In this paper, we have investigated the optical properties of a newly synthesized material consisting of a few-nm-thin flakes of ruby ( Al2O3:Cr3+), referred to as rubyene. Both theoretical and experimental approaches focus on the photoluminescence of Cr3+, particularly exploring the effects of the refractive index of the surrounding medium on the radiative and nonradiative lifetimes of the photoexcited chromium ions, and the consequences of the diverse shapes of the thin rubyene flakes. Notably, we demonstrate how such susceptibility of the radiative rates to the refractive index allows for insight into the orientation of the crystallographic axes relative to the surface of the flakes. Although the effect of the environment on the nonradiative relaxation rates is an order of magnitude smaller than its effect on the radiative rates, the achieved sensitivity of our measurements was sufficient to observe both. The presented theoretical analysis of nonradiative transitions has broader implications for F & ouml;rster-type energy transfer, especially in scenarios where the refractive index of the medium is non-uniform. Our results demonstrate good agreement between the theory and the experiment and establish the potential of rubyene in optical nanosensing applications, highlighting its sensitivity to environmental refractive index changes.

Forster resonance energy transfer (FRET) provides a unique means to probe processes occurring on the nanoscale. Efficient point-to-plane FRET between acceptors arrayed in two-dimensional (2D) sheets and point-dipole donors is known to exhibit an energy transfer proportional to d(-4), where d is the distance from the donor to the acceptor-plane. We developed a 2D nanomaterial with surface-adjacent acceptors based on chromium-doped aluminum oxide (ruby) that supports 2D-FRET architecture. Ruby exhibits bright, narrow-band photoluminescence with a long lifetime and excellent photostability, and it was synthesized and processed to yield 2D ruby nanoflakes of 5 nm thickness, termed "rubyene". Rubyenes exhibit FRET with a remarkable efficiency of 96% as the donor paired with the acceptor indocyanine green (ICG) dye, exhibiting a distance dependence of d(-n), where n varies from 4 to 6, as determined by the acceptor surface density. The dependence approaches d(-4) in the limit of the acceptors' continuum distribution. The developed model of the random distribution of donor Cr3+ ions inside rubyenes and a discrete planar array of the acceptor ICG molecules in combination with high-density surface traps acting as nonresonant acceptors provides a nearly perfect fit to the experimental results and explains the emission lifetime variation from 5.8 to 0.7 versus the ICG surface density. We envisage potential applications of the demonstrated rubyenes for environmental sensing, optical labeling, FRET-scaled precision measurement, and engineered emission lifetime for multiplexed imaging.

We propose a method for obtaining a fluorescence tomographic image for visualization and diagnosis of tissues of a living organism. The method is based on the excitation of the luminescence of multicolor upconverting nanoparticles localized in the depth of the biological tissue or a phantom imitating it by IR light. By recording the changes in the shape of the spectrum of the intensity of luminescence radiation from luminescent nanoparticles on the surface of the tissue, it is possible to obtain information about the depth of their occurrence. To implement this approach, upconverting nanoparticles were synthesized on the base of β-NaYF 4 crystal matrix doped with rare-earth elements Yb 3+ , Er 3+ , and Tm 3+ . The luminescence spectra of the produced nanoparticles upon excitation at a wavelength of 980 nm contain three narrow bands with maxima at wavelengths 540, 655, and 800 nm.

Rationale: Riboflavin (vitamin B2) is one of the most promising agents for photodynamic therapy (PDT). However, its use is limited by the excitation in the ultraviolet (UV) and visible spectral ranges and, as a result, by a small penetration into biological tissue not exceeding a few millimeters. This problem could be solved by approaches ensuring excitation of riboflavin molecules within tumor tissues by infrared (IR) light. Upconversion nanoparticles (UCNPs) can be potentially considered as mediators able to effectively convert the exciting radiation of the near IR range, penetrating into biological tissue to a 3 cm depth, into the photoluminescence in the UV and visible spectral ranges.Aim: To evaluate the efficacy of UCNPs for IR-mediated riboflavin activation in the depth of tumor tissue during PDT. Materials and methods: The water-soluble riboflavin flavin mononucleotide (FMN, Pharmstandard-UfaVITA, Russia) was used as a photosensitizer in in vitro and in vivo experiments. The in vitro experiments were performed on human breast adenocarcinoma SK-BR-3, human glioblastoma U-87 MG, and rat glioma C6 cell lines. Lewis lung carcinoma (LLC) inoculated to hybrid BDF1 mice was used as a model to demonstrate the delivery of FMN to the tumor. UCNPs with a core/shell structure [NaYF4:Yb3+, Tm3+/NaYF4] were used for photoactivation of FMN in vivo. PDT based on FMN, UCNPs and laser radiation 975 nm (IR) was performed on mouse xenografts of human breast adenocarcinoma SKBR-3.Results: We were able to show that FMN could act as an effective in vitro photosensitizer for SK-BR-3, U-87 MG, and C6 cell lines. FMN IC50 values for glioma cells were ~30 μM, and for SK-BR-3 cell line ~50 μM (24 h incubation, irradiation 4.2 J/cm2). In the LLC model, the appropriate concentration of FMN (30 μM and above) can be achieved in the tumor as a result of systemic administration of FMN (at 2 and 24 hours after injection). The effect of PDT using near IR light for UCNP-mediated excitation of FMN was demonstrated in mouse xenografts SKBR-3, with the tumor growth inhibition of 90±5%.Conclusion: The study has demonstrated the possibility to use riboflavin (vitamin B2) as a photosensitizer for PDT. The photoexcitation of FMN via the anti-Stokes photoluminescence of UCNPs allows for implementation of the PDT technique with the near IR spectral range.

AbstractWe propose a method for obtaining a fluorescence tomographic image for visualization and diagnosis of tissues of a living organism. The method is based on the excitation of the luminescence of multicolor upconverting nanoparticles localized in the depth of the biological tissue or a phantom imitating it by IR light. By recording the changes in the shape of the spectrum of the intensity of luminescence radiation from luminescent nanoparticles on the surface of the tissue, it is possible to obtain information about the depth of their occurrence. To implement this approach, upconverting nanoparticles were synthesized on the base of β-NaYF_4 crystal matrix doped with rare-earth elements Yb^3+, Er^3+, and Tm^3+. The luminescence spectra of the produced nanoparticles upon excitation at a wavelength of 980 nm contain three narrow bands with maxima at wavelengths 540, 655, and 800 nm.

We present the concept and the experimental demonstration of near-infrared photopolymerization assisted by specially designed upconversion nanophosphors. The principle of this technique is based on conversion of 980 nm laser irradiation to ultraviolet photons subsequently absorbed by photoinitiator. The nonlinearity of upconversion allows for activation of the process locally in the laser beam waist. This approach enables precise fabrication of 3D constructs directly in the volume of photocurable composition. Furthermore, the presented technique is suitable for polymerization of a wide range of photocurable resins as well as gelation of hydrogels for biomedical applications.

Purpose: an experimental implementation of scleral collagen crosslinking using a new device that enables low-invasive delivery of UVA radiation combined with riboflavin onto the equatorial and posterior pole areas of the eye. For UVA sclera crosslinking, a device was manufactured which contains a LED source of continuous UVA radiation (wavelength 370 nm, radiation intensity 3 mW/cm(2)), connected via a matching optics with multimode quartz optical fiber encased in a polymer shell. This fiber is located in one of the two channels of a dual removable metal ferrule; the second (hollow) channel is designed for simultaneous delivery of riboflavin solution onto the surface of the sclera. The device was used to perform scleral crosslinking on 8 eyes of Chinchilla rabbits. The intact fellow eyes served as controls. Prior to the procedure, as well as 2 days after it and 1 month after it, the acoustic density of the sclera (ADS) was measured in vivo using an ultrasound device, VOLUSON 730 Pro (Kretz). At the same time points, the elasticity modulus of scleral samples were determined on the testing machine (Autograph AGS-H, SHIMADZU, Japan) and the level of collagen crosslinking was measured using differential scanning calorimetry (calorimeter, Phoenix DSC 204, Netzsch, Germany). After UVA treatment, ADS grew from 86.7 +/- 5.1 to 98 +/- 4.9 dB, the elasticity modulus was found to be 1.5 times higher than the control, while denaturation temperature growth matched the 15-18% increase of cross linking of scleral collagen. The outcome of experimental implementation of low-invasive technology for scleral collagen crosslinking shows that it as a promising method of scleral strengthening treatment of progressive myopia which requires further clinical studies.

Non-contact optical diagnostics of structural disorders of the eye has a number of advantages: high speed, accuracy and a large range of parameters available for analysis. The paper presents the results of studies of the photoluminescence of the fibrous tunic of the eye, excited by polarized light, depending on the intraocular pressure. In the experiments, isolated de-epithelized eyes of the rabbit were used, inside of which pressure up to 50 mm Hg was artificially created. Under these conditions, the cornea and sclera were illuminated with linearly polarized light at wavelengths of 250, 350 and 450 nm, exciting photoluminescence in the wavelength range up to 700 nm. Cross and co-polarized photoluminescence spectra excited by linearly polarized light were obtained. It has been established that, when excited by polarized light, the photoluminescence of the cornea is partially polarized. Depending on the wavelength of the photoluminescence, the degree of polarization varies from 0.2 to 0.35. It is shown that the degree of polarization of the photoluminescence of the cornea of the eye upon excitation by linearly polarized light can be used as a measurable parameter for assessing the physiological state of the eye. It is shown that the photoluminescence spectrum consists of two bands with maxima near 460-470 and 430-440 nm. These bands are assigned, respectively, to pyridinnucleotides and glycosylated collagen. A significant contribution can be made by the epithelium of the eye, which contains riboflavin with characteristic absorption bands near 450 and 365 nm. When excited at 450 nm, the photoluminescence maximum is located near 540 nm, which corresponds to the spectrum of fluorophores in the endothelium and epithelium. The spectrum of photoluminescence upon excitation at a wavelength of 250 nm can be attributed to tryptophan located in the intraocular lens.

Three-dimensional (3D) rapid prototyping technology based on near-infrared light-induced polymerization of photocurable compositions containing upconversion nanomaterials has been explored. For this aim, the rationally-designed core/shell upconversion nanoparticles NaYF 4 :Yb 3+ ,Tm 3+ /NaYF 4 , with the distinct ultraviolet-emitting lines and unprecedentedly high near-infrared to ultraviolet conversion efficiency of η_UC^(UV)=2% have been used. The upconverted ultraviolet photons were capable to efficiently activate photoinitiators contained in light-sensitive resins under moderate intensities of NIR excitation below 10 W cm −2 and induce generation of radicals and photopolymerization in situ . Near infrared-activated polymerization process, both at the millimeter and sub-micron scales, was investigated. Polymeric macro- and microstructures were fabricated by means of near infrared laser scanning photolithography in the volume of liquid photocurable compositions with focused laser light at 975 nm wavelength. Examination of the polymerization process in the vicinity of the nanoparticles shows strong differences in the rate of polymer shell growth on flat and edge nanoparticle sides. This phenomenon mainly defines the resolution of the demonstrated near infrared - ultraviolet 3D printing technology at the micrometer scale level.

In recent years, the overwhelming majority of the upconversion nanoparticles (UCNPs) prominent applications have originated from their unique luminescent properties. Due to original properties of inorganic UCNPs they attract the interest in numerous fields. We discussed a number of UCNP assisted techniques, such as biomedical imaging, therapy agents, anti-counterfeit labels and 3D printing, showing highly versatile and translatable UCNP photoluminescent nanotechnology for the applications in industry and biomedicine.

3D printing became a widely used technique for tissue engineering applications. This additive technology enables easy fabrication of very complicated structures. However, selection and preparation of initial compositions for 3D printing satisfying high biocompatibility and processability requirements still remains challenging. One of the most promising materials for mimicking of the living tissues are hydrogels possessing properties close to native tissues. In this work, the printability of hydrogels based on hyaluronic acid and poly(ethylene glycol) derivatives dissolved in phosphate buffer saline in presence of flavin mononucleotide as an endogenous photosensitizer has been studied. To produce a hydrogel pattern, the extrusion of photocurable composition has been combined with its simultaneous photoinduced crosslinking under laser irradiation at 450 nm. Cytotoxicity of fabricated films and 3D scaffolds has been tested in vitro using human fibroblasts BJ-5ta.

Hyaluronic acid and poly(ethylene glycol) derivatives attract considerable attention as precursors for tissue engineering. In this paper photocuring of biocompatible hyaluronic acid-glycidyl methacrylate (HAGM) and poly(ethylene glycol) diacrylate (PEG-DA) aqueous solutions, using flavin mononucleotide (FMN) as an endogenous photoinitiator, has been studied. The required threshold concentrations of initial macromolecules in water for the strengthening (increase of the Young's modulus) of irradiated hydrogels have been determined as 57 wt% for 2D cross-linking of PEG-DA compositions and 16 wt% for 3D cross-linking of HAGM compositions. These concentrations are in a good agreement with correspondent values derived from the percolation theory for 2D and 3D lattices. It has been demonstrated that cross-linking proceeds predominantly by the radical mechanism and does not require co-initiators. Hydrogel scaffolds with specific and predetermined architectonics for biocompatibility and biomechanical studies have been produced by photopolymerizable micromolding. (C) 2017 Elsevier B.V. All rights reserved.

Recently introduced upconversion nanoparticles (UCNPs) have pushed the depth of photodynamic therapy (PDT) treatment to the centimetre range by converting deeply-penetrating near-infrared (NIR) radiation to visible radiation for photoexcitation of PDT drugs. Here we demonstrate that the direct exposure of the cancer tissue to phototoxic ultraviolet radiation generated by NIR-photoexcited UCNPs enabled successful PDT. To this aim, core/shell UCNPs of the formula NaYF4:Yb3+Tm3+/NaYF4 featuring an enhanced band in the ultraviolet UV-A and UV-B spectral bands were rationally designed and synthesised. Coupling UCNPs to the recombinant modules of the Designed Ankyrin Repeat Protein (DARPin) fused to a fluorescent protein mCherry allowed the target delivery of DARPin-mCherry/UCNP to human breast adenocarcinoma SK-BR-3 cells overexpressing HER2/neu receptors, as confirmed by fluorescence microscopy. DARPin-mCherry/UCNPs were demonstrated to be phototoxic to SK-BR-3 cells under 975 nm laser irradiation at a dose of 900 J cm-2 due to the UV photoexcitation of endogenous photosensitizers and concomitant generation of reactive oxygen species. The Lewis lung cancer mouse model was employed to demonstrate the feasibility of PDT using UCNP-mediated UV excitation of endogenous photosensitizers in the tumor tissue at a NIR dose of 1200 J cm-2. This study paves the way for exploring and harnessing UV photoexcitation processes in deep tissues in vivo.

Prospects for using upconversion nanoparticles as markers for tumor optical imaging are discussed. Using a model of epidermoid Lewis lung carcinoma engrafted in mice, luminescent signals from nanoparticles delivered into the tumor tissue are registered in vivo.

Biocompatible PEG-containing UCNPs were designed for in vivo passive targeting of tumor associated with UCNP efficient accumulation and tumor contrast visualization.

AIM To realize two minimally invasive techniques of scleral collagen cross-linking (SXL) at the equator and posterior pole of the eye: 1) targeted irradiation of the region with ultraviolet A (UVA) and 2) sub-Tenon injection of Sklerateks. MATERIAL AND METHODS To perform UVA-SXL, a tool was developed that includes a UV-LED light source (370 nm, 3 mW/cm2) and a polymer-coated silica multimode optical fiber located in one of the two channels of a detachable metal tip. The other channel is used to deliver riboflavin to the scleral surface. The study included 8 Chinchillas' eyes. Intact fellow eyes served as the controls. Scleral echodensity was measured in vivo with Voluson 730 Pro (Kretz) prior to the procedure and then 2 days and 1 month after. After enucleation, the elastic modulus and the degree of scleral cross-linking were established at the same time-points. A placebo-controlled study on the safety and effectiveness of sub-Tenon Sklerateks injections (solution of amino acid salts in the form of succinates) was conducted on 47 Chinchilla rabbits (94 eyes). Sklerateks or placebo (0.1 ml) was injected below the Tenon's capsule of either eye once a week for 1 month (4 injections; 1st series) or 3 months (12 injections; 2nd series). After the end of the course, 22 eyes were studied morphologically. In 72 eyes, scleral samples were obtained in order to evaluate the elastic modulus (Autograph AGS-H tester, SHIMADZU, Japan) and the rate of cross-linking (judging from the denaturation temperature) by differential scanning calorimetry (Phoenix DSC 204 calorimeter, Netzsch, Germany). RESULTS After UVA irradiation, the scleral echodensity increased from 86.7±5.1 to 98±4.9 dB. The elastic modulus appeared 1.5 times higher than that of the control samples. The denaturation temperature also increased indicating the rate of scleral cross-linking as high as 15-18%. Weekly Sklerateks for 1-3 months has been shown to induce neither clinical, nor morphological signs of local irritative, damaging, or toxic effect. The findings also include: a 1.8 times higher rate of scleral cross-linking, activation of cellular elements, neoformation of connective tissue on the scleral surface, and vascular growth, which together indicate a pronounced metabolic and strengthening effect of Sklerateks on the sclera. CONCLUSION Experimental results on minimally invasive techniques of SXL allow to recommend them for further clinical investigation as a promising treatment of progressive myopia.

Background: To improve quality of surgery in oncology, it is necessary to completely remove the tumor, including its metastases, to minimize injury to normal tissues and to reduce duration of an intervention. Modern methods of detection based on radiological computerized tomography and magnetic resonance imaging can identify a tumor after its volume has become big enough, i.e. it contains more than 10 billion cells. Therefore, an improvement of sensitivity and resolution ability of diagnostic tools to identify early stages of malignant neoplasms seems of utmost importance. Aim: To demonstrate the potential of a new class of anti-Stokes luminescence nanoparticles for deep optical imaging with high contrast of malignant tumors. Materials and methods: Upconversion nanoparticles with narrow dispersion and a size of 70 to 80 nm, with a core/shell structure of NaYF4:Yb3+:Tm3+/NaYF4 were used in the study. The nanoparticles have an intensive band of anti-Stokes photoluminescence at a wavelength of 800 nm under irradiation with a wavelength of 975 nm (both wavelengths are within the transparency window for biological tissues). The conversion coefficient of the excitation radiation into the anti-Stokes luminescence was 9%. To increase the time during which nanoparticles can circulate in blood flow of small animals, the nanoparticles were covered by a biocompatible amphiphilic polymer shell. As a tumor model we used Lewis epidermoid carcinoma transfected to mice. Results: We were able to obtain stable water colloids of nanoparticles covered with amphiphilic polymer that could preserve their initial size at least for one month. The use of upconversion nanoparticles with a hydrophilic shell made of intermittent maleic anhydride and octadecene co-polymer with subsequent coating with diglycidyl polyethylene glycol ether allowed for reduction of non-specific reaction of nanoparticles with plasma proteins. In its turn, it resulted in an increased time of their circulation in blood flow of small animals for up to 1 hour. With the Lewis lung carcinoma transfected to mice model we demonstrated аn in-life transportation of upconversion nanoparticles into the tumor with a high degree of localization due to a passive EPR effect. The contrast of luminescent signal in the tumor compared to adjacent tissues was at least 70%. The possibility of visualization of upconverted nanoparticles up to 15 mm of biological tissue was shown. Conclusion: The optical imaging techniques with anti-Stokes photoluminescent markers ensure a high contract real-time detection of tumor tissues that allows for their use for intra-operative diagnostics.

Modifications of the matrix of the tissue of costal cartilage under the impact of UV (λ = 365 nm) and a flavin mononucleotide (FMN) is studied. The changes in the macroscopic properties of the tissue are detected by means of differential scanning calorimetry and under the conditions of uniaxial compression during mechanical testing. The endothermic effects of the denaturation of the collagen framework of the tissue and the Young’s modulus are determined. It is shown that the presence of a flavin mononucleotide in the interstitial fluid leads lowers the temperature of collagen denaturation by 2.5°С and doubles the Young’s modulus. It is found that the temperature of denaturation and the Young’s modulus grow gradually after treating the tissue with the UV radiation, and their values ultimately exceed by far the corresponding values for intact samples. It is concluded that the obtained data indicate the possibility of stabilizing the framework of the matrix of costal cartilage under the impact of UV radiation and a flavin mononucleotide.