Generation of singlet oxygen with the use of optically excited fullerenes and fullerene-like nanoparticles

Experimental results and a kinetic model of generation of singlet oxygen during the interaction of oxygen molecules with optically pumped (lamp or laser radiation) fullerenes or fullerene-like nanoclusters in solutions, suspensions, and the form of various solid-phase membranes (surfaces) are presented. The experimental data on the photoluminescence of singlet oxygen in solutions of fullerenes are compared with the results of numerical simulation on the basis of the kinetic model with specified constants of photochemical processes. On the basis of the experimental results, it is shown that evaporation of a solution caused by pumping radiation yields long-lived gas-phase singlet oxygen. Release of gas-phase singlet oxygen from solid-phase fullerene-containing membranes (surfaces) is also demonstrated; however, this process is hindered by adsorption of singlet oxygen on the membrane surface. The prospects for creation of a singlet-oxygen generator on the basis of photoexcited fullerene molecules and fullerene-like nanoclusters are discussed.     

EPR diagnostics of the photosensitized generation of singlet oxygen on the surface of silicon nanocrystals

Electron paramagnetic resonance spectroscopy is used to determine the concentration of excited (singlet) molecular oxygen photosensitized by silicon nanocrystals. The generation of singlet oxygen in the porous silicon layers is studied quantitatively at various oxygen pressures and exciting light intensities with the use of the technique proposed. The experimental results indicate that silicon nanoclusters as the photosensitizers of singlet oxygen are promising for biomedical applications.     

Photosensitization of oxygen molecules by surface-modified hydrophilic porous Si

Hydrophilic porous Si is prepared by surface modification with polyethylene oxide (PEO) molecules. The surface modification is confirmed by infrared absorption spectroscopy and photoluminescence spectroscopy. The effect of surface modification on the efficiency of photosensitization of oxygen molecules, i.e., the efficiency of singlet oxygen generation, is studied. The PEO-terminated hydrophilic porous Si is shown to hold the photosensitization ability although the efficiency is reduced by the modification.     

Investigation of the generation of singlet oxygen in ensembles of photoexcited silicon nanocrystals by electron paramagnetic resonance spectroscopy

The generation of singlet oxygen is investigated and its concentration upon photoexcitation of silicon nanocrystals in porous silicon layers is determined using electron paramagnetic resonance spectroscopy. The relaxation times of spin centers, i.e., silicon dangling bonds, in vacuum and in an oxygen atmosphere in the dark and under illumination of the samples are measured for the first time. It is revealed that the spin-lattice relaxation in porous silicon is retarded as compared to that in a single-crystal substrate. From analyzing experimental data, a microscopic model is proposed for interaction of oxygen molecules in the triplet state and spin centers at the surface of silicon nanocrystals. The results obtained have demonstrated that porous silicon holds promise for the use as a photosensitizer of molecular oxygen in biomedical applications.     

Quenching of porous silicon photoluminescence by molecular oxygen and dependence of this phenomenon on storing media and method of preparation of pSi photosensitizer

The quenching of porous silicon photoluminescence (pSi PL) by molecular oxygen has been studied in different storing media in an attempt to clarify the mechanism of the energy transfer from the silicon photosensitizer to the oxygen acceptor. Luminescent materials have been prepared by two methods: electrochemical anodizing and chemical etching. Different structural forms were used: porous layers on silicon wafer and two kinds of differently prepared powder. Dry air and liquid water were employed as storing media; quenching behaviour was under observation until total degradation of quenching properties. Singlet oxygen molecules generation through energy transfer from photoluminescent pSi was the only photosensitizing mechanism observed under dry gas conditions. This PL quenching process was preferentially developed at 760 nm (1.63 eV) that corresponds to the formation of the ¹Σ singlet oxygen state. Oxidation of the pSi photosensitizer was the main factor that led to its total deactivation in a time scale of few weeks. Regarding water medium, different photosensitizing behaviour was observed. In watery conditions, two preferred energy levels were found: the one detected in dry gas and another centred at approximately 2.2 eV (550 nm). Formation of reactive oxygen species (ROS) different from singlet oxygen, such as superoxide anion or superoxide radical, can be responsible for the second one. This second quenching process developed gradually after the initial contact of pSi photosensitizer with water and then degraded. The process lasted only several hours. Therefore, functionalization of the pSi photosensitizer is probably required to stabilize its PL and quenching properties in the watery physiological conditions required for biomedical applications.     

Optical spectra of high-symmetry isomers 60(CH3-r 6-H)n at n=3, 6

Earlier, we found the energies of formation and the electron band structures of the fullerene molecule C₆₀ and its methylated and hydrogenated chemical derivatives with saturated r ₆ bonds of the type C₆₀(CH₃-r ₆-H)_n with n from 1 to 6. Based on the self-consistent molecular-orbital method, we found the energies of singlet and triplet excitations for each molecule by the ΔSCF technique. We compared the electron structure of the fullerene molecule with experimental data and other theoretical calculations and showed that the semiempirical quantum-chemical technique used in our work satisfactorily explains the experimental photoluminescence spectra of fullerene-containing star-shaped polystyrenes. Partial or complete removal of the dipole inhibition for the transitions in isomers that are formed upon chemical saturation of double bonds makes it possible to follow changes in the electron structure of the pπ shell of the fullerene molecule by spectroscopic techniques. Specific optical spectra of the first excited singlet states (spectra of absorption, luminescence, and excitation of luminescence) as well as phosphorescence of the first spin-triplet state are described.     

On the possibility of writing thin amplitude-phase holograms in the near infrared range (λ=1315 nm) using polyimide-based fullerene-containing conjugated organic structures

The process of writing thin amplitude-phase holograms in polyimide-based fullerene-containing conjugated organic media using an iodine laser operating at λ=1315 nm was studied. It is shown that such polymeric structures are promising media for reversible optical data recording in the IR spectral range.     

Silicon nanocrystals as photo- and sono-sensitizers for biomedical applications

Silicon nanocrystals (nc-Si) with sizes of about 2÷5 nm prepared from porous Si act as photosensitizers of the singlet oxygen generation revealed by direct detection of the luminescence at 0.98 eV (1270 nm). In vitro experiments show a suppression of the cancer cell proliferation because of the effect of photo-excited nc-Si. Aqueous suspensions of nc-Si formed by mechanical grinding (milling) of crystalline and porous Si exhibit properties of efficient sonosensitizers. A destruction of cancer cells under ultrasound irradiation in the presence of nc-Si is observed in vitro. Possible applications of nc-Si as photo- and sono-sensitizers for cancer therapy are discussed.     

Time-resolved luminescence and singlet oxygen formation under illumination of hypericin in acetone

We present time- and spectral-resolved phosphorescence study of hypericin as well as evolution of singlet oxygen formation and elimination under the illumination of hypericin in acetone solution. The obtained time-resolved hypericin phosphorescence can be satisfactorily fitted by using a two-exponential decay curve. The value of shorter component is about 0.29 μs and is independent of the hypericin concentration in the studied range (2–200 μM). The rise time of singlet oxygen production matches this value perfectly. It confirms that singlet oxygen formation represents the significant channel of hypericin triplet state deactivation under aerobic conditions at room temperature. The total phosphorescence intensity of hypericin is linearly proportional to the hypericin concentration within the studied concentration range, but the singlet oxygen phosphorescence intensity exhibits saturation behavior. This observation is a result of at least two effects: quenching of singlet oxygen by hypericin, as well as quenching of singlet oxygen by singlet oxygen.     

Luminescence and photosensitization properties of ensembles of silicon nanocrystals in terms of an exciton migration model

The relaxation processes that occur in ensembles of coupled silicon nanocrystals are described by a quantitative model that takes into account the energy transfer between them during exciton migration. This model is used to study the formation of singlet oxygen during the photoexcitation of silicon nanocrystals in porous silicon layers under various external conditions. It is experimentally found that, upon fine milling of as-deposited porous silicon films, the photoluminescence decay time increases despite an increase in the concentration of point defects. The photosensitized activity of ensembles of silicon nanocrystals degrades monotonically during their photostimulated oxidation. These experimental results agree completely with the conclusions of the model and are explained by a decrease in the number of exciton migration ways between nanocrystals when the granule size of a porous silicon powder decreases and by an increase in the efficiency of nonradiative recombination during the photostimulated oxidation of the nanocrystals. Our data indicate that nanocrystalline silicon is a promising material for the methods of nontoxic photodynamic therapy of oncological diseases.     

射流式氧发生器的三维模拟研究

实现了对射流式氧发生器的三维仿真模拟,给出了氧发生器内部流场结构、各组分的分布状态等信息。研究了射流孔结构对氧发生器性能的影响。指出即便是具有相同比表面积的不同射流孔排布方式,也会对发生器性能产生影响。此外,逆向射流式氧发生器反应器中气体从双侧进入对于减小发生器对气体的阻力具有重要作用。     

Singlet Oxygen Generation Enhanced by Silver-Pectin Nanoparticles

We demonstrate the potential application of silver-pectin nanoparticles on photodynamic therapy, on a solution-base platform. Photodynamic therapy is a medical technique which uses a combination of photosensitizing drugs and light to induce selective damage on the target tissue, by electronically excited and highly reactive singlet state of oxygen. Metal enhanced singlet oxygen generation in riboflavin water solution with silver-pectin nanoparticles was observed and quantified. Here 13 nm silver nanospheres enclosed by a pectin layer were synthesized and it interaction with riboflavin molecule was analyzed. Pectin, a complex carbohydrate found in plants primary cell walls, was used to increase the biocompatibility of the silver nanoparticles and to improve metal enhanced singlet oxygen generation (28.5 %) and metal-enhanced fluorescence (30.7 %) processes at room temperature. The singlet oxygen sensor fluorescent green reagent was used to quantify the enhancement of the riboflavin singlet oxygen production induced by the silver colloid. We report a 1.7-fold increase of riboflavin emission and a 1.8-fold enhancement of singlet oxygen production.     

Metal-enhanced Singlet Oxygen Generation: A Consequence of Plasmon Enhanced Triplet Yields

In this Rapid Communication, we report the first observation of Metal-Enhanced singlet oxygen generation (ME¹O₂). Rose Bengal in close proximity to Silver Island Films (SiFs) can generate more singlet oxygen, a three-fold increase observed, as compared to an identical glass control sample but containing no silver. The enhanced absorption of the photo-sensitizer, due to coupling to silver surface plasmons, facilitates enhanced singlet oxygen generation. The singlet oxygen yield can potentially be adjusted by modifying the choice of MEF (Metal-Enhanced Fluorescence) & MEP (Metal Enhance Phosphorescence) parameters, such as distance dependence for plasmon coupling and wavelength emission of the coupling fluorophore. This is a most helpful observation in understanding the interactions between plasmons and lumophores, and this approach may well be of significance for singlet oxygen based clinical therapy.     

The influence of excitation radiation parameters on photosensitized generation of singlet oxygen in water

Photosensitized generation of singlet oxygen with the aid of Radahlorin® photosensitizer has been investigated. The dependences of the intensity of singlet oxygen phosphorescence and photosensitizer fluorescence on the excitation radiation wavelength in the range of 350–440 nm and on the irradiation dose have been obtained. The dependence of the ratio of the sensitizer fluorescence intensity at about 670 nm to the singlet oxygen phosphorescence intensity at a wavelength of 1270 nm on the excitation radiation wavelength is found to be nonmonotonic and have a minimum near the center of the absorption band on its red wing. The results obtained can be used to monitor the singlet oxygen concentration in solutions.     

关于PDT光敏剂敏化效应光谱及其量子产率的研究

从实验的角度研究了HA光敏剂激发态的敏化特性,建立了单态氧量子产率在近红外区的荧光光谱测量系统,测定了HA光敏剂的单态氧量子产率为0．78。结果表明,该类光敏剂具有较强的敏化效应,是一类有前途的光动力治疗(PDT)候选光敏剂。     

射流式单重态氧发生器理论模型

 射流式单重态氧发生器(JSOG)是化学氧碘激光器十分重要的能源部分,它主要是通过解气相、液相扩散方程来求解发生器出口的氯的利用率和单重态氧的产率。在实际工作中的射流发生器非常复杂,其扩散方程和边界条件为非线性,非齐次边界条件,非齐次泛定方程组,求解难度较大。通过边界条件,采用试探解的方法,解得氯、总氧、单重态氧的气相、液相扩散方程,得到了氯的利用率,及单重态氧产率的解析解,与实验结果基本相符。     

Structural and optical properties of solid-phase singlet oxygen photosensitizers based on fullerene aqueous suspensions

The relationship between the structural and photosensitizing properties of solid-phase particles of fullerene C₆₀ in aqueous suspensions is studied using the methods of absorption spectroscopy, electron spin resonance spectroscopy (ESR), X-ray diffraction, and spectrophotometry of solutions of singlet oxygen chemical traps—histidine in combination with p-nitrosodimethylaniline. Two new variants are proposed for obtaining aqueous suspensions of particles of solid-phase fullerene whose structures are disordered and whose degrees of amorphization are 67 and 40%, respectively. It is shown that an increase in the disorder of the structure of particles in suspensions and a decrease in their average size facilitate an increase in the formation efficiency of singlet oxygen by solid-phase fullerene presumably due to an in increase in the concentration of surface localized excitons.     

Recording of dynamic holograms by nanosecond and picosecond laser pulses in solid-state fullerene-containing matrices

The results of a complex investigation of the recording of dynamic holograms by pulsed radiation with a duration of 20 ns and 300 ps in fullerene-containing media based on porous glasses and polymethyl methacrylate matrices are reported. Spectral analysis of these media in the range 300–700 nm was performed. The efficiency of hologram recording was found to relate with the occurrence of a band at 330 nm in the absorption spectrum of a medium. It is shown that dynamic holograms can be recorded in the fullerene-containing media by nanosecond and picosecond pulses. In the latter case, holograms arise mainly due to a change in the electronic polarizability of fullerene molecules, which is almost inertialess. The results obtained can be used in the development of ultrafast switching devices based on dynamic holograms.     

Biophysical Properties of Phenyl Succinic Acid Derivatised Hyaluronic Acid

Modification of hyaluronic acid (HA) with aryl succinic anhydrides results in new biomedical properties of HA as compared to non-modified HA, such as more efficient skin penetration, stronger binding to the skin, and the ability to blend with hydrophobic materials. In the present study, hyaluronic acid has been derivatised with the anhydride form of phenyl succinic acid (PheSA). The fluorescence of PheSA was efficiently quenched by the HA matrix. HA also acted as a singlet oxygen scavenger. Fluorescence lifetime(s) of PheSA in solution and when attached to the HA matrix has been monitored with ps resolved streak camera technology. Structural and fluorescence properties changes induced on HA-PheSA due to the presence of singlet oxygen were monitored using static light scattering (SLS), steady state fluorescence and ps time resolved fluorescence studies. SLS studies provided insight into the depolymerisation kinetics of PheSA derivatised HA matrix in the presence of singlet oxygen. Time resolved fluorescence studies grave insight into the dynamics of the reaction mechanisms induced on HA-PheSA by singlet oxygen. These studies provided insight into the medical relevance of PheSA derivatised HA: its capacity of scavenging singlet oxygen and of quenching PheSA fluorescence. These studies revealed that HA-PheSA is a strong quencher of electronic excited state PheSA and acts as a scavenger of singlet oxygen, thus medical applications of this derivatised form of HA may protect tissues and organs, such as skin, against reactive oxygen species damage.     

Chemically pumped O2(a-X) laser

A theoretical and experimental study was conducted aimed at achieving laser oscillation in the (a-X) electronic transition of oxygen molecules. Although this transition is highly forbidden by rigorous selection rules, it may nevertheless concede stimulated emission, if the population inversion is high enough. The idea is based on a recently developed apparatus, namely, a porous pipe type high-pressure chemical singlet oxygen generator. A numerical model which describes the characteristics of this generator was developed to estimate the population inversion and small-signal gain achievable in a laser cavity using this source. The calculations showed that the small-signal gain ought to be sufficient to achieve laser oscillation. Preliminary experiments were conducted, but lasing was not yet observed. It is shown that the scattering losses caused by water droplet aerosols are mainly responsible for preventing our system from laser oscillation.