Direct electrochemical detection of purine- and pyrimidine-based nucleotides with sinusoidal voltammetry

Sinusoidal voltammetry was employed to detect both purine- and pyrimidine-based nucleic acids. Adenine and cytosine, representing these two classes of nucleic acids, could be measured with submicromolar detection limits at a copper electrode under these conditions, where the sensitivity for adenine was much higher than that for cytosine. Detection limits for purine-containing nucleotides [e.g., adenosine 5'-monophosphate (AMP), adenosine 5'-diphosphate (ADP), and adenosine 5'-triphosphate (ATP)] were on the order of 70-200 nM using this method. These detection limits are achieved for native nucleotides and are over 2 orders of magnitude lower than those found with UV absorbance detection. Submicromolar detection limits were also obtained for pyrimidine-based nucleotides, which could also be detected with high sensitivity due to the presence of a sugar backbone that is electroactive at the copper surface. This detector is not fouled by the nucleotides and may be used for the sensitive detection of analytes eluting continuously in a flowing stream, i.e., from a chromatography column or an electrophoresis capillary.     

Study of electropolymerised polyaniline films using cyclic voltammetry, atomic force microscopy and optical spectroscopy

Electropolymerisation of polyaniline (PANI) has been investigated using cyclic voltammetry in aqueous bath. The effect of dopant on the structure, morphology & optical properties of electrodeposited PANI has also been studied using x-ray diffraction (XRD), atomic force microscopy (AFM), optical absorbance & luminescence spectroscopy. It is shown that the presence of a neutral salt (KI) in the deposition matrix imparts enhanced crystallinity to PANI films.     

Direct laser writing of surface reliefs in dry, self-developing photopolymer films

Fabrication of surface reliefs is achieved by raster scanning dry photopolymer films under a focused laser beam. The formation of the structure takes place subsequent to illumination without any chemical treatment or wet processing. Computer-generated optical elements can be recorded quickly, easily, and at low cost. The technology is particularly well suited for rapid prototyping and design purposes. These photopolymer films have potential in photonics applications, such as diffractive optical elements and waveguide structures.     

Fabrication, characterization, and enzymatic activity of encapsulated fungal protease--fatty lipid biocomposite films

Encapsulation of an aspartic protease from the fungus Aspergillus saitoi (F-prot) in thermally evaporated fatty acid films by a simple beaker-based immersion technique under enzyme-friendly conditions is described. The approach is based on diffusion of the enzyme from aqueous solution, driven primarily by attractive electrostatic interaction between charged groups on the enzyme surface and ionized lipid molecules in the film. The encapsulated enzyme molecules could be "pumped out" of the biocomposite film into solution by modulating the electrostatic interaction between the enzyme and fatty acid molecules via solution pH variation. The kinetics of F-prot diffusion into the acid films was followed using quartz crystal microgravimetry measurements while the secondary and tertiary structure of the enzyme in the lipid matrix was studied using Fourier transform infrared (FT-IR) and fluorescence spectroscopies. FT-IR and fluorescence measurements indicated little perturbation to the native structure of the enzyme. A chemical analysis of the F-prot-fatty acid biocomposite film was also performed using X-ray photoelectron spectroscopy. The encapsulated F-prot molecules showed catalytic activity (as estimated by reaction with hemoglobin) comparable to free enzyme molecules in solution, indicating facile access of biological analytes/reactants in solution to the enzyme molecules. The advantages/disadvantages of this approach vis-à-vis methods currently used for encapsulation of biomolecules are briefly discussed.     

Direct observations of the magnetic structure in thin films of Pb,Sn, and In

Direct, high-resolution observations of magnetic structures in evaporated films of the type I superconductors lead, tin, and indium are presented for a range of applied fields. The films are polycrystalline and range in thickness from 200 to 20,000 Å. the transition from the intermediate state to the mixed state is observed. The observation of the single-fluxoid vortex mixed state in the thin films with Ginzburg-Landau parameter κ less than \(1/\sqrt 2\) confirms theoretical prediction by Tinkham, Maki, and Lasher. No ordered array of vortices is observed and this is shown to be caused by the effects of the grain boundaries on the magnetic structures.     

Dynamics and performance of fast linear scan anodic stripping voltammetry of cd, pb, and cu using in situ-generated ultrathin mercury films

The dynamics of fast linear scan (LS) ASV for the simultaneous detection of Cd, Pb, and Cu was investigated at various scan rates (0.5-10 V/s) and at different metal ion concentrations (50-800 nM) utilizing ultrathin mercury films (9 nm) at a conventional size (d(0) = 1 mm) electrode. Results of the investigation show that when the thin films were utilized, diffusion of metals through the mercury film was not the rate-limiting step of the stripping process at moderate to fast scan rates (0.5-10 V/s). A fairly linear relationship between the peak height and scan rate was observed at scan rates (0.5-10 V/s) beyond the upper limit of the theoretical model for the behavior of LS-ASV. In addition, peak width at half-height (b(1/2)) as low as 33 mV was achieved at 0.5 V/s. The behavior of LS-ASV in terms of peak width at these scan rates is thus different from what the theoretical model of LS-ASV would have predicted. For the ultrathin mercury films, at least two additional factors, kinetics and concentration, have significant effects on practical LS-ASV. Experimental results show that the stripping process of Cu was primarily kinetic-controlled for fast scans, while those for Cd and Pb were dependent on both scan rates and concentrations. The ultrathin mercury film resulted in a significant enhancement of the ratio of signal-to-baseline slope (i(p)/Δi(b), a ratio used to measure the effectiveness of discrimination of the peak signal against the steep sloping baseline in LS-ASV) for Cd and Pb stripping peaks, but only a slight enhancement for Cu stripping peaks. The optimal performance of LS-ASV in terms of sensitivity, peak width, and enhancement of the i(p)/Δi(b) ratio for the three metals was achieved at 2 V/s. Because of the high reproducibility of the background currents of the stable in situ MTFs, background subtraction was carried out at 2 V/s with little hysteresis. This feature, combined with the enhancement of the i(p)/Δi(b) ratio at the fast scan rate of 2 V/s, allowed for the detection of sub-ppb levels of Cd, Pb, and Cu at a deposition time of 2 min.     

Formulation,optimization, and characterization of rifampicin-loaded solid lipid nanoparticles for the treatment of tuberculosis

Abstract

Mycobacterium tuberculosis, being the causative infectious agent, is the leading cause of death worldwide amongst the infectious disease. The low bioavailability of rifampicin (RIF), one of the vital constituent of antitubercular therapy, instigates an urge to develop nanocarrier, which can prevent its degradation in the acidic pH of the stomach. Solid lipid nanoparticles (SLNs) have been proven to be promising versatile platform for oral delivery of lipophilic drugs. Therefore, the current investigation demonstrates development of RIF-loaded solid lipid nanoparticles (RIF-SLNs) using high-pressure homogenization technique by employing a three-level, three-factor Box–Behnken design. Concentration of drug, concentration of emulsifier, and homogenization pressure were selected as an independent variables, and %drug loading (%DL), %entrapment efficiency (%EE), and particle size were selected as dependent variables. The developed RIF-SLNs were characterized for particle size, polydispersity index, zeta potential, %EE, %DL, differential scanning calorimetry, X-ray diffraction, and TEM analysis. The mean diameter of RIF-SLNs was found to be 456?±?11?nm, %EE of 84.12?±?2.78%, and %DL of 15.68?±?1.52%. The in vitro lipolysis experiments revealed that RIF-SLNs stabilized using poloxamer 188, exhibited antilipolytic effect. Furthermore, the in vitro GI stability studies (at pH 1.2, pH 4.5, pH 6.8, and pH 7.4) revealed that the developed system could withstand various gastrointestinal tract media. The in vitro dissolution studies depicted biphasic drug release profile for drug-loaded SLNs revealing best fit with Weibull model. The accelerated stability studies for 6?months does not revealed any significant change in characteristics of developed RIF-SLNs.     

Model studies in catalysis with uhv-deposited metal particles and clusters

The motivation for extending well-controlled surface and microstructural studies of model catalytic systems into the regime of small metal particles and clusters is discussed. The possibility of accomplishing this successfully at the present time is related to the availability of proven uhv techniques for the deposition and characterization of thin film deposits; the deposits in this case being either continuous supporting substrates or discrete metallic particles ranging in size to less than 10 Å. A review of the known physical properties of small metal aggregates is given relating their thermodynamic, morphological, crystallographic, and electronic properties to size, support, and gaseous environment. Whenever possible, the chemical properties of supported small particles and clusters are correlated with their observed physical characteristics although it is often extremely difficult to separate intrinsic size and electronic effects from support-induced surface compositional changes. Metal/support interactions (MSI) in vacuum and in different gaseous environments are considered and are related to catalyst preparation and sintering processes. A general experimental concept for studies with evaporated model catalysts is discussed and demonstrated with several instrumental approaches. It consists of effectively combining microstructural techniques of high spatial resolution (TEM) with large-area surface-analytical methods of high detection sensitivity. In conclusion, some key research areas are identified where model studies with thin film systems would seem most promising.     

Determination of trace iodine in food and biological samples by cathodic stripping voltammetry.

This paper describes a sensitive and selective method for the determination of iodine in food and biological samples. The method involves treatment of samples by combustion in an oxygen flask and determination of iodide by cathodic stripping voltammetry of the solid phase formed with the quaternary ammonium salt Zephiramine as the ionic associating agent; Br- is used as the complexing agent in the preconcentration process. We have studied the effect of concentration of Zephiramine, Br-, I-, and some other elements presented, deposition potential, preelectrolysis time, and scan rate, on the stripping curve shape and maximum stripping current. Determinations of trace iodine in table salt, laver, and eggs were demonstrated as practical examples.     

Direct current electric field adjustable phase transformation behavior in (Pb,La)(Zr,Ti)O3 antiferroelectric thick films

(Pb,La)(Zr,Ti)O₃ antiferroelectric 1.4 μm-thick films have been prepared on Pt (111)/Ti/SiO₂/Si(100) substrates by sol–gel process. The structures and dielectric properties of the antiferroelectric thick films were investigated. The films displayed pure perovskite structure with (100)-preferred orientation. The surface of the films was smooth, compact and uniform. The antiferroelectric (AFE) characterization have been demonstrated by P (polarization)-E (electric field) and C(capacitance)-V (DC bias) curves. The AFE–ferroelectric (FE) and FE-to-paraelectric (PE) phase transition were also investigated as coupling functions of temperature and direct current electric field. With the applied field increased, the temperature of AFE-to-FE phase transition decreased and the FE-to-PE phase shifted to high temperature. The AFE-to-FE phase transition was adjustable by direct current electric field. (Pb,La) (Zr,Ti) O₃ antiferroelectric films have broad application prospects in microelectromechanical systems because of the phase transition.     

Protein dynamics in iron-starved Mycobacterium tuberculosis revealed by turnover and abundance measurement using hybrid-linear ion trap-Fourier transform mass spectrometry

To study the proteome response of Mycobacterium tuberculosis H37Rv to a change in iron level, iron-starved late-log-phase cells were diluted in fresh low- and high-iron media containing [ (15)N]-labeled asparagine as the sole nitrogen source for labeling the proteins synthesized upon dilution. We determined the relative protein abundance and protein turnover in M. tuberculosis H37Rv under these two conditions. For measurements, we used a high-resolution hybrid-linear ion trap-Fourier transform mass spectrometer coupled with nanoliquid chromatography separation. While relative protein abundance analysis shows that only 5 proteins were upregulated by high iron, 24 proteins had elevated protein turnover for the cells in the high-iron medium. This suggests that protein turnover is a sensitive parameter to assess the proteome dynamics. Cluster analysis was used to explore the interconnection of protein abundance and turnover, revealing coordination of the cellular processes of protein synthesis, degradation, and secretion that determine the abundance and allocation of a protein in the cytosol and the extracellular matrix of the cells. Further potential utility of the approach is discussed.     

Simultaneous determination and speciation of zinc, cadmium, lead, and copper in natural water with minimum handling and artifacts, by voltammetry on a gel-integrated microelectrode array

The paper reports a new approach based on a gel-integrated Hg-plated-Ir-based microelectrode array (GIME), for measuring Cu, Pb, Cd, and Zn speciation in natural waters. This paper focuses on the quantitative discrimination between mobile and colloidal metal species (size limit of a few nanometers), for which most classical separation techniques present severe drawbacks. Previous papers have shown qualitatively that GIME combined with square wave anodic stripping voltammetry (SWASV) has the basic characteristics required to discriminate between these two fractions directly on the unperturbed sample. In addition, because of the large sensitivity provided by GIME, complexation parameters (equilibrium constants and site concentrations) can be determined in little-perturbed samples, particularly without metal addition or with small addition compared with natural concentrations. The advantages of this procedure are exemplified and the possible artifacts occurring when titrating the sample with metals, in particular intermetallic compound formation and other problems, are discussed in detail. The present paper shows that the characteristics of GIME make it a unique tool to get quantitative information on metal speciation at nanomolar or even subnanomolar levels, with only minor sample handling.