Synthesis and surface functionalization of silica nanoparticles for nanomedicine

There are a wide variety of silica nanoformulations being investigated for biomedical applications. Silica nanoparticles can be produced using a wide variety of synthetic techniques with precise control over their physical and chemical characteristics. Inorganic nanoformulations are often criticized or neglected for their poor tolerance; however, extensive studies into silica nanoparticle biodistributions and toxicology have shown that silica nanoparticles may be well tolerated, and in some case are excreted or are biodegradable. Robust synthetic techniques have allowed silica nanoparticles to be developed for applications such as biomedical imaging contrast agents, ablative therapy sensitizers, and drug delivery vehicles. This review explores the synthetic techniques used to create and modify an assortment of silica nanoformulations, as well as several of the diagnostic and therapeutic applications.     

ZnO nanoparticles embedded in UVM-7-like mesoporous silica materials: Synthesis and characterization

ZnO nanodomains embedded in bimodal mesoporous silica (UVM-7) materials with high Zn content (4≤Si/Zn≤30) have been synthesized by an one-pot surfactant-assisted procedure from a hydro alcoholic medium using a cationic surfactant (CTMABr=cetyltrimethylammonium bromide) as structural directing agent, and starting from molecular atrane complexes of Zn and Si as hydrolytic inorganic precursors. This chemical procedure allows optimizing the dispersion of the ZnO particles in the silica walls. The bimodal mesoporous nature of the final high surface area nano-sized materials is confirmed by XRD, TEM, and N₂ adsorption–desorption isotherms. The small intra-particle mesopore system is due to the supramolecular templating effect of the surfactant, while the large pores have their origin in the packing voids generated by aggregation of the primary nanometric mesoporous particles. A limited pore blocking and a high accessibility to the ZnO active nanoparticles have been achieved. The effects induced by the progressive incorporation of ZnO nanoparticles into the mesostructure have been examined, including a careful optical spectroscopic study (PL and UV–visible).     

Surface-induced structural modification in ZnO nanoparticles

Cobalt?Ccobalt carbide [Co _x C (x?=?2 or 3)] and cobalt (FCC-Co) microwires have been synthesized using a polyol method in the presence of a high external magnetic field of 4.3?kOe. It was reported before that the synthesis of these particles in the absence of magnetic field leads to the formation of spherical particles. Analysis of the X-ray diffraction (XRD) scans indicates that the synthesized Co _x C wires consist of four phases?? ??-Co, ??-Co, Co₃C, and Co₂C. The percent composition of these phases was 53.3?% Co₃C, 26.8?% Co₂C, 12.5?% ??-Co, and 7.4?% ??-Co. XRD analysis of the as-synthesized cobalt wires shows that it consists of single-phase FCC-Co. Based on Scherrer analysis of the XRD data, the average crystallite sizes of the cobalt carbide and the cobalt particles are 18.5 and 16.3?nm, respectively. Scanning electron microscopy (SEM) studies show that the diameter of Co _x C wires is in the range of 1.6(±0.2)???m with their length varying between 18 and 30???m while the diameter of the cobalt wires is 1.65(±0.1). The SEM results infer that the morphology of the growing particles was controlled by the magnetic field with the applied field directs the growth of the particles into wires. The magnetic measurements indicate a superparamagnetic character of the cobalt wires and a soft ferromagnetic nature of the synthesized Co _x C chains. The degree and field range of the interactions between magnetic domains have been investigated using a Henkel plot.     

Silk-mediated synthesis and modification of photoluminescent ZnO nanoparticles

In this article, a bio-inspired silk-mediated method was established to produce natural material-modified photoluminescent zinc oxide nanoparticles (nano-ZnO). Silk fibroin fibers were employed as the reactive substrates to synthesize nano-ZnO, and silk fibroins (SF) were taken as the biocompatible stabilizers to modify dispersed nano-ZnO. As-prepared nano-ZnO were mainly hexagonal phase particles with diameter around 13 nm. The resulting nano-ZnO/SF hybrids displayed orange emission and good biocompatibility in aqueous system.     

Sensitization of ZnO photoconductivity by chemical modification of surface states

Surface States on ZnO have been investigated through their effect on photoconductivity. Low energy photons (0·7 ～ 1·5 eV) are found to induce a feeble photocurrent in ZnO which is attributable to the direct electron injection from surface levels to the conduction band. A definite correlation has been found between the i.r. induced photocurrent and the intrinsic or the dye sensitized photocurrent excited by UV or visible radiation. It is proposed that phthalic anhydride on ZnO modifies the distribution of surface levels, by a chemical interaction with chemisorbed oxygen. Surface levels originating in chemisorbed oxygen ions are transformed by phthalic anhydride into new levels which are shallower but thermally more stable. These traps are found to enhance the photoconductivity of ZnO. The chemical nature of them and the mechanism of sensitization are discussed.     

Preferred orientation of ZnO nanoparticles formed by post-thermal annealing zinc implanted silica

High quality zinc oxide nanoparticles with (002) preferred orientation were prepared by post-thermal annealing zinc implanted silica at 700 °C using two methods. One method was annealing zinc implanted silica at 700 °C for 2 h in oxygen ambient; the other method was sequentially annealing zinc implanted silica at 700 °C in nitrogen and oxygen ambient for 1 h, respectively. X-ray diffraction (XRD), absorption and microphotoluminescence (micro-PL) results indicated that the latter method could create high quality ZnO nanoparticles with (002) preferred orientation and narrow size-distribution. X-ray photoelectron spectra (XPS) showed the formation of ZnO nanoparticles on a silica surface, where the ZnO nanoparticle content increased with increasing oxidation time in an oxygen environment. The processes of the transformation from Zn to ZnO are discussed.     

Synthesis of nickel nanoparticles in silica by alcogel electrolysis

We report a novel technique for the formation of metal nanoparticles, based on electrolysis of the alcogels containing metal chlorides. The alcogel was formed from TEOS, water, ethanol, and nickel chloride, and subjected to galvanostatic electrolysis. This resulted in successful formation of Ni nanoparticles inside the silica gel. Average particle size of FCC Ni lies between 18 and 20 nm. The formation of tetragonal nickel (a sub-oxide of nickel) as well as NiO were also detected by XRD and SAED. The resistivity measurements showed that the nickel nanoparticles were separated from each other by Ni(O) present between them. Magnetic studies based on ZFC and FC measurements below room temperature (up to 5 K) and above room temperature (up to 700 K) were conducted using SQUID and Magnetic TGA, respectively, which showed strong magnetic irreversibility as attributable to exchange interaction between metallic and oxide phases and mutual interactions among metallic particles in the network structure. The blocking temperature (~600 K) of the samples was above room temperature. M–H studies based on VSM showed an increase in magnetic coercivity with the formation of NiO. A magnetic transition associated with tetragonal nickel was seen at 10 K.     

Linear and nonlinear optical properties of luminescent ZnO nanoparticles embedded in PMMA matrix

ZnO nanoparticles embedded in the PMMA matrix were prepared by wet chemical synthesis. The optical band gap of the ZnO nanoparticles decreases with increase in NaOH concentration. The photoluminescence spectra of the ZnO colloids show strong UV, green and blue emissions. The optical absorptive nonlinearity of the ZnO:PMMA composites was analyzed using an open aperture Z-scan technique which shows optical limiting type nonlinearity due to the two photon absorption in ZnO. The efficiency of limiting is found to increase with decrease in the band gap. ZnO:PMMA shows a negative value for nonlinear refractive index n₂ and the magnitude of n₂ increases with decrease of band gap. Stability as well as the mechanical properties of the nanoparticles embedded in the PMMA matrix makes it more suitable for device fabrication as compared to the ZnO nanoparticles dispersed in solution.     

ZnO microparticles,ZnO nanoparticles and Zn0.9Cu0.1O nanoparticles toward ethanol vapor sensing: A comparative study

ZnO and Zn_0.9Cu_0.1O nanoparticles were synthesized by the sonochemical method. Structural and morphological properties of the synthesized nanoparticles were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive analysis of X-ray (EDAX). The results revealed the formation of ZnO and Zn_0.9Cu_0.1O nanoparticles in wurtzite phase with average crystallite diameter of 30–40 nm calculated from Debye–Scherrer equation. Moreover, the ethanol vapor sensing properties of ZnO and Zn_0.9Cu_0.1O nanoparticles were investigated at different operating temperatures and they were compared with commercial ZnO microparticles. Comparative results demonstrated that Zn_0.9Cu_0.1O nanoparticles exhibit highest and fastest response to 250 ppm of ethanol at 300 °C. Results on response/recovery time, sensing mechanism, conductance variation and thermodynamics/kinetics of ethanol sensing is also studied and discussed.     

Multifunctional magnetite and silica–magnetite nanoparticles: Synthesis,surface activation and applications in life sciences

A method for the introduction of amine groups onto the surface of magnetite and silica-coated magnetite nanoparticles has been established based on the condensation of aminopropyltriethoxysilane. Amine-modified particles were grafted with an oligonucleotide and used in the capture of a complimentary sequence. The particles’ efficiency at capture was observed to correlate directly with amine group surface density.     

Synthesis and analysis of ZnO and CdSe nanoparticles

Zinc oxide and cadmium selenide particles in the nanometer size regime have been synthesized using chemical routes. The particles were capped using thioglycerol in case of ZnO and 2-mercaptoethanol in case of CdSe to achieve the stability and avoid the coalescence. Zinc oxide nanoparticles were doped with europium to study their optical properties. A variety of techniques like UV-Vis absorption spectroscopy, X-ray diffraction (XRD), photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and transmission electron microscopy (TEM) were used to carry out structural and spectroscopic characterizations of the nanoparticles.     

Cu-doped ZnO nanoparticles: Synthesis, structural and electrical properties

Pure and Cu doped ZnO nanopowders (5, 10, 15, 20, 25 and 30 at% Cu) have been synthesized using co-precipitation method. Transmission Electron Microscopic analysis has shown the morphology of ZnO nanopowders to be quasi-spherical. Powder X-ray Diffraction studies have revealed the systematic doping of Cu into the ZnO lattice up to 10% Cu, though the peaks corresponding to CuO in 10% Cu are negligibly very small. Beyond this level, there was segregation of a secondary phase corresponding to the formation of CuO. Fourier Transform Infrared spectra have shown a broad absorption band at ∼490 cm⁻¹ for all the samples, which corresponds to the stretching vibration of Zn-O bond. DC electrical resistivity has been found to decrease with increasing Cu content. The activation energy has also been observed to decrease with copper doping i.e. from ∼0.67 eV for pure ZnO to ∼0.41 eV for 30 at% Cu doped ZnO.     

Formation of metal nanoparticles in silica by the sequential implantation of Ag and Cu

Spherical-like nanoparticles have been formed by sequentially ion-implanting Ag/Cu into silica glasses. During sequential Ag/Cu ion implantation, the diameter of Cu nanoparticles is increased and the average Ag nanoparticle diameter is decreased with increasing Cu ion dose. The evolution of nanoparticles is characterized by grazing incidence X-ray diffraction, extended X-ray absorption fine structure spectroscopy and transmission electron microscopy. Nanovoids in the nanoparticles are formed by sequential ion implantation. PACS 61.72.Ww; 61.46.-W     

Structural properties of core and surface of silica nanoparticles investigated by Raman spectroscopy

We studied the experimental Raman spectra of various commercial silica nanoparticles of average diameter from 7 to 40 nm and specific surface from 50 to 380 m²/g. We found that the peculiarities of the particles Raman spectra systematically depend on their specific surface. In detail, the peak position of the R band at about 440 cm⁻¹ shifts towards high wavenumbers following an almost linear dependence on the specific surface. Similarly, the amplitudes of the D1 and D2 bands, at about 495 and 605 cm⁻¹, respectively, increase linearly with the same quantity. Our results are interpreted in the frame of the shell model for the nanoparticles clarifying that the network of the core of the nanoparticles is comparable to the bulk silica materials, whereas the surface shell has a ring statistic shifted to the low member rings and features an higher density. Copyright © 2013 John Wiley & Sons, Ltd.     

Luminescence enhancement of ZnO nanoparticles on metal surface

We have studied luminescence enhancement of zinc oxide (ZnO) nanoparticles with the average size of 30 nm on several metal surfaces at low temperatures. Bandedge luminescence originated from bound exciton (BE) annihilation is observed at 3.360 eV, and strongly depends on the kind and surface roughness of metal. The luminescence intensity is about 10 times larger for Ag surface than that for quartz surface. Furthermore, the luminescence increases remarkably when the roughness of Ag surface is almost the same as the particle size. The intensity ratio of the fast decay component to the slow one decreases for Ag surface compared with quartz. These results suggest that the luminescence enhancement is partially attributed to suppressing of the nonradiative recombination process in ZnO nanoparticles on metal surface.     

Synthesis of Cu nanoparticles by condensation from the gas phase

A series of computer experiments was conducted by the raw material evaporation and subsequent condensation to determine the most efficient regimes of copper nanoparticles synthesis. By variation of the cooling rate of the metal vapor the formation of Cu clusters were studied. The computer experiments showed the influence of different final temperatures on the shape of the resultant particles. This allowed to determine the conditions for a predominant formation of worm-like clusters of a spherical shape in the gas phase synthesis.     

熔石英表面铜颗粒污染激光诱导损伤

利用SAGA-S激光器输出的355 nm波长激光,研究了熔石英表面铜颗粒污染的激光损伤规律。采用磁控溅射的方式在洁净熔石英表面制备不同尺寸的颗粒状污染物,用1-on-1,10-on-1,20-on-1的方式测试经污染后的熔石英基底的损伤阈值,并采用光学显微镜观察损伤形貌、CCD在线测量损伤斑尺寸。结果表明:污染后的熔石英基底的损伤主要发生在后表面,而且以热烧蚀和热应力为主,基底的损伤阈值与熔石英前表面污染颗粒尺寸呈负指数关系,随后表面污染物颗粒尺寸的增大呈略微下降。前表面颗粒污染物诱导损伤斑尺寸为颗粒污染物尺寸的4倍,后表面颗粒污染物引起的损伤斑尺寸约为颗粒污染物尺寸的2倍。并绘出损伤斑尺寸与颗粒尺寸、辐照方式之间的关系。     

Synthesis, characterisation and functionalisation of luminescent silica nanoparticles

The synthesis of highly monodispersed, homogeneous and stable luminescent silica nanoparticles, synthesized using a process based on the Stöber method is reported here. These particles have been functionalised with the ruthenium and europium complexes: bis (2,2??-bipyridine)-(5-aminophenanthroline) Ru bis (hexafluorophosphate), abbreviated to (Ru(bpy)₂(phen-5-NH₂)(PF₆)), and tris (dibenzoylmethane)-mono (5-aminophenanthroline) europium(III), abbreviated to (Eu:TDMAP). Both dyes have a free amino group available, facilitating the covalent conjugation of the dyes inside the silica matrix. Due to the covalent bond between the dyes and the silica, no dye leaching or nanoparticle diameter modification was observed. The generic and versatile nature of the synthesis process was demonstrated via the synthesis of both europium and ruthenium-functionalised nanoparticles. Following this, the main emphasis of the study was the characterisation of the luminescence of the ruthenium-functionalised silica nanoparticles, in particular, as a function of surface carboxyl or amino group functionalisation. It was demonstrated that the luminescence of the ruthenium dye is highly affected by the ionic environment at the surface of the nanoparticle, and that these effects can be counteracted by encapsulating the ruthenium-functionalised nanoparticles in a plain 15 nm silica layer. Moreover, the ruthenium-functionalised silica nanoparticles showed high relative brightness compared to the free dye in solution and efficient functionalisation with amino or carboxyl groups. Due to their ease of fabrication and attractive characteristics, the ruthenium-functionalised silica nanoparticles described here have the potential to be highly desirable fluorescent labels, particularly, for biological applications.