Voltammetric study of khellin at a DNA-coated carbon paste electrode

Trace assay of insulin in a pharmacy drug with a paste electrode

This paper describes the development of a voltammetric assay of insulin using a DNA immobilized onto a carbon nanotube paste electrode (CNPE), the peak potential of which was 0.2 V, vs. Ag/AgCl on the CNPE. The cyclic voltammetry (CV) and square-wave (SW) stripping voltammetry parameters of the optimized conditions were determined. Low analytical working ranges of 10-80 ugL-1 CV and 0.01-0.1 ngL-1 SW were attained. The precision of the insulin concentration of 0.01 ugL-1 was 0.14 (n = 15) RSD using the optimum conditions, in which the detection limit was 0.004 ngL-1 (6.9 × 10-12 M) (S/N = 3) using only an accumulation time of 400 s. The developed method was applied to determine insulin in a pharmacy drug from analytical-grade chemicals (from Aldrich).

Development of Gel-in-Oil Emulsions for Khellin Topical Delivery

Hypopigmentation is a progressive dermatological condition caused by a reduction in the skin pigment, melanin. Its treatment is considered a challenge due to the lack of a highly efficient single therapy. Currently, the main treatments include photochemotherapy, application of corticosteroids and immunosuppressants, and laser. Khellin-based gel-in-oil emulsions appear as a promising alternative since they ensure a concentration of the drug, a natural furanochromone, at the desired location, skin surface. Khellin promotes repigmentation as it forms a dark colored complex after solar irradiation. The aim of this study was the development and characterization (e.g., rheological behaviour, droplet size, tackiness, adhesion and spreadability) of three topical gel-in-oil emulsions prepared with different emollients, formulated through a cold emulsification process, and suitable for the incorporation of khellin. In vitro studies were performed to evaluate the drug release and permeation profiles across artificial membranes and excised human skin, respectively, using Franz-type vertical diffusion cells. The W/O emulsions developed showed macroscopic appearance, shear-thinning behavior with a mean droplet size from 3.28 to 4.28 μm, suitable for topical application. In vitro studies revealed permeation values of about 1% of khellin across the stratum corneum, making these gel-in-oil emulsions promising for preclinical and clinical studies. The cold process, being an easy and low energy production method, represents an innovative strategy to produce khellin-based gel-in-oil emulsions to treat patients with hypopigmentation.

From mercury to nanosensors: Past, present and the future perspective of electrochemistry in pharmaceutical and biomedical analysis

Polarography was the first developed automated method of voltage-controlled electrolysis with dropping mercury electrode (DME). Then, hanging mercury drop and static mercury drop electrodes were added as an alternative indicator electrode. In this way, polarography turned formally into voltammetry with mercury electrodes in the electroreduction way. Solid electrodes such as noble metal and carbon based electrodes can be used for the investigation of the compounds for both oxidation and reduction directions, which is called voltammetry. The voltammetric and polarographic techniques are more sensitive, reproducible, and easily used electroanalytical methods that can be alternative to more frequently used separation and spectrometric methods. Furthermore, in some cases there is a relationship between voltammetry and pharmaceutical samples, and the knowledge of the mechanism of their electrode reactions can give a useful clue in elucidation of the mechanism of their interaction with living cells. The voltammetric and polarographic analysis of drugs in pharmaceutical preparations are by far the most common use of electrochemistry for analytical pharmaceutical problems. Recent trends and challenges in the electrochemical methods for the detection of DNA hybridization and pathogens are available. Low cost, small sample requirement and possibility of miniaturization justifies their increasing development.

Voltammetric Assay of Mercury Ion in Fish Kidneys

Voltammetric analysis of mercury ions was developed using paste electrodes (PEs) with DNA and carbon nanotube mixed electrodes. The optimized analytical results of the cyclic voltammetry (CV) of the 1∼14 ng L⁻¹ Hg(II) concentration and the square wave (SW) stripping voltammetry of the 1∼12 ng L⁻¹ Hg(II) working range within an accumulation time of 400 seconds were obtained in 0.1 M NH₄H₂PO₄ electrolyte solutions of pH 4.0. For the relative standard deviations of the 1 ng L⁻¹ Hg(II), which were observed at 0.078% (n = 15) at the optimum conditions, the low detection limit (S/N) was pegged at 0.2 ng L⁻¹ (7.37 × 10⁻¹³M) for Hg(II). The results can be applied to assays in biological fish kidneys and wastewater samples.

Rapid electrochemical genosensor assay using a streptavidin carbon-polymer biocomposite electrode

A sensor capable of detecting a specific DNA sequence was designed by bulk modification of a graphite epoxy composite electrode with streptavidin (2% w/w). Streptavidin is used to immobilise a biotinylated capture DNA probe to the surface of the electrode. Simultaneous hybridisation occurs between the biotin DNA capture probe and the target-DNA and between the target-DNA and a digoxigenin modified probe. The rapid binding kinetic of streptavidin-biotin allows a one step immobilisation/hybridisation procedure. Secondly, enzyme labelling of the DNA duplex occurs via an antigen-antibody reaction between the Dig-dsDNA and an anti-Dig-HRP. Finally, electrochemical detection is achieved through a suitable substrate (H2O2) for the enzyme-labelled duplex. Optimisation of the sensor design, the modifier content and the immobilisation and hybridisation times was attained using a simple nucleotide sequence. Regeneration of the surface is achieved with a simple polishing procedure that shows good reproducibility. The generic use of a modified streptavidin carbon-polymer biocomposite electrode capable of surface regeneration and a one step hybridisation/immobilisation procedure are the main advantages of this approach. In DNA analysis, this procedure, if combined with the polymerase chain reaction, would represent certain advantages with respect to classical techniques, which prove to be time consuming in situations where a simple and rapid detection is required. This innovative developed material may be used for the detection of any analyte that can be coupled to the biotin-streptavidin reaction, as is the case of immunoassays.