We investigate the enhancement of the electromagnetic field and the surface-enhanced Raman scattering (SERS) effect in a silver-plastic metasurface. Localized plasmon modes are excited and manifest as pronounced local maxima of the electric field, spatially confined within the dented regions of the metasurface where the silver layer exhibits minimal thickness. The spectral position of these plasmonic resonances is highly sensitive to both the silver film thickness and the non-uniformity of its distribution across the metasurface. Experimental results show good agreement with numerical simulations performed for a double-periodic metal-dielectric metasurface. The fabricated metasurface was evaluated as a SERS substrate for direct detection of individual extracellular vesicles from the Human Embryonic Kidney 293T cell line.

In some cases, a reaction in the oscillatory mode has a higher selectivity for the target product. To organize production in this mode, it is necessary to determine the conditions under which fluctuations occur, as well as to consider the very nature of the fluctuations. In this work, a parametric analysis of the basic kinetic model of an oscillatory reaction without autocatalysis was made. The boundaries of the parameters at which the system oscillates were found. Phase portraits of the system and bifurcation curves were constructed. Stationary states of the system were analyzed. The type and number of stationary states were identified. It was shown that the system at certain parameters has three stationary states: two unstable nodes and a saddle. Parametric analysis of basic models will allow selecting initial approximations for calculations of more complex models of real reactions.

A method of injecting barium hexaferrite-based ferromagnetic implants into the brain of animals is proposed. Behavioral responses of mice to external magnetic influence after the introduction of non-toxic nanomagnetic particles of barium hexaferrite were studied. A decrease in the BOLD-signal value at nitric oxide "outflow" within the framework of the proposed kinetic model was shown.

An analytical theory and experiments are proposed to study surface-enhanced Raman scattering (SERS) from molecules located inside a hollow metal resonator. The EM mechanism is considered for the confined SERS. Raman scattering measured from bare as well as from silver-coated polystyrene spheres is consistent with our theory of the confined SERS.

We explore the optical properties of plasmon localization and local field enhancement in metal-plastic metasurface. The flexible metal-dielectric metasurfaces are made from modulated polycarbonate substrate coated by a thin silver film. Localization of an optical excitation is experimentally observed by near-field scanning optical microscopy within subwavelength areas in the regular open-resonator metasurface. The localized modes are seen as giant fluctuations of the local electric field spatially concentrated in hotspots, where the local field is much larger than the amplitude of the incident light. Local near-field spatial spectra consist of regularly distributed strong peaks. The maxima of the electric field are highly dependent on the sample structure. The form of the regularly distributed strong resonance peaks follows the topography obtained by atomic force microscopy. It is shown that strong electromagnetic field is concentrated in recesses where the silver film is typically thinner than on the bumps. This experimental observation is consistent with the results of computer simulations of a double-periodic metal-dielectric metasurface and the predictions of our analytical theory. It is found the silver nanofilm has strong adhesion to polycarbonate substrate.

We present an analytical theory of plasmons excited in spherical metal resonators filled with the molecules under study. A simple L‒C model of plasmons generated in a metal nanoshell is developed. The electromagnetic mechanism of surface-enhanced (giant) Raman scattering (SERS) can be investigated qualitatively and quantitatively. The theoretical results are in qualitative agreement with computer simulations. The results of the SERS experiment in polystyrene spheres coated with a silver nanolayer are presented.

The analytical theory as well as experimental observation of the plasmons excited in the spherical metal resonator stuffed by investigated molecules is presented. A simple lumped model of the plasmons generated in the metal nanosphere is developed. The electromagnetic mechanism of the surface-enhanced Raman Scattering (SERS) can be investigated qualitatively and quantitatively. The theoretical results are in a qualitative agreement with our experiment on SERS in silver coated polystyrene spheres.

The kinetics of elongation of nucleic acids as a multistep sequential reaction forming a cycle was studied. A mathematically rigorous proof was given for the empirical formulas used to estimate the elongation time as a function of the length of the nucleotide chain. Estimates of the characteristic elongation time for typical chain lengths were proposed, including for the novel coronavirus (SARS-CoV-2). The stability of the elongation kinetics was investigated, and it was determined that, at typical chain lengths, increasing-amplitude unstable oscillating components appear along with the main exponential component.

A kinetic model of functioning of synapses and synaptic circuits responsible for cognitive function was developed. Cholinergic synapse functioning upon a change in the neurotransmitter concentration and acetylcholinesterase activity was analyzed in the framework of this model, and the principles of formation of a “neuroimage” and a “conduction track” in the synaptic system were explained. The effects of signal intensity, impulse frequency, receptor desensitization rate, and acetylcholinesterase expression level were analyzed. The dynamic regularities of the system behavior under constant neuron excitation (variant of stroke and action of nerve agents) were constructed. The kinetic trends upon blocking of acetylcholine receptors by physiologically active compounds and drugs were determined. The kinetic model of the synapse system was modified with involvement of elements of the mathematical theory of neural networks (artificial intelligence) with the definition of “ideal synapse” and “ideal synaptic network”.

The article investigates kinetics of nucleic acid elongation as a multistage consequent reaction curling up to cycle. There is represented a matematically precise proof of empiric formulae used to estimate elongation time depending on nucleotide chain length. There are given some estimations of characteristic elongation time for typical chain lengths, for example for new coronavirus (SARS-nCoV-2). There is also investigated stability of elongation kinetics and at typical chain lenghts is shown an existance of instable oscillating solution component in addition to main exponential component.

The work considers an electrodynamic model of radiation from molecules placed in a metal shell. The model qualitatively describes the enhancement of the surface-enhanced Raman scattering (SERS) signal from spherical nanoparticles coated with a thin silver film. The change in the SERS signal is calculated depending on the thickness of the metal nanolayer on top of the spherical particles. The radiating molecular dipole interacts with the metal shell and excites surface plasmons. Plasmonic oscillations reach a maximum when the frequency of the dipole is close to the plasmon resonance of the metal shell, and the dipole itself is close to the plasmonic shell. It has been theoretically shown that the intensity of secondary radiation generated by spherical nanoparticles coated with a silver film several nanometers thick can reach up to six or more orders of magnitude. The effect of a tenfold amplification of the SERS signal was experimentally demonstrated using the example of a large ensemble of single polystyrene microspheres with an average diameter of about 300 nm, coated with a silver nanolayer, which have characteristic Stokes frequencies of 1001 cm-1, 1602 cm-1. We believe that the tenfold enhancement of Raman scattering is due to the electromagnetic amplification mechanism.

Spatially inhomogeneous structures (SIS) are important to realize the integrated optical devices transmitting and processing light signals. Nowadays, there are several methods used to create such structures with different characteristics and topologies. However, research on the methods of forming and modifying the characteristics of these structures continues to this day. In this work, we create and study SIS in a lithium niobate crystal surface-doped with copper ions. The results prove that SIS can be created by the point-by-point method using a continuous-wave frequency-doubled YAG:Nd3+ laser. The realized structures were formed as diffraсtion and waveguide optical elements with different characteristics and topologies. It is demonstrated that we can change the refractive index up to 10–3 by the point-by-point illumination of an X‑cut lithium niobate crystal during the structure formation. The properties of the fabricated structures were investigated by diffraction analysis, laser interferometry, and the optical probing method using He–Ne laser radiation. On the formed diffraction structures (DSs), the far-field diffraction patterns (DPs) show that the light power transfers from the incident radiation to first-order maxima. The first-order maxima intensity can exceed the intensity of the zero-order maximum up to several times. The near-field study after the excitation of waveguide structures (WSs) shows that they exhibit the properties of mode filters. The point-by-point method of forming SIS may be useful for creating integrated optical circuits and modifying the characteristics of optoelectronic and photonic devices.

Electrodynamic model of the radiation of molecules placed in a metal shell has been developed. The model qualitatively describes the secondary Raman radiation from protein globules coated with a thin silver film. The model makes it possible to calculate the change in the SERS signal depending on the thickness of the metal nanolayer over the protein globule. The radiating molecular dipole interacts with the metal shell and excites surface plasmons. Plasmon oscillations reach a maximum when the dipole frequency is close to the plasmon resonance of the metal envelope, and the dipole itself is located near the plasmon envelope.

A kinetic study of the effect of thermoheliox (inhalation of a helium and oxygen mixture, 70 °C) on the functional hemodynamics of the human brain by functional magnetic resonance imaging was carried out. The dynamic responses of the BOLD signal were found to be biphasic. An empirical equation describing the first phase of the hemodynamic response to visual stimulus was proposed. It was shown that preliminary inhalation of thermoheliox stimulates the hemodynamic responses by slowing down the vasoconstriction.

Surface-enhanced Raman scattering (SERS) spectroscopy is a surface- or cavity-enhanced variant of Raman scattering spectroscopy that allows the detection of analytes with a sensitivity down to single molecules. This method involves the use of SERS-active surfaces or cavities capable of concentrating incident radiation into small mode volumes containing the analyte. Here, we have engineered an ultranarrow metal–dielectric nano-cavity out of a film of the receptor-binding domain (RBD) of SARS-CoV-2 spike (S) glycoprotein and a silver surface, held together by interaction between reduced protein sulfhydryl groups and silver. The concentration of light in this nano-cavity allows the label-free recording of the characteristic Raman spectra of protein samples smaller than 1 pg. This is sufficient for the ultrasensitive detection of viral protein antigens at physiologically relevant levels. Moreover, the protein SERS signal can be increased by several orders of magnitude by coating the RBD film with a nanometer-thick silver shell, thereby raising the cavity Q-factor. This ensures a sub-femtogram sensitivity of the viral antigen detection. A simple theoretical model explaining the observed additional enhancement of the SERS signal from the silver-coated protein is proposed. Our study is the first to obtain the characteristic Raman and SERS spectra of the RBD of S glycoprotein, the key SARS-CoV-2 viral antigen, directly, without the use of Raman-reporter molecules. Thus, our approach allows label-free recording of the characteristic spectra of viral antigens at concentrations orders of magnitude lower than those required for detecting the whole virus in biological media. This makes it possible to develop a high-performance optical detection method and conformational analysis of the pathogen and its variants.

We present metal-dielectric metasurfaces fabricated from metal periodical nanograting deposited on a dielectric substrate. The metasurface consists of a modulated dielectric, which is covered by a thin silver layer. The metasurface operates as an open plasmon resonator. The theory of plasmons excited in the open resonator formed by a metal nanograting is presented. The large local electromagnetic field is predicted for optical frequencies. The excitation of plasmons is experimentally demonstrated in the metasurface designed on a 4-in. Si wafer. The enhancement of the local electric field results in surface-enhanced Raman scattering (SERS). To investigate the SERS effect, the metasurface is covered with a thin layer of the 4-mercaptophenylboronic acid that molecules form covalent bonds with the silver nanolayer. The enhancement of the Raman scattering serves as a proof of concept. We obtain a detection limit of 230 nM for molecules of 4-mercaptophenylboronic acid.

The Indium Tin Oxide (ITO) platform is one of the promising solutions for state-of-the-art integrated optical modulators towards low-loss silicon photonics applications. One of the key challenges on this way is to optimize ITO-based thin films stacks for electro-optic modulators with both high extinction ratio and low insertion loss. In this paper we demonstrate the e-beam evaporation technology of 20 nm-thick ITO films with low extinction coefficient of 0.14 (N c = 3.7·10 20 cm −3 ) at 1550 nm wavelength and wide range of carrier concentrations (from 1 to 10 × 10 20 cm −3 ). We investigate ITO films with amorphous, heterogeneously crystalline, homogeneously crystalline with hidden coarse grains and pronounced coarsely crystalline structure to achieve the desired optical and electrical parameters. Here we report the mechanism of oxygen migration in ITO film crystallization based on observed morphological features under low-energy growth conditions. Finally, we experimentally compare the current–voltage and optical characteristics of three electro-optic active elements based on ITO film stacks and reach strong ITO dielectric permittivity variation induced by charge accumulation/depletion (Δn = 0.199, Δk = 0.240 at λ = 1550 nm under ± 16 V). Our simulations and experimental results demonstrate the unique potential to create integrated GHz-range electro-optical modulators with sub-dB losses.

Subject of study. The capabilities of the technologies for marking products and security holograms based on the analysis of the spectral properties of molecular structures introduced to the holograms are considered in combination with the adoption of quantum dots and magnetic microparticles (MPs). The primary focus is on the issues of the analysis of the Raman spectra of molecules excited by plasmonic-resonant electromagnetic fields. Method. Modern technologies for hologram security are based on the use of various protective optical effects concealed from visual observation. These effects reveal themselves only under the relevant illumination of holograms when specialized optical equipment is employed. Unique methods for marking and identification of holograms using the magneto-optical, fluorescent, and spectral properties of the emission of MPs and molecular structures with sizes ranging from tens of nanometers to tens of micrometers, which are excited by localized electromagnetic fields, are considered. The plasmonic-resonant methods for the excitation of marking molecular labels introduced into the hologram structures are the most relevant, together with the arising spectra of surface-enhanced Raman scattering that are used for the identification and authenticity verification of the holograms. Main results. The use of plasmonic-resonant methods for concentrating electromagnetic fields for the excitation of marking molecular labels was demonstrated to be able to ensure the amplification of their Raman emission by several orders of magnitude, which results in the significant enhancement of recognizability and identification of security holograms. Practical significance. The technologies for hologram protection proposed in this work are based on the combination of different types of markings such as hidden holographic images, magneto-optical and fluorescent images of MPs, and Raman spectra of molecular structures that are enhanced by plasmonic-resonant methods. These technologies significantly increase the reliability, security, and authenticity of the marking and its identification. The results of this study will help in forming the basic technical requirements for design of portable devices for the identification of security hologram markings. (C) 2022 Optica Publishing Group

Changes in the refractive index induced in the Cu-doped surface layer of a lithium niobate crystal were investigated experimentally. The changes were induced by sequential point-by-point exposure of an experimental sample by focused laser radiation at a wavelength of $$\lambda=532$$ nm.