polymer. In contrast, the refractive indices of PVCz films are governed mainly by the film thickness. Finally, we would like to emphasize that the combination of ellipsometry and other techniques such as NMR and surface profilometry provide information not only on the film thickness and refractive index but also on the aggregation structure in thin films with thicknesses on the order of 50 nm.     

Synthesis, spectral and thermal studies of new nonlinear optical crystal: l-valinium fumarate

An organic nonlinear optical material, l-valinium fumarate (abbreviated as LVF) has been successfully synthesized and good quality single crystals have been grown by low temperature solution growth method. The purified form of LVF is achieved by repeated crystallization. The cell parameters of LVF have been determined using single crystal X-ray diffraction technique and the crystal system is found as monoclinic. From the UV-Vis-NIR absorption spectrum, the good transparency is revealed from 300 nm to 1100 nm. The mode of vibration of different molecular groups present in LVF was identified by FT-IR spectral analysis. The thermogravimetric (TGA) and differential thermal analysis (DTA) studies show the thermal behavior and crystal was thermally stable up to 266 °C. Second harmonic generation (SHG) conversion test was made to explore the nonlinear optical behavior of this material using Kurtz and Perry method.     

Solid phase extraction of ultra traces mercury (II) using octadecyl silica membrane disks modified by 1,3-bis(2-ethoxyphenyl)triazene (EPT) ligand and determination by cold vapor atomic absorption spectrometry

A facile and highly efficient method was developed for the preconcentration of the ultra trace amounts of mercury (II) ions. Octadecyl silica membrane disk was modified by the recently synthesized triazene ligand, 1,3-bis(2-ethoxyphenyl)triazene (EPT), and cold vapor atomic absorption spectrometry was used to determine the resultant preconcentrated Hg(II) ions. Solution studies with EPT and a series of metal ions were done in advance, and the results showed a strong affinity of EPT to the mercury ions. To perform solid phase extraction, various parameters such as pH of the sample, flow rates and the amount of the ligand were optimized. A linear calibration curve was obtained in the range of 0.02-1.90 μg L⁻¹ with r² = 0.9990 (n = 8), and the limit of detection (LOD) based on three times the standard deviation of the blank was 10.6 ng L⁻¹. The relative standard deviation (RSD) for the determination of 0.1 μg L⁻¹ Hg(II) found to be 2.9% while a RSD value of 1.1% was obtained for the determination of 1.0 μg L⁻¹ Hg(II) (n = 8). The preconcentration and improvement factors were 380 and 74, respectively. The newly developed method was successfully applied to the determination of mercury ions in real water samples.     

Synthesis and application of chloromethylated polystyrene modified with 1-phenyl-1,2-propanedione-2-oxime thiosemicarbazone (PPDOT) as a new sorbent for the on-line preconcentration and determination of copper in water, soil, and food samples by FAAS

In this paper, we report a simple and sensitive on-line solid phase extraction system for the preconcentration and determination of Cu(II) by flame atomic absorption spectrometry (FAAS). This method is based upon the on-line retention of copper at pH 5.0 on a minicolumn packed with chloromethylated polystyrene modified by 1-phenyl-1,2-propanedione-2-oxime thiosemicarbazone (PPDOT) as a new solid-phase extraction (SPE) sorbent. The retained Cu(II) ions were eluted with 1.0 M HNO₃, and transported directly to FAAS for determination. Several chemical and flow variables were studied and optimized for a quantitative preconcentration and determination of copper(II). At the optimized conditions, for preconcentration of 10.0 mL of a sample solution, a linear calibration graph was obtained over the concentration range of 3.00-120.0 μg L⁻¹ for Cu(II). The limit of detection (3σ), limit of quantification (10σ), and enrichment factor are 0.56 μg L⁻¹, 2.0 μg L⁻¹ and 41, respectively. The relative standard deviation (n = 6) at 20 μg L⁻¹ of Cu(II) is 2.0%. This method could be applied for determination of trace amounts of Cu(II) in water, soil, and food samples with satisfactory results.     

In vitro bioactivity of chitosan/poly (d,l-lactide-co-glycolide) composites

Porous composites scaffolds of chitosan/poly(d,l-lactide-co-glycolide) were fabricated for tissue engineering applications by thermally induced phase separation and lyophilization techniques. The in vitro bioactivity evaluation of the scaffolds was carried out by analyzing the apatite layers produced on them using SBF as incubation medium. The apatite formation was analyzed using FTIR spectroscopy and Field emission scanning electron microscopy coupled to energy-dispersive electron X-ray spectroscopy. The cumulative results obtained from the IR spectra and SEM-EDS suggest that the developed composites might have potential applications in tissue engineering.     

Interlocked chitosan/poly(dl-lactide) blends

A novel processing method was developed to prepare chitosan/poly(dl-lactide) blends. These blends were further examined for their structures. SEM micrographs exhibited that under optimized processing conditions and with appropriate composition proportions, the resulting blends could possess interlocked internal microstructures. The results obtained from TGA and DMA measurements complementarily confirmed that two components could be well blended into a solid construct at a partially miscible level. The main mechanical properties of the blends were also investigated in both dry and hydrated states.     

Electrochemical characterization of deoxyribonucleic acid on aluminum(III)/poly(l-glutamic acid) film and its application for the detection of phosphinothricin acetyltransferase gene-specific sequence

A simple strategy of transgenic sequence-specific detection without a special amplification procedure was developed on the basis of aluminum(III)/poly(l-glutamic acid) (PLGA) film. An aluminum ion (Al(III)) thin film was assembled on the surface of PLGA via the electrostatic binding of Al(III) with carboxyl, namely Al(III)/PLGA. The immobilization of deoxyribonucleic acid (DNA) was carried out on this Al(III)/PLGA film by Al(III)-single strand DNA (ssDNA) interaction. Surface hybridization between the immobilized ssDNA and its complementary ssDNA was monitored by electrochemical impedance spectroscopy (EIS) using [Fe(CN)₆]^3−/4− as a redox probe. Under the optimal conditions, this DNA electrochemical sensor was applied to determine the specific gene sequence related to phosphinothricin acetyltransferase transgene (PAT) in the transgenic plants by label-free EIS.     

Concentration dependence of solution crystallization for poly(l-lactide) in p-xylene

The macromolecular chain conformation in solution changes with the solvent and temperature, which will affect the formation of crystalline structure in the subsequent crystallization process. The crystallization behavior of poly(l-lactide) samples prepared from solutions with various concentrations was studied by differential scanning calorimetric and X-ray diffraction. It is found that the sample recovered from a dilute solution exhibits higher crystallinity, higher non-isothermal crystallization temperature and faster crystallization rate. The condensation process of polymer chain in dilute solutions has an influence on the crystallization of polymer in the solid state. This results in the acceleration of the melt crystallization rate and the rise of non-isothermal crystallization temperature of PLLA recovered from the dilute solution.     

Biomolecule-assisted synthesis of copper indium sulfide microspheres with nanosheets

Copper indium sulfide product was successfully synthesized via a mild solvothermal approach involving CuCl₂·2H₂O as the copper source, InCl₃ as the indium source, l-cysteine as the sulfur source and N,N-dimethylformamide as the reaction medium respectively at 200 °C for 12 h. Morphology, structure, and phase constituents of the as-prepared CuInS₂ powders were characterized by XRD, FE-SEM, XPS, and TEM (HRTEM). Results showed that the synthesized powder consists of microspheres made up of nanosheets and the thickness of the CuInS₂ nanosheets was found to vary from 50 to 100 nm. A possible formation mechanism was put forward and briefly discussed. The proposed solvothermal method using l-cysteine as the sulfur source offers a potential alternative avenue to prepare other ternary semiconductor nanomaterials.     

Treatment of Terasil Red R Dye Wastewater using H2O2/pyridine/Cu(II) System

The H₂O₂/pyridine/Cu(II) advanced oxidation system was used to assess the efficiency of the treatment of a 1 g L⁻¹ Terasil Red R dye solution. This system was found to be capable in reducing the concentration of chemical oxygen demand (COD) of the dye solution up to 90%, and achieving 99% in decolorization at the optimal concentration of 5.5 mM H₂O₂, 38 mM pyridine and 1.68 mM Cu(II). The final concentration of COD was recorded at 117 mg L⁻¹ and color point at 320 PtCo. Full 2⁴ factorial design and the response surface methodology using central composite design (CCD) were utilized in the screening and optimization of this study. Treatment efficiency was found to be pH independent. The amount of sludge generation was in the range of 100–175 mg L⁻¹ and the sludge produced at the optimal concentration was 170 mg L⁻¹.     

Synthesis and electrochemical characterization of myoglobin-antibody protein immobilized self-assembled gold nanoparticles on ITO-glass plate

We report a protein immobilized self-assembled monolayer (SAM) of gold nanoparticles (GNPs) on indium-tin-oxide (ITO) coated glass plate. The protein-antibody, Mb-Ab, was covalently immobilized over the self-assembly of GNPs through a mixed SAM of 11-mercapto undecanoic acid (MUA) and 3-mercapto propionic acid (MPA) via carbodiimide coupling reaction using N-(3-dimethylaminopropyl)-N′-ethyl carbodiimide (EDC) and N-hydroxy succinimide (NHS). The whole assembly was constructed on 0.25 cm² area of ITO-glass plate (Mb-Ab/MUA-MPA/GNPs/APTES/ITO-glass) and an impedimetric study was carried out for its application in myoglobin detection. This prototype assembly was characterized by scanning electron microscopy, atomic force microscopy and electrochemical techniques. The modified electrode showed an increased electron-transfer resistance on coupling with protein antigen, Mb-Ag, in the presence of a redox probe [Fe(CN)₆]^3−/4−. Its exhibits an electrochemical impedance response to protein myoglobin-antigen, Mb-Ag, concentration in a linear range from 0.01 μg to 1.65 μg mL⁻¹ with a lowest detection limit of 1.4 ng mL⁻¹.     

Sequential eluent injection technique as a new approach for the on-line enrichment and speciation of Cr(III) and Cr(VI) species on a single column with FAAS detection

This paper introduces a sequential eluent injection (SEI) technique combined with an on-line preconcentration/separation system for a fast and sensitive FAAS determination of trace amounts of Cr(III) and Cr(VI) species. The method is based on the simultaneous retention of Cr(III) and Cr(VI) on a single mini-column packed with a chloromethylated polystyrene functionalized with N,N-bis(naphthylideneimino)diethylenetriamine (PS-NAPdien) at pH 6.7. The retained chromium species was eluted by sequential injection of HCl for desorption of Cr(III), and NH₃ and NH₄NO₃ buffer solutions for desorption of Cr(VI). All the chemical and flow injection variables were optimized for the quantitative preconcentration and speciation of Cr(III) and Cr(VI). Under the optimum conditions, the calibration graph obtained is linear over the concentration range of 2.0-60.0 μg L⁻¹ for Cr(III), and 8.0-180.0 μg L⁻¹ for Cr(VI). The preconcentration factors for Cr(III) and Cr(VI) were 70 and 30, respectively. The 3σ detection limits were 0.6 μg L⁻¹ and 2.5 μg L⁻¹ for Cr(III) and Cr(VI), respectively. The relative standard deviations were 2.55% and 0.8%, respectively, for 6 replicate determinations of Cr(III) and Cr(VI) at the 40.0 μg L⁻¹ level. The proposed method was applied for determination of Cr(III) and Cr(VI) in different water samples with satisfactory results.     

Improved photoelectrochemical detection of mercury (II) with a TiO2-modified composite photoelectrode

The spectrophotometric change of a mercury (II) (Hg²⁺) selective small molecule chemosensor has been successfully converted into a photovoltaic response upon ligating Hg²⁺. The photon excitation was followed by charge separation facilitated by TiO₂ and polyaniline (PANI), resulting in an electron transfer to an electrical back contact. The photoresponse of the Hg²⁺ selective chromophore was converted to an electron current equivalent to the amount of Hg²⁺ in solution. The favourable properties of a Hg²⁺ sensitive chemosensor was combined with the semiconductor capabilities of TiO₂ to construct a sensor that is capable of generating a current in the presence of Hg²⁺ under illumination. A composite of the fluorescent chemosensor rhodamine 6G hydrozone derivative (RS) and PANI was immobilized on indium tin oxide (ITO) plates coated with TiO₂ and subjected to photovoltammetric measurements. The photovoltammetric responses of the coated layers were investigated to determine the sensitivity and selectivity of the immobilized sensor to Hg²⁺ in the presence of background ions. The photo-response increased linearly with increasing Hg²⁺ concentration from 10 to 200 μg L⁻¹ with a limit of quantification (LOQ) of 4 μg L⁻¹. The pH independence for the photoresponse was limited by the TiO₂ layer and was optimal between pH 6 and 7.     

A nano-structured Ni(II)–chelidamic acid modified gold nanoparticle self-assembled electrode for electrocatalytic oxidation and determination of methanol

A nano-structured Ni(II)–chelidamic acid (2,6-dicarboxy-4-hydroxypyridine) film was electrodeposited on a gold nanoparticle–cysteine–gold electrode. The morphology of Ni(II)–chelidamic acid gold nanoparticle self‐assembled electrode was investigated by scanning electron microscopy (SEM). Electrocatalytic oxidation of methanol on the surface of modified electrode was studied by cyclic voltammetry and chronoamperometry methods. The hydrodynamic amperometry at a rotating modified electrode at constant potential versus reference electrode was used for detection of methanol. Under optimized conditions the calibration plots are linear in the concentration range 0–50 mM with a detection limit of 15 μM. The formed matrix in our work possessed a 3D porous network structure with a large effective surface area, high catalytic activity and behaved like microelectrode ensembles. The modified electrode indicated reproducible behavior and a high level stability during the experiments, making it particularly suitable for analytical purposes.     

Highly sensitive interfacial fluorescence sensing of deoxyribonucleic acid based on self-assembled multilayers

Fluorescent dye Acridine Orange (AO) was indirectly assembled onto the surface of colloidal gold nanoparticles modified quartz and gold wafer, with cysteine as mediation. Strong fluorescence emission was observed from AO self-assembled multilayers. Formation of the self-assembled multilayers was confirmed and primarily characterized by electrochemical and fluorescence methods. The effect of assembling substrate on fluorescence intensity of the film was discussed. The self-assembled multilayers offer a high sensitive interfacial fluorescence sensing of deoxyribonucleic acid with the detection limit of 7.145 × 10^− 9 g L^− 1 (3 S.D./K), which was five orders of magnitude lower than that of the bulk solution-phase. The self-assembled multilayers film has higher stability and good regeneration capacity.     

Thorough removal of inorganic and organic mercury from aqueous solutions by adsorption on Lemna minor powder

The adsorption ability of duckweed (Lemna minor) powders for removing inorganic and organic mercury (methyl and ethyl mercury) has been studied using cold vapour atomic absorption spectrometry. The optimal adsorption conditions were: (a) the pH value of the solution 7.0 for inorganic and ethyl mercury, 9.0 for methyl mercury, and (b) equilibrium adsorption time 10, 20, and 40 min for inorganic mercury, methyl mercury, and ethyl mercury, respectively. After adsorption by L. minor powder for 40 min, when the initial concentrations of inorganic and organic mercury were under 12.0 μg L⁻¹ and 50.0 μg L⁻¹, respectively, the residual concentrations of mercury could meet the criterion of drinking water (1.0 μg L⁻¹) and the permitted discharge limit of wastewater (10.0 μg L⁻¹) set by China and USEPA, respectively. Thorough removal of both inorganic and organic mercury from aqueous solutions was reported for the first time. The significant adsorption sites were C–O–P and phosphate groups by the surface electrostatic interactions with aqueous inorganic and organic mercury cations, and then the selective adsorption was resulted from the strong chelating interaction between amine groups and mercury on the surface of L. minor cells.