Of all modern nanosensors using the principle of measuring variations in electric conductance, point-contact sensors stand out in having a number of original sensor properties not manifested by their analogues. The nontrivial nature of point-contact sensors is based on the unique properties of Yanson point contacts used as the sensing elements. The quantum properties of Yanson point contacts enable the solution of some of the problems that could not be solved using conventional sensors measuring conductance. In the present paper, we demonstrate this by showing the potential of quantum point-contact sensors to selectively detect components of a gas mixture in real time. To demonstrate the high efficiency of the proposed approach, we analyze the human breath, which is the most complex of the currently known natural gas mixtures with extremely low concentrations of its components. Point-contact sensors allow us to obtain a spectroscopic profile of the mixture. This profile contains information about the complete set of energy interactions occurring in the point contact/breath system when the breath constituents adsorb to and desorb from the surface of the point-contact conduction channel. With this information we can unambiguously characterize the analyzed system, since knowing the energy parameters is key to successfully identifying and modeling the physicochemical properties of various quantum objects. Using the point-contact spectroscopic profile of a complex gas mixture it is possible to get a functional dependence of the concentration of particular breath components on the amplitude of the sensor output signal. To demonstrate the feasibility of the proposed approach, we analyze the point-contact profiles from the breath of several patients and compare them with the concentrations of serotonin and cortisol in the body of each patient. The obtained results demonstrate that the proposed methodology allows one to get an effective calibration function for a non-invasive analysis of the level of serotonin and cortisol in the human body using the point-contact breath test. The present study indicates some necessary prerequisites for the design of fast detection methods using differential sensor analysis in real time, which can be implemented in various areas of science and technology, among which medicine is one of the most important.
Original fundamental properties of Yanson point contacts allow their application to research and technology development at a wide range of surrounding conditions. At low temperature these nanoobjects can be used as a main instrument of Yanson point-contact spectroscopy. At room temperature they can serve as a sensitive element of advanced nanosensors with excellent performance. The most important advantage of point-contact sensors in investigating complex gas media is the spectral nature of the response signal. The discovery of the spectral capabilities of point-contact sensors in the analysis of complex gas media allows us to speak in terms of spectral multifunctionality of Yanson point contacts and the expansion of the possibilities of their spectral application from the spectroscopy of electron-phonon interaction at low temperatures to spectroscopy of gaseous media at room temperatures. Using the spectral response of point-contact sensors, in this work we propose a new non-invasive method for the determination of melatonin, one of the important hormones characterizing the state of the human body. A series of procedures was proposed to find melatonin concentration in the human body as function of the response of a point-contact sensor to the action of the exhaled breath. It has been shown that the proposed method is accurate enough to be used for medical purposes in real time. The results of the study suggest that the problem of non-invasive determination of melatonin concentration in the human body can be successfully solved by using breath tests based on Yanson point contacts.
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