The Synthesis of Magnetic and Fluorescent Bi-functional Silica Composite Nanoparticles via Reverse Microemulsion Method

In this paper, a simple synthesis method of small-size( about 50 nm in diameter), high magnetic and fluorescent bi-functional silica composite nanoparticles were developed, in which water-soluble Fe₃O₄ magnetic nanoparticlels (MNs) and CdTe quantum dots (QDs) were directly incorporated into a silica shell by reverse microemulsion method. The high luminescent QDs can be used as luminescent marker, while the high magnetic MNs allow the manipulation of the bi-functional silica composite nanoparticles by external magnetic field. Poly (dimethyldiallyl ammonium chloride) was used to balance the electrostatic repulsion between CdTe QDs and silica intermediates to enhance the fluorescence intensity of MNs-QDs/SiO₂ composite nanoparticles. The optical property, magnetic property, size characterization of the bi-functional composite nanoparticles were studied by UV-Vis and PL emission spectra, VSM, TEM, SEM. The stabilities toward time, pH and ionic strength and the effect of MNs on the fluorescence properties of bi-functional silica composite nanoparticles were also studied in detail. By modifying the surface of MNs-QDs/SiO₂ composite nanoparticles with amino and methylphosphonate groups, biologically functionalized and monodisperse MNs-QDs/SiO₂composite nanoparticles can be obtained. In this work, bi-functional composite nanoparticles were conjugated with FITC labeled goat anti-rabbit IgG, to generate novel fluorescent-magnetic-biotargeting tri-functional composite nanoparticles, which can be used in a number of biomedical application.     

Non-invasive Near Infrared Fluorescence Imaging of CdHgTe Quantum Dots in Mouse Model

Near infrared CdHgTe quantum dots (QDs) acted as biomarker for in vivo imaging were synthesized in aqueous solution. The size and the fluorescence wavelength of the synthesized quantum dots can be arbitrary manipulated by using different refluxing time. In particular, the fluorescence wavelength was extended to near infrared range (700∼900 nm), which make the in vivo imaging possible. Meanwhile, the characteristics, such as morphology, size, spectra, stability and toxicity were investigated. The dynamic bio-distribution, clearance from blood, liver and intestine in living animal were in vivo monitored by a NIR imaging system. The circulation of CdHgTe QDs in living mice was addressed semi-quantitatively according to the changes of fluorescence intensity. The high stability as well as high fluorescence intensity makes QDs particular interested candidates for in vivo imaging studies.     

Tailoring Cu2−xTe quantum-dot-decorated ZnO nanoparticles for potential solar cell applications

Cu_2−xTe QDs on ZnO nanoparticles were synthesized using a successive ionic layer absorption and reaction technique (SILAR) at room temperature. The as-synthesized QDs which were distributively deposited on ZnO nanoparticles surface were characterized by field emission scanning electron microscope (FE-SEM), X-ray diffraction and high-resolution transmittance microscope (HR-TEM). It revealed that the average diameter of the QDs was ∼2 nm. The synthesized Cu_2−xTe QDs were solely orthorhombic Cu_1.44Te phase. The growth mechanism was supposed that it based on ions deposition. The energy gap of as-synthesized Cu_2−xTe QDs was determined ∼1.1 eV and the smallest energy gap of 0.76 eV was obtained, equal to that of bulk material. Raman spectroscopy and FTIR were also used to study the Cu_2−xTe QDs on ZnO nanoparticles. These characteristics suggest a promising implication for a potential broadband sensitizer of QDSCs.     

Folate Conjugated CdHgTe Quantum Dots with High Targeting Affinity and Sensitivity for In vivo Early Tumor Diagnosis

CdHgTe-folate conjugates, acting as novel active-targeting fluorescence probes, were prepared by covalent conjugation of CdHgTe QDs and folic acid. Their characteristics, such as optical spectra, stability and cancer cell targeting were investigated in detail. The fluorescence wavelength of CdHgTe-folate conjugates was 790 nm and a full width at half-maximum (FWHM) of them was 50–70 nm. Their fluorescence stability could satisfy the need of long and continuous fluorescence imaging. The in vivo dynamic bio-distribution of CdHgTe-folate conjugates in S180 tumor beard mouse model was monitored by a NIR imaging system. The resultes indicated that CdHgTe-folate conjugates targeted to tumor effectively. The high fluorescence intensity together with targeting effect makes CdHgTe-folate conjugates promising candidates for imaging, monitoring and early diagnosis of cancer at molecular and cell level.     

Room-temperature observation of current bistability and fine structures in germanium quantum dots/SiO2 resonant tunneling diodes

The steady-state and time-dependent current–voltage (I–V) characteristics are experimentally investigated in Ge quantum dot (QD)/SiO₂ resonant tunneling diodes (RTDs). Ge QDs embedded in a SiO₂ matrix are naturally formed by thermal oxidation of Si_0.9Ge_0.1 nanowires (30 nm×50 nm) on silicon-on-insulator substrates. The average dot size and spacing between dots are 9±1 and 25 nm, respectively, from TEM observations, which indicate that one or two QDs are embedded between SiO₂ tunneling barriers within the nanowires. Room-temperature resonant oscillation, negative differential conductance, bistability, and fine structures are observed in the steady-state tunneling current of Ge-QD/SiO₂ RTDs under light illumination. Time-dependent tunneling current characteristics display periodic seesaw features as the Ge-QDs RTD is biased within the voltage regime of the first resonance peak while they exhibit harmonic swing behaviors as the RTD is biased at the current valleys or higher-order current peaks. This possibly originates from the interplay of the random telegraph signals from traps at the QD/SiO₂ interface as well as the electron wave interference within a small QD due to substantial quantum mechanics effects.     

Fluorescence Property of ZnO Nanoparticles and the Interaction with Bromothymol Blue

We synthesized ZnO quantum dots (QDs) simply in alcoholic solution, and investigated the interaction between ZnO QDs and bromothymol blue. The structural, morphological, size and spectral properties of ZnO QDs were studied. It was found that ZnO QDs were spherical nanoparticles in the crystal structure, and the average diameter of ZnO QDs was about 4.8 nm. The excitation and emission peaks were located at 346 nm and 520 nm, respectively, which were obtained on a common fluorophotometer. The quantum yield of ZnO QDs was obtained by using quinine sulfate as a reference reagent. In addition, the fluorescence of ZnO QDs can be quenched by bromothymol blue, and the quenching mechanism was proposed in a dynamic quenching mode.     

Optical properties of sol-gel fabricated Mn/SiO2 nanocomposites: Observation of surface plasmon resonance in Mn nanoparticles

Manganese nanoparticles were grown in silica glass and silica film on silicon substrate by annealing of the sol-gel prepared porous silicate matrices doped with manganese nitrate. Annealing of doped porous silicate matrices was performed at various conditions that allowed to obtain the nanocomposite glasses with various content of metallic Mn. TEM of Mn/SiO₂ glass indicates the bimodal size distribution of Mn nanoparticles with mean sizes of 10.5 nm and 21 nm. The absorption and photoluminescence spectra of Mn/SiO₂ glasses were measured. In the absorption spectra at 300 nm (4.13 eV) we observed the band attributed to the surface plasmon resonance in Mn nanoparticles. The spectra proved the creation of Mn²⁺ and Mn³⁺ ions in silica glass as well. The absorption spectra of Mn/SiO₂ glasses annealed in air prove the creation of manganese oxide Mn₂O₃. The measured reflection spectra of Mn/SiO₂ film manifest at 240-310 nm the peculiarity attributed to surface plasmons in Mn nanoparticles.     

All‐optical modulation based on silicon quantum dot doped SiOx:Si‐QD waveguide

All‐optical modulation based on silicon quantum dot doped SiO_x:Si‐QD waveguide is demonstrated. By shrinking the Si‐QD size from 4.3 nm to 1.7 nm in SiO_x matrix (SiO_x:Si‐QD) waveguide, the free‐carrier absorption (FCA) cross section of the Si‐QD is decreased to 8 × 10⁻¹⁸ cm² by enlarging the electron/hole effective masses, which shortens the PL and Auger lifetime to 83 ns and 16.5 ps, respectively. The FCA loss is conversely increased from 0.03 cm⁻¹ to 1.5 cm⁻¹ with the Si‐QD size enlarged from 1.7 nm to 4.3 nm due to the enhanced FCA cross section and the increased free‐carrier density in large Si‐QDs. Both the FCA and free‐carrier relaxation processes of Si‐QDs are shortened as the radiative recombination rate is enlarged by electron–hole momentum overlapping under strong quantum confinement effect. The all‐optical return‐to‐zero on‐off keying (RZ‐OOK) modulation is performed by using the SiO_x:Si‐QD waveguides, providing the transmission bit rate of the inversed RZ‐OOK data stream conversion from 0.2 to 2 Mbit/s by shrinking the Si‐QD size from 4.3 to 1.7 nm.     

Cytotoxicity and drug release behavior of PNIPAM grafted on silica-coated iron oxide nanoparticles

The nanoparticles containing thermosensitive and magnetic properties were investigated for their potential use as a novel drug carrier for targeted and controlled release drug delivery system. These thermosensitive and magnetic nanoparticles were prepared by grafting thermosensitive poly (N-isopropylacrylamide) (PNIPAM) on the surface of silica (SiO₂)-coated Fe₃O₄ nanoparticles with the particle size of 18.8 ± 1.6 nm. Adsorption and desorption behavior of bovine serum albumin (BSA) on the surface of PNIPAM-grafted SiO₂/Fe₃O₄ nanoparticles was studied, and the results indicated that these nanoparticles were able to absorb protein at temperature above the lower critical solution temperature (LCST) and to be desorbed below the LCST. Cytotoxicity studies conducted on Chinese hamster ovary (CHO-K1) cells using methyl tetrazolium (MTT) assays revealed that cell viability of 1 mg/mL PNIPAM-grafted nanoparticles was slightly decreased after 24 h of incubation as compared to the lower concentration of nanoparticles. Furthermore, the concentration of 0.5 mg/mL PNIPAM-grafted nanoparticles was totally biocompatible for 48 h, but had low cytotoxicity after 72 h of incubation. These PNIPAM-grafted nanoparticles did not induce morphological change in their cellularity after exposure for 24 and 108 h. These results demonstrate that PNIPAM-grafted nanoparticles are biocompatible and have potential use as drug carriers.     

Nanoparticle Tracking Analysis: Enhanced Detection of Transparent Materials

This study proposes a novel and simple in-house design of a nanoparticle tracking analysis (NTA) device for the online characterization of nanoparticles in an aqueous solution. The particle size distribution of two sets of model nanoparticles, for example, transparent (SiO₂) and opaque (TiO₂) materials with respect to water as a dispersion medium could be successfully analyzed. Experiments are conducted using two different laser wavelengths of 632.8 (red) and 510 nm (green) and a range of concentrations. The accuracy of the green laser is larger compared to the red laser for all particle concentrations used. The measured average diameter using the presented in-house NTA setup is in the acceptable range compared to the electron microscopy data. The average diameter of the transparent (SiO₂) and opaque (TiO₂) samples is calculated as 36.29 and 27.26 nm using NTA, 36.44 and 27.8 nm analyzing field emission scanning electron microscopy images, and 23.97 and 19.7 nm analyzing transmission electron microscopy images. In the new viewing sample holder, nanoparticles undergo mere Brownian motion with no bulk drift velocity. The effect of solid concentration and wavelength of the laser light on the performance of the NTA sensor is investigated, and the optimal concentration range for model particles is reported.     

Toxicity of amorphous silica nanoparticles in mouse keratinocytes

The present study was designed to examine the uptake, localization, and the cytotoxic effects of well-dispersed amorphous silica nanoparticles in mouse keratinocytes (HEL-30). Mouse keratinocytes were exposed for 24 h to various concentrations of amorphous silica nanoparticles in homogeneous suspensions of average size distribution (30, 48, 118, and 535 nm SiO₂) and then assessed for uptake and biochemical changes. Results of transmission electron microscopy revealed all sizes of silica were taken up into the cells and localized into the cytoplasm. The lactate dehydrogenase (LDH) assay shows LDH leakage was dose- and size-dependent with exposure to 30 and 48 nm nanoparticles. However, no LDH leakage was observed for either 118 or 535 nm nanoparticles. The mitochondrial viability assay (MTT) showed significant toxicity for 30 and 48 nm at high concentrations (100 μg/mL) compared to the 118 and 535 nm particles. Further studies were carried out to investigate if cellular reduced GSH and mitochondria membrane potential are involved in the mechanism of SiO₂ toxicity. The redox potential of cells (GSH) was reduced significantly at concentrations of 50, 100, and 200 μg/mL at 30 nm nanoparticle exposures. However, silica nanoparticles larger than 30 nm showed no changes in GSH levels. Reactive oxygen species (ROS) formation did not show any significant change between controls and the exposed cells. In summary, amorphous silica nanoparticles below 100 nm induced cytotoxicity suggest size of the particles is critical to produce biological effects.     

Preparation of copper–silicon dioxide nanoparticles with chemical vapor synthesis

Atmospheric pressure chemical vapor synthesis was used to produce copper nanoparticle composites in an amorphous silicon dioxide, i.e., either copper nanoparticles coated with amorphous silicon dioxide or copper nanoparticles embedded in amorphous silicon dioxide matrix. Synthesized metal–organic copper(I) complex was used as a precursor that provided well-defined ratio (1:2) of copper and silicon. The thermal decomposition of the Cu(I) complex molecule leads to homogenous nucleation and formation of copper nanoparticles which are subsequently coated with Si/SiO₂ in the gas phase. The decomposition was greatly enhanced when reductive atmosphere, i.e., H₂/N₂ 10 v% were used instead of pure nitrogen. A narrow size distribution with the geometric mean diameter of the particle agglomerates around 30 nm was observed while the primary size of the copper core particles was around 5 nm.     

Preparation and Characterization of CdHgTe Nanoparticles and Their Application on the Determination of Proteins

CdHgTe nanoparticles (NPs) with the emission in the near-infrared regions were prepared in aqueous solution, and were characterized by transmission electron microscopy, X-ray diffraction spectrometry, spectrofluorometry and ultraviolet-visible spectrometry. Based on the fluorescence quenching of CdHgTe NPs in the presence of proteins, a novel method for the determination of proteins with CdHgTe NPs as a near-infrared fluorescence probe was developed. Maximum fluorescence quenching was observed with the excitation and emission wavelengths of 500 and 693 nm, respectively. Under the optimal conditions, the calibration graphs were linear in the range of 0.04 × 10⁻⁶–5.6 × 10⁻⁶ g ml⁻¹ for lysozyme (Lyz) and 0.06 × 10⁻⁶–6.1 × 10⁻⁶ g ml⁻¹ for bovine hemoglobin (BHb), respectively. The limits of detection were 13 ng ml⁻¹ for Lyz and 27 ng ml⁻¹ for BHb, respectively. Four synthetic samples were determined and the results were satisfied.     

Self-organization of bimetallic PdAu nanoparticles on SiO<Subscript>2</Subscript> surface

Bimetallic PdAu nanoparticles on SiO₂ substrate were produced by a sequential room-temperature sputtering deposition method. By the atomic force microscopy technique we studied the nanoparticles self-organization mechanisms in various conditions. First, Pd nucleation and growth proceeds at the substrate defects and the Pd nanoparticles density increase rapidly. During the second sputtering deposition, Au atoms adsorb on the SiO₂ and diffuse toward Pd nanoparticles without forming new nuclei. The Au atoms are trapped by the preformed Pd nanoparticles, forming PdAu bimetallic nanoparticles which size increases. Furthermore, fixing the amount of deposited Pd and increasing the amount of deposited Au, we analyzed the evolution of the PdAu film surface morphology: we observe that the PdAu grows initially as three-dimensional islands; then the PdAu film morphology evolves from compact three-dimensional islands to partially coalesced worm-like structures, followed by a percolation morphology and finally to a continuous and rough film. The application of the interrupted coalescence model allowed us to evaluate the critical mean island diameter R _c ≈ 2.8 nm for the partial coalescence process. The application of the dynamic scaling theory of growing interfaces allowed us to evaluate the dynamic growth exponent β = 0.21 ± 0.01 from the evolution of the film surface roughness. Finally, fixing the amount of deposited Pd and Au we studied the self-organization mechanism of the PdAu nanoparticles induced by thermal processes performed in the 973–1173 K temperature range. The observed kinetic growth mechanism is consistent with a surface diffusion-limited ripening of the nanoparticles with a temperature-dependent growth exponent. The dependence of the growth exponent on the temperature is supposed to be linked to the variation with the temperature of the characteristics of the PdAu alloy. The activation energy for the surface diffusion process was evaluated in 0.54 ± 0.03 eV.     

Silicon nanoparticles formation in annealed SiO/SiO2 multilayers

We present a study on amorphous SiO/SiO₂ superlattice performed by grazing-incidence small-angle X-ray scattering (GISAXS). Amorphous SiO/SiO₂ superlattices were prepared by high-vacuum evaporation of 3 nm thin films of SiO and SiO₂ (10 layers each) onto Si(1 0 0) substrate. After the deposition, samples were annealed at 1100 °C for 1 h in vacuum, yielding to Si nanocrystals formation. Using a Guinier approximation, the shape and the size of the crystals were obtained. The size of the growing nanoparticles in the direction perpendicular to the film surface is well controlled by the bilayer thickness. However, their size varies more significantly in the direction parallel to the film surface.     

One-step flame method for the synthesis of coated composite nanoparticles

A simple in situ flame coating method has been developed by designing a new type of coflow diffusion flame burner having a sliding unit. The sliding unit was shown to be very effective in finding a right position where the precursor for coating layer should meet with core particles. SiO₂-coated TiO₂ nanoparticles were first prepared and whether most surfaces of particles were coated was examined by both direct observation of particles through a transmission electron microscope and Zeta potential measurements. Mean core sizes varied from 28 to 109 nm and mean coating thickness was about 2.4 nm for silica-coated titania particles. By simply changing chemical precursors, we demonstrated that SiO₂-coated SnO₂, SnO₂-coated TiO₂, SiO₂–SnO₂-coated TiO₂ nanoparticles could be also synthesized.     

Application of SAXS to the study of particle-size-dependent thermal conductivity in silica nanofluids

Knowledge of the size and distribution of nanoparticles in solution is critical to understanding the observed enhancements in thermal conductivity and heat transfer of nanofluids. We have applied small-angle X-ray scattering (SAXS) to the characterization of SiO₂ nanoparticles (10–30 nm) uniformly dispersed in a water-based fluid using the Advanced Photon Source at Argonne National Laboratory. Size distributions for the suspended nanoparticles were derived by fitting experimental data to an established model. Thermal conductivity of the SiO₂ nanofluids was also measured, and the relation between the average particle size and the thermal conductivity enhancement was established. The experimental data contradict models based on fluid interfacial layers or Brownian motion but support the concept of thermal resistance at the liquid–particle interface.     

Electroluminescence with micro-watt output from ultra-small sized Si quantum dots/amorphous SiO2 multilayers prepared by laser crystallization method

We report the fabrication of Si quantum dots (QDs)/SiO₂ multilayers by using KrF excimer laser (248 nm) crystallization of amorphous Si/SiO₂ multilayered structures on ITO coated glass substrates. Raman spectra and transmission electron microscopy demonstrate the formation of Si QDs and the size can be controlled as small as 1.8 nm. After laser crystallization, Al electrode is evaporated to obtain light emitting devices and the room temperature electroluminescence (EL) can be detected with applying the DC voltage above 8 V on the top gate electrode. The luminescent intensity increases with increasing the applied voltage and the micro-watt light output is achieved. The EL behaviors for samples with different Si dot sizes are studied and it is found that the corresponding external quantum efficiency is significantly enhanced in sample with ultra-small sized Si QDs.     

Light scattering calculations from Au and Au/SiO2 core/shell nanoparticles

Given the importance of the optical properties of Au and Au/SiO₂ core/shell nanoparticles, in this article we focus our attention on the light scattering properties of such systems and on a relative comparison. In particular, we report theoretical results of angle-dependent light scattering intensity and scattering efficiency for Au and Au/SiO₂ core/shell nanoparticles increasing the Au particle radius from 30 to 130 nm, and for Au/SiO₂ core/shell particles changing the core-to-shell sizes ratio. Finally, a comparison between the scattering efficiency of the Au and Au/SiO₂ core/shell nanoparticles is drawn. The results of this work can be used in the design of tunable efficiency light scattering devices (biological and molecular sensors, solar cells).     

Avidin conjugation to up-conversion phosphor NaYF4:Yb3+, Er3+ by the oxidation of the oligosaccharide chains

NaYF₄:Yb³⁺, Er³⁺ nanoparticles were successfully prepared by a polyol process using diethyleneglycol (DEG) as solvent. After being functionalized with SiO₂–NH₂ layer, these NaYF₄:Yb³⁺, Er³⁺ nanoparticles can conjugate with activated avidin molecules (activated by the oxidation of the oligosaccharide chain). The as-formed NaYF₄:Yb³⁺, Er³⁺ nanoparticles, NaYF₄:Yb³⁺, Er³⁺ nanoparticles functionalized with amino groups, avidin conjugated amino-functionalized NaYF₄:Yb³⁺, Er³⁺ nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), Fourier transform infrared (FT-IR), UV/Vis absorption spectra, and up-conversion luminescence spectra, respectively. The biofunctionalization of the NaYF₄:Yb³⁺, Er³⁺ nanoparticles has less effect on their luminescence properties, i.e., they still show the up-conversion emission (from Er³⁺, with ⁴S_3/2 → ⁴I_15/2 at ~540 nm and ⁴F_9/2 → ⁴I_15/2 at ~653 nm), indicative of the great potential for these NaYF₄:Yb³⁺, Er³⁺ nanoparticles to be used as fluorescence probes for biological system.