Application of silver solid amalgam electrodes in electrochemical detection of DNA damage

In this study, a mercury meniscus-modified silver solid amalgam electrode was used for the first time for the detection of UV-induced DNA damage. The integrity of the double-stranded DNA (dsDNA) layer was detected indirectly using the evaluation of the methylene blue reduction within its accumulation into dsDNA after the UV irradiation of the biosensor surface with two different wavelengths (254 nm and 365 nm), monitored by differential pulse voltammetry. Moreover, a simple electrochemical characterization of the biosensor surface was performed using cyclic voltammetry of the redox indicator hexaammineruthenium chloride (RuHex) present in the solution. Electrochemical impedance spectroscopy (EIS) was used in both cases for the verification of results. Individual electrochemical signals depend on the time of biosensor exposure to UV irradiation as well as on the selected wavelengths and are different for both used types of dsDNA (salmon sperm and calf thymus). The highest degradation degree up to 60% was observed using sensitive EIS of methylene blue after 10 min irradiation of the biosensor at 254 nm. The use of RuHex seems to be less sensitive for the detection of dsDNA structural changes, when the degradation degree up to 40% was observed, using EIS at the same conditions.

Comparison Study of Voltammetric Behavior of Muscle Relaxant Dantrolene Sodium on Silver Solid Amalgam and Bismuth Film Electrodes

Voltammetric behavior of muscle relaxant dantrolene sodium (DAN) was studied and the voltammetric methods for its determination using polished and mercury meniscus modified silver solid amalgam electrodes (p-AgSAE and m-AgSAE) as well as using bismuth film electrode (BiFE, ex situ plating on GCE) have been proposed. These working electrodes represent the most commonly used alternatives to mercury ones which come wrongfully into disfavor because of alleged toxicity of mercury. Within this work, the obtained results of DAN determination have been completed by corresponding statistical parameters and also some electrochemical characteristics of AgSAEs and BiFE were assessed, especially in comparison with the mercury electrodes.

Label-free bead-based metallothionein electrochemical immunosensor

A novel microfluidic label-free bead-based metallothionein immunosensors was designed. To the surface of superparamagnetic agarose beads coated with protein A, polyclonal chicken IgY specifically recognizing metallothionein (MT) were immobilized via rabbit IgG. The Brdicka reaction was used for metallothionein detection in a microfluidic printed 3D chip. The assembled chip consisted of a single copper wire coated with a thin layer of amalgam as working electrode. Optimization of MT detection using designed microfluidic chip was performed in stationary system as well as in the flow arrangement at various flow rates (0-1800 μL/min). In stationary arrangement it is possible to detect MT concentrations up to 30 ng/mL level, flow arrangement allows reliable detection of even lower concentration (12.5 ng/mL). The assembled miniature flow chip was subsequently tested for the detection of MT elevated levels (at approx. level 100 μg/mL) in samples of patients with cancer. The stability of constructed device for metallothionein detection in flow arrangement was found to be several days without any maintenance needed.

Sensitive and selective detection of adenine using fluorescent ZnS nanoparticles

We have used fluorescent ZnS nanoparticles as a probe for the determination of adenine. A typical 2 × 10(-7) M concentration of adenine quenches 39.3% of the ZnS fluorescence. The decrease in ZnS fluorescence as a function of adenine concentration was found to be linear in the concentration range 5 × 10(-9)-2 × 10(-7) M. The limit of detection (LOD) of adenine by this method is 3 nM. Among the DNA bases, only adenine quenched the fluorescence of ZnS nanoparticles in the submicromolar concentration range, thus adding selectivity to the method. The amino group of adenine was important in determining the quenching efficiency. Steady-state fluorescence experiments suggest that one molecule of adenine is sufficient to quench the emission arising from a cluster of ZnS consisting of about 20 molecules. Time-resolved fluorescence measurements indicate that the adenine molecules block the sites on the surface of ZnS responsible for emission with the longest lifetime component. This method may be applied for the determination of adenine in biological samples since the measurements have been carried out at pH 7.

Study of Copper and Purine-Copper Complexes on Modified Carbon Electrodes by Cyclic and Elimination Voltammetry

Using a paraffin impregnated graphite electrode (PIGE) and mercury-modified pyrolytic graphite electrode with basal orientation (Hg-PGEb) copper(II) and Cu(II)-DNA purine base solutions have been studied by cyclic (CV) and linear sweep voltammetry (LSV) in connection with elimination voltammetry with linear scan (EVLS). In chloride and bromide solutions (pH 6), the redox process of Cu(II) proceeded on PIGE with two cathodic and two anodic potentially separated signals. According to the elimination function E4, the first cathodic peak corresponds to the reduction Cu(II) + e^- → Cu(I) with the possibility of fast disproportionation 2Cu(I) → Cu(II)+ Cu(0). The E4 of the second cathodic peak signalized an electrode process controlled by a surface reaction. The electrode system of Cu(II) on Hg-PGEb in borate buffer (pH 9.2) was characterized by one cathodic and one anodic peak. Anodic stripping voltammetry (ASV) on PIGE and cathodic stripping voltammetry (CSV) on Hg-PGEb were carried out at potentials where the reduction of copper ions took place and Cu(I)-purine complexes were formed. By using ASV and CSV in combination with EVLS, the sensitivity of Cu(I)-purine complex detection was enhanced relative to either ASV or CSV alone, resulting in higher peak currents of more than one order of magnitude. The statistical treatment of CE data was used to determine the reproducibility of measurements. Our results show that EVLS in connection with the stripping procedure is useful for both qualitative and quantitative microanalysis of purine derivatives and can also reveal details of studied electrode processes.