Upconverting nanoparticles have unique spectral and photophysical properties that make them suitable for development of theranostics for imaging and treating large and deep-seated tumors. Nanoparticles based on NaYF4 crystals doped with lanthanides Yb3+ and Er3+ were obtained by the high-temperature decomposition of trifluoroacetates in oleic acid and 1-octadecene. Such particles have pronounced hydrophobic properties. Therefore, to obtain stable dispersions in aqueous media for the study of their properties in vivo and in vitro, the polyethylene glycol (PEG)-glycerolipids of various structures were obtained. To increase the circulation time of PEG-lipid coated nanoparticles in the bloodstream, long-chain substituents are needed to be attached to the glycerol backbone using ether bonds. To prevent nanoparticle aggregation, an L-cysteine-derived negatively charged carboxy group should be included in the lipid molecule.

In the natural fluidic environment of a biological system, nanoparticles swiftly adsorb plasma proteins on their surface forming a “protein corona”, which profoundly and often adversely affects their residence in the systemic circulation in vivo and their interaction with cells in vitro. It has been recognized that preformation of a protein corona under controlled conditions ameliorates the protein corona effects, including colloidal stability in serum solutions. We report on the investigation of the stabilizing effects of a denatured bovine serum albumin (dBSA) protein corona formed on the surface of upconversion nanoparticles (UCNPs). UCNPs were chosen as a nanoparticle model due to their unique photoluminescent properties suitable for background-free biological imaging and sensing. UCNP surface was modified with nitrosonium tetrafluoroborate (NOBF4) to render it hydrophilic. UCNP-NOBF4 nanoparticles were incubated in dBSA solution to form a dBSA corona followed up by lyophilization. As produced dBSA-UCNP-NOBF4 demonstrated high photoluminescence brightness, sustained colloidal stability after long-term storage and the reduced level of serum protein surface adsorption. These results show promise of dBSA-based nanoparticle pretreatment to improve the amiability to biological environments towards theranostic applications.

Upconversion nanoparticles (UCNPs) are a promising nanoplatform for bioreagent formation for in vivo imaging, which emit UV and blue light under the action of near-infrared radiation, providing deep tissue penetration and maintaining a high signal-to-noise ratio. In the case of solid tumor visualization, the UCNP surface functionalization is required to ensure a long circulation time, biocompatibility, and non-toxicity. The effective UCNP accumulation in the solid tumors is determined by the disturbed architecture of the vascular network and lymphatic drainage. This work demonstrates an approach to the UCNP biofunctionalization with endogenous polysialic acid for in vivo bioreagent formation. Bioreagents possess a low level of nonspecific protein adsorption and macrophage uptake, which allow the prolongation of the circulation time in the bloodstream up to 3 h. This leads to an intense photoluminescent signal in the tumor.

Lanthanide-doped upconversion nanoparticles (UCNPs) are promising bioimaging agents that emit light under near infra-red excitation, capable of penetrating deep in biotissues with a high signal-to-noise ratio. Their successful implementation is principally associated with surface functionalization. Here, we report on UCNP surface modification with highly hydrophilic, endogenous, non-toxic, non-immunogenic colominic acid, conferring "stealth" properties. We proposed surface functionalization of UCNPs based on a two-step strategy, which consists of hydrophilization with polyethyleneimine and attachment of colominic acid by electrostatic or covalent bond formation. Analysis revealed that regardless of the nature of the bond, colominic acid acted as a non-cytotoxic UCNP surface coating with low nonspecific blood protein adsorption. UCNP-colominic acid nanocomplexes exhibited low uptake by macrophages in vitro, which plays an active role in inflammatory reactions. We demonstrated the superiority of colominic acid compared to polyethylene glycol coating in terms of the prolonged circulation time in the bloodstream of small animals when injected intravenously. The colominic acid coating made it possible to prolong the UCNP circulation time up to 3 h. This led to the efficient UCNP accumulation in the inflammation site due to microvascular remodeling, accompanied by an enhanced uptake and retention effect. UCNP-assisted imaging of inflammation in the whole-body mode as well as local visualization of blood vessels were acquired in vivo. These collective findings validate the functional significance of UCNP decoration with colominic acid for their application in bioimaging.

Local overheating of biotissue is a critical step for biomedical applications, such as photothermal therapy, enhancement of vascular permeability, remote control of drug release, and so on. Overheating of biological tissue when exposed to light is usually realized by utilizing the materials with a high-absorption cross section (gold, silica, carbon nanoparticles, etc.). Here, we demonstrate core/shell NaYF4:Yb3+, Tm3+/NaYF4 upconversion nanoparticles (UCNPs) commonly used for bioimaging as promising near-infrared (NIR) absorbers for local overheating of biotissue. We assume that achievable temperature of tissue labeled with nanoparticles is high enough because of Yb3+ resonance absorption of NIR radiation, whereas the use of auxiliary light-absorbing materials or shells is optional for photothermal therapy. For this purpose, a computational model of tissue heating based on the energy balance equations was developed and verified with the experimentally obtained thermal-graphic maps of a mouse in response to the 975-nm laser irradiation. Labeling of biotissue with UCNPs was found to increase the local temperature up to 2°C compared to that of the non-labeled area under the laser intensity lower than 1 W/cm2. The cellular response to the UCNP-initiated hyperthermia at subcritical ablation temperatures (lower than 42°C) was demonstrated by measuring the heat shock protein overexpression. This indicates that the absorption cross section of Yb3+ in UCNPs is relatively large, and microscopic temperature of nanoparticles exceeds the integral tissue temperature. In summary, a new approach based on the use of UCNP without any additional NIR absorbers was used to demonstrate a simple approach in the development of photoluminescent probes for simultaneous bioimaging and local hyperthermia.

The lanthanide-doped upconversion nanoparticles (UCNPs) gained great attention as nanoplatforms for optical bioimaging and drug delivery systems. In this work, we developed the multimodal system based on UCNPs modified with thermosensitive polymer and Ag nanoparticles (AgNPs), containing chemotherapeutics, such as doxorubicin and flavin mononucleotide, for visualization and therapy. The drug delivery, cytotoxicity and optical properties were studied.

Transformation of 3-vinylchlorins into azidomethyl-derivatives was investigated for chlorin p(6) trimethyl ester. The azide group allows modifying chlorophyll derivatives on pyrrole ring A by the use of "click reaction" with terminal alkynes. As an example, reaction with phenylacetylene was carried out.

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.

Detection systems with deferred registration of luminescence signals are promising for performing complex tasks of imaging of biological objects due to their simplicity and low cost. In the present work, β‑NaYF 4 :Tm 3+ Yb 3+ /NaYF 4 nanocrystals with anti-Stokes photoluminescence have been used in deferred registration systems. It has been shown that there is a significant time delay between the exciting laser pulse and luminescence signal, which makes it possible to use this class of nanoparticles in the creation of wide-field imaging systems with deferred registration. The possibility of using nanoparticles for detecting a photoluminescence signal in the second transparency window of biotissue has been demonstrated. This system can be based on the resonance excitation and detection of the photoluminescence signal of Yb 3 + ions.

Photopolymerization of nanocomposite materials using near infrared light is one of the unique technologies based on the luminescent properties of lanthanide-doped upconversion nanoparticles (UCNPs). We explored the UCNP-triggered radical polymerization both in oligomer bulk and on the nanoparticle surface in aqueous dispersion. Core/shell UCNPs NaYF4:Yb3+ and Tm3+/NaYF4 with emitting lines in the ultraviolet and blue regions were used to activate a photoinitiator. The study of the bulk photopolymerization in an initially homogeneous reaction mixture showed the UCNP redistribution due to gradient density occurring in the volume, which led to formation of UCNP superlattices and spheres frozen in a polymer matrix. We also developed a strategy of grafting from the surface, providing polymer shell growth directly on the nanoparticles. The photosensitization of the endogenous water-soluble photoinitiator riboflavin by the resonance energy transfer from UCNPs was demonstrated in the course of monomer glycidyl methacrylate polymerization followed by photocrosslinking with poly(ethylene glycol) diacrylate on the nanoparticle surface.

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.

AbstractDetection systems with deferred registration of luminescence signals are promising for performing complex tasks of imaging of biological objects due to their simplicity and low cost. In the present work, β‑NaYF_4:Tm^3+Yb^3+/NaYF_4 nanocrystals with anti-Stokes photoluminescence have been used in deferred registration systems. It has been shown that there is a significant time delay between the exciting laser pulse and luminescence signal, which makes it possible to use this class of nanoparticles in the creation of wide-field imaging systems with deferred registration. The possibility of using nanoparticles for detecting a photoluminescence signal in the second transparency window of biotissue has been demonstrated. This system can be based on the resonance excitation and detection of the photoluminescence signal of Yb^3 + ions.

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.

Upconversion nanoparticles (UCNPs) coated with polyethylenimine (PEI) are popular background-free optical contrast probes and efficient drug and gene delivery agents attracting attention in science, industry, and medicine. Their unique optical properties are especially useful for subsurface nanotheranostics applications, in particular, in skin. However, high cytotoxicity of PEI limits safe use of UCNP@PEI, and this represents a major barrier for clinical translation of UCNP@PEI-based technologies. Our study aims to address this problem by exploring additional surface modifications to UCNP@PEI to create less toxic and functional nanotheranostic materials. We designed and synthesized six types of layered polymer coatings that envelop the original UCNP@PEI surface, five of which reduced the cytotoxicity to human skin keratinocytes under acute (24 h) and subacute (120 h) exposure. In parallel, we examined the photoluminescence spectra and lifetime of the surface-modified UCNP@PEI. To quantify their brightness, we developed original methodology to precisely measure the colloidal concentration to normalize the photoluminescence signal using a nondigesting mass spectrometry protocol. Our results, specified for the individual coatings, show that, despite decreasing the cytotoxicity, the external polymer coatings of UCNP@PEI quench the upconversion photoluminescence in biologically relevant aqueous environments. This trade-off between cytotoxicity and brightness for surface-coated UCNPs emphasizes the need for the combined assessment of the viability of normal cells exposed to the nanoparticles and the photophysical properties of postmodification UCNPs. We present an optimized methodology for rational surface design of UCNP@PEI in biologically relevant conditions, which is essential to facilitate the translation of such nanoparticles to the clinical applications.

We report on hybrid nanocomposite scaffolds on the base of cross-linked hyaluronic acid derivative with embedded upconversion nanoparticles (UCNPs). The unique photoluminescence properties of specially designed hydrophilic UCNPs enable visualization of hydrogel using NIR irradiation. Formation of scaffold structure can be produced by means of 3D printing or direct laser writing. For the first time, we present visualization of nanohybrid scaffolds in live small animal aiming to demonstrate new possibilities of their luminescent remote control for tissue engineering.

We report of surface modification approaches of nanoparticles with anti-Stokes luminescence, known as upconversion nanoparicles (UCNPs), comprised of inorganic host NaYF4 codoped with Yb3+ and Er3+ or Tm3+ . These approaches enabled the facile, lossless preparation of hybrid polymer-encapsulated UCNPs suitable for bioassays. These probes inherited UCNP properties, such as excellent photoluminescence under excitation with NIR light from the biotissue “transparency window”, as well as they were dispersible in aqueous media and physiological buffers, exhibiting chemical stability. The feasibility of the hybrid UCNPs was demonstrated for in vitro bioassay and in vivo optical whole animal imaging using a home-built epiluminescence imaging system.

In this work are shown the prospects of using upconversion nanoparticles (UCNPs) as markers for contrast optical imaging of a tumor. For using nanoparticles for biomedical purposes is implemented a technique for coating nanoparticles with polymers, such as PEG and PSA. This approach provides low non-specific adsorption, which prolongs the circulation of UCNPs in mouse bearing Lewis Lung Cancer (LLC) up to 10 hours. These properties allow nanoparticles to quickly accumulate in the tumor. Effective delivery of particles with different polymer coatings in the tumor is demonstrated with the help of an epiluminescent imaging system.

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.