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ABSTRACT: Mono-dispersed 3,4,9,10-perylene tetracarboxylic acid (PTCA) functionalized graphene sheets (PTCA-graphene) were fabricated by a chemical route and dispersed well in aqueous solution. PTCA-graphene with plenty of -COOH groups as electrostatic absorbing sites were beneficial to the loading of Cytochrome c (Cyt c). Cyt c, which was tightly immobilized on the PTCA-graphene modified glassy carbon electrode, maintained its natural conformation. Direct electron transfer of Cyt c and the electro-catalytic activity towards the reduction of H2O2 were also achieved. It has been substantiated that PTCA-graphene is a preferable biocompatible matrix for Cyt c.
Talanta 03/2013; 107C:195-202. · 3.79 Impact Factor
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ABSTRACT: In very recent years, polyaniline or its derivatives have been adopted to efficiently immobilize probe DNA via π-π interaction between conjugated interface and DNA bases. In this work, self-doped polyaniline (SPAN)-DNA hybrid was adopted as the platform to construct a DNA biosensor with label-free, reagentless and electrochemical self-signal amplifying features. This was achieved by the π-π interaction between conjugated SPAN and DNA bases, also the intrinsic differences between single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). The tightly cross-linked hybrid was tethered to Au electrode, which had been anchored by p-aminothiophenol (PATP) self-assembled monolayer (SAM) previously, based on the phosphoramidate bond between PATP and ssDNA. SPAN in the recognition surface exhibited well-defined redox signals under neutral conditions. Due to the intrinsic property differences between ssDNA and dsDNA, such as rigidity, π-stacked bases, charge distribution and long-range electron transfer, SPAN-DNA underwent a major conformational change after hybridization. The redox behaviors of SPAN were modulated by DNA, which served as signals to monitor hybridization. As an example, the gene fragment related to one of the screening genes for the genetically modified plants, cauliflower mosaic virus 35S gene was satisfactorily detected with this strategy. Under optimal conditions, the dynamic range for the DNA assay was from 1.0 × 10(-14) mol L(-1) to 1.0 × 10(-8) mol L(-1) with the detection limit of 2.3 × 10(-15) mol L(-1). This work presents the construction of a recognition surface for the highly-sensitive electrochemical DNA hybridization detection via the self-signal amplifying procedure of conjugated SPAN-DNA hybrid. Unlike most signal amplifying processes using outer indicators, complex labels or other reagents, this procedure possesses simplicity and convenience.
The Analyst 01/2013; · 4.23 Impact Factor
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ABSTRACT: This paper for the first time reports a chemical method to prepare graphene quantum dots (GQDs) from GO. Water soluble and surface unmodified GQDs, serving as a novel, effective and simple fluorescent sensing platform for ultrasensitive detection of 2,4,6-trinitrotoluene (TNT) in solution by fluorescence resonance energy transfer (FRET) quenching. The fluorescent GQDs can specifically bind TNT species by the π-π stacking interaction between GQDs and aromatic rings. The resultant TNT bound at the GQDs surface can strongly suppress the fluorescence emission by the FRET from GQDs donor to the irradiative TNT acceptor through intermolecular polar-polar interactions at spatial proximity. The unmodified GQDs can sensitively detect down to ∼0.495ppm (2.2μM) TNT with the use of only 1mL of GQDs solution. The simple FRET-based GQDs reported here exhibit high and stable fluorescence. Eliminating further treatment or modification, this method simplifies and shortens the experimental process. It possesses good assembly flexibility and can thus find many applications in the detection of ultratrace analytes.
Talanta 11/2012; 101:192-7. · 3.79 Impact Factor
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ABSTRACT: Exploring graphene oxide (GO), DNA hybridization detection usually relies on either GO decoration or DNA sequences labeling. The former endows GO with desired chemical, optical, and biological properties. The latter adopts labeled molecules to indicate hybridization. In the present work, we propose a simple, label-free DNA assay using undecorated GO directly as the sensing platform. GO is anchored on diazonium functionalized electrode through electrostatic attraction, hydrogen bonding or epoxy ring-opening. The π-π stacking interaction between hexagonal cells of GO and DNA base rings facilitates DNA immobilization. The adsorbed DNA sequence is specially designed with two parts, including immobilization sequence and probe sequence. In the absence of target, the two sequences lie nearly flat on GO platform. In the presence of target, probe hybridizes with it to form double helix DNA, which 'stands' on GO. While the immobilization sequence part remains 'lying' on GO surface. Hence, DNA hybridization induces GO interfacial property changes, including negative charge and conformational transition from 'lying' ssDNA to 'standing' dsDNA. These changes are monitored by electrochemical impedance spectroscopy and adopted as the analytical signal. This strategy eliminates the requirement for GO decoration or DNA labeling, representing a comparatively simple and effective way. Finally, the principle is applied to the detection of conserved sequence of the human immunodeficiency virus 1 pol gene fragment. The dynamic detection range is from 1.0×10(-12) to 1.0×10(-6)M with detection limit of 1.1×10(-13)M with 3σ. And the sequences with double- or four-base mismatched are readily distinguishable. In addition, this strategy may hold great promise for potential applications from DNA biosensing to nanostructure framework construction based on the versatile DNA self-assembly.
Analytica chimica acta 11/2012; 753:82-9. · 4.31 Impact Factor
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ABSTRACT: A perylene ligand, N,N-bis-(1-aminopropyl-3-propylimidazol salt)-3,4,9,10-perylene tetracarboxylic acid diimide ligand (PDI), which consisted of π-conjugated perylene moiety and hydrophilic side chains with positively charged imidazole rings, was used to wrap G-quadruplex for fluorescence turn-on K(+) recognition. Electrostatic attraction between PDI's positively charged imidazole rings and DNA's negatively charged phosphate backbones enabled PDI to accumulate on DNA. Upon trapping K(+), these G-rich DNA sequences transitioned to G-quadruplex. Subsequently, PDI ligands wrapped G-quadruplex, in which the flat aromatic core of PDI ligand interacted with G-quartet through π-π stacking and the side chains were positioned in grooves through electrostatic interactions. Consequently, the interaction mode change and conformational transition from PDI stacked G-sequence to PDI wrapped G-quadruplex led to PDI fluorescence enhancement, which was readily monitored as the detection signal. This strategy excluded the sequence tagging step and exhibited high selectivity and sensitivity towards K(+) ion with the linear detection range of 10-150 nM. Besides, PDI ligands may hold diagnostic and therapeutic application potentials to human telomere and cancer cells.
Biosensors & bioelectronics 07/2012; 38(1):396-401. · 5.43 Impact Factor
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ABSTRACT: An efficient DNA impedance biosensing platform is constructed, in which positively charged N,N-bis-(1-aminopropyl-3-propylimidazol salt)-3,4,9,10-perylene tetracarboxylic acid diimide (PDI) is anchored to graphene sheets. The π-π stacking and electronic interactions are elucidated by the distinct absorption features in UV-vis spectra and by quenching perylene fluorescence in contact with graphene. The rational design and tailoring of graphene surface invest it with desired properties (dispersive, structural, photoelectrical and conductive, etc.) and boost its application. Electrostatic interaction between PDI's positively charged imidazole rings and negatively charged phosphate backbones of single-stranded DNA (ssDNA) facilitates ssDNA immobilization. This manner is different from these mainly based on the attraction between the rings in DNA bases and the hexagonal cells of graphene, which is disturbed after hybridization and causes the leaving of formed double-stranded DNA from graphene surface. The electrostatic ssDNA grafting occupies phosphate backbones and particularly leaves the bases available for efficient hybridization. DNA immobilization and hybridization lead to PDI/graphene interfacial property changes, which are monitored by electrochemical impedance spectroscopy and adopted as the analytical signal. The conserved sequence of the pol gene of human immunodeficiency virus 1 is satisfactorily detected via this PDI/graphene platform and shows high reproducibility, selectivity.
Biomaterials 11/2011; 33(4):1097-106. · 7.40 Impact Factor
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ABSTRACT: Sensitive electrochemical impedance assay of DNA hybridization by using a novel graphene sheets platform was achieved. The graphene sheets were firstly functionalized with 3,4,9,10-perylene tetracarboxylic acid (PTCA). PTCA molecules separated graphene sheets efficiently and introduced more negatively-charged -COOH sites, both of which were beneficial to the decoration of graphene with gold nanoparticles. Then amine-terminated ionic liquid (NH₂-IL) was applied to the reduction of HAuCl₄ to gold nanoparticles. The green-synthesized gold nanoparticles, with the mean diameter of 3 nm, dispersed uniformly on graphene sheets and its outer layer was positively charged imidazole termini. Due to the presence of large graphene sheets and NH₂-IL protected gold nanoparticles, DNA probes could be immobilized via electrostatic interaction and adsorption effect. Electrochemical impedance value increased after DNA probes immobilization and hybridization, which was adopted as the signal for label-free DNA hybridization detection. Unlike previously anchoring DNA to gold nanoparticles, this label-free method was simple and noninvasive. The conserved sequence of the pol gene of human immunodeficiency virus 1 was satisfactorily detected via this strategy.
Biosensors & bioelectronics 07/2011; 26(11):4355-61. · 5.43 Impact Factor
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ABSTRACT: The electropolymerization of thionine with the guidance of DNA molecular template was described in this paper. The prepared polythionine (PTH) dispersed uniformly on the electrode surface and presented a novel flexual nanostrip morphology with the average diameter of 90nm and length of 500nm. However, PTH fabricated without DNA-guided electropolymerization presented a clustered granular morphology. The electrochemical redox behavior of PTH via DNA-guided electropolymerization was considerably enhanced compared to that of PTH without DNA molecular template. The significant improvement of the redox property might be attributed to the in situ PTH chains growth along DNA strands. In neutral environment, the PTH/DNA on the carbon paste electrode showed a pair of well-defined redox peaks and excellent electrocatalytic activity toward the reduction of H(2)O(2). Under optimal conditions, H(2)O(2) was amperometrically determined by using the as-prepared PTH/DNA nanostrips in the concentration range of 0.99-8.26mM.
Colloids and surfaces. B, Biointerfaces 03/2011; 83(1):179-82. · 2.60 Impact Factor
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ABSTRACT: Negative-charge change and conformation transition upon DNA immobilization and hybridization on functionalized graphene sheets were monitored by the EIS technique and adopted as the signal for label-free electrochemical DNA hybridization detection.
Chemical Communications 02/2011; 47(6):1743-5. · 6.17 Impact Factor
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ABSTRACT: The responses of organisms to temperature variations may be via short term responses of the phenotype (phenotypic plasticity), or they could involve long-term evolutionary change and adaptation (via selection) to the genotype. These could involve changes to the mean size of the animal or to the thermal reaction norm. We examined the effects of various temperatures (of 22, 25, 28, and 31 °C) on development time, adult body size and preadult survivorship in three populations of the cockroach, Eupolyphaga sinensis (Walker), collected at different latitudes. We found substantial temperature-induced plasticity in development time, body size, and preadult survivorship, indicating that developmental temperatures have strong impacts on growth and life history traits of E. sinensis. Genetic differences for development time, body size, and preadult survivorship were detected among populations, and the three traits exhibited highly significant variations in the responses of different populations to various temperature conditions, indicating genetic differences among populations in terms of thermal reaction norms. We also found that two populations seem to support the beneficial acclimation hypothesis whereas the third mid-latitude population does not. The results are likely because of differences in season length and voltinism, indicating that not only temperature regime but also its interactions with generation time (and development time), voltinism, and season length are likely to have considerable effects on insect development time and body size. Overall, changes in development time, body size, and preadult survivorship in E. sinensis can all be regarded as adaptations to changing thermal regimes.
Environmental Entomology 02/2011; 40(1):1-7. · 1.56 Impact Factor
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ABSTRACT: 1. There is wide intra-specific variation in sexual size dimorphism (SSD). Much of this variation is probably as a result of sexual differences in the selective pressure on body size. However, environmental variables could affect males and females differently, causing variation in SSD.2. We examined the effects of two temperatures (20 and 30 °C) on SSD in six populations of the blowfly, Chrysomya megacephala.3. We found that body size increased with temperature in all the populations studied, and the sexes differed in phenotypic plasticity of body size in response to rearing temperature. This created substantial temperature-induced variation in SSD (i.e. sex × temperature interaction). Males were often smaller than females, but the degree of dimorphism was smaller at the higher temperature (30 °C) and larger at the lower temperature (20 °C). This change in SSD was not because of a gender difference in the effect of temperature on development time. Further studies should address whether this variation can be produced by adaptive canalisation of one sex against variation in temperature, or whether it may be a consequence of non-adaptive developmental differences between the sexes.4. Although most studies assume that the magnitude of SSD is fixed within a species, the present study demonstrates that rearing temperature can generate considerable intra-specific variation in the degree of SSD.
Ecological Entomology 12/2010; 36(1):111 - 115. · 2.00 Impact Factor
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ABSTRACT: Sexual size dimorphism (SSD) is a common phenomenon in animals and varies widely among species and among populations within species. Much of this variation is likely due to variance in selection on females vs. males. However, environmental variables could have different effects on females vs. males, causing variation in dimorphism. In this study, we test the differential-plasticity hypothesis, stating that sex-differential plasticity to environmental variables generates among-population variation in the degree of sexual dimorphism. We examined the effect of temperature (22, 25, 28, and 31 °C) on sexual dimorphism in four populations of the cockroach Eupolyphaga sinensis Walker (Blattaria: Polyphagidae), collected at various latitudes. We found that females were larger than males at all temperatures and the degree of this dimorphism was largest at the highest temperature (31 °C) and smallest at the lowest temperature (22 °C). There is variation in the degree of SSD among populations (sex*population interaction), but differences between the sexes in their plastic responses (sex*temperature interaction) were not observed for body size. Our results indicated that sex-differential plasticity to temperature was not the cause of differences among populations in the degree of sexual dimorphism in body size.
Entomologia Experimentalis et Applicata 10/2010; 137(2):204 - 209. · 1.53 Impact Factor
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ABSTRACT: Carboxylic group-functionalized single-walled carbon nanotubes (SWNTs) were assembled vertically on the glassy carbon electrode using ethylenediamine as linking agent to fabricate an aligned electrode (SWNTE). Single-stranded DNA (ssDNA) wrapped around the SWNTs to form ssDNA-wrapped SWNTE structures based on the interaction between ssDNA and SWNT. A sensitive differential pulse voltammetric (DPV) response was obtained at the ssDNA-wrapped SWNTE owing to the electrooxidation of guanine bases. Double-stranded DNA (dsDNA) was formed when ssDNA on the ssDNA-wrapped SWNTE was hybridized with complementary ssDNA (cDNA). The dsDNA was removed from the SWNTs by undergoing a process of preconditioning at -0.6 V. Consequentially, the DPV response of guanine bases decreased. The used SWNTE could be renewed easily via ultrasonically rinsing. On the basis of this mechanism, a label-free and readily reusable electrochemical DNA hybridization biosensor was designed by directly monitoring the current change of guanine bases. Under optimum conditions, the plot of the measurement signal of guanine bases versus the cDNA concentrations was a good straight line in the range of 40-110 nM with a detection limit of 20 nM (3s). The biosensor can be switched to detect different target DNAs easily.
Analytical Chemistry 08/2009; 81(15):6006-12. · 5.86 Impact Factor
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ABSTRACT: Government has a natural concern about the investment performance and associated risks of pension funds. If these funds are poorly managed and unable to pay pensions to retirees, government may have to step in. In addition to solvency regulation, this risk can be controlled by establishing investment regulations that impact portfolio composition. There are two basic regulatory approaches. One approach is to impose quantitative asset restrictions (QAR, involves direct limits on holdings of specific assets). The other is to establish prudent person rules (PPR, requires following prudent investment policies and practices). This article assesses the pros and cons of both approaches, considering finance theory and empirical evidence. Both theory and empirical evidence suggest the PPR approach is likely more efficient.
Pension Risk Management eJournal. 05/2009;
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ABSTRACT: The much-enhanced electrochemical responses of potassium ferricyanide and methylene blue (MB) were firstly explored at the glassy carbon electrode modified with single-walled carbon nanotubes (SWNT/GCE), indicating the distinct electrochemical activity of SWNTs towards electroactive molecules. A hydrophobic room temperature ionic liquid (RTIL), 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6), was used as electrode modification material, which presented wide electrochemical windows, proton permeation and selective extraction ability. In consideration with the advantages of SWNTs and RTIL in detecting target molecules (TMs), a novel strategy of ‘sandwich–type’ electrode was established with TMs confined by RTIL between the SWNT/GCE and the RTIL membrane. The strategy was used for electrochemical detection of ascorbic acid (AA) and dopamine (DA), and detection limits of 400 and 80 fmol could be obtained, respectively. The selective detection of DA in the presence of high amount of AA could also be realized. This protocol presented many attractive advantages towards voltammetric detection of TMs, such as low sample demand, low cost, high sensitivity, and good stability.
Electroanalysis 09/2008; 20(17):1909 - 1916. · 2.87 Impact Factor
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ABSTRACT: Pension fund assets have increased markedly during recent decades, and there are signs that this trend will continue, particularly given demographic changes and the current pattern of pension reform towards funded systems. However, research on the extent to which growth in pension assets contributes directly to economic growth is quite scarce. This is surprising since superiority of funding to pay-as-you-go links notably to the question whether funding improves economic performance sufficiently to generate the resources required to meet the needs of an ageing population. In this paper, we design a modified Cobb-Douglas production function with pension assets as a shift factor. We then employ a dataset covering 38 countries to investigate the direct link between pension assets and economic growth, using a variety of appropriate econometric methods. We find positive results for both OECD countries and Emerging Market Economies (EMEs), with some evidence for a larger effect for EMEs than OECD countries.
01/2005;
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ABSTRACT: Organisms can respond to variation in temperature through the direct effect of temperature on phenotypes (phenotypic plasticity), or through long-term adaptation to temperature (and thus evolution of either mean size or thermal reaction norm). We examined the effects of various temperatures (of 20 and 30 °C) on development time, adult body size (body length and body width) and pre-adult survivorship in six populations of Chrysomya megacephala, collected at different latitudes. We found that temperature changes induced substantial plasticity in terms of development time, body size and pre-adult survivorship, indicating that developmental temperature significantly affects growth and life history traits of C. megacephala. We also detected genetic differences among populations for body size and development time, and these two traits exhibited highly significant variations in the responses of different populations to various temperature conditions, indicating genetic differences among populations in terms of thermal reaction norms. The latitude of origin of the different populations (and hence mean temperature regimes in the environments from where the populations originated) did not appear to fully explain these genetic differences. In short, changes in development time and body size in C. megacephala can be regarded as adaptations to changing thermal regimes.
Journal of Thermal Biology.
