Attempts to get electrochemical responses towards small redox-inactive proteins are provided by analytical importance of these biological compounds. The common analysis either requires poisoning of animals or involves complicated and expensive technologies of molecular biology. Also great effort has been recently devoted to the new protocols development for the detection of DNA. Direct or label-free electrochemical detection of biomolecules is useful because it eliminates indicator addition/association/detection step and allows real time monitoring of binding.

Since water-soluble proteins and DNA molecules contain charged groups, and can even be considered as polyelectrolytes in aqueous solutions, it might be possible to detect them by means of electrochemical methods at soft interfaces either by changes of interfacial properties of supported layers of amphiphiles or by their transfer from water to organic phase or by bioaffinity interactions affecting the ion transfer through the interface.

The uniform bilayers of water-insoluble surfactants can be formed as a result of self-assembling at solid electrode support [1]. It was shown that bilayers are sensitive for binding events on the their surface and can be used as transducers for affinity interaction detection [2].

The novel system based on a hydrophobic electrode modified with thin liquid film of solution of water-insoluble redox probe in water-immiscible organic solvent was elaborated and applied for investigation of thermodynamics of ion transfer across liquid|liquid interface [3]. In contrast to the conventional four-electrode electrochemical setup [4], the potential window did not changed dramatically in the presence of surfactants in sufficient concentration. The redoxactivity of probe in organic phase was sufficiently enhanced after extraction of protein molecules into the thin film with the reversed micelles of surfactant AOT [5, 6]. Unlike the pure buffer the incubation in protein solution lead to the sufficient increase of currents of redox-activity of polymer, which in certain cases exceeds two orders of magnitude. Our studies gave strong evidence, that the raise in current at liquid|liquid interface is generated by the proteins. The mechanism of electrode process is elaborated. The peak current of electroactivity is dependent on the protein content in a wide concentration range, which gives promise for analytical applications of the system. The certain selectivity was achieved by electrochemical impedance spectroscopy.

In parallel route of research, it was suggested to use ion transfer at thin film electrodes modified with adsorbed oligonucleotides as an electrochemical probe for DNA hybridization. The setup based on ITIES supported by gel onto common disposable screen-printed electrode allowing thermodynamic controlled ion transfer was proposed. The ion transfer of organic cathions from organic into aqueous phase has been achieved in certain conditions. The adsorption of DNA probes onto ITIES was observed with electrochemistry. The increase of conductivity has been observed in impedance spectra after hybridization [7]. The sensitivity of the system allowed determining the single mismatch in target sequence.

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1. Ion transfer across the liquid|liquid interface studied with membrane-modified screen-printed electrodes
2. New materials based on nanostructured Prussian blue for development of hydrogen peroxide sensors for biomedical applications.