We demonstrate that white coatings consisting of silicone embedded with randomly distributed microbubbles provide highly efficient daytime radiative cooling with inexpensive materials and fabrication processes. In our material system, sunlight is strongly scattered with minimal absorption, and heat is effectively removed through mid-infrared (IR) radiation. In our previous study, solid microsphere-based coatings outperformed commercial solar-rejection white paint in cooling efficiency, but their mechanical robustness needed improvement for practical applications. The material system in our work substantially enhances the mechanical robustness while providing superior cooling performance to commercial solar-rejection paint. For ease of processing, we use nonoptimized structures with reduced optical scattering strength. Strong solar rejection is yet achieved by increasing coating thickness. This strategy is desirable for practical rooftop applications where coating thickness is of minor importance in comparison to cooling performance and materials cost. In addition, silicone is stable in extraterrestrial environments and efficiently radiates heat over broad mid-IR spectrum. These material properties of our silicone coatings promise great potential for radiative cooling in space applications.
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.
John Plumley, Brian Akins, Gema Alas, Madalyn Fetrow, Jane Nguyen, Priyanka Jain, Stephanie Yang, Yekaterina Brandt, Gennady Smolyakov, Wojciech Ornatowski, Erin Milligan, Marek Osiński
Quantum dots (QDs) are of high interest in the biomedical field. The most widely used and commercially available CdSe/ZnS QDs have a highly toxic Cd component. High-efficiency luminescent Cd-free Mn-doped ZnSe/ZnS QDs are a reasonable alternative to CdSe/ZnS QDs; however the actual cytotoxicity of ZnSe:Mn/ZnS QDs is relatively unknown. In this study, we apply the ApoTox-GloTM Triplex assay to test for cell cytotoxicity, viability, and induced apoptosis, by treating macrophage cells with different concentrations of peptide-coated ZnSe:Mn/ZnS QDs at four different incubation times: 6, 12, 24, and 48 hours. At the concentrations used, which varied between 0.03 μM to 0.25 μM, the macrophage cells showed very little cytotoxic effect. However, cell viability began to decrease with increasing QD concentration beginning with the 12 hour incubation time, with fairly consistent results for 24 and 48 hour incubation times as well. Also, the macrophage cells expressed a measurable degree of induced apoptosis, which scaled with concentration. While cytotoxicity did not seem to be an issue with macrophage cells treated with the peptide-coated Mn-doped ZnSe/ZnS QDs, the drop in cell viability and the increase in induced apoptosis suggest an antiproliferation effect within the macrophage cell culture.
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.
Lanthanide fluoride colloidal nanocrystals offer a way to improve the diagnosis and treatment of cancer through the
enhanced absorption of ionizing radiation, in addition to providing visible luminescence. In order to explore this
possibility, tests with a kilovoltage therapy unit manufactured by the Universal X-Ray Company were performed to
estimate the energy sensitivity of this technique. La0.2Ce0.6Eu0.2F3 nanocrystals capped with polyethylene glycol of
molecular weight 6000 were synthesized, suspended in deionized water, and made tolerant to biological ionic pressures
by incubation with fetal bovine serum. These nanocrystals were characterized by dynamic light scattering, muffle
furnace ashing, and photoluminescence spectroscopy. Clonogenic assays were performed on the cells to assay the
cytotoxicity and radiotoxicity of the nanocrystals on the human pancreatic cancer cell line PANC-1, purchased from
ATCC.
Cystic fibrosis (CF) is an inherited childhood-onset life-shortening disease. It is characterized by increased respiratory
production, leading to airway obstruction, chronic lung infection and inflammatory reactions. The most common bacteria
causing persisting infections in people with CF is Pseudomonas aeruginosa. Superparamagnetic Fe3O4 iron oxide
nanoparticles (NPs) conjugated to the antibiotic (tobramycin), guided by a gradient of the magnetic field or subjected to
an oscillating magnetic field, show promise in improving the drug delivery across the mucus and P. aeruginosa biofilm
to the bacteria. The question remains whether tobramycin needs to be released from the NPs after the penetration of the
mucus barrier in order to act upon the pathogenic bacteria. We used a zero-length 1-ethyl-3-[3-dimethylaminopropyl]
carbodiimide hydrochloride (EDC) crosslinking agent to couple tobramycin, via its amine groups, to the carboxyl groups
on Fe3O4 NPs capped with citric acid. The therapeutic efficiency of Fe3O4 NPs attached to the drug versus that of the
free drug was investigated in P. aeruginosa culture.
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.
Naturally occurring dysprosium is attractive as a neutron detector because of its high thermal neutron capture cross
section and high natural abundance. Neutron-induced transmutation of 164Dy results in production of stable isotopes of
holmium and erbium (the latter only at sufficiently high neutron fluxes), due to beta decays caused by nucleus
instability. This mechanism, unaffected by gamma radiation, can be used to unambiguously detect neutrons, without
having to discriminate against an accompanying gamma flux. Optically-enabled thermal neutron detection can be based
on significant differences in optical properties of Dy and Ho or Er, which allows to determine the relative fractions of
Dy, and Ho, and E in an irradiated sample. In our search for the most sensitive method of differentiating between Dy and
Ho residing in the same host material, we produced various Dy- and Ho-containing nanocrystals and uniformly dispersed
them in a PMMA polymer matrix. Optical properties of the nanocomposites were analyzed by means of absorption and
PL spectroscopy. We also report on neutron irradiation experiments with Dy-containing nanocrystals and our attempts to
optically detect neutron-induced conversion of Dy into Ho.
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.
The concept of detection of thermal neutrons using gadolinium oxide nanocrystals is explored. Gadolinium is an element
with by far the highest thermal neutron capture cross section among all stable isotopes. Colloidal synthesis of Gd2O3 nanocrystals, Gd2O3 nanocrystals doped with Ce, Gd2O3 nanocrystals doped with Eu, and Gd2O3 nanocrystals co-doped
with Ce and Eu is reported. The nanocrystals were characterized by transmission electron microscopy, energy-dispersive
X-ray spectroscopy, dynamic light scattering analysis, and steady-state UV-VIS optical absorption and
photoluminescence spectroscopy. Neutron detection has been modeled with MCNPX and confirmed in experiments with
Gd-containing nanocrystalline samples irradiated with 252Cf neutron source.
Cerium-doped lanthanum fluoride colloidal nanocrystals (NCs) offer a way to improve radiation therapy through the
enhanced absorption of high-energy photons. The use of Monte Carlo simulation allows the direct calculation of the
macroscopic dose enhancement factor (MDEF), a figure of merit for NC-enhanced radiation therapy. Our simulations of
brachytherapy using an Ir-192 source agree with previous work on the subject for gold NCs and show effectiveness of
LaF3:10%Ce NCs to be approximately 50% that of gold. Polyethylene-glycol-capped LaF3:10%Ce NCs were
synthesized, isolated, suspended in phosphate buffered saline (PBS), and characterized with transmission electron
microscopy, dynamic light scattering, photoluminescence spectroscopy, and absorption spectroscopy. LaF3:10%Ce NCs
were used in radiation dose enhancement experiments that involved an incoming 662 keV gamma flux from dual Cs-137
sources to test the mortality of Saccharomyces cerevisiae. At a small loading of 1.8 mg NC/g of PBS, the experiment did
not produce a measurable increased mortality. To understand the results, additional Monte Carlo simulations revealed
that the photon energy of 662 keV gamma rays is far from optimal, providing only a 4% increase in dose for a
concentration of 18 mg of NCs / g of PBS. Further simulations showed that the optimal photon energy for this technique
is 60 keV, tripling the absorbed dose for a concentration of 18 mg of NCs / g of PBS.
A novel concept for detection of thermal neutrons based on lanthanide halide nanocrystals containing gadolinium, an
element with by far the highest thermal neutron capture cross section among all stable isotopes, is presented. Colloidal
synthesis of GdF3 nanocrystals, GdF3 nanocrystals doped with Ce, and LaF3 nanocrystals doped with Gd is reported. The
nanocrystals were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy
(EDS), dynamic light scattering (DLS) analysis, and steady state UV-VIS optical absorption and photoluminescence
spectroscopy. Neutron detection has been confirmed in experiments with Gd-containing nanocrystalline material
irradiated with 252Cf neutron source.
Cerium-doped lanthanum fluoride colloidal nanocrystals offer a way to improve radiation therapy through the enhanced
absorption of high-energy photons. Lanthanum fluoride nanocrystals doped with 10% cerium and capped with oleic acid
were synthesized in anhydrous methanol as platelets 3-6 nm in diameter and 1-3 nm thick. The nanocrystals were
characterized by transmission electron microscopy and photoluminescence spectroscopy. Previously synthesized
lanthanum fluoride nanocrystals doped with 10% cerium and capped with hydroxyl were used in radiation dose
enhancement experiments that involved an incoming gamma flux from a 137Cs source and a FOX assay to measure
absorbed energy. Possibility for lanthanide ions to be released into solution under gamma irradiation and to interfere
with the assay was shown after the results were compared with the outcome of a similar previous experiment with the
Fricke dosimeter solution. Finally, increased cell mortality of S. cerevisiae under gamma irradiation was observed in the
presence of hydroxyl-capped lanthanum fluoride nanocrystals in the solution.
Colloidal synthesis of core/shell nanocrystals with cerium-doped lanthanum fluoride core and undoped lanthanum
fluoride shell, and of core/shell nanocrystals with hygroscopic cerium-doped lanthanum bromide core and undoped
lanthanum fluoride shell is reported. The nanocrystals were characterized by transmission electron microscopy (TEM),
energy dispersive X-ray spectroscopy (EDS), dynamic light scattering (DLS) analysis, steady state UV-VIS optical
absorption and photoluminescence spectroscopy, and by photoluminescence lifetime measurements. Scintillation tests
were performed on the cerium-doped lanthanum fluoride nanocrystalline material exposed to low-level gamma
irradiation.
Lead-iodide-based PbI2, PbIOH and Pb3O2I2 nanocrystals were synthesized by various chemical and mechanochemical solution methods. The nanocrystals were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), dynamic light scattering (DLS), steady-state UV-visible optical absorption and photoluminescence spectroscopy, and by photoluminescence lifetime and quantum efficiency measurements. Scintillation tests were performed on the lead-iodide based material exposed to low-level gamma irradiation.
Colloidal synthesis of cerium-doped lanthanum fluoride nanocrystals is reported. The nanocrystals were characterized by transmission electron microscopy, energy-dispersive X-ray spectroscopy,
steady-state UV-VIS optical absorption and photoluminescence (PL) spectroscopy, and by PL lifetime measurements. Cerium doping concentration was optimized for the maximum PL intensity. Radiation hardness of the synthesized nanocrystals was tested using a 137Cs 662-keV gamma source. Finally, scintillation was observed from the cerium-doped lanthanum fluoride nanocrystals exposed to
low-level gamma radiation.
Cerium-doped lanthanum fluoride colloidal nanocrystals offer a way to improve external radiation therapy through the
enhanced absorption of high energy photons, as well as through the emission of UV light in the presence of radiation,
providing a second cell killing mechanism. Lanthanum fluoride nanocrystals doped with 10% cerium were anhydrously
synthesized in methanol as platelets 10-12 nm in diameter and 4-6 nm thick. The nanocrystals were characterized by transmission electron microscopy, energy dispersive spectroscopy (EDS), and by steady state UV-visible optical absorption and photoluminescence spectroscopy. Using an incoming gamma flux from a 137Cs source and a Fricke dosimeter solution to measure absorbed energy, a 55% enhancement of absorbed dose was measured for a 1.2 mg/ml loading of nanocrystals over exposure range from one to four kiloroentgens.
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