Search

A ratiometric fluorescence method based on carboxylated graphitic carbon nitride nanosheets (C-g-C3N4) and Eu3+ (C-g-C3N4-Eu3+) is described for the detection of tetracyclines (TCs), a broad-spectrum antibiotic. C-g-C3N4, which was used as a fluorescence enhancer of Eu3+, was prepared by direct pyrolysis of melamine and post-functionalization. In the presence of TCs, the fluorescence intensity of Eu3+ at 616 nm increased, accompanied by a decrease of fluorescence intensity of C-g-C3N4 at 435 nm. Under the optimal conditions, the ratio of fluorescence intensity at 616 nm to the one at 435 nm (I616/I415) increases linearly in the 10 nM to 40 μM TC concentration range with a detection limit of 7.7 nM (S/N = 3). It has been successfully applied in the detection of TCs in spiked tap water and soil samples with satisfactory recovery (96.6–107.2%) and high precision. Furthermore, a test paper and smartphone can assist in rapidly detecting TCs due to the emission color change from blue to red with the addition of TCs. This shows that the proposed method has great potential for the rapid detection TCs in real samples. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles containing multiform heteroatoms on their surface have great potential for metal-ion recovery with a high throughput. In this study, a novel adsorbent (Fe3O4@CPTES@PEG) was developed to adsorb Au(III) from aqueous solution, which was synthesized by functionalizing Fe3O4 magnetic nanoparticles with poly(ethylene glycol) via a simple two-step reaction. Various techniques including Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric analysis (TGA), vibrating sample magnetometry (VSM), transmission electron microscopy (TEM) and X-ray diffraction spectroscopy (XRD) were used to characterize the adsorbent, demonstrating that poly(ethylene glycol) was successfully grafted onto the Fe3O4 magnetic nanoparticles. Batch experiments were performed to investigate the effects of the initial concentration of Au(III), contact time and coexisting ions on the absorption of Au(III) from an aqueous solution at pH = 1.0. Simultaneously, the adsorption process was well-fitted with the Langmuir and pseudo-second-order models. The as-synthesized core–shell structured Fe3O4@CPTES@PEG showed a high performance towards Au(III) adsorption with the maximum adsorption capacity of about 83 mg g−1. Significantly, the material exhibited highly selective adsorption toward Au(III) in the presence of coexisting ions (Fe(III), Mn(II), Pb(II), Cd(II), Cu(II), Cr(III), Al(III), Mg(II), Zn(II) and Au(III)). Also, the material could be regenerated using ferrous sulfate, and exhibited excellent reutilization for at least three times without significant loss in its adsorption capacity after a simple post-treatment. Therefore, the proposed method shows enormous potential for practical applications in the selective separation and enrichment of Au(III) from aqueous solution at pH = 1.0. [ABSTRACT FROM AUTHOR]

The polymerase chain reaction (PCR) has become an indispensable technique in molecular biology, however, it suffers from low efficiency and specificity problems. Developing suitable additives to effectively avoid nonspecific PCR reactions and explore the mechanism for PCR enhancing is a significant challenge. In this paper, we report three different modified gold nanoparticles (AuNPs) with different surface charge polarities and poly (diallyl dimethylammonium) chloride (PDDA) for use as novel PCR enhancers to improve the efficiency and specificity. These AuNPs included the positively charged PDDA protected AuNPs (PDDA-AuNPs), the neutral PDDA-AuNPs modified with excess chloride ion (PDDA.C-AuNPs), and the negatively charged sodium citrate (Na3Ct) protected AuNPs (Na3Ct-AuNPs). Our data clearly suggests that the positively charged PDDA-AuNPs with an optimum concentration as low as 1.54 pM could significantly enhance the specificity and efficiency of PCR, however, the optimum concentration of the negatively charged Na3Ct-AuNPs (2.02 nM) was more than 3 orders of magnitude higher than that of positively charged PDDA-AuNPs. The PCR specificity and efficiency are also improved by the neutral PDDA.C-AuNPs with an optimum concentration, much more than that of the PDDA-AuNPs. This suggests that there should be an electrostatic interaction between the positively charged PDDA-AuNPs and the negatively charged PCR components, and the surface charge polarities of PDDA-AuNPs may play an important role in improving the PCR specificity and efficiency. [ABSTRACT FROM AUTHOR]

The effect of chiral metal complexes ([Co(en)3]I3·H2O, cis-[CoBr(NH3)(en)2]Br2, K[Co(edta)]·2H2O and [Ru(phen)3](PF6)2) on the polymer-bound J-aggregates in aqueous mixtures of pesudoisocyanine (PIC) iodine and poly(acrylic acid, sodium)(PAAS) have been studied by UV–vis absorption, circular dichroism (CD) and fluorescence spectra. At low concentration, the PIC monomers could self-assemble to form supermolecules by binding to each of the COO−groups on the polymer chains through electrostatic interactions. After the addition of chiral metal complexes to the formed PIC-PAAS J-aggregates, we found that only the chiral multiple π-conjugated phenanthroline metal complexes could transfer their metal-centered chiral information to the formed J-aggregates. The chiral J-aggregates showed a characteristic induced circular dichroism (ICD) in the visible region of J-band chromophore, and the ICD signals depend on the absolute configuration, concentration of the chiral multiple π-conjugated metal complexes, as well as temperature. More interestingly, the supramolecular chirality of the polymer supported PIC J-aggregates could be memorized even after the addition of an excess opposite chiral complex enantiomers. This is in sharp contrast to the behavior in the high concentrated NaCl induced PIC-J aggregates, in which the optical rotation of a mixture of two enantiomers varies linearly with their ratio. [ABSTRACT FROM AUTHOR]

The non-covalent interactions of chiral metal complexes with the achiral 5,10,15,20-tetrakis (4-sulonatophenyl) porphyrin (H4TTPS2−) have been investigated by UV-vis and circular dichroism (CD) spectra. The results show that under acidic environments, only the chiral complex cations ([CoBr(NH3)(en)2]+, [Co(en)3]3+, [Ru(phen)3]2+) could interact with H4TTPS2− to form chiral aggregates, accompanied with the metal-centered chirality information transferred to the formed J-aggregates. However, the chiral complex anion ([Co(edta)]−) does not cause the self-assembly process. The competitive binding interactions between an achiral water-soluble cationic surfactant (N-hexadecyltrimethyl ammonium chloride, CTAC) and a cationic polyelectrolyte (polyallylamine, PAA) with the chiral metal complex H4TTPS2− J-aggregates, respectively, were also investigated. It was found that chiral-symmetry-breaking phenomena occur in the cationic surfactant induced event. In the case of a cationic polyelectrolyte, it could change the conformational flexibility of the H4TTPS2− aggregates. These results may lead us to understand the possible mechanism of the supramolecular self-assembly process by the non-covalent interactions. [ABSTRACT FROM AUTHOR]

A partial cation exchange reaction between CdTe nanoparticles and Bi3+ions gives rise to spontaneous formation of two-dimensional Bi2Te3/CdTe nanosheets. The average size and thickness of the nanosheets are around 200 and 6.9 nm, respectively. Both CdTe and Bi2Te3, which are there as the form of nanoparticles with average sizes of 3.4 nm, are found to be homogenously distributed in the nanosheets. The Bi2Te3/CdTe nanosheets are further integrated into a pellet by using spark plasma sintering for optimizing thermoelectric performance. Compared with the bulk n-type Bi2Te3, the pellets composed of Bi2Te3/CdTe nanosheets exhibit a considerably low thermal conductivity, 0.63 W m−1K−1, and a slightly high Seebeck coefficient, −182.2 μV K−1, at room temperature. [ABSTRACT FROM AUTHOR]

Λ- and Δ-enantiomers of cis-[CoBr(NH3)(en)2]Br2were obtained by absolute asymmetric synthesis. The interactions between the achiral 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) and two chiral cationic Co(iii) complexes were studied by UV-vis spectroscopy, circular dichroism (CD), fluorescence spectroscopy and atomic force microscopy (AFM). It was found that the cationic Co(iii) complexes can induce the formation of chiral porphyrin J-aggregates, that the metal-centered chirality can be transferred to the J-aggregates, and that the chirality was able to be memorized and amplified in the porphyrin J-aggregates. Therefore, this should be a good chiral model for understanding similar processes in physical and biological systems. [ABSTRACT FROM AUTHOR]

Reversible assembly of Janus particles was manipulated by host–guest interaction of β-cyclodextrin (β-CD) and azobenzene. One side of every Janus particle was modified with β-CD. Superstructures of Janus particles were formed by adding azobenzene-containing polymers to the dispersion of Janus particles. The superstructures were reversibly disassembled by adding α-CD or light irradiation. [ABSTRACT FROM AUTHOR]

A ratiometric fluorescence method based on carboxylated graphitic carbon nitride nanosheets (C-g-C 3 N 4 ) and Eu 3+ (C-g-C 3 N 4 -Eu 3+ ) is described for the detection of tetracyclines (TCs), a broad-spectrum antibiotic. C-g-C 3 N 4 , which was used as a fluorescence enhancer of Eu 3+ , was prepared by direct pyrolysis of melamine and post-functionalization. In the presence of TCs, the fluorescence intensity of Eu 3+ at 616 nm increased, accompanied by a decrease of fluorescence intensity of C-g-C 3 N 4 at 435 nm. Under the optimal conditions, the ratio of fluorescence intensity at 616 nm to the one at 435 nm (I 616 /I 415 ) increases linearly in the 10 nM to 40 μM TC concentration range with a detection limit of 7.7 nM (S/N = 3). It has been successfully applied in the detection of TCs in spiked tap water and soil samples with satisfactory recovery (96.6-107.2%) and high precision. Furthermore, a test paper and smartphone can assist in rapidly detecting TCs due to the emission color change from blue to red with the addition of TCs. This shows that the proposed method has great potential for the rapid detection TCs in real samples.

Reversible assembly of Janus particles was manipulated by host-guest interaction of β-cyclodextrin (β-CD) and azobenzene. One side of every Janus particle was modified with β-CD. Superstructures of Janus particles were formed by adding azobenzene-containing polymers to the dispersion of Janus particles. The superstructures were reversibly disassembled by adding α-CD or light irradiation.

A novel one-pot synthesis of graphene nanosheet/SnO 2 nanoparticle hybrid nanocomposites (GN/SnO 2 ) was realized by using graphene oxide nanosheets (GONs) functionalized with sodium dodecyl sulfonate and SnCl 2 as the starting materials. The morphology and structure of the synthesized SDS-GN/SnO 2 nanocomposites were characterized by Raman spectroscopy, transmission electron microscopy (TEM) and X-ray diffraction analysis. It was found that SnO 2 nanoparticles were homogeneously distributed on the graphene nanosheets. The electrochemical behavior of dopamine (DA) at the SDS-GN/SnO 2 nanoparticle modified electrode was studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). The results showed that the modified electrode exhibited excellent electrocatalytic activity towards the electrochemical oxidation of DA. The separation of the oxidation peak potentials for ascorbic acid (AA)-DA, uric acid (UA)-DA and UA-AA obtained by DPV is about 132 mV, 128 mV and 260 mV, respectively, which allows selective and sensitive detection of DA in the presence of AA and UA. The anodic peak currents were linear with the concentration of DA in the range from 1.0 × 10 -7 to 1.0 × 10 -5 M with a coefficient of 0.9980. The detection limit was 80 nM (S/N = 3). The proposed method could be applied for the determination of DA in real human urine samples.

We have developed a colorimetric assay for the highly sensitive and selective detection of Cd(2+) using gold nanoparticles (AuNPs) cofunctionalized with 6-mercaptonicotinic acid (MNA) and L-Cysteine (L-Cys) through the formation of an Au-S bond. In the presence of Cd(2+), the aggregation of functionalized AuNPs occurred by means of a metal-ligand interaction that led to visible color changes. Most importantly, cofunctionalized AuNPs had better responses for Cd(2+) than that functionalized by either MNA or L-Cys. Cd(2+) could be detected by the colorimetric response of AuNPs that could be detected by the naked eye or a UV-vis spectrophotometer. The absorbance ratio (A(620)/A(523)) was linear with the Cd(2+) concentration in the range of 2.0 × 10(-7) to 1.7 × 10(-6) M. Under optimum conditions (2.0 × 10(-5) M MNA, 2.0 × 10(-6) M L-Cys and 0.020 M NaCl at pH 10.0), the detection limit (3σ) of Cd(2+) could be as low as 1.0 × 10(-7) M. Interference experiments showed that Pb(2+) and Cu(2+) caused a slight interference for Cd(2+) determination while other metal ions caused no interference. The proposed method was successfully applied to determine the concentration of Cd(2+) in environmental samples (lake water).