Olga Cherkasova, Novosibirsk State University; Institute of Laser Physics SB RAS, Novosibirsk, Russia
Alexander Milekhin, Novosibirsk State University; A.V. Rzhanov Institute of Semiconductor Physics, Novosibirsk, Russia
Ilya Milekhin, Novosibirsk State University
Sergei Kuznetsov,Novosibirsk State University
Ekaterina Rodyakina, Novosibirsk State University; Institute of Laser Physics SB RAS, Novosibirsk, Russia
Alexander Latyshev, A.V. Rzhanov Institute of Semiconductor Physics, Novosibirsk, Russia
The steroid hormones influence on many physiological processes in humans is well known. The determination of the levels of steroid hormones is an important issue for the inspection of endocrinological disorders related to adrenal or gonadal function.
Spectral properties of steroids are well described in infrared (IR) spectral range . In studies of small amounts of molecules, conventional IR spectroscopy suffers from relative low molecular IR absorption signals compared to background noise. One way to increase sensitivity is to use field-enhanced spectroscopy techniques as surface-enhanced infrared spectroscopy (SEIRS) . The basic principle of the method is resonant excitation in the infrared of specially designed metal nanoparticles known as resonant plasmonic nanoantennas to provide the local electromagnetic field of high intensities . Steroids have not been investigated by using this technique yet. This work discusses a creation of a special nanoantenna and its application for cortisol analysis. Cortisol is the major glucocorticoid hormone secreted by the adrenal gland.
The method of nanostructuring metal surfaces by means of nanolithography was optimized and Au nanoantenna arrays with the controllable structural and optical parameters on the Si and SiO2 surfaces were formed. Based on the comparison of the data obtained by IR spectroscopy with those of modelling, the interrelation between the energy of the localized surface plasmon resonance (LSPR) and structural parameters of nanoantennas was established. We designed our nanoantenna with specific lengths L in order to obtain the energy of the fundamental plasmonic resonance close to that of the absorption bands of cortisol and therefore to exploit the maximum near field enhancement.
Cortisol was dissolved in ethanol with different concentrations and dropped onto the substrate surface from solutions. The ratio between IR spectra polarized along and perpendicular to nanoantennas was analyzed. IR spectrum of as-prepared nanoantenna arrays demonstrates a broad absorption band near 1600 cm-1 corresponding to the LSPR absorption. After dropping cortisol a blue shift of LSPR energy which is due to the change of the dielectric function of the media surrounding the nanoantennas is observed. Three additional features at 1470 cm-1 (deformation vibrations of C-H bonds), 1660 cm-1 (stretching vibrations С3=O3 bond), and 1735 cm-1 (stretching vibrations С20=O20 bond) which are characteristic vibrational modes of cortisol are also seen in IR spectrum. Thus, a possibility of application of nanoantenna arrays for cortisol analysis was shown.
This work was supported by Russian Science Foundation (project 14-12-01037).
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 Nanoantenna: Plasmon-Enhanced Spectroscopies for Biotechnological Applications, ed. Chapelle, M. L. de la and Pucci, A. CRC Press.Taylor & Francis Group: Boca Raton, 2013. 405 p.
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Prof. Olga Pavlovna Cherkasova
Institute of Laser Physics SB RAS, Novosibirsk State Technical University, Head of Biophysics Laboratory
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