E. V. Khaydukov

Feasibility study of the optical imaging of a breast cancer lesion labeled with upconversion nanoparticle biocomplexes

Abstract. Innovative luminescent nanomaterials, termed upconversion nanoparticles (UCNPs), have demonstrated considerable promise as molecular probes for high-contrast optical imaging in cells and small animals. The feasibility study of optical diagnostics in humans is reported here based on experimental and theoretical modeling of optical imaging of an UCNP-labeled breast cancer lesion. UCNPs synthesized in-house were surface-capped with an amphiphilic polymer to achieve good colloidal stability in aqueous buffer solutions. The scFv4D5 mini-antibodies were grafted onto the UCNPs via a high-affinity molecular linker barstar:barnase (Bs:Bn) to allow their specific binding to the human epidermal growth factor receptor HER2/neu, which is overexpressed in human breast adenocarcinoma cells SK-BR-3. UCNP-Bs:Bn-scFv4D5 biocomplexes exhibited high-specific immobilization on the SK-BR-3 cells with the optical contrast as high as 10:1 benchmarked against a negative control cell line. Breast cancer optical diagnostics was experimentally modeled by means of epi-luminescence imaging of a monolayer of the UCNP-labeled SK-BR-3 cells buried under a breast tissue mimicking optical phantom. The experimental results were analyzed theoretically and projected to in vivo detection of early-stage breast cancer. The model predicts that the UCNP-assisted cancer detection is feasible up to 4 mm in tissue depth, showing considerable potential for diagnostic and image-guided surgery applications.

PEG-modified upconversion nanoparticles for in vivo optical imaging of tumors

A novel surface modification approach of brightly luminescent upconversion nanoparticles (UCNPs) is reported. Inorganic core@shell UCNPs (core – NaYF4 co-doped with Yb3+ and Tm3+ ions, shell – NaYF4) were modified by intercalation with amphiphilic copolymer poly(maleic anhydride-alt-1-octadecene) followed by cross-linking with poly(ethylene glycol) diglycidyl ether (PEG-DGE). The proposed approach enables preparation of UCNPs with an outmost PEG-containing layer, which provides steric stabilization and low non-specific protein adsorption. Intravenous injection of PEG-functionalized UCNPs into the mice results in extension of the UCNP blood circulation time up to 1 hour. In vivo epi-luminescence imaging of the mouse model with Lewis lung carcinoma is ensured by the high quantum yield of the modified UCNPs and passive targeting associated with efficient UCNP accumulation in solid tumors.

Enhanced spatial resolution in optical imaging of biotissues labelled with upconversion nanoparticles using a fibre-optic probe scanning technique

The new generation of synthetic nanomaterials, upconversion nanoparticles (UCNPs), have the potential for high-contrast optical imaging of biological tissue by virtue of their unique luminescent properties which enable the autofluorescence and excitation signals to be completely suppressed and avoid biotissue absorption. The potential for deep tissue imaging, such as whole animal imaging, is demonstrated in this report on a comparative study of two epiluminescent imaging methods suitable for the localization of a UCNP-labelled pathology site buried in highly scattering biological tissue modelled by an optical tissue phantom. The lateral resolution exhibited in scanning imaging by an illumination-collection fibre-optic probe appeared to be almost 1.73 times better than that shown by the wide-field CCD commonly used in diffuse optical tomography systems. We attribute this improved lateral resolution to the enhanced angular selectivity of the illumination-collection regime and to the nonlinear dependence of the UCNP luminescence on the excitation intensity.

Determination of the refractive index of β-NaYF4/Yb3+/Er3+/Tm3+ nanocrystals using spectroscopic refractometry

A method for measuring refractive index n of nanosize particles in the visible and near-IR spectral ranges is proposed. The method is based on comparing refractive index ncolloid of a colloid solution of nanoparticles in several solvents with refractive indices nsolvent of corresponding pure solvents and has an accuracy of ±2 × 10−4. Upconversion nanosize phosphors (UCNPs) are synthesized in the form of a β-NaYF4 crystalline matrix doped with Yb3+, Er3+, and Tm3+ rare earth ions. UCNPs have a doped core with a diameter of 40 ± 5 nm and undoped shell with a thickness of 3–5 nm. Synthesized nanocrystals possess intense photoluminescence in the blue, green, and red spectral ranges upon excitation by IR radiation with a wavelength of 977 nm. Using a spectroscopic refractometer, the dispersion of the refractive index of β-NaYF4/Yb3+/Er3+/Tm3+ nanocrystals was measured for the first time in the spectral range of 450–1000 nm with an accuracy of ±2 × 10−4.

Ternary alloys Cd y Zn 1 − y O and Mg x Zn 1 − x O as materials for optoelectronics

Thin films of CdyZn1 − yO and MgxZn1 − xO (y = 0−0.35, x = 0−0.45) ternary alloys have been grown by pulsed laser deposition onto sapphire substrates. The record solubility limits of Cd (y = 0.3) and Mg (x = 0.35) have been achieved in hexagonal zinc oxide. The mismatch of the lattice parameters a of Cd0.2Zn0.8O and Mg0.35Zn0.65O does not exceed 1%; in this case, the band gap discontinuity is 1.3 eV. The surface roughness of the films does not exceed 2.5 nm at x = 0−0.27 and y = 0−0.20.

Epitaxial growth and properties of MgxZn1-xO films produced by pulsed laser deposition

The MgxZn1-xO thin films with a Mg content corresponding to x = 0–0.45 are grown by pulsed laser deposition on ablation of ceramic targets. The conditions for epitaxial growth of the films on the single-crystal Al2O3 (00.1) substrates are established. The record limit of solubility of Mg in hexagonal ZnO, x = 35 is attained. In this case, the lattice mismatch for the parameter a of the ZnO and Mg0.35Zn0.65O films does not exceed 1%, whereas the band gaps of the films differ by 0.78 eV. The surface roughness of the films corresponds to 0.8–1.5 nm in the range of x = 0–0.27.

Multicomponent nanocrystals with anti-Stokes luminescence as contrast agents for modern imaging techniques

Lanthanide-doped upconversion nanoparticles (UCNPs) have recently attracted great attention in theranostics due to their exceptional optical and physicochemical properties, which enable the design of a novel UCNP-based nanoplatform for luminescent imaging, temperature mapping, sensing, and therapy. In addition, UCNPs are considered to be ideal building blocks for development of multimodal probes for cells and whole body imaging, exploiting simple variation of host matrix, dopant ions, and surface chemistry. Modalities responsible for magnetic resonance imaging (MRI), computed tomography (CT), and positron emission tomography (PET)/single-photon emission computed tomography (SPECT) are embedded in a single UC nanocrystal, providing integrating effect over any modality alone in terms of the efficiency and sensitivity for clinical innovative diagnosis through multimodal bioimaging. In particular, we demonstrate applications of UCNPs as a new nanoplatform for optical and multimodal cancer imaging in vitro and in vivo and extend discussions to delivery of UCNP-based therapeutic agents for photodynamic and photothermal cancer treatments.

Visualization of upconverting nanoparticles in strongly scattering media

Optical visualization systems are needed in medical applications for determining the localization of deep-seated luminescent markers in biotissues. The spatial resolution of such systems is limited by the scattering of the tissues. We present a novel epi-luminescent technique, which allows a 1.8-fold increase in the lateral spatial resolution in determining the localization of markers lying deep in a scattering medium compared to the traditional visualization techniques. This goal is attained by using NaYF4:Yb(3+)Tm(3+)@NaYF4 core/shell nanoparticles and special optical fiber probe with combined channels for the excitation and detection of anti-Stokes luminescence signals.

Ion energy spectrum control in modified cross-beam pulsed laser deposition method

The time-of-flight curves of the ion current to a probe in a plasma beam formed by crossing plumes from two laser-ablated silicon targets have been measured using the Langmuir probe technique. It is established for the first time that the ion energy spectrum of the plasma beam formed by the two laser erosion plumes and oriented in the direction of the bisector of the angle between the initial plumes can be modified by changing the angle between them (i.e., between the erosion plume). A modified cross-beam pulsed laser deposition method is proposed, which allows the energies of deposited particles to be controlled in a broad range.

Biocompatible upconversion ink for hidden anticounterfeit labeling

Ink for rapid the application of anticounterfeit labels by means of standard printing devices has been developed based on upconversion nanoparticles (nanophosphors). Printing ink is made of an aqueous dispersion of nanoparticles with a NaYF4:YbTm/NaYF4 core–shell structure at a concentration of 0.5 mg/mL. The surface of nanoparticles is modified with amphiphilic polymers. The biosafety of ink is demonstrated in primary cultures of human fibroblasts. The hidden labeling, which is invisible in ambient lighting, is performed by the method of inkjet printing on paper. A printed image is visualized by IR laser irradiation at a wavelength of 975 nm. It is demonstrated that additional modalities of protection can be obtained by encoding the spectra and intensities of the anti-Stokes luminescence lines when combining the dopant lanthanides in nanoparticles.