We have successfully synthesized near-infrared photoluminescent erbium-doped lithium yttrium fluoride nanocrystals using a facile coprecipitation approach. The nanocrystals are capped with oleic acid, enabling dispersion in nonpolar solvents such as toluene and cyclohexane. The relative amounts of yttrium and erbium precursors were adjusted during the synthesis to obtain different concentrations of Er between 1% and 15%. The composition and structure of the nanocrystals were studied via X-ray fluorescence spectroscopy and X-ray powder diffraction. The nanocrystals were optically characterized by extensive photoluminescence studies, including Stokes and anti-Stokes emission. When excited with 1.55-μm light, the nanocrystals displayed strong anti-Stokes emission associated with the 4I13/2 → 4I15/2 transition. These nanocrystals therefore have a high potential to be used in optical cooling applications with telecommunication-wavelength excitation.
Synthesized nanoparticles with strong luminescence in the second near-infrared window show great potential for applications in biomedical imaging and diagnosis. Nanoscale dimensions and tunable optical properties can enable nanoparticles to operate as fluorescent probes in the imaging of tumors and lymphatic tissues. Lanthanide-doped rare-earth fluoride nanoparticles with photoluminescence tuned to the second near-infrared window can circumvent many of the issues currently limiting the clinical utility of fluorescence imaging technology and show promise as tools for the early detection of cancer. We report on the synthesis and characterization of colloidal LiYF4 nanoparticles doped with erbium. The nanoparticles were synthesized through a coprecipitation method using rare-earth chlorides, LiOHꞏH2O, and NH4F as precursors. 1-octadecene was used as a high-temperature solvent, and oleic acid was used as an organic capping agent. The reaction took place under the protection of nitrogen atmosphere. The size, morphology, and colloidal stability of the nanoparticles were determined using data obtained from transmission electron microscopy, dynamic light scattering, and zeta potential techniques. Optical characterization data were collected using NIR absorption spectroscopy and fluorescence spectroscopy. The Er3+-doped LiYF4 nanoparticles show NIR-II emission peaks at 1001 nm, 1490 nm, 1531 nm, and 1558 nm upon NIR-II excitation at 972 nm. The excellent luminescence in the NIR-II range makes them a strong candidate for bioimaging applications.
LiYF4 nanocrystals (NCs) doped with 1% and 10% of Yb3+ and capped with oleic-acid were synthesized via a previously reported and modified co-precipitation method. Size, morphology, composition, and colloidal stability of these NCs are reported with data obtained from TEM, XRD, TGA/DSC, XRF, and zeta potential techniques. TEM analysis shows a monodisperse size distribution, with the nanocrystal size of ~20 nm. Optical characterization is described using data collected from UV-Vis-NIR absorption spectrophotometry and photoluminescence spectroscopy. The excellent luminescence in the NIR-II spectral region makes these NCs potential candidate for bioimaging applications.
We have successfully synthesized lithium yttrium fluoride (YLF) nanocrystals doped with ytterbium. The Yb content was varied between 1% and 10%. The nanocrystals emit in near-infrared, with the emission spectrum extending from 960 nm to 1060 nm when excited with the 900 nm light. Strong anti-Stokes photoluminescence was observed when using excitation wavelengths ranging from 1010 nm to 1020 nm. The temperature-dependence of the anti-Stokes photoluminescence was measured over the range from 10 °C till 70 °C. These nanocrystals have a high potential to be used in optical cooling applications.
CdSexS1-x/ZnS quantum dots (QDs) can cover a broader spectral range than the commonly used CdSe/ZnS QDs and are potentially useful as biomarkers for tagging cell lines such as HeLa, A549, and MCF-7 due to their high photoluminescence intensity and stability in solution. So far, there have been few studies of colloidal CdSexS1-x/ZnS QDs that would simultaneously investigate changes in a) the molar composition of QD cores, and b) the shell thickness, as well as the effects of these changes on the photoluminescence and quantum yield properties of the QDs. CdSeyS1-y QDs and CdSexS1-x/ZnS core/shell QDs were synthesized via a previously reported and modified hot-injection procedure and via a telescoping one-pot synthesis based on the modified hot-injection procedure. Size, morphology, composition, and colloidal stability of these QD core/shell systems is reported with data obtained from TEM, XRD, TGA, DSC, DLS, and zeta potential techniques. Optical characterization is described using data collected from UV-Vis absorption spectrophotometry and photoluminescence spectroscopy.
Colloidal quantum dots (QDs) emitting in the near-infrared (NIR) spectrum are of interest for many biomedical applications, including bioimaging, biosensing, drug delivery, and photodynamic therapy. However, a significant limitation is that QDs are typically highly cytotoxic, containing materials such as indium arsenide (InAs), cadmium, or lead, which makes prospects for their FDA approval for human treatment very unlikely. Previous work on QDs in the NIR has focused on indium arsenide or cadmium chalcogenide cores coated with cadmium sulfide shells or zinc sulfide shells. Lead-based nanoparticles, such as lead selenide (PbSe) or lead sulfide (PbS) are also popular materials used for NIR emission. However, these nanoparticles have also been shown to be cytotoxic. Coating these Pb-based QDs with a biocompatible shell consisting of tin chalcogenides, such as tin sulfide (SnS) or tin selenide (TnSe), could be a reasonable alternative to improve their biocompatibility and reducing their cytotoxicity. In this paper, we report on our recent studies of PbSe-core QDs with Sn-containing shells, including synthesis, structural characterization, and investigation of optical properties. Characteristics of these QDs synthesized under different conditions are described. We conclude that their synthesis is challenging and still requires further work to avoid shell oxidation.
Anti-Stokes photoluminescence from colloidal CdSeS/ZnS quantum dots (QDs) is observed. The QDs were inserted into the core of wider-bandgap SiO2/Si3N4/SiO2 structure by thin film deposition and confirmed as promising nanoemitters for laser cooling due to efficient anti-Stokes emission. The nanoemitters were optically pumped by semiconductor lasers coupled to the waveguides using free-space optics. A direct evidence of local optical cooling in the waveguide structure has been demonstrated with a luminescence thermometry based on the detection of photoluminescence signal phase change versus power of the pumping laser, using a lock-in amplifier.
Colloidal quantum dots (QDs) emitting in the visible spectrum are of interest for many biomedical applications, including bioimaging, biosensing, drug delivery, and photodynamic therapy. However, a significant limitation is that QDs typically contain cadmium, which is highly cytotoxic and makes prospects for their FDA approval for human treatment very unlikely. Previous work on biocompatible QDs has focused on indium phosphide and zinc oxide as alternative materials for QDs. However, these nanoparticles have also been shown to be cytotoxic. High-efficiency luminescent ZnTe-based QDs could be a reasonable alternative to Cd-containing QDs. We started our recent studies of ZnTe core, zinc chalcogenide shell QDs with synthesis, structural characterization, and investigation of optical properties of ZnTe/ZnSe colloidal QDs that displayed a blue-green photoluminescence under UV excitation. In this paper, the characteristics of ZnTe/ZnS QDs are compared to those of ZnTe/ZnSe QDs. We conclude that ZnTe/ZnS QDs are appealing candidates for various biomedical applications instead of the currently prominent alternative: cadmium-chalcogenide core QDs.
The human mouth is a host of a large gamut of bacteria species, with over 700 of different bacteria strains identified. Most of these bacterial species are harmless, some are beneficial (such as probiotics assisting in food digestion), but some are responsible for various diseases, primarily tooth decay and gum diseases such as gingivitis and periodontitis. Dental plaque has a complicated structure that varies from patient to patient, but a common factor in most cases is the single species of bacterium acting as a secondary colonizer, namely Fusobacterium nucleatum, while the actual disease is caused by a variety of tertiary colonizers. We hypothesize that destruction of a compound biofilm containing Fusobacterium nucleatum will prevent tertiary colonizers (oral pathogens) from establishing a biofilm, and thus will protect the patient from developing gingivitis and periodontitis. In this paper, we report on the effects of exposure of compound biofilms of a primary colonizer Streptococcus gordonii combined with Fusobacterium nucleatum to iron oxide nanoparticles as possible bactericidal agent.
Quantum dots (QDs) emitting in the visible are of interest for many biomedical applications, including bioimaging, biosensing, drug targeting, and photodynamic therapy. However, a significant limitation is that QDs typically contain cadmium, which makes prospects for their FDA approval very unlikely. Previous work has focused on InP and ZnO as alternative semiconductor materials for QDs. However, these nanoparticles have also been shown to be cytotoxic. High-efficiency luminescent ZnTe-based QDs could be a reasonable alternative to Cd-containing QDs. In this paper, we present preliminary results of our recent studies of ZnTe-based QDs, including their synthesis, structural characterization, and optical properties.
Human mouth is a host of a large gamut of bacteria species, with over 700 of different bacteria strains identified. Most of these bacterial species are harmless, some are beneficial (such as probiotics assisting in food digestion), but some are responsible for various diseases, primarily tooth decay and gum diseases such as gingivitis and periodontitis. For example, Streptococus mutans produces enamel-eroding acids, while Porphyromonas gingivalis is strongly linked to periodontitis. In this paper, we report on the effects of exposure of oral biofilms to iron oxide nanoparticles and static magnetic fields as possible bactericidal agent.
Pseudomonas aeruginosa bacterium is a deadly pathogen, leading to respiratory failure in cystic fibrosis and nosocomial pneumonia, and responsible for high mortality rates in these diseases. P. aeruginosa has inherent as well as acquired resistance to many drug classes. In this paper, we investigate the effectiveness of two classes; aminoglycoside (tobramycin) and fluoroquinolone (ciprofloxacin) administered alone, as well as conjugated to iron oxide (magnetite) nanoparticles. P. aeruginosa possesses the ability to quickly alter its genetics to impart resistance to the presence of new, unrecognized treatments. As a response to this impending public health threat, we have synthesized and characterized magnetite nanoparticles capped with biodegradable short-chain carboxylic acid derivatives conjugated to common antibiotic drugs. The functionalized nanoparticles may carry the drug past the mucus and biofilm layers to target the bacterial colonies via magnetic gradient-guided transport. Additionally, the magnetic ferrofluid may be used under application of an oscillating magnetic field to raise the local temperature, causing biofilm disruption, slowed growth, and mechanical disruption. These abilities of the ferrofluid would also treat multi-drug resistant strains, which appear to be increasing in many nosocomial as well as acquired opportunistic infections. In this in vitro model, we show that the iron oxide alone can also inhibit bacterial growth and biofilm formation.
Colloidal quantum dots (QDs) are of interest for a variety of biomedical applications, including bioimaging, drug
targeting, and photodynamic therapy. However, a significant limitation is that highly efficient photoluminescent QDs
available commercially contain cadmium. Recent research has focused on cadmium-free QDs, which are anticipated to
exhibit significantly lower cytotoxicity. Previous work has focused on InP and ZnO as alternative semiconductor
materials for QDs. However, these nanoparticles have been shown to be cytotoxic. Recently, we have synthesized high
quantum efficiency (exceeding 90%), color tunable MnSe/ZnSeS nanoparticles, as potentially attractive QDs for
biomedical applications. Additionally, the manganese imparts magnetic properties on the QDs, which are important for
magnetic field-guided transport, hyperthermia, and potentially magnetic resonance imaging (MRI). The QDs can be
further biofunctionalized via conjugation to a ligand or a biomarker of disease, allowing combination of drug delivery
with visual verification and colocalization due to the color tunability of the QDs.
Iron oxide colloidal nanoparticles (ferrofluids) are investigated for application in the treatment of cystic fibrosis lung
infections, the leading cause of mortality in cystic fibrosis patients. We investigate the use of iron oxide nanoparticles to
increase the effectiveness of administering antibiotics through aerosol inhalation using two mechanisms: directed
particle movement in the presence of an inhomogeneous static external magnetic field and magnetic hyperthermia.
Magnetic hyperthermia is an effective method for decreasing the viscosity of the mucus and biofilm, thereby enhancing
drug, immune cell, and antibody penetration to the affected area. Iron oxide nanoparticles of various sizes and
morphologies were synthesized and tested for specific losses (heating power). Nanoparticles in the superparamagnetic to
ferromagnetic size range exhibited excellent heating power. Additionally, iron oxide / zinc selenide core/shell
nanoparticles were prepared, in order to enable imaging of the iron oxide nanoparticles. We also report on synthesis and
characterization of MnSe/ZnSeS alloyed quantum dots.
Iron oxide colloidal nanocrystals (ferrofluids) are investigated for application in the treatment of cystic fibrosis lung
infections, the leading cause of mortality in cystic fibrosis patients. We investigate the use of iron oxide nanocrystals to
increase the effectiveness of inhalation aerosol antibiotics therapy through two mechanisms: directed particle movement
in the presence of a static external magnetic field and magnetic hyperthermia. Magnetic hyperthermia is an effective
method for decreasing the viscosity of the mucus and biofilm thereby increasing drug, immune cell, and antibody
penetration to the affected area. Iron oxide nanocrystals of various sizes and morphologies were synthesized and tested
for specific losses (heating power) using frequencies of 111.1 kHz and 629.2 kHz, and corresponding magnetic field
strengths of 9 and 25 mT. Nanocrystals in the superparamagnetic to ferromagnetic size range exhibited excellent heating
power. Additionally, iron oxide-zinc selenide core-shell nanoparticles were prepared in parallel in order to allow
imaging of the iron oxide nanoparticles.
Self-assembling block copolymer thin films have attracted considerable attention as a promising high resolution
lithographic tool due to the 10 nm scale of microdomain ordering and their facility for modulation of size
and pattern. However, for block copolymer lithography to be a viable solution for advanced nano-lithographic
technologies, several critical requirements need to be satisfied. Our research has focused on developing complementary
mixed polymer brush lithography tools satisfying the required criteria, by means of Self-Consistent Field Theory (SCFT) simulations. Specifically, we have concentrated on graphoepitaxial techniques that are widely tested and considered a particularly promising method for controlling the microdomain ordering.
Sandia is exploring two classes of integrated systems involving bioactive materials: 1) microfluidic systems that can be used to manipulate biomolecules for applications ranging from counter-terrorism to drug delivery systems, and 2) fluidic systems in which active biomolecules such as motor proteins provide specific functions
such as active transport. An example of the first class involves the development of a reversible protein trap based on the integration of the thermally-switchable polymer poly(N-isopropylacrylamide)(PNIPAM) into a micro-hotplate device. To exemplify the second class, we describe the technical challenges associated with integrating microtubules and motor proteins into microfluidic systems for: 1) the active transport of nanoparticle cargo, or 2) templated growth of high-aspect ratio nanowires. These examples illustrate the
functions of bioactive materials, synthesis and fabrication issues, mechanisms for switching surface chemistry and active transport, and new techniques such as the interfacial force microscope (IFM) that can be used to characterize bioactive surfaces.
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