Photocatalytic Performance of Undoped and Al-Doped ZnO Nanoparticles in the Degradation of Rhodamine B under UV-Visible Light:The Role of Defects and Morphology

Quasi-spherical undoped ZnO and Al-doped ZnO nanoparticles with different aluminum content, ranging from 0.5 to 5 at% of Al with respect to Zn, were synthesized. These nanoparticles were evaluated as photocatalysts in the photodegradation of the Rhodamine B (RhB) dye aqueous solution under UV-visible light irradiation. The undoped ZnO nanopowder annealed at 400 °C resulted in the highest degradation efficiency of ca. 81% after 4 h under green light irradiation (525 nm), in the presence of 5 mg of catalyst. The samples were characterized using ICP-OES, PXRD, TEM, FT-IR, 27Al-MAS NMR, UV-Vis and steady-state PL. The effect of Al-doping on the phase structure, shape and particle size was also investigated. Additional information arose from the annealed nanomaterials under dynamic N2 at different temperatures (400 and 550 °C). The position of aluminum in the ZnO lattice was identified by means of 27Al-MAS NMR. FT-IR gave further information about the type of tetrahedral sites occupied by aluminum. Photoluminescence showed that the insertion of dopant increases the oxygen vacancies reducing the peroxide-like species responsible for photocatalysis. The annealing temperature helps increase the number of red-emitting centers up to 400 °C, while at 550 °C, the photocatalytic performance drops due to the aggregation tendency

Early structural build-up behavior, setting mechanism, and nanostructure of alkali-activated GGBFS mixtures

The initial changes in the microstructure of alkali-activated slag cement (AAS) characterize the rheological behavior, initial structuration, and setting times of the mixture. In this study, the relationships among the rheological behavior, solidification process, and nanostructure changes of sodium hydroxide-activated slag (NH–AAS) and sodium silicate-activated slag (SS–AAS) pastes over time are investigated by small amplitude oscillation shear test, isothermal calorimetry, scanning electron microscopy analyses, and 1H–29Si cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy (CP MAS NMR) and 29Si MAS NMR spectroscopy. Test results showed that the NH–AAS reaches its initial setting time following a continuously proceeding structuration process, whereas the SS–AAS reaches its initial setting with an abrupt increase in the structuration process. At their initial setting times, the NH–AAS and SS–AAS mixtures release similar heat and reach a similar reaction degree. The SS–AAS mixture had more N–A–S–H formation than C–A–S–H at the initial setting time. On the other hand, the amount of C–A–S–H was similar to N–A–S–H in the NH–AAS mixture. The gradual N–A–S–H gel degradation to form C–A–S–H was observed during the acceleration period for the SS–AAS mixture

Electronic DNA hybridisation detection in low-ionic strength solutions

Fast DNA detection remains of great interest in human genetics, medicine, and drug discovery. The detection of DNA hybridisation makes the screening of point mutations in potential cancer genes or DNA fingerprinting for phylogenesis purposes possible (S.W. Yeung, T.M.H. Lee, H. Cai, and I.M. Hsing, A DNA biochip for on-the-spot multiplexed pathogen identification, Nucleic Acids Research 34 (2006), p. e118; P. Liepold, H. Wieder, H. Hillebrandt, A. Friebel, G. Hartwich, DNA-arrays with electrical detection: a label-free low cost technology for routine use in life sciences and diagnostics, Bioelectrochemistry, 67 (2005), pp. 143-150). The speed, cost and reliability of the hybridisation detection is of high importance. Electronic detection of hybridisation events using standard CMOS-fabricated devices such as Field Effect Transistors (FETs) promises fast, label-free and multiplexed read-out systems. Moreover, they hold the advantage of high-throughput and minimalisation, which makes them ideal for implementation in fast diagnostic tools such as lab-on-chip systems. Field-effect devices, however, imply the necessity of low-ionic strength buffer solutions for signal maximisation because of the occurrence of charge screening effects near the electrolyte-oxide interface layer. In this article, we present a surface chemistry-based methodology that allows FET-based recordings of hybridisation events in low-ionic strength solutions. Quartz Crystal Microbalance results show that positively-charged surfaces promote DNA hybridisation, even when performed in lower salt concentrations then commonly used. Fluorescence measurements were performed on the different surfaces to reveal the optimal DNA adsorption conditions on the surface. For proof-of-principle, the surface chemistry was applied on the surface of a floating-gate field-effect transistor, and online recordings of DNA hybridisation events were performed in low-ionic strength solutions.status: publishe

Magnetic particles as labels in bioassays: Interactions between a biotinylated gold substrate and streptavidin magnetic particles

Magnetic particles (MPs) have been attracting much interest as a labeling material for advanced biological and medical applications, such as biomagnetic separation, drug delivery, magnetic resonance imaging, and hyperthermia. In most of these applications, the MPs have been designed to specifically interact with a target, such as cells or proteins, moving freely in a solution. However, for surface-based applications, such as magnetic biosensing, these MPs must bind specifically with a target that is immobilized onto a planar substrate. Consequently, new interaction phenomena, which influence the binding of the MPs to the substrate, have to be taken into account. To achieve adequate binding characteristics and to optimize the MPs toward substrate labeling, these physicochemical interactions should be properly identified. In this paper, the interactions between 16 commercially available streptavidin MPs and a biotinylated gold substrate were monitored in real time by surface plasmon resonance technology and the particle surface coverage was calculated by optical microscopy. On the basis of the type of interactions, the MPs studied in this paper could be classified into three different cases: (I) MPs that bind to the biotinylated substrate via the specific streptavidin-biotin interactions, without showing any nonspecific interactions; (II) MPs that do not bind to the substrate; and (III) MPs that bind to the biotinylated substrate via nonspecific interactions rather than via specific streptavidin-biotin interactions. The three cases were understood by determining the surface charges of both the particle and the substrate in zeta potential measurements. It was found that binding of MPs to the substrate was strongly dependent on the amount and the sign of the charges on both surfaces. The strong influence of electrostatic interactions was validated by simulating the total interaction force between a streptavidin MP and a biotinylated substrate by use of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, while the gravitational force and the streptavidin-biotin force were accounted for. Finally, we conclude that apart from a well-controlled streptavidin coating, the surface charge of the particle and the substrate plays a pivotal role in the construction of MP assays on surfaces.status: publishe

Crystallization inhibition of polyethylene glycol by indomethacin: formation and disruption of hydrogen bonds

PURPOSE We recently found that indomethacin (IMC) can effectively act as a crystallization inhibitor for polyethylene glycol 6000 (PEG) despite the fact that the absence of interaction between the drug and the carrier in the solid state was reported in the literature. However, in the present study, we investigate the possibility of drug-carrier interaction in the liquid state to explain the crystallization inhibition effect of IMC. METHODS Dispersions made up of IMC and PEG were prepared by heating the mixture of the drug and the carrier to above the melting temperatures of both components, followed by solidification of the melt. Drug-carrier interaction in both molten and solid state was characterized by variable temperature Fourier Transform Infrared Spectroscopy (FTIR) and cross-polarization magic-angle spinning 13C nuclear magnetic resonance spectroscopy (NMR). RESULTS FTIR data show the strong IMC-PEG interaction in the molten state that was exhibited by the significant decrease in intensity and then the disappearance of asymmetric carbonyl vibration of the IMC cyclic dimer, suggesting the breaking of hydrogen bonding of the IMC dimer to form an interaction of the IMC monomer with PEG. The drug-carrier interaction was disrupted upon storage and polymer crystallization, resulting in segregation of IMC from PEG crystals that can be observed under polarized light microscopy. This process was further confirmed by NMR since in the liquid (molten) state, when the IMC:PEG unit ratio is below 2:1, almost all signals of IMC are undetectable because of the loss of cross polarization efficiency of too mobile IMC molecules upon attachment to PEG chains via hydrogen bonding. Only signals of carbons with more protons can be observed due to higher cross polarization efficiency. This suggests that each ether oxygen of the PEG unit can form hydrogen bonds with two IMC molecules, possibly owing to the perfect arrangement of drug molecules along the carrier chains that in turn is originating from π-π stacking between the aromatic rings of neighbouring IMC molecules. In molten dispersions containing more IMC e.g. IMC:PEG unit ratio of 3:1 and 6:1, free IMC molecules with lower mobility that do not involve in interaction with PEG can be cross polarized and the signals are visible. The NMR spectrum of IMC shows no change in solid dispersions with PEG upon crystallization, indicating the absence of interaction in the solid state, hence confirming previous studies. The crystallization inhibition of IMC on PEG is independent on the carrier molecular weight. This only depends on the number of hydrogen bonded forming centers i.e. IMC:PEG unit ratio. When the hydroxyl group of IMC is substituted by a methoxy group, no interaction between the new compound and PEG can be detected in both liquid and solid state, and the methoxy derivative of IMC is unable to inhibit crystallization of PEG. CONCLUSION This work demonstrates the formation of hydrogen bonding between IMC and PEG in the liquid state, which is vital for the crystallization inhibition effect on IMC on PEG, and the disruption of the bonds upon crystallization of the carrier, leading to the exclusion of IMC from PEG crystals. Both the presence of a hydrogen bonding forming center and an aromatic ring of IMC are required for the crystallization inhibition effect on PEG.status: publishe

Comparison of random and oriented immobilisation of antibody fragments on mixed self-assembled monolayers

The sensitivity of immunosensors is strongly dependent on the amount of immobilised antibodies and their remaining antigen binding properties. The use of smaller and well-oriented antibody fragments as bioreceptor molecules influences the final immunosensor signal. The aim of this study was to compare the immunosensor responses of different immobilised antibody fragments, such as F(ab')2 and Fab', with their parental IgG. In addition, we evaluated the oriented versus the random covalent immobilisation method of the Fab' fragments. First, an optimisation of cleavage protocol to generate these F(ab')2 and Fab' fragments was performed. Subsequently, we pursued a study with limited denaturation effects during immobilisation of the bioreceptor molecules and with reduced steric hindrance during antigen binding using mixed self-assembled monolayers (SAM) of thiols as the chemical linking layer. The Surface Plasmon Resonance technique was used to evaluate the degree of immobilisation of the antibody fragments and their parental IgGs on the mixed SAMs and the binding signals of their specific antigens. In this study, we demonstrate that for a particular antibody/antigen system (anti-hIgG/hIgG), the optimised fragmentation protocol in combination with an oriented immobilisation of Fab' fragments on mixed SAMs leads to a >2-fold increase of the antigen binding signals compared to randomly covalent immobilised full-length antibodies.status: publishe