Sergey Burikov

Raman and IR spectroscopy research on hydrogen bonding in water–ethanol systems

Vibrational spectroscopy provides invaluable information about hydrogen bonding in aqueous solutions. To study changes in H-bonding due to increase of ethanol concentration in water, we perform research on water–ethanol binary mixtures with various mixing ratios using a combination of Raman scattering and IR absorption techniques. We study Raman spectra from 200 to 4000 cm−1 excited at 488 nm and IR spectra from 500 and 4000 cm−1 for solutions with different ethanol concentrations from pure water to pure ethanol. Using the intensity ratio of OH stretching band taken at 3200 and 3420 cm−1 for Raman spectra and at 3240 and 3360 cm−1 for IR spectra we evaluate the strength of H-bonding. Maximal strength of H-bonding in water–ethanol mixture corresponds to ethanol concentration 15–20% w/w. We explain it by the presence of transient ethanol hydrates similar in composition to gaseous clathrates with stoichiometric water/ethanol ratio 5:1. Further weakening of H-bonding with ethanol concentration is caused by the formation of chain aggregates from ethanol/water molecules. In addition, we apply other approaches, such as multivariate curve resolution-alternating least squares analysis, decomposition of water Raman stretching band, and comparison of water Raman stretching band in ethanol solutions to that of gas clathrates to support this hypothesis.

Core-shell designs of photoluminescent nanodiamonds with porous silica coatings for bioimaging and drug delivery I: fabrication

A multifunctional core-shell nanocomposite platform consisting of a photoluminescent nanodiamond (ND) core with uniform porous silica coatings is presented. This design intended for drug delivery applications allows simultaneous stable fluorescent imaging with high loading capacity of bioactive molecules. Despite irregularly shaped starting cores, well-dispersed and uniformly shaped nanocomposite particles can be produced. Moreover, after optimization of the silica source-to-diamond ratio, the thickness of the porous layer can be tuned by adjusting the ethanol amount, allowing rational nanoparticle size control. The ND key property, photoluminescence, is not quenched regardless of coating with thick silica layers. The high loading capacity for incorporation of active agents, provided by the introduced porous layer, is demonstrated by adsorption of a hydrophobic model drug to the composite particles. The loading degree, as compared to a pure ND, increased by two orders of magnitude from 1 wt% for the ND to >100 wt% for the composite particles. Combining these two material classes, which both have well-documented excellent performance especially in biomedical applications, for the NDs with emphasis, but not exclusively, on imaging and mesoporous silica (MSN) on drug delivery, the advantages of both are shown here to be synergistically integrated into one multifunctional nanocomposite platform.

The effect of hydration of ions of inorganic salts on the shape of the raman stretching band of water

The shape of the Raman stretching band of water molecules in aqueous solutions of electrolytes KBr, KCl, KI, NaCl, and NaI is studied. It is confirmed that the characteristics of the stretching band strongly depend on the concentration and type of salt. The behavior of different parameters of the band is explained in terms of the theory of hydration of salts.

Decomposition of water Raman stretching band with a combination of optimization methods

In this study, an investigation of the behaviour of stretching bands of CH and OH groups of water–ethanol solutions at alcohol concentrations ranging from 0 to 96% by volume has been performed. A new approach to decomposition of the wide structureless water Raman band into spectral components based on modern mathematical methods of solution of inverse multi-parameter problems–combination of Genetic Algorithm and the method of Generalized Reduced Gradient–has been demonstrated. Application of this approach to decomposition of Raman stretching bands of water–ethanol solutions allowed obtaining new interesting results practically without a priori information. The behaviour of resolved spectral components of Raman stretching OH band in binary mixture with rising ethanol concentration is in a good agreement with the concept of clathrate-like structure of water–ethanol solutions. The results presented in this paper confirm existence of essential structural rearrangement in water–ethanol solutions at ethanol concentrations 20–30% by volume.

Application of artificial neural networks to solve problems of identification and determination of concentration of salts in multi-component water solutions by Raman spectra

In this paper, the results of elaboration and comparative analysis of approaches concerned with application of neural network algorithms for effective solution of problem of pattern recognition (inverse problem with discrete output) along with inverse problem with continuous output are presented. Consideration is carried out at the example of problem of identification and determination of concentrations of inorganic salts in multi-component water solutions by Raman spectra. The studied approach is concerned with solution of both problems (classification and determination of concentrations) using a single neural network trained on experimental or quasi-model data.

Adaptive methods for solving inverse problems in laser raman spectroscopy of multi-component solutions

This study provides comparative analysis of approaches connected with application of neural network based algorithms for efficient solution of pattern recognition problem (inverse problem with discrete output) combined with solution of inverse problem with continuous output. The analysis is performed at the example of the problem of identification and determination of concentrations of inorganic salts in multi-component aqueous solutions by Raman spectrum.

Comparison of the quality of solving the inverse problems of spectroscopy of multi-component solutions with neural network methods and with the method of projection to latent structures

This study provides comparative analysis of application of artificial neural networks and method of projection to latent structures (partial least squares) for simultaneous determination of types and concentrations of dissolved inorganic salts in multicomponent water solutions by Raman spectra. It is shown that the method of projection to latent structures has several advantages, such as the quality of the solution and the time of construction of a regression model, when solving problems with low level of nonlinearity.

Neural Network Approaches to Solution of the Inverse Problem of Identification and Determination of Partial Concentrations of Salts in Multi-сomponent Water Solutions

The studied inverse problem is determination of partial concentrations of inorganic salts in multi-component water solutions by their Raman spectra. The problem is naturally divided into two parts: 1) determination of the component composition of the solution, i.e. which salts are present and which not; 2) determination of the partial concentration of each of the salts present in the solution. Within the first approach, both parts of the problem are solved simultaneously, with a single neural network (perceptron) with several outputs, each of them estimating the concentration of the corresponding salt. The second approach uses data clusterization by Kohonen networks for consequent identification of component composition of the solution by the cluster, which the spectrum of this solution falls into. Both approaches and their results are discussed in this paper.

Optical imaging of fluorescent carbon biomarkers using artificial neural networks

Abstract. The principle possibility of extraction of fluorescence of nanoparticles in the presence of background autofluorescence of a biological environment using neural network algorithms is demonstrated. It is shown that the methods used allow detection of carbon nanoparticles fluorescence against the background of the autofluorescence of egg white with a sufficiently low concentration detection threshold (not more than 2  μg/ml for carbon dots and 3  μg/ml for nanodiamonds). It was also shown that the use of the input data compression can further improve the accuracy of solving the inverse problem by 1.5 times.

Identification of inorganic salts and determination of their concentrations in aqueous solutions based on the valence Raman band of water using artificial neural networks

The characteristic features of the valence Raman band of water in the solutions of electrolytes are revealed. These features allow the noncontact recognition of the type of salt and the determination of its concentration in aqueous solutions using artificial neural networks.