F.V. Vereshchagin, V.M. Gusev, O.N. Kompanets, M.A. Pavlov, D.P. Chulkov

One of the alternatives to traditional analytical methods and devices for biomedicine is biosensor methods and devices based on using sensing units specific to certain chemical and biologically active compounds (BAC) to be determined, in combination with various transducers and converters of the signals of their specific interaction. The example of such analysis is the nanobiotechnological approach developed at the Rus. Ac. Sci. Engelhardt - Molecular Biology Institute (EMBI) and proposing the use of ordered nanoconstructions on the base of rigid double-stranded DNA molecules as the biosensing units responding to the presence of BAC in a physiological liquid. Due to high density of the ordered molecule packing with a helical structure of layers an abnormal optical activity of the DNA nanoconstructions appears that reveals itself as an abnormal big signal of circular dichroism (CD) observed both in UV band in the absorption area of the nitrogen bases of DNA (~270 nm), and in additional bands in UV and visible due to interaction of BAC with DNA molecules causing either a change of the DNA secondary structure or intercalation of BAC between pairs of DNA nitrogen bases without disturbance of the DNA ordering character, or formation of «bridges» between neighboring molecules of the DNA nanoconstruction. The change of abnormal optical activity signal (down to the total disappearance) of the DNA biosensing unit under the BAC action is easily registered with a portable CD spectrometer (dichrometer) and in certain conditions is directly connected with a BAC concentration in a liquid. The BAC concentration is determined with a help of the previously obtained analytical (calibration) curve describing the dependence of the abnormal CD signal generated by the DNA biosensing unit on concentration of the BAC being in the contact with DNA. A result of every analytical measurement is represented on the analytical curve in the form of the point with identification of the value of the BAC concentration revealed in the sample under investigation. For the first time the practical problem of determining BAC with the help of biosensing units on the base of DNA nanoconstructions was solved with the development at the Rus. Ac. Sci. Institute of Spectroscopy RAS (ISAN) and the manufacturing in 2003 experimental models of the portable polyfunctional dichrometer (CDS-2) with the working range of 250-750 nm in ISAN and a set of 10 such prototypes at the Rus. Ac. Sci. Experimental Plant (Chernogolovka). The device was certificated (No.26900-04 in the Federal Agency on Technical Regulation and Metrology) as a liquid analyzer on the CD principle and is effectively used up to now in many laboratories in combinations with DNA biosensing units for detection of low concentrations of a number of BAC and medicines both in test solutions and blood preparations. The device is compared in sensitivity with the best commercial CD spectrometers of well known companies, and, having its dimensions and weight several times less, it is characterized with low operational expenditures, low prime cost of a single test and the possibility of conducting straight rapid analysis of liquids containing BAC. The bioanalytical system (biosensor) on the base of DNA nanoconstructions and the portable dichrometer has no analogues in the world with the same operating principle. Analytical possibilities of such the biosensor have been demonstrated and appreciated on the examples of detection in physiological liquids of more than 60 compounds of 15 different species at the EMBI and other establishments including medical ones. Everything said above however can not deny the fact that for the period of almost ten years exploitation of the portable dichrometer CDS-2 many wishes were obtained from the device users to expand its working range to UV (up to 200 nm) with increasing the light flow in this field important for applications, to change the driver of wavelength tuning complicated in adjustment, to ensure higher stability towards external effects, to increase an accuracy of setting the temperature in the sample box, to lower a value of the CD noise component, to improve the dichrometer software and so on. All these proposals on the device modernization in fact are connected with broadening functional possibilities of the dichrometer and improving reliability of its work as a whole, as well as reducing its dimensions, which could be realized only on the way of using modern radio electronics and new design solutions that compiled the essence of the development of a new improved portable dichrometer model described in the article.