Gold nanoparticles have been studied for many biomedical applications. However, alterations in the gold nanoparticles’ environment
frequently lead to the formation of aggregates and agglomerates, which have not been well characterized. These new structures
could significantly change the biological impact of the nanoparticles, so the appropriate characterization of these structures
prior to biological administration is vital for the correct interpretation of toxicology results. By varying the solvent or
heating under pressure, four reproducible gold nanoparticles structures were created: 10 nm primary particles, aggregates
of the primary particles that contain non-reversible bonds between the individual nanoparticles, agglomerates of primary particles
that contain reversible interactions between the individual nanoparticles, and agglomerated aggregates that have reversible
bonds linking individual aggregates. Ultraviolet–visible (UV–Vis) spectroscopy, thermal gravitational analysis, and neutron
activation analysis were each found to accurately measure the concentration of the primary particles. The primary particles
measured 10 nm by dynamic light scattering (DLS) and had a spherical morphology by transmission electron microscopy (TEM)
while the aggregates measured 110 nm by DLS and had a distorted morphology by TEM. The agglomerate and aggregated agglomerate
samples both measured >1,000 nm by DLS, but the individual particles had significantly different morphologies by TEM. Multiple
other analytical techniques, including ultracentrifugation, gel electrophoresis, and X-ray diffraction, also showed unique
traits for each structure. The structural differences did not change in the presence of cell culture media or rat serum. In
addition, the primary particles, aggregates, and agglomerates each had a unique UV–Vis spectrum, allowing for an inexpensive,
rapid method to differentiate between the structures. 相似文献
A differential interference contrast microscopy technique that employs a photonic crystal fiber as a white-light source is used to measure both the real and the imaginary part of the complex dielectric constant of single 10 and 15 nm gold nanoparticles over a wavelength range of 480 to 610 nm. Noticeable deviations from bulk gold measurements are observed at short wavelengths and for individual particles even after taking into account finite-size surface damping effects. 相似文献
The luminescence and luminescence excitation spectra of 3-hydroxyflavone in acetonitrile obtained at different excitation/recording wavelengths are studied. The dependences of the position of the normal luminescence band maximum and of the intensity ratio of the normal and proton-transfer bands, on the excitation wavelength are found and studied for the first time. It is found that the spectral contour of dual luminescence also depends on the excitation wavelength and the blue emission band is cut off at a sufficiently long-wavelength excitation in the region of 390 nm. In the luminescence excitation spectrum, an additional wide band is observed in the proton-transfer region at 200–260 nm. Excitation in the region of 380–440 nm allowed us to reveal a wide structureless band near 470 nm (with the maximum of its excitation near 420 nm) belonging to the anionic form of 3-hydroxyflavone. Addition of water at a concentration of ~2.2 M quenches this band almost completely. 相似文献
CdS nanoparticles with different size are prepared by chemical bath deposition method. These particles show strong fluorescence
at emission wavelength of 507 nm. It has been observed that this emission peak changes through a range of 147 nm, by varying
the excitation wavelengths through 370–480 nm.The emission peak can thus be tuned by varying the excitation wavelengths. This
peak emission wavelength shift is due to the selective excitation of vibronic levels in the surface state of the CdS nanoparticles. 相似文献
The luminescence properties of Sm(TTFA)3 complex in presence of the silver (Ag) nanoparticles with size ranged from 80 nm to 120 nm and different shapes (nanorod,
cube, tetrahedron, and nanowire) were investigated at two different excitation wavelengths of 397 nm and 350 nm, which was
resonant and off-resonant excitation, respectively. The luminescence enhancement for the resonant excitation was much greater
than that for the off-resonant excitation. The electric and magnetic dipole transitions were affected by the Ag nanoparticles
and the results showed that their emission enhancement depended on the balance of the overlap between the emission wavelengths
and the localized surface plasmon resonant of nanoparticles and their sensibility to the variation of local environments.
The enhancement and quenching of the luminescence were both observed at the resonant excitation. 相似文献
The possibilities of LiNbO3-Ho3+ crystals for optical cooling based on the anti-Stokes luminescence in the wavelength range 2000-2200 nm are investigated. The efficiency and cooling temperature under the continuous wave (CW) excitation at the wavelengths 2035-2071 nm by ~100 W power are estimated. It is shown that under the CW excitation at 2035 nm wavelength the maximum cooling temperature is equal to 2.5 K, and at 2071 nm wavelength is equal to 10.9 K. 相似文献
Because highly luminescent lanthanide compounds are limited to Eu3+ and Tb3+ compounds with red (Eu, ~615 nm) and green (Tb, ~545 nm) emission colors, the development and application of time-resolved
luminescence bioassay technique using lanthanide-based multicolor luminescent biolabels have rarely been investigated. In
this work, a series of lanthanide complexes covalently bound silica nanoparticles with an excitation maximum wavelength at
335 nm and red, orange, yellow and green emission colors has been prepared by co-binding different molar ratios of luminescent
Eu3+–Tb3+ complexes with a ligand N,N,N1,N1-(4′-phenyl-2,2′:6′,2′′-terpyridine-6,6′′-diyl)bis(methylenenitrilo) tetrakis (acetic acid) inside the silica nanoparticles.
The nanoparticles characterized by transmission electron microscopy and luminescence spectroscopy methods were used for streptavidin
labeling, and time-resolved fluoroimmunoassay (TR-FIA) of human prostate-specific antigen (PSA) as well as time-resolved luminescence
imaging detection of an environmental pathogen, Giardia lamblia. The results demonstrated the utility of the new multicolor luminescent lanthanide nanoparticles for time-resolved luminescence
bioassays. 相似文献
Plasmonic metal nanoparticles have shown great promise in enhancing the light absorption of organic dyes and thus improving the performance of dye-sensitized solar cells (DSSCs). However, as the plasmon resonance of spherical nanoparticles is limited to a single wavelength maximum (e.g., ~ 520 nm for Au nanoparticles), we have here utilized silica-coated gold nanorods (Au@SiO2 NRs) to improve the performance at higher wavelengths as well. By adjusting the aspect ratio of the Au@SiO2 NRs, we can shift their absorption maxima to better match the absorption spectrum of the utilized dye (here we targeted the 600–800 nm range). The main challenge in utilizing anisotropic nanoparticles in DSSCs is their deformation during the heating step required to sinter the mesoporous TiO2 photoanode and we show that the Au@SiO2 NRs start to deform already at temperatures as low as 200 °C. In order to circumvent this problem, we incorporated the Au@SiO2 NRs in a TiO2 nanoparticle suspension that does not need high sintering temperatures to produce a functional photoanode. With various characterization methods, we observed that adding the plasmonic particles also affected the structure of the produced films. Nonetheless, utilizing this low-temperature processing protocol, we were able to minimize the structural deformation of the gold nanorods and preserve their characteristic plasmon peaks. This allowed us to see a clear redshift of the maximum in the incident photon-to-current efficiency spectra of the plasmonic devices (Δλ ~ 14 nm), which further proves the great potential of utilizing Au@SiO2 NRs in DSSCs.
Silicon clusters were produced by sputtering of a p-doped Si target and aggregation of the Si atoms in an argon gas atmosphere. The clusters were deposited in ultra high vacuum onto either (i) carbon transmission electron microscope (TEM) grids or (ii) a liquid nitrogen cooled finger on which a thick layer of ice was co-deposited during the exposure to the cluster beam. The ice layer containing the clusters was melted to form a liquid sample which showed luminescence peaking at 421 nm when excited at 307.5 nm. The luminescence is attributed to electron-hole recombination in oxygen deficient defects in the Si–SiO2 interface region. TEM images of the nanoparticles deposited on the carbon grids show spherical particles with diameters ranging from 4 to 50 nm, flake-like structures or nanotube-like shapes. Grids with higher deposited densities reveal clusters that are agglomerated into chains, TEM images of the dried liquid sample show a network of fibres indicating that growth into fibres is further promoted when the clusters gain mobility in the melted ice. 相似文献
A 4-pointed gold nanostar is proposed to form the array on a fiber facet to achieve a greatly enhanced near field intensity for Surface-Enhanced Raman Scattering (SERS) detection. The proposed gold nanostar array has a Surface Plasmon Resonance (SPR) peaked at a wavelength of ~650 nm with up to 45 times electric field intensity enhancement compared with the state-of-the-art nanorod design. It has a wideband SPR field enhancement spanned from 600 to 720 nm, which covers the wavelengths for both the excitation light (632.8 nm) and the Raman signal of the analytes (675–706 nm); With symmetrical structure it forms four hot spots in every unit cell and can detect best for light polarized horizontal or perpendicular to the waist of the nanostars. It also could be altered to tune the SPR and allows the fiber sensor to resonate at different wavelengths, as demonstrated by an example at 533 nm. All the above features make the gold nanostar-based compact and portable fiber sensor an attractive solution for SERS detection. 相似文献
Luminescent core-shell europium(III)-silica nanoparticles were prepared using europium(III) chelate core structure and polyvinylpyrrolidone
synthesis strategy for silica shell. Europium(III):naphtoyltrifluoroacetone:trioctylphosphineoxide complex was spontaneously
agglomerated from organic solvent to water. Polyvinylpyrrolidone was adsorbed onto the core structure and stable silica shell
was synthesized using tetraethylorthosilicate. Nanosized particles with a diameter of 71 ± 5 nm and 11 nm shell thickness
were obtained with fluorescence decay rate of 517 μs and excitation and emission wavelengths of 334 and 614 nm, respectively. 相似文献
Laser energy absorption results in significant heating of metallic nanoparticles and controlling the heating of nanoparticles is one of the essential stages of selective cell targeting. It is necessary to note that the laser action should be done by laser pulses with a wavelength that is strongly absorbed by the particles and it is important to select wavelengths that are not absorbed by the medium. Laser pulse duration must be chosen sufficiently short to minimize heat flow emitted from absorbing particles. Numerical calculations based on Mie theory were used to obtain the effect of laser wavelength and particle size on absorption factor for colloidal silver nanoparticles with radii between 5 and 50 nm. Calculations for acquiring temperatures under irradiations of pulsed KrF laser and pulsed Nd:YAG laser were performed. We showed that for low wavelengths of the laser, smaller nanoparticles have larger absorption efficiency compared to larger nanoparticles and in high wavelengths, temperature of all particles increased in the same way. 相似文献
Gold nanoparticles appear to be superior handles in optical trapping assays. We demonstrate that relatively large gold particles (R(b)=50 nm) indeed yield a sixfold enhancement in trapping efficiency and detection sensitivity as compared to similar-sized polystyrene particles. However, optical absorption by gold at the most common trapping wavelength (1064 nm) induces dramatic heating (266 degrees C/W). We determined this heating by comparing trap stiffness from three different methods in conjunction with detailed modeling. Due to this heating, gold nanoparticles are not useful for temperature-sensitive optical-trapping experiments, but may serve as local molecular heaters. Also, such particles, with their increased detection sensitivity, make excellent probes for certain zero-force biophysical assays. 相似文献
Upconversion luminescence was obtained from CdSeS nanocrystals (NCs) under 800 nm femtosecond laser excitation. The structural
and optical characteristics of the CdSeS NCs were investigated experimentally by use of UV–visible absorption spectroscopy,
transmission electron microscopy, X-ray diffractometry, and time-resolved luminescence dynamics. Peak shift of luminescence
in CdSeS NCs can be readily observed under different wavelength femtosecond excitation. The pump power dependence of the luminescence
intensity and time-resolved decay revealed that one, two, and three-photon absorption occur. It was found that upconversion
luminescence is composed of photoinduced trapping and a band-edge excitonic state, and two types of species are involved in
the biexponential luminescence decay kinetics. With increasing Se-doped composition, luminescence lifetimes of CdSeS NCs with
similar sizes become shorter. This is not consistent with the changes of undoped CdS NCs and is ascribed to impurity level
increased doping in the energy gap, which is favorable for trapping luminescence. A simple energy level of doping NCs is used
to interpret upconversion luminescence and the peak shift of steady-state emission. 相似文献
In this work we report the results of investigation of silver (Ag) nanoparticles prepared on a silica substrate by laser ablation. Our attention was focused on the mean diameter, size distribution and optical absorption properties of nanoparticles prepared in vacuum by using different laser wavelengths. The fundamental wavelength and the second, third, and fourth harmonics of a nanosecond Nd:YAG laser were used for nanoparticles fabrication. The corresponding values of the laser fluence for each wavelength were: 0.6 J/cm2 at 266 nm, 0.8 J/cm2 at 355 nm, 2.8 J/cm2 at 532 nm, and 2 J/cm2 at 1064 nm. The Ag nanoparticles produced have mean diameters in the range from 2 nm to 12 nm as the nanoparticles’ size decreases with the decrease of the wavelength used. The presence of the Ag nanoparticles was also evidenced by the appearance of a strong optical absorption band in the measured UV-VIS spectra associated with surface plasmon resonance (SPR). A redshift and widening of the absorption peak were observed as the laser wavelength was increased. Some additional investigations were performed in order to clarify the structure of the Ag nanoparticles. 相似文献