Yu. V. Ryabchikov

Silicon Nanocrystals As Photosensitizers of Active Oxygen for Biomedical Applications

Silicon nanocrystals dispersed in water have been used to photosensitize the generation of active oxygen. The photosensitizing efficiency has been estimated through the quenching of the exciton photoluminescence of silicon nanocrystals. Experiments have revealed a strong (up to 80%) decrease in the number of cancer mouse fibroblast cells when they come into contact with photoexcited silicon nanocrystals. The obtained results show that the use of silicon nanocrystals for biomedical applications, in particular, for photodynamic therapy of cancer, is feasible.

Femtosecond nanostructuring of silicon surfaces

Nanostructures were formed upon the irradiation of single-crystal silicon surfaces with femtosecond laser pulses. These nanostructures were detected using scanning electron microscopy, Raman spectroscopy, and a photoluminescence technique.

Detection of Listeria innocua on roll-to-roll produced SERS substrates with gold nanoparticles

The rapid and accurate detection of food pathogens plays a critical role in the early prevention of foodborne epidemics. Current bacteria identification practices, including colony counting, polymerase chain reaction (PCR) and immunological methods, are time consuming and labour intensive; they are not ideal for achieving the required immediate diagnosis. Different SERS substrates have been studied for the detection of foodborne microbes. The majority of the approaches are either based on costly patterning techniques on silicon or glass wafers or on methods which have not been tested in large scale fabrication. We demonstrate the feasibility of analyte specific sensing using mass-produced, polymer-based low-cost SERS substrate in analysing the chosen model microbe with biological recognition. The use of this novel roll-to-roll fabricated SERS substrate was combined with optimised gold nanoparticles to increase the detection sensitivity. Distinctive SERS spectral bands were recorded for Listeria innocua ATCC 33090 using an in-house build (785 nm) near infra red (NIR) Raman system. Results were compared to both those found in the literature and the results obtained from a commercial time-gated Raman system with a 532 nm wavelength laser excitation. The effect of the SERS enhancer metal and the excitation wavelength on the detected spectra was found to be negligible. The hypothesis that disagreements within the literature regarding bacterial spectra results from conditions present during the detection process has not been supported. The sensitivity of our SERS detection was improved through optimization of the concentration of the sample inside the hydrophobic polydimethylsiloxane (PDMS) wells. Immunomagnetic separation (IMS) beads were used to assist the accumulation of bacteria into the path of the beam of the excitation laser. With this combination we have detected Listeria with gold enhanced SERS in a label free manner from such low sample concentrations as 104 CFU ml−1.

Photoluminescence in semiconductor structures based on butyl-substituted erbium phthalocyanine complexes

The study is concerned with the luminescence properties of ensembles of semiconductor structures containing organic phthalocyanine molecules with erbium ions as complexing agents. The photoluminescence spectra of the structures of the type of erbium monophthalocyanine, bisphthalocyanine, and triphthalocyanine are recorded. The photoluminescence peaks are detected at the wavelengths 888, 760, and 708 nm (and photon energies 1.4, 1.6, and 1.75 eV) corresponding to electronic transitions within the organic complexes. It is found that, when a metal complexing agent is introduced into the molecular structure of the ligand, the 708 nm luminescence peak becomes unobservable. It is shown that, in the bisphthalocyanine samples, the photoluminescence signal corresponding to transitions from the 4F9/2 level of erbium ions is enhanced.

Photosensitized generation of singlet oxygen in powders and aqueous suspensions of silicon nanocrystals

The photoluminescence spectra and kinetics in powders and aqueous suspensions produced from porous silicon layers are studied. The systematic features of photosensitized generation of singlet oxygen by silicon nanocrystals in the samples are established. The dependence of the efficiency of generation of singlet oxygen on the pressure of molecular oxygen is analyzed. It is concluded that the generation can be described on the basis of concepts of energy transfer from photoexcited silicon nanocrystals to oxygen molecules adsorbed at the nanocrystal surface to the concentration described by Langmuir’s adsorption model. The processes limiting the efficiency of photosensitized generation of singlet oxygen in the systems are discussed.

Vibronic properties of organic semiconductors based on phthalocyanine complexes with asymmetrically distributed electron density

This study is concerned with the optical properties of organic semiconductors based on lanthanide (III) biphthalocyanine and triphthalocyanine complexes with asymmetrically distributed electron density. The ClPcLutBuPc biphthalocyanine and ClPcEuBuPcLuBuPc triphthalocyanine solid films (ClPc = 2, 3, 9, 10, 16, 17, 23, 24-octachlorophthalocyaninate, tBuPc = 2(3), 9(10), 16(17), 23(24)-tetra- tretbutylphthalocyani-nate, BuPc = 2, 3, 9, 10, 16, 17, 23, 24-octabutylphthalo cyaninate) are fabricated, and their transmittance spectra in the middle infrared region are studied. Analysis of the transmittance spectra shows that the addition of complexity to phthalocyanine molecules yields some changes in the spectra. Specifically, the isoindole group can exhibit vibronic properties in the form of four absorption lines in the range 1400–1450 cm-1. New absorption lines that may be due to chlorine-carbon bonds are observed in the far-infrared region.

Features of the spectral dependences of transmittance of organic semiconductors based on tert-butyl substituted lutetium phthalocyanine molecules

Vibronic properties of organic semiconductors based on tert-butyl substituted phthalocyanine lutetium diphthalocyanine molecules are studied by IR and Raman spectroscopy. It is shown that substitution of several carbon atoms in initial phthalocyanine (Pc) ligands with 13C isotope atoms causes a spectral shift in the main absorption lines attributed to benzene, isoindol, and peripheral C-H groups. A comparison of spectral characteristics showed that the shift can vary from 3 to 1 cm−1.

Silicon nanocrystals as efficient photosensitizer of singlet oxygen for biomedical applications

Luminescent silicon nanocrystals (nc-Si) are shown to be efficient photosensitizers of singlet oxygen (SO) generation. Photoluminescence (PL) spectroscopy method is used to study the mechanism and efficiency of the SO photosensitization in gaseous and aqueous ambiences. In vitro experiments demonstrated that the SO, photosensitized by nc-Si dispersed in nutrient solutions, could kill cancer cells. This finding opens a broad opportunity for biomedical applications of nc-Si, e.g. for the photodynamic therapy of cancer or antibacterial treatments.

Effect of adsorption of the donor and acceptor molecules at the surface of porous silicon on the recombination properties of silicon nanocrystals

The effect of adsorption of the donor and acceptor molecules on the spectra of photoluminescence and electron spin resonance (ESR) of microporous silicon is studied. It is found that photoluminescence of microporous silicon is quenched, the photoluminescence peak shifts to shorter wavelengths, and the intensity of the ESR signal increases after adsorption of molecules of nitrogen dioxide and pyridine. The results obtained are interpreted using a model of radiative excitonic recombination in porous silicon that takes into account the formation of both the charged (NO2)− and (C5H5N)+ complexes and defects (e.g., dangling bonds at the silicon surface) at the surface of silicon nanocrystals.

Structural properties of gold-silicon nanohybrids formed by femtosecond laser ablation in water at different fluences

A gold target was ablated by femtosecond laser radiation in aqueous solutions of preliminarily prepared Si nanoparticles. The ablation process led to the formation of Au-based spherical colloids with the mean size around 5–10 nm and a weak abundance of larger species. Transmission Electron Microscopy (TEM) and Energy Dispersive X-ray (EDX) analysis revealed the presence of Au and Si in colloid composition, while the stoichiometry of colloids did not depend on laser fluence during the fabrication experiments. The formation of Au-Si nanohybrid structure was explained by an effect of the interaction of laser-ablated Au nanoclusters with water-dispersed Si nanoparticles. The fabricated structures can be of importance for biomedical, catalysis, and photovoltaics applications.