Recently, there has been a great deal of interest in fluorescent and upconverting rare earth-based nanoparticles for biomedical imaging and photodynamic therapy applications. While many of the widely explored upconverting contrast agents are comprised of fluoride or oxide crystal structures, very little work has been done to investigate the up- and downconversion emission in rare earth-doped carbon nanocomposites. Of particular interest, graphene-UCNP nanocomposites and sesquicarbide nanoparticles may offer a wide range of new applications when coupled with the extraordinary optical properties of rare earth-doped systems, such as potential use as nano-transducers. Carbon-based nanocomposites and sesquicarbides doped with rare earth elements were synthesized using the microwave and solvothermal methods with additional brief high temperature heat treatments. They were then characterized by XRD, visible and NIR excitation and emission spectroscopy, as well as Raman spectrsocopy. Tuning of the emission manifold ratios was explored through different compositions and size. Also, energy transfer between the emitting ions and the electronic states of the host structure was explored. Finally, cytotoxicity was tested, and cellular uptake of these nanomaterials was performed with confocal microscopy.
Fluorescent nanoparticles (NPs) such as KYb2F7:Tm3+ potential in biomedical applications due to their ability to absorb and emit within the biological window, where near infrared light is less attenuated by soft tissue. This results in less tissue damage and deeper tissue penetration making it a viable candidate in biological imaging. Another big factor in determining their ability to perform in a biological setting is the surface chemistry. Biocompatible coatings, including polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), pluronic and folic acid are commonly used because they pose several advantages such as ease of functionalization, better dispersion, and higher cellular uptake. To study the effects of the NP surface chemistry, KYb2F7:Tm3+ a solvothermal method using PEG, PVP, pluronic acid, and folic acid as a capping agent, followed by thorough optical characterizations. Optical changes were thoroughly studied and compared using absorption, emission, and quantum yield data. Cell viability was obtained by treating Rhesus Monkey Retinal Endothelial cells (RhREC) with KYb2F7:Tm3+ and counting viable cells following a 24 hour uptake period. The work presented will compare the optical properties and toxicity dependency on the surface chemistry on KYb2F7:Tm3+. The results will also indicate that KYb2F7:Tm3+ nanoparticles are viable candidates for various biomedical applications.
Recently, there has been a great amount of interest in nanoparticles which are able to provide a platform with high contrast for multiple imaging modalities in order to advance the tools available to biomedical researchers and physicians. However, many nanoparticles do not have ideal properties to provide high contrast in different imaging modes. In order to address this, ultrasmall lanthanide doped oxide and fluoride nanoparticles with strong NIR to NIR upconversion fluorescence and a strong magnetic response for magnetic resonance imaging (MRI) have been developed. Specifically, these nanoparticles incorporate gadolinium, dysprosium, or a combination of both into the nano-crystalline host to achieve the magnetic properties. Thulium, erbium, and neodymium codopants provide the strong NIR absorption and emission lines that allow for deeper tissue imaging since near infrared light is not strongly absorbed or scattered by most tissues within this region. This also leads to better image quality and lower necessary excitation intensities. As a part of the one pot synthesis, these nanoparticles are coated with peg, pmao, or d-glucuronic acid to make them water soluble, biocompatible, and bioconjugable due to the available carboxyl or amine groups. Here, the synthesis, morphological characterization, magnetic response, NIR emission, and the quantum yield will be discussed. Cytotoxicity tested through cell viability at varying concentrations of nanoparticles in growth media will also be discussed.
Until recently, many contrast agents widely used in biological imaging have absorbed and emitted in the visible region, limiting their usefulness for deeper tissue imaging. In order to push the boundaries of deep tissue imaging with non-ionizing radiation, contrast agents in the near infrared (NIR) regime, which is not strongly absorbed or scattered by most tissues, are being sought after. Upconverting nanoparticles (UCNPs) are attractive candidates since their upconversion emission is tunable with a very narrow bandwidth and they do not photobleach or blink. The upconversion produced by the nanoparticles can be tailored for NIR to NIR by carefully choosing the lanthanide dopants and dopant ratios such as KYb2F7: RE3+ (RE = Tm, Er). Spectroscopic characterization was done by analyzing absorption, fluorescence, and quantum yield data. In order to study the toxicity of the nanoparticles Monkey Retinal Endothelial Cells (MREC) were cultivated in 24 well plates and then treated with nanoparticles at different concentrations in triplicate to obtain the optimal concentration for in vivo experiments. It will be shown that these UCNPs do not elicit a strong toxic response such as quantum dots and some noble metal nanoparticles. 3-D optical slices of nanoparticle treated fibroblast cells were imaged using a confocal microscope where the nucleus and cytoplasm were stained with DAPI and Alexa Fluor respectively. These results presented support the initial assumption, which suggests that KYb2F7: RE3+ would be excellent candidates for NIR contrast agents.
In this paper, we study the computational modeling of the localized surface plasmonic and scattering field
effect arising from of gold nanorods. We also report the synthesis and optical characterization of core-spacer-shell
nanocomposites composed of gold nanorods coated with SiO2 and finally coated with Y2O3:Er3+/Yb3+
(Aunanorods@mSiO2@Y2O3:Er3+/Yb) through a layer-by-layer method. Preliminary upconversion analysis of singly
(Aunanorods@mSiO2@Y2O3:Er3+/Yb) at 980 excitation indicates that the composition has to be optimized to
understand the role of silica as a spacer and near field enhancer (gold nanorod) in the system.
Nanoparticles doped with rare earth ions for biomedical imaging and infrared photodynamic therapy (IRPDT) have been
synthesized, characterized, and compared. Specifically, these nanoparticles utilize two primary modalities: near infrared
excitation and emission for imaging, and near infrared upconversion for photodynamic therapy. These nanoparticles are
optimized for both their infrared emission and upconversion energy transfer to a photoactive agent conjugated to the
surface. Finally, these nanoparticles are tested for toxicity, imaged in cells using the near infrared emission pathway, and
used for selective killing of cells through the upconversion driven IRPDT.
Highly efficient upconverting phosphors (NaYF4) doped with erbium ions are bio-conjugated and used for cancer
imaging and photodynamic therapy. Once they are conjugated, the particles are injected into mice to demonstrate that
cancer imaging with a near-infrared excitation source is possible. Finally, the particles are also conjugated with a
photosensitive molecule with strong absorption near the upconversion emission peak (~ 550nm). The upconversion
energy causes the photosensitive molecule to create highly reactive oxidative species, which puncture and kill the cell to
which it is attached. These particles are then used in a mouse model, and the size of the tumors is modeled as a function
of the dosage and duration of the photodynamic therapy.
Nonlinear optical properties of barium titanate (BaTiO3) nanoparticles are investigated as a function of size and shape.
BaTiO3 is an attractive option as a nonlinear material because it can exhibit a high second and third order electronic
susceptibility even at the nanoscale. These particles are employed as contrast agents/biomarkers and phase conjugate
nanomirrors in imaging, utilizing second harmonic generation for two-photon microscopy and four-wave mixing for
three-photon microscopy and scattering reversal image enhancement. Silver is also used to create a shell around the
BaTiO3 nanoparticle to see if a core/shell structure enhances any of the nonlinear effects.
Barium titanate (BaTiO3) is a good candidate for phase conjugation on the nano-scale, as four-wave mixing has been
shown in nanoparticles of this type. Also, the ability to dope this material with rare earth elements, with strong
absorption and emission lines, makes it possible to use these as multi-functional, multi-modal probes for biomedical
applications. BaTiO3 nanoparticles are synthesized using a precipitation method and fully characterized. These particles
are used in a four wave mixing setup to optically conjugate scattered light traveling through turbid media, such as tissue,
to re-obtain lost image information due to the scattering process.
The near-infrared (NIR) optical properties of human retinal pigmented epithelial (RPE) cells and rare earth nanopowders
were studied using a double-integrating sphere setup. The Kubelka-Munk and Inverse Adding-Doubling techniques were
applied to obtain absorption and scattering coefficients. These are compared with the coefficients obtained through the
Representative Layer Theory described by the Dahm equation. Retinal pigmented epithelial monolayers were cultured
from an ARPE19 line in thin cell culture windows, and the nanopowders were pressed into samples of varying thickness.
Samples were optically characterized as a function of wavelength. A brief discussion of the shortcomings of existing
techniques for computing optical properties when applied to physically thin samples is provided, followed by a
comparison between the optical properties of the samples returned by the different techniques.
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