Lateral flow devices for nucleic acid analysis exploiting quantum dots as reporters

There is a growing interest in the development of biosensors in the form of simple lateral flow devices that enable visual detection of nucleic acid sequences while eliminating several steps required for pipetting, incubation and washing out the excess of reactants. In this work, we present the first dipstick-type nucleic acid biosensors based on quantum dots (QDs) as reporters. The biosensors enable sequence confirmation of the target DNA by hybridization and simple visual detection of the emitted fluorescence under a UV lamp. The ‘diagnostic’ membrane of the biosensor contains a test zone (TZ) and a control zone (CZ). The CZ always fluoresces in order to confirm the proper function of the biosensor. Fluorescence is emitted from the TZ, only when the specific nucleic acid sequence is present. We have developed two general types of QD-based nucleic acid biosensors, namely, Type I and Type II, in which the TZ consists of either immobilized streptavidin (Type I) or immobilized oligodeoxynucleotides (Type II). The control zone consists of immobilized biotinylated albumin. No purification steps are required prior to the application of the DNA sample on the strip. The QD-based nucleic acid biosensors performed accurately and reproducibly when applied to (a) the visual detection of PCR amplification products and (b) visual genotyping of single nucleotide polymorphisms (SNPs) in human genomic DNA from clinical samples. As low as 1.5 fmol of double-stranded DNA were clearly detected by naked eye and the dynamic range extended to 200 fmol. The %CV were estimated to be 4.3–8.2.     

The Effect of Area Measurement Tools on Student Strategies: The Role of a Computer Microworld

This study focuses on the role of tools, provided by a computer microworld (C.AR.ME), on the strategies developed by 14-year-old students for the area measurement of a non-convex polygon. Students' strategies on a transformation and a comparison task were interpreted and classified into categories in terms of the tools used for their development. The analysis of the data shows that an environment providing the students with the opportunity to select various tools and asking them to produce solutions `in any possible way' can stimulate them to construct a plurality of solution strategies. The students selected tools appropriate for their cognitive development and expressed their own individual approaches regarding the concept of area measurement. The nature of tools used affected the nature of solution strategies that the students constructed. Moreover, all students were involved in the tasks and succeeded in completing them with more than one correct solution strategy thereby developing a broader view of the concept, although not all of them realized the same strategies. Three different approaches to area measurement emerged from the strategies which were constructed by the students in this microworld: automatic area measurement, provided by the environment, the operation of area measurement using spatial units and the use of area formulae. Almost all the students experienced qualitative aspects of area measurement through being involved in the process of covering areas using spatial units. Students also managed to use the area formulae meaningfully by studying it in relation to automatic area measurement and to area measurement using spatial units. Through these strategies, the concepts of conservation of area and its measurement as well as area formulae were viewed by the students as interrelated. Finally, some basic difficulties regarding area measurement were overcome in this computer environment.This revised version was published online in September 2005 with corrections to the Cover Date.     

An electroanalytical study of the drug proflavine

A square wave adsorptive stripping voltammetric (SWAdSV) method was developed for the determination of proflavine. The electrochemical behaviour of proflavine was investigated by cyclic (CV) and square wave voltammetry (SWV) at the hanging mercury drop electrode (HMDE) and carbon paste electrode (CPE). Different parameters were tested to optimize the conditions of the determination. Better results were obtained by square wave voltammetry using CPE where two oxidation and a reduction peak, appeared, at 0.19, 0.94 and 0.20 V, respectively. The peak at 0.19 V is quasi-reversible and deposition dependent. Linearity was observed in the range of (0.2–23.4) × 10⁻⁸ M (r = 0.998) during the anodic scan and in the range of (1.17–117) × 10⁻⁸ M (r = 0.999) during the cathodic scan. The second peak at 0.94 V is irreversible and deposition independent. The linearity of this peak was observed in the range of (1.29–11.7) × 10⁻⁸ M (r = 0.998). The method was applied to the analysis of bovine serum and gave satisfactory results. Correspondence: S. Th. Girousi, Laboratory of Analytical Chemistry, Department of Chemistry, Aristotle University, Thessaloniki 54124, Greece     

Theoretical and experimental investigation of the semiquinone forms of protocatechuic acid. The effect of manganese

Ten oxidized, oxygenated and dimeric forms of protocatechuic acid (PCA, 3,4-dihydroxybenzoic acid, 3,4-DHBA) have been studied using DFT calculations (at the B3LYP/TZVP level of theory) and their structural and spectroscopic parameters (electronic transitions, NMR resonances) have been calculated. Combination with experimental results (under anaerobic or aerobic environment) determines the conditions for the existence of protonated, fully deprotonate and/or oxygenated semiquinones of PCA. Several energy optimized conformers containing manganese–(PCA–semiquinones) and water or/and peroxo-groups have been drawn (species 11–16) and their structural and spectroscopic properties have been calculated at the same level of theory. Experimental parallel to the theoretical results provide evidence for the existence of Mn(II)– and Mn(III)–[PCA–semiquinone] as well the conditions of dioxygen activation. Two of the blue solids (17 and 18) isolated from these solutions, have been characterized. Elemental analyzes, TGA, IR and ESR spectra support the formulation Mn₂(PCA)₂(O₂)(OH)₂(AcO)(ClO₄)₂(H₂O)₃ (17), and Mn₂(PCA)₂(O₂)₂(OH)₂(AcO)H₂O (18). Their ESR spectra, in solution (blue solutions), are almost identical and indicative of Mn(IV) existence. From the whole investigation, the activation of dioxygen by the PCA, its relocation on manganese and the oxidation of the metal ion have been provided.     

Preparation, spectroscopic and high field NMR relaxometry studies of gadolinium(III) complexes with the asymmetric tetraamine 1,4,7,11-tetraazaundecane

The reaction of Gd(III) with asymmetric tetramine 1,4,7,11-tetraazaundecane (2,2,3-tet, L¹) ligand has been studied via NMR spectroscopy. The ligand proton longitudinal relaxation rates (R₁) have been used to estimate the distances of these protons from the Gd(III) center, in Gd(III)–L¹ reaction solutions, in H₂O/D₂O 5/1 mixtures.Two Gd(III) complexes [Gd(III)(L¹)(NH₃)(H₂O)₄](CH₃COO)₃·2H₂O (1) and [Gd(III)(L¹)(NH₃)(H₂O)₂]Cl₃·EtOH (2) have been isolated and characterized by elemental analyses, TGA, IR, NMR and relaxometry measurements. The NMR relaxation measurements of 2 in aqueous solutions have been performed, under various temperature or concentration conditions, and compared with those of the commercial contrast agents Gd(III)–DTPA and Gd(III)–DTPA-BMA. It has also been studied the influence of (i) the Gd(III) inner-sphere water molecule number (q) alteration and (ii) the steric constraint enhancement on the metal site, over the relaxation rate values of the parent aqueous solution of Gd(III)–2,2,3-tet, and of the aqueous solutions of 2.     

Light-controlled directional liquid drop movement on TiO2 nanorods-based nanocomposite photopatterns

Patterned polymeric coatings enriched with colloidal TiO(2) nanorods and prepared by photopolymerization are found to exhibit a remarkable increase in their water wettability when irradiated with UV laser light. The effect can be completely reversed using successive storage in vacuum and dark ambient environment. By exploiting the enhancement of the nanocomposites hydrophilicity upon UV irradiation, we prepare wettability gradients along the surfaces by irradiating adjacent surface areas with increasing time. The gradients are carefully designed to achieve directional movement of water drops along them, taking into account the hysteresis effect that opposes the movement as well as the change in the shape of the drop during its motion. The accomplishment of surface paths for liquid flow, along which the hydrophilicity gradually increases, opens the way to a vast number of potential applications in microfluidics.     

Synthesis and characterisation of benzyl phosphino-thioether and -thiolato Pd(II) complexes and their applications in Suzuki coupling reactions

The synthesis of the benzyl phosphinothioether derivatives Ph(2)PCH(2)CH(Et)SR and their corresponding palladium complexes are reported, where R = CH(2)Ph, R = CH(2)-3,5-Me-C(6)H(3) and R = 1-CH(2)C(10)H(7)(5). Crystallographic data obtained for the complexes Pd(3)Cl(2) and Pd(4)Cl(2) show intra- and inter-molecular pi-pi interactions between the aromatic rings on the P and S substituents, and NOE experiments for Pd(4)Cl(2) show that these interactions persist in solution. The performance of the phosphinothioether palladium complexes in aryl-aryl cross-coupling reactions is compared with that of the corresponding complex of the parent phosphinothiolato ligand Ph(2)PCH(2)CH(Et)S(-)(1). High turnover numbers up to 2000000 are reported for the coupling of bromobenzene, using the palladium dimer [Pd(1)I](2) as the catalyst precursor. Kinetic studies show a linear dependence of the reaction on catalyst loading. The effect of other variables on the cross-coupling reaction, such as temperature, solvent and base, is also reported.     

Vektorräume,die Strahlensystemen zugeordnet sind

Let (S_o) be the set of rectilinear congruences in Euclidean space E³ which have a common middle enveloppe with a given congruence S_o. In this paper we supply the set (S_o) with the structure of a vector space and prove that it is a real infinite dimensional vector space. Some properties of subspaces of (S_o) are also discussed.     

Identification of photocatalytic degradation products of diazinon in TiO2 aqueous suspensions using GC/MS/MS and LC/MS with quadrupole time-of-flight mass spectrometry

The photocatalytic degradation of the organophosphorus insecticide diazinon in aqueous suspensions has been studied by using titanium dioxide as a photocatalyst. The degradation of the insecticide was a fast process and included the formation of several intermediates that were identified using GC/ion-trap mass spectrometry with EI or CI in positive and negative ionization mode and HPLC/electrospray-QqTOF mass spectrometry. Since primarily hydroxy derivatives were identified in these aqueous suspensions, the mechanism of degradation was probably based on hydroxyl radical attack. The initial oxidative pathways of the degradation of diazinon involved the substitution of sulfur by oxygen on the Pz.dbnd6;S bond, cleavage of the pyrimidine ester bond, and oxidation of the isopropyl group. Exact mass measurements of the derivatives allowed the elemental formula of the molecules to be determined confidently. Similarities to the metabolic pathways occurring in living organisms were observed.     

Electrochemical and spectroscopic studies of 2,3-dihydroxybenzoic acid,its oxidation products and their interaction with manganese(II), in dimethyl sulfoxide solutions

The electrochemical and spectroscopic behaviour of 2,3-dihydroxybenzoic acid (2,3-DHBA) and its oxidized forms have been studied in dimethyl sulfoxide solutions under aerobic and anaerobic conditions. The products resulting from the reaction with manganese(II) (in dimethyl sulfoxide) are also studied by cyclic voltammetry, u.v–vis., n.m.r. and e.s.r. spectroscopies. Under anaerobic conditions the anions of the ligand form stable complexes with manganese(II) and (III) of MnL₂ type, while in the presence of air the oxidized forms of the ligand react with manganese(II) to give mixed-valence species. The chemical stability of the semiquinone and its manganese complexes in addition to its photosensitivity is noteworthy. Calculations show that the electrogenerated manganese(III)–(2,3-DHB–semiquinone) system is stable, but redox-active and can undergo a two-electron exchange (per monomer). The dimeric (or oligomeric) species should be good candidates for water oxidation studies.