Interaction of lectin Sambucus nigra with sialylated trisaccharides in the presence of osmolytes. Chronopotentiometric sensing.

Trisaccharides bind to their interaction partners-lectins relatively weakly, which makes detection of their complexes challenging. In this work, we show that an osmolyte presence improves the distinguishing complexes of lectin Sambucus nigra with trisialyllactoses with various binding affinities. The addition of osmolyte, non-binding sugar mannose significantly improved the precision of binding experiments performed using chronopotentiometric stripping at the electrode surface and fluorescence analysis in solution. Osmolytes minimized nonspecific interactions between binding sugar and lectin. Obtained findings can be utilized in any in vitro methods studying interactions of carbohydrates, respectively their conjugates with proteins. The study of carbohydrate interactions appears important since they play essential roles in a variety of biological processes including carcinogenesis.

Optical analysis of adsorption sensitivity of titanium, Ti-6Al-4V, and Ti-35Nb-6Ta.

Here we report the optical analysis of protein adsorption sensitivity of titanium (Ti), Ti(6)Al(4)V, and Ti(35)Nb(6)Ta. The optical sensor used was a diffractive optical element based sensor, which analyzes magnitude and coherence of probe beam reflected from the measured surfaces. Also, the roughness and other necessary parameters were taken into account on the final verdict. The material Ti(35)Nb(6)Ta showed positive initial reaction to the human plasma fibrinogen, which was the protein used. The Ti(35)Nb(6)Ta was observed to be more active than the grade 2 titanium.

Diffractive-optics-based sensor as a tool for detection of biocompatibility of titanium and titanium-doped hydrocarbon samples.

Adsorption of the elongated human plasma fibrinogen (HPF) and globular human serum albumin molecules on a titanium-based surface is monitored by analyzing permittivity and optical roughness of protein-modified surfaces by using a diffractive optical element (DOE)-based sensor and variable angle spectro-ellipsometry (VASE). Both DOE and VASE confirmed that fibrinogen forms a thicker and more packed surface adlayer compared to a more porous and weakly adsorbed albumin adlayer. A linear relation of the permittivity (ε(')) and dielectric loss (ε('')) was found for some of the dry titanium-doped hydrocarbon (TDHC) surfaces with excellent HPF adsorption ability. We discuss some aspects of TDHC's aging and its possible effects on fibrinogen adsorption.

Simultaneous electrochemical monitoring of metabolites related to the xanthine oxidase pathway using a grinded carbon electrode.

Using a mechanically grinded pyrolytic graphite electrode in edge orientation, a sensitive electrochemical method was developed for simultaneous determination of uric acid (UA), xanthine (XAN), hypoxanthine (HYP) (products of purine catabolism in human), allopurinol (ALO), and oxypurinol (OXY) (a drug used in treatment of purine catabolism disorders and its metabolite, respectively). It is demonstrated that differential pulse voltammetry in connection with this electrode can serve as a simple and efficient tool for monitoring transformation of purine catabolites (HYP --> XAN --> UA) catalyzed by xanthine oxidase (XO) as well as inhibition of this pathway by ALO being enzymatically converted to OXY. Our protocol is based on direct electrochemical measurement of oxidation peaks for each of the substances during in vitro reactions in a single detection step by the same electrode system. In addition, we show that the proposed electrochemical technique can be applied to parallel detection of metabolites involved in the XO pathway excreted in urine without any pretreatment of the clinical samples.

Sensing of human plasma fibrinogen on polished, chemically etched and carbon treated titanium surfaces by diffractive optical element based sensor.

Adsorption of human plasma fibrinogen (HPF) on 6 differently treated titanium samples (polished, polished and etched, and 4 titanium carbide coatings samples produced by using plasma-enhanced chemical vapour deposition (PECVD) method) is investigated by using diffractive optical element (DOE) sensor. Permittivity (susceptibility) change and fluctuation in optical roughness (R(opt)) of treated titanium surface in the presence of background electrolyte without and with HPF molecules are sensed by using DOE sensor and optical ellipsometry. Correlation between transmitted light and thickness of molecule layer was found. The findings allow to sense temporal organization and severity of adsorption of nano-scale HPF molecules on polished, on polished and etched, and on titanium carbide surface.

Two-dimensional condensation of nucleic acid components at mercury film and gold electrodes.

The adsorption of cytidine at the mercury film electrodes and at the Au (111) single crystal electrode has been investigated. Some kinetic aspects such as the influence of pH and temperature on the formation or dissolution of cytidine adlayer on the pyrolytic graphite electrode covered by a mercury film or on the Au (111) have been studied.

On the formation kinetics of two-dimensional cytidine films.

The kinetics of phase transitions of cytidine adsorbed on mercury are studied by chronoamperometry and capacitance measurements. Cytidine forms highly ordered two-dimensional adlayers in a broad range of pH. In acid solvent, only one kind of condensed layer is formed. In the alkaline solution, cytidine forms two different two-dimensional (2D) adlayers. The minimum capacitance value in adlayer II at pH 5 is 7.0 microF cm(-2) and, at pH 8.3, it is 5.1 microF cm(-2); in adlayer III, the minimum capacitance is 10.6 microF cm(-2). The formation of a physisorbed film of cytidine molecules adsorbed at the mercury surface proceeds by complex mechanisms. From j-t transients, it can be seen that the phase transformations from dilute adlayer Ia to condensed physisorbed film II is accompanied by the reorientation of cytidine molecules at the mercury surface (inverted current transient). The interfacial transformations of the cytidine film yield a sigmoidal C-t transient. This experimentally measured C-t transient were analysed by Avrami theorem. The rate of the transformations from dilute adlayer Ia to condensed film II of cytidine at pH 5 depends strongly on temperature but is only slightly affected by temperature at pH 8.3. The effect of pH and ionic composition of the supporting electrolyte on the rate of transformation of cytidine films was studied as well.

Application of thin film mercury electrodes and solid amalgam electrodes in electrochemical analysis of the nucleic acids components: detection of the two-dimensional phase transients of adenosine.

The optical diffractive (DOE)-based sensor was used to the study of the optical roughness of different carbon/graphite electrodes modified by mercury film (MFEs) and solid amalgam-alloy electrodes (S-MeAEs). The electrode surfaces were visualised by an optical metallurgical microscope. The adsorption of adenosine at the MFEs and S-MeAEs has been investigated by capacitance measurement. Some kinetics aspects, such as the influence of the surface morphology, nature of the substrate and thickness of the mercury film and amalgam-alloy on the formation of two-dimensional (2D) physisorbed adenosine adlayer on the MFEs and S-MeAEs, were studied.

Label-free sequence-specific DNA sensing using copper-enhanced anodic stripping of purine bases at boron-doped diamond electrodes.

Stripping voltammetric determination of purine bases in the presence of copper ions at mercury, amalgam, or carbon-based electrodes has recently been utilized in analysis of DNA or synthetic oligodeoxynucleotides (ODNs). Here we report on copper-enhanced label-free anodic stripping detection of guanine and adenine bases in acid-hydrolyzed DNA at anodically oxidized boron-doped diamond electrode (AO-BDDE). The AO-BDDE was successfully applied in a three-electrode microcell in which an approximately 50 microL drop of the analyte solution can be efficiently stirred during the accumulation step by streaming of an inert gas. Accelerated mass transport due to the solution motion in the presence of copper resulted in enhancement of the guanine oxidation signal by about 2 orders of magnitude (compared to accumulation of the analyte from still solution not containing copper), allowing an easy detection of approximately 25 fmol of the ODNs. The proposed technique is shown to be suitable for a determination of purine (particularly guanine) content in DNA samples. Applications of the technique in magnetic bead-based DNA assays (such as hybridization with DNA sequences exhibiting asymmetrical distribution of purine/pyrimidine nucleotides between the complementary strands or monitoring of amplification of specific DNA fragments in a duplex polymerase chain reaction) are demonstrated.

Amplified oligonucleotide sensing in microliter volumes containing copper ions by solution streaming.

We present a simple, cost-effective design for amplifying oligodeoxynucleotide (ODN) sensing, in microliter ODN volumes containing copper ions, by solution streaming (bubbling). The inert gas streaming (bubbling) at a constant pressure of 0.04 bar drives the motion of a 30-microL ODN droplet containing a three-electrode circuit (inverted drop microcell), and in the presence of copper ions offers an approximately 50-times improvement in the detection of ODN samples. The detection of ODNs at the carbon paste electrode is based on the enhancement of the oxidation peaks of purine bases (adenine and guanine) by the anodic stripping of the electrochemically accumulated complex of Cu(I) with purine base residues of acid hydrolyzed ODN samples (Cu(I)-ahODN complex). We used the proposed method for (i) the determination of the percentage content of adenine and guanine units within analyzed ODN samples at subnanomolar concentrations (related to monomer content) and (ii) the detection of the (TTC)n triplet expansion using magnetic DNA hybridization with reporter probes containing guanine units (the TTC trinucleotide repeat expansion is associated with serious hereditary diseases, including Friedreich ataxia).

Microanalysis of oligodeoxynucleotides by cathodic stripping voltammetry at amalgam-alloy surfaces in the presence of copper ions.

The application of gold amalgam-alloy electrode (AuAE) for a sensitive voltammetric detection of different oligodeoxynucleotides (ODNs) containing the purine units within the ODN-chains in the presence of copper is described. The detection of ODNs is based on the following procedure: (i) the first step includes an acidic hydrolysis of the ODN (ahODN) samples performing the release of the purine bases from ODN-chain; (ii) the second step includes an electrochemical accumulation of the complex of the purine base residues released from ODN-chain with copper ions Cu(I) (ahODN-Cu(I) complex) at the potential of reduction of copper ions Cu(II) on the amalgam-alloy electrode surfaces; (iii) finally followed the cathodic stripping of the electrochemically accumulated ahODN-Cu(I) complex from the electrode surface. The proposed electrochemical method was used for: (a) detection of different ODN lengths containing only adenine units (the number of adenine units within the ODN-chains was changed from 10 to 80), and (b) determination of the number of purine units within the 30-mer ODNs containing a random sequence segments involving both the purine and pyrimidine units. The intensity of the cathodic stripping current density peak (j(CSP)) of the electrochemically accumulated ahODN-Cu(I) complex increased linearly with the increasing number of purine units within the ODN-chains. We observed a good correlation between the percentage content of purine units to the whole length of different 30-mer ODNs and the percentage content of the intensity of the j(CSP) of the electrochemically accumulated 30-mer ahODN-Cu(I) complexes. The detection of acid hydrolysed 80-mer (A(80)) in the bulk solution and in a 20-mul volume is possible down to 200pM and 2nM at the AuAE, respectively. For the shortest 10-mer (A(10)) a detectable value of 5nM in the bulk solution on the AuAE was observed. The sensitive detection of different ODNs containing the purine units in their chains in the presence of copper can be also performed at the platinum amalgam-alloy (PtAE) and copper amalgam-alloy (CuAE) contrary to a lower sensitivity at the silver amalgam-alloy (AgAE) electrode.

Interaction of DNA with echinomycin at the mercury electrode surface as detected by impedance and chronopotentiometric measurements.

The capacitance measurement (dependence of the differential capacitance C of the electrode double layer on potential E, C-E curves), electrochemical impedance spectroscopy (frequency response of the impedance Z of the electrode double layer-EIS) and constant current chronopotentiometry (dependence of dt/dE on potential at constant current, chronopotentiometric stripping analysis-CPSA) have been used for electrochemical study of echinomycin and its interaction with single-stranded (ss) and double-stranded (ds) DNA at the hanging mercury drop electrode (HMDE). The capacitance measurement showed that echinomycin gives a pseudocapacitance redox peak strongly dependent on the a.c. voltage frequency at the potential of -0.53 V. This peak is observed with dsDNA-echinomycin complex as well, but not with ssDNA treated by echinomycin. Similar results were obtained using CPSA measurements. Thus capacitance measurements and CPSA can distinguish with the aid of the bis-intercalator echinomycin the single-stranded and double helical form of DNA adsorbed at the mercury electrode surface. Impedance measurement in connection with adsorptive transfer technique can find the differences between ssDNA and dsDNA, which promise to use this technique for detection of dsDNA in hybridisation reactions.