Lateral flow immunochromatographic assay for sensitive pesticide detection by using Fe3O4 nanoparticle aggregates as color reagents

Magnetic Fe(3)O(4) particle aggregates were prepared by cross-linking Fe(3)O(4) nanoparticles bearing surface carbonyl groups with poly-L-lysine. Upon further coupling with antiparaoxon methyl polyclonal antibody, the resultant particle aggregate-based probes were used in a lateral flow immunochromatographic assay (LFIA) of pesticide residue of paraoxon methyl. The results were compared with that achieved by using the mother Fe(3)O(4) nanoparticles. More quantitative results on the signal amplification effect endowed by the controlled aggregation of Fe(3)O(4) nanoparticles were extracted by relative optical density analysis. Under optimized conditions, a detection limit of 1.7 ng/mL for paraoxon methyl was achieved by using the particle aggregates, which is almost 40-fold lower than that based on the mother Fe(3)O(4) nanoparticles.     

Relationship of Surface Area of pH-Dependent Suspensions and Water Retention

The equilibrium water retention, M_W/M_S, of suspensions having a pH-dependent surface charge (carbonate-containing aluminum hydroxide and fumed silica) appears to be due to water adsorbed by the surface as well as water retained in pores. The water retained in pores has a lower limit determined by the closest packing porosity. Maximal water retention occurred when the pH was equal to the point of zero charge and attractive particle interactions predominated. The contribution of pore water to M_W/M_S can be minimized by selecting a pH significantly different from the point of zero charge. The water retention properties of the suspension under these conditions are believed to be due to adsorption and the closest packing porosity. Preliminary results indicate that this M_W/M_S can be related to the surface area of the suspended solid.     

Control of flow direction in microfluidic devices with polyelectrolyte multilayers

Electroosmotic flow (EOF) is commonly utilized in microfluidics. Because the direction of the EOF can be determined by the substrate surface charge, control of the surface chemical state offers the potential, in addition to voltage control, to direct the flow in microfluidic devices. We report the use of polyelectrolyte multilayers (PEMs) to alter the surface charge and control the direction of flow in polystyrene and acrylic microfluidic devices. Relatively complex flow patterns with simple arrangements of applied voltages are realized by derivatization of different arms of a single device with oppositely charged polyelectrolytes. In addition, flow in opposite directions in the same channel is possible. A positively derivatized plastic substrate with a negatively charged lid was used to achieve top-bottom opposite flows. Derivatization of the two sides of a plastic microchannel with oppositely charged polyelectrolytes was used to achieve side-by-side opposite flows. The flow is characterized using fluorescence imaging and particle velocimetry.     

Relationship of Surface Area of pH-Dependent Suspensions and Water Retention

Abstract

The equilibrium water retention, M_W/M_S, of suspensions having a pH-dependent surface charge (carbonate-containing aluminum hydroxide and fumed silica) appears to be due to water adsorbed by the surface as well as water retained in pores. The water retained in pores has a lower limit determined by the closest packing porosity. Maximal water retention occurred when the pH was equal to the point of zero charge and attractive particle interactions predominated. The contribution of pore water to M_W/M_S can be minimized by selecting a pH significantly different from the point of zero charge. The water retention properties of the suspension under these conditions are believed to be due to adsorption and the closest packing porosity. Preliminary results indicate that this M_W/M_S can be related to the surface area of the suspended solid.     

Nanoparticle syntheses using non-porous and porous polyelectrolyte multilayers for biological applications

Polyelectrolyte multilayers comprised of poly(allylamine hydrochloride) and poly(acrylic acid) were assembled by layer-by-layer technique for metal nanoparticle syntheses. Using weak polyelectrolytes in LbL process, it is readily available to tune the deposited film properties by simple changing of the dipping solution pH. The PAH/PAA multilayer systems exhibit different surface morphologies and functionalities depending on the assembly conditions. We have studied two distinctive PAH/PAA multilayer films to utilize them for nanoparticle synthesis. The reactive functional groups of the polyelectrolytes within the films were remained after the film deposition or reactivated by a simple pH stimulus, and therefore they were allowed to undergo further chemical reactions to synthesize Pd and Au nanoparticles. Synthesized metal nanoparticles were easily characterized by their optical properties including surface plasmon absorption. These metal nanoparticle-embedded multilayers may have great potentials for biomolecule sensing or catalytically active coatings.     

The influence of polymer architecture on nanosized hydroxyapatite precipitation

In this work we present a facile way to produce hydroxyapatite (HAP) nanoparticles by wet chemical synthesis in the presence of polyelectrolytes under controlled temperature, pH, and atmospheric conditions. The resulting calcium rich carbonated HAP is sintered in an air atmosphere to investigate the thermal stability of the synthesized powders. The morphology and microstructure of the HAP nanoparticles were investigated by XRD, SEM, FTIR spectroscopy, thermal analysis, and particle size analyzer. Polyelectrolytes affect the coherent length of the crystalline domain, the dimension and particle size distribution of the crystals. The reduction in size is greater in the direction of the c-axis. The SEM micrograph shows the formation of well-crystallized, agglomerated small particles of HAP. The mean size of the subunit is smaller than that of the surface of the grain observed in SEM. X-ray analysis have shown that the resulting particles have high thermal stability.     

Coagulation of wood extractives in chemical pulp bleaching filtrate by cationic polyelectrolytes

The purpose of this research was to investigate the effectiveness of short-chain cationic polyelectrolytes of different molecular weights and charge densities in reducing turbidity and selectively removing toxic wood extractives from chemical birch pulp filtrate. The effects of chemical type, dosage and temperature were of interest. An effective performance was achieved with a copolymer of acrylamide and methacrylate of medium molecular weight and medium charge density at 72 degrees C and pH 5-6. The dosage range optimum for reducing the turbidity was 102-142 mg/L. Up to 92% of the wood extractives was selectively removed.     

Conjugated Polyelectrolytes Bearing Various Ion Densities: Spontaneous Dipole Generation,Poling‐Induced Dipole Alignment,and Interfacial Energy Barrier Control for Optoelectronic Device Applications

Conjugated polyelectrolytes (CPEs) with π‐delocalized main backbones and ionic pendant groups are intensively studied as interfacial layers for efficient polymer‐based optoelectronic devices (POEDs) because they facilitate facile control of charge injection/extraction barriers. Here, a simple and effective method of performing precise interfacial energy level adjustment is presented by employing CPEs with different thicknesses and various ion densities under electric poling to realize efficient charge injection/extraction of POEDs. The effects of the CPE ion densities and electric (positive or negative) poling on the energy level tuning process are investigated by measuring the open‐circuit voltages and current densities of devices with the structure indium tin oxide/zinc oxide/CPE/organic active layer/molybdenum oxide/gold while changing the CPE film thickness. The performances of inverted polymer light‐emitting diodes and inverted polymer solar cells are remarkably improved by precisely controlling the interfacial energy level matching using optimum CPE conditions.     

Synthesis and characterization of heterogeneous ZnO/CuO hierarchical nanostructures for photocatalytic degradation of organic pollutant

In the current study, ZnO, CuO and ZnO/CuO mixed metal oxide nano-composites with different molar ratio of Zn/Cu (10:1, 8:1, 6:1, 4:1, 2:1) were prepared via low temperature hydrothermal synthesis technique. The consequences of different synthesis conditions such as molar ratio, pH and processing temperature on physicochemical properties of ZnO/CuO nano-composites were also studied. The surface morphology, elemental composition, crystal structure, chemical states and optical characteristics of the prepared nano-composite materials were determined using various techniques such as field emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDX), X-ray diffraction analysis (XRD), X-ray photo-electron spectroscopy (XPS) and UV–visible diffused reflectance spectra (UVDRS). A morphological change in bitter gourd structured ZnO as well as improved optical response of ZnO after incorporation of CuO was observed. The decreased recombination rate of charge carriers, effectual generation of photoinduced charge carriers, formation of hetero-junction system and unique morphology are the responsible factors for improved photodegradation characteristics of prepared ZnO/CuO nano-composites. Role of active species and pH of dye solution in degradation process was also studied.     

Synthesis and characterization of ZnO nanostructures with varying morphology

Uniform fine particles of zinc oxide were prepared in three different morphologies and sizes by the controlled precipitation process from aqueous solutions of zinc nitrate in the presence of ethylene glycol. Ammonium hydroxide solution was used as the precipitant. Composition of the reactant solution, pH and temperature significantly affected the particle uniformity with respect to shape and size. Uniformity in the particles morphological feature was achieved under a narrow set of experimental conditions. pH of the reactant solutions and isoelectric point of zinc oxide were considered the master variables, controlling the particle size. One of the batch of the as-prepared zinc oxide particles was calcined at \(750{^{\circ }}\hbox {C}\), which increased its crystallinity, changed its various lattice parameters, Zn–O bond length and preferred orientation of the crystal hkl planes. Calcination had little effect on the original morphology of the zinc oxide particles.     

Determination of Particle Size Distribution of Zirconium Dioxide Powders by Static Laser Scattering and Optical Microscopy

Dispersing conditions of powdered zirconium dioxide with addition of 3 mol % yttrium oxide are determined. The particle size distribution of the powders is determined by static laser scattering and optical microscopy. The zeta potential of suspension of zirconium dioxide particles as a function of pH of medium is measured by electrophoresis with titration. The influence of acidity on suspension stability during measurements is studied. It is demonstrated that a stable suspension can be obtained by shift of pH to both the acid and alkaline regions as well as by addition of surfactants, such as Dolapix CE 64.     

Particulate structures produced by electrosprays of colloidal silica suspensions in both negative and positive zeta potentials

Interaction between surface charge (zeta potential) of colloidal silica nanoparticles and the charge-induced droplets suspended in the gas phase by electrospray is investigated for the first time based on the particle physical (morphology, size, and size distribution) and optical properties. Colloidal silica nanoparticles having negative and positive zeta potential were subjected to electrospray in both negative and positive mode, and deposited on a substrate (silicon wafer). Visual observation of the substrate with particle deposition shows various white shades, corresponding to the changes in optical properties, as supported by the ultraviolet-visible–near-infrared spectroscopy. Microscopic analysis revealed the strong correlation between the colloid surface charge and charging mode (positive or negative) of the sprayed droplets to the particle morphology and size. The findings of the present study demonstrate the capability of the electrospray method to tune the physical and optical properties of colloidal silica nanoparticles with different surface charges.     

Silica alcogels for possible nuclear waste confinement — A simulated study

A new method for possible incorporation of nuclear wastes has been attempted here by using silica alcogels as a host precursor for confinement. The large pore volume of the silica alcogel is used as a sponge to incorporate chemical species. Neodymium nitrate is used as a simulant for high level waste. The alcogels have been immersed in 5, 10, 20 and 30% neodymium nitrate solution and the resulting alcogels are dried under controlled conditions at 70 °C. The bulk density of the gels increases on absorption of neodymium nitrate. The BET analysis shows a decrease in surface area and total pore volume as the percentage of neodymium nitrate is increased. On sintering the gels at 1200 °C neodymium was confined which was confirmed by negative leachability. The percentage of loading has been found out by calculating the difference in weight of the neodymium incorporated gel before and after incorporation of neodymium. XRD studies of the sintered samples reveal the formation of neodymium silicates.     

Microstructuring of polyelectrolyte coated surfaces for directing capsule adhesion

We use microcontact printing (/spl mu/CP) of polyelectrolytes (PEs) onto flat substrates for creating surfaces with regions of negative and positive surface charge. Subsequent incubation of these surfaces with solutions containing hollow PE capsules leads to preferential adsorption of the capsules on regions of opposite charge, while regions of like charge are passivated against adhesion. As well, adsorption of fluorescently labeled PEs is found to be directed toward oppositely charged regions at neutral pH. This approach could lead to novel functional surfaces for combinatorial chemistry or sensor applications and could also be expanded toward cell immobilization.     

Factorial electrochemical design for tailoring of morphological and optical properties of Cu2O

The electrodeposition of cuprous oxide (Cu₂O) onto FTO-coated glass substrate was studied by using a statistical approach in order to control the Cu₂O morphology and optical properties. The factorial design considered four electrodeposition conditions at two representative levels as input variables (electrolyte temperature and pH, deposition potential and duration) and the deposition charge and morphology of obtained Cu₂O as the output variables. The morphology analysis showed the highest influence on crystal shape was exhibited by electrolyte temperature and pH, reaching significance levels of 95 and 98%, respectively. Temperature as low as 35°C and pH 12.2 results in cubic morphology, while other parameters result in octahedron shape. The highest absorbance was exhibited by the Cu₂O with cubic morphology.     

Study of nickel passivation in a borate medium

The adsorption of borate ions at the nickel and/or nickel oxide-electrolyte electrochemical interface was studied at various concentrations and pH values in lithium and borate solutions. First, the passivation range of nickel was estimated using cyclic voltammetry. The nickel passive layer formation kinetics (transfer resistance, capacitance of passive film formed, adsorption capacitance), as well as the semiconducting properties of this oxide layer, were studied using electrochemical impedance spectroscopy (E.I.S.). These electrochemical techniques were used in conjunction with adsorption measurements performed with an electrochemical quartz crystal microbalance (E.Q.C.M.) and with surface analyses (Auger spectroscopy). The nickel oxide showed type p semiconducting properties and was depleted at, corrosion potential. Moreover, very little borate adsorption was observed during the different tests. This may have been the result of the negative surface charge, in the pH and potential conditions applied.     

Investigation on Stability and Optical Properties of Titanium Dioxide and Aluminum Oxide Water-Based Nanofluids

Water is regarded as a poor absorber of solar energy. This affects the efficiency of solar thermal systems. The addition of nanoparticles to heat transfer fluids used in solar thermal systems can enhance their optical properties. These new-generation heat transfer fluids are known as nanofluids. The present study investigates the stability and optical properties of three nanofluids, including aluminum oxide (13 nm and <50 nm) and titanium dioxide (21 nm) nanofluids. The stability of the nanofluids was observed through a photo-capturing method and zeta potential measurements. Ultraviolet–visible (UV–Vis) spectrophotometer was used to measure the absorbance and transmittance of the prepared nanofluids. The effect of factors such as type of particle, type of surfactant, and pH of the solution on the optical properties of the nanofluids was also investigated. We found that the titanium dioxide nanofluid had better optical properties but lower stability compared to aluminum oxide nanofluids.     

Experimental factors controlling analyte ion generation in laser desorption/ionization mass spectrometry on porous silicon

Desorption/ionization on porous silicon (DIOS) is a relatively new laser desorption/ionization technique for the direct mass spectrometric analysis of a wide variety of samples without the requirement of a matrix. Porous silicon substrates were fabricated using the recently developed nonelectrochemical H2O2-metal-HF etching as a versatile platform for investigating the effects of morphology and physical properties of porous silicon on DIOS-MS performance. In addition, laser wavelength, mode of ion detection, pH, and solvent contributions to the desorption/ionization process were studied. Other porous substrates such as GaAs and GaN, with similar surface characteristics but differing in thermal and optical properties from porous silicon, allowed the roles of surface area, optical absorption, and thermal conductivities in the desorption/ionization process to be investigated. Among the porous semiconductors studied, only porous silicon has the combination of large surface area, optical absorption, and thermal conductivity required for efficient analyte ion generation under the conditions studied. In addition to these substrate-related factors, surface wetting, determined by the interaction of deposition solvent with the surface, and charge state of the peptide were found to be important in determining ion generation efficiency.     

聚丙烯酸对水基磁流变液稳定性的改良

以羰基铁粉为悬浮介质、水为分散介质的悬浮液中加入聚丙烯酸(PAA),分别测量不同条件下悬浮液的电泳淌度及吸光度随时间的变化.结果表明,磁性颗粒对聚丙烯酸分子的吸附,增加了其表面电势,颗粒之间的静电斥力阻碍了团聚的发生,提高了体系的抗团聚、抗沉降稳定性.同时也研究了pH值及PAA浓度对悬浮液稳定性的影响.