Fabrication and characterization of a new MRI contrast agent based on a magnetic dextran–spermine nanoparticle system

This study aims to fabricate and formulate a new magnetic resonance imaging (MRI) contrast agent based on a dextran?Cspermine nanoparticulate system loaded with super paramagnetic iron oxide nanoparticles (SPION). SPION-loaded spermine?Cdextran nanoparticles were prepared according to a procedure based on the ionic gelation of dextran?Cspermine with sodium tripolyphosphate (TPP) anions. The effects of process parameters such as pH, concentration of spermine dextran, TPP to dextran?Cspermine and SPION to dextran?Cspermine weight ratios, and TPP addition rate were fully investigated to find the optimized formulation through the response surface methodology. At the optimum condition, 75% of the magnetic iron oxide nanoparticles added to the polymeric solution were entrapped in dextran?Cspermine nanoparticles. Samples were investigated by transmission electron microscopy. The mean particle size of the nanoparticles determined by particle size analyzer was found to be 65?nm at the optimum condition with zeta potential of +90?mV. The SPION-loaded dextran?Cspermine nanoparticle formulation has the same superparamagnetic properties as SPIONs and at same iron concentration the saturation magnetization (Ms) of the SPION-loaded dextran?Cspermine nanoparticles was larger than SPIONs. In vitro MRI was performed with gradient echo and spin-echo sequences at 1.5?T. By increasing of iron concentration, the T ₂ relaxation times were reduced. Thus, indicating that the saturation magnetization and r ₂ and $ r_{2}^{*} $ relaxivities were enhanced, and the contrast effects were improved in comparison to commercial SPIONs.     

Polyethylene glycol assisted facile sol-gel synthesis of lanthanum oxide nanoparticles: Structural characterizations and photoluminescence studies

In this study, lanthanum oxide nanoparticles (La₂O₃ NPs) synthesised via the facile sol-gel method, using a solution of micro-sized lanthanum oxide powders containing 20% nitric acid and high molecular weight polyethylene glycol (PEG). The as synthesised La₂O₃ NPs were then characterized using X-ray diffraction (XRD), environmental scanning electron microscopy (ESEM), energy-dispersive X-ray (EDS) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and photoluminescence (PL) spectroscopy. Our findings indicated that the concentration of PEG strongly influences the particle size and the lattice strain of the La₂O₃ NPs. A single phase hexagonal crystal structure was confirmed via XRD studies with lattice constants, a =?b =?0.3973?nm and c =?0.6129?nm. The average crystallite size and lattice strains estimated were in the range of approximately 25–28?nm and 0.0050–0.0055 respectively. The incremental nature of the crystallinity and lattice strains of the NPs was observed with the subsequent enhancement of PEG-contents, while the average particle size was reduced. The average particle size of La₂O₃ NPs estimated from ESEM imaging was consistent with that obtained from the XRD data. The photoluminescence spectra revealed a strong emission band located at a wavelength of 365?nm (typical green band) for all La₂O₃NPsamples. This is ascribed to the recombination of delocalized electrons around the conduction band with a single charged state of a surface oxygen vacancy.     

Formation of retinyl palmitate-loaded poly(l-lactide) nanoparticles using rapid expansion of supercritical solutions into liquid solvents (RESOLV)

Poly(l-lactide) (PLLA) nanoparticles loaded with retinyl palmitate (RP) were successfully prepared by rapid expansion of a supercritical carbon dioxide (CO₂) solution into an aqueous receiving solution containing a stabilizing agent (RESOLV). Three stabilizing agents, Pluronic F127, Pluronic F68, and sodium dodecyl sulfate (SDS) have been employed and the Pluronic F127 was found to be more effective for stabilizing PLLA/RP nanoparticles than Pluronic F68 and SDS, as RESOLV into a 0.1 wt% Pluronic F127 solution produced a stable nanosuspension consisting mainly of well-dispersed, individual nanoparticles. The effect of rapid expansion processing conditions (i.e., degree of saturation (S), pre-expansion temperature (T_pre), and concentrations of PLLA and RP (C_PLLA, C_RP)) on the particle size, form, and RP loading was systematically investigated. It was found that spherical PLLA/RP nanoparticles with an average size range of ∼40-110 nm and RP loadings of 0.9-6.2 wt% were consistently produced by RESOLV. The size of PLLA/RP nanoparticles increased from ∼30-80 to ∼30-160 nm as the solution degree of saturation changed from S < 1 to S > 1, independent of T_pre, C_PLLA, and C_RP. The entrapment capacity of RP in PLLA nanoparticles was predominantly determined by T_pre and C_RP. Increasing the T_pre from 70 to 100 °C and the C_RP from 0.05 to 0.15 wt% increased the encapsulated RP content at least twofold. Our results show that the technique with benign supercritical CO₂ should be generally applicable to nanoparticle fabrications of other important active ingredients, especially in liquid form, in polymeric nanoparticles.     

Highly Insensitive/Reactive Thermite Prepared from Cr2O3 Nanoparticles

Thermites prepared from nanoparticles are currently the subject of growing interest due to their increased performances compared to classical micrometer‐sized thermites. Here, we studied the combustion behavior of energetic composite composed of Al and chromium (III) oxide (Cr₂O₃) as function of the oxide particle size. Homogeneous composites were prepared by mixing Al nanoparticles (Φ≈50 nm) with Cr₂O₃ micro‐ and nanoparticles (Φ≈20 nm), respectively, in hexane solution. The dried Cr₂O₃/Al composite powders were ignited by using a CO₂ laser beam. The use of nanosized Cr₂O₃ particles incontestably improves the energetic performances of the Al/Cr₂O₃ thermite since the ignition delay time was shortened by a factor 3.5 (16±2 vs 54±4 ms) and the combustion rate (340±10 mm s⁻¹) was significantly accelerated in contrast to those reported until now. Interestingly, the sensitivity to friction of the Al‐based thermites formulated from Cr₂O₃ is two orders of magnitude lower than the thermite prepared from other metal oxide nanoparticles (MnO₂, WO₃). Finally, our study shows that the decrease of Cr₂O₃ particle size has an interesting and beneficial effect on the energetic properties of Cr₂O₃/Al thermites and appears as an alternative to tune the properties of these energetic materials.     

Microbial deposition of gold nanoparticles by the metal-reducing bacterium Shewanella algae

Microbial reduction and deposition of gold nanoparticles was achieved at 25 °C over the pH range 2.0-7.0 using the mesophilic bacterium Shewanella algae in the presence of H₂ as the electron donor. The reductive deposition of gold by the resting cells of S. algae was a fast process: 1 mM AuCl₄⁻ ions were completely reduced to elemental gold within 30 min. At a solution pH of 7, gold nanoparticles 10-20 nm in size were deposited in the periplasmic space of S. algae cells. At pH 2.8, gold nanoparticles 15-200 nm in size were deposited on the bacterial cells, and the biogenic nanoparticles exhibited a variety of shapes that included nanotriangles: in particular, single crystalline gold nanotriangles 100-200 nm in size were microbially deposited. At a solution pH of 2.0, gold nanoparticles about 20 nm in size were deposited intracellularly, and larger gold particles approximately 350 nm in size were deposited extracellularly. The solution pH was an important factor in controlling the morphology of the biogenic gold particles and the location of gold deposition. Microbial deposition of gold nanoparticles is potentially attractive as an environmentally friendly alternative to conventional methods.     

Reforming of C6 Hydrocarbons Over Model Pt Nanoparticle Catalysts

Size-controlled model Pt nanoparticle catalysts, synthesized by colloidal chemistry, were used to study the hydrogenative reforming of three C₆ hydrocarbons in mixtures with 5:1 excess of H₂: methylcyclopentane, n-hexane and 2-methylpentane. We found a strong particle size dependence on the distribution of different reaction products for the hydrogenolysis of methylcyclopentane. The reactions of 50?Torr methylcyclopentane in 250?Torr H₂ at 320 °C, using 1.5 and 3.0 nm Pt nanoparticles produced predominantly C₆ isomers, especially 2-methylpentane, whereas 5.2 and 11.3 nm Pt nanoparticles were more selective for the formation of benzene. For the hydrogenolysis of n-hexane and 2-methylpentane, strong particle size effects on the turnover rates were observed. Hexane and 2-methylpentane reacted up to an order of magnitude slower over 3.0 nm Pt than over the other particle sizes. At 360 °C the isomerization reactions were more selective than the other reaction pathways over 3.0?nm Pt, which also yielded relatively less benzene.     

Tin oxide nanoparticle formation using a surface modifying agent

This work presents results concerning the preparation of redispersible tin oxide nanoparticles achieved by using Tiron molecule ((OH)₂C₆H₂(SO₃Na)₂) as surface modifying agent. The adsorption isotherm measurements show that an amount of 10 wt.% of Tiron is need to recover the SnO₂ nanoparticles surface with a monolayer. These nanoparticles can be easily redispersed in tetramethylammonium hydroxide at pH ≥11 until a powder concentration of 12 vol.% of tin. Under these conditions, hydrodynamic particle size is about 7 nm and increases until 52 nm at pH 6 due to the aggregation phenomenon. The time evolution of the viscoelastic properties indicates that the suspensions at pH 12.5, containing 12 vol.% tin oxide and 10 wt.% of surface modifier are kinetically stable. After thermal treatment at different temperature the powder characterisation evidences that the presence of Tiron monolayer at the nanoparticles surface increases the thermal stability of the porous texture and prevent the micropore size growth. This set of results contributes to satisfy the demand for more controlled synthesis of nanoparticles with high thermal stability as required for fabrication of ultrafiltration ceramic membranes.     

A novel one-pot biosynthesis of pure alpha aluminum oxide nanoparticles using the macroalgae Sargassum ilicifolium: A green marine approach

A novel biological method is proposed for producing ceramic alpha aluminum oxide nanoparticles using an extract of the algae Sargassum ilicifolium. The algal extract functions as a bioreducing as well as a stabilizer agent. The presence of an absorption peak at 227?nm, confirmed the formation of the aluminum oxide nanoparticles using a UV–visible spectroscopy. FTIR analysis indicated that bioreduction of aluminum ions and nanoparticle stabilization probably occurred by interactions between aluminum and the biofunctional groups of algal extract. The XRD pattern revealed that after calcination at ~ 1200?°C, the Al₂O₃ nanoparticles were alpha crystalline in nature with a diameter of 35?nm and had a rhombohedral structure. TEM indicated that the alumina nanoparticles were well-dispersed and spherical in shape with an average size of 20?±?2.1?nm. EDX spectroscopy revealed that the sample contained only aluminum (46.31%) and oxygen (53.69%), confirming the high purity of the alumina nanopowder. The results demonstrated that alpha alumina NPs has an optical band gap of 5.46?eV.     

Degradation Treatment of 4-Nitrophenol by <Emphasis Type="Italic">Moringa oleifera</Emphasis> Synthesised GO-CeO<Subscript>2</Subscript> Nanoparticles as Catalyst

A facile microwave-assisted reaction was used to synthesize graphene oxide with cerium oxide nanoparticles (GO-CeO₂ NPs) from water extracts of Moringa oleifera flower. The one step microwave synthesis treatment was used for reduction of ceria atom to cerium oxide nanoparticles along with the reduction of graphene oxide. The synthesized GO-CeO₂ NPs were analysed by various analytical instrumentation techniques and we found the size of nanoparticles as 50 nm with a spherical shape. Further, the green synthesized GO-CeO₂ NPs were employed as a catalyst to reduce 4-nitrophenol and achieved a degradation rate of 95.45%.     

Narrowing size distribution widths of small α-Al2O3 nanoparticles by addition of large nanoparticles in coagulation separation

α-Al₂O₃ nanoparticles separated by fractionated coagulation still have broad size distributions which limit their wider applications. By adding 20-time mass of large α-Al₂O₃ (40.5 nm) into α-Al₂O₃ nanoparticles to be separated in coagulation separation, the average size of separated α-Al₂O₃ nanoparticles decrease from 6.6 nm without addition of large α-Al₂O₃ NPs to 4.4 nm, and the size distribution changes from 3–10 nm without addition of large α-Al₂O₃ NPs to 3–6 nm. With increasing amount of large α-Al₂O₃ NPs added, separated α-Al₂O₃ NPs exhibit smaller average sizes and narrower size distribution widths at the same separation concentrations. This approach may be applied to narrow size distribution widths in large-scale size-selective separations of other nanoparticles.     

Gold-silver alloy nanoshells: a new candidate for nanotherapeutics and diagnostics

We have developed novel gold-silver alloy nanoshells as magnetic resonance imaging (MRI) dual T₁ (positive) and T₂ (negative) contrast agents as an alternative to typical gadolinium (Gd)-based contrast agents. Specifically, we have doped iron oxide nanoparticles with Gd ions and sequestered the ions within the core by coating the nanoparticles with an alloy of gold and silver. Thus, these nanoparticles are very innovative and have the potential to overcome toxicities related to renal clearance of contrast agents such as nephrogenic systemic fibrosis. The morphology of the attained nanoparticles was characterized by XRD which demonstrated the successful incorporation of Gd(III) ions into the structure of the magnetite, with no major alterations of the spinel structure, as well as the growth of the gold-silver alloy shells. This was supported by TEM, ICP-AES, and SEM/EDS data. The nanoshells showed a saturation magnetization of 38 emu/g because of the presence of Gd ions within the crystalline structure with r₁ and r₂ values of 0.0119 and 0.9229 mL mg^-1 s^-1, respectively (Au:Ag alloy = 1:1). T₁- and T₂-weighted images of the nanoshells showed that these agents can both increase the surrounding water proton signals in the T₁-weighted image and reduce the signal in T₂-weighted images. The as-synthesized nanoparticles exhibited strong absorption in the range of 600-800 nm, their optical properties being strongly dependent upon the thickness of the gold-silver alloy shell. Thus, these nanoshells have the potential to be utilized for tumor cell ablation because of their absorption as well as an imaging agent.     

Formation of palladium fullerides and their thermal decomposition into palladium nanoparticles

Formation of palladium fullerides from various Pd:C₆₀ compositions was studied by XRD, Raman spectroscopy and TEM. Raman spectra of Pd_xC₆₀ samples show close similarity to spectra of C₆₀ polymers obtained under high pressure/high temperature conditions and suggest the formation of chain-like and two-dimensional polymeric structures in Pd_xC₆₀ of various compositions. Thermal decomposition of Pd_xC₆₀ results in the formation of fine 5-10 nm size nanoparticles of palladium which can be used for catalytic applications.     

Molecular characterization of α,β-poly(N-2-hydroxyethyl)-dl-aspartamide derivatives as potential self-assembling copolymers forming polymeric micelles

A family of graft copolymers derivatives obtained from α,β-poly(N-2-hydroxyethyl)-dl-aspartamide (PHEA) have been studied as potential self-assembling macromolecules forming stable polymeric micelles at low critical micellar concentration. These polymers are obtained grafting on PHEA poly(ethylene glycol) (PEG) (M_w 5000 g/mol) (PHEA-PEG), hexadecylamine (PHEA-C₁₆) or both moieties (PHEA-PEG-C₁₆). The PHEA derivatives were characterised by a multi-angle light scattering (MALS) photometer on line to a size exclusion chromatography system in obtaining the molar mass distribution of the polymers. In addition, to investigate the capacity to form micellar aggregates in aqueous medium the MALS photometer was used in off-line batch mode in obtaining molar mass and dimension of the polymeric aggregates.     

Synthesis route and three different core-shell impacts on magnetic characterization of gadolinium oxide-based nanoparticles as new contrast agents for molecular magnetic resonance imaging

Despite its good resolution, magnetic resonance imaging intrinsically has low sensitivity. Recently, contrast agent nanoparticles have been used as sensitivity and contrast enhancer. The aim of this study was to investigate a new controlled synthesis method for gadolinium oxide-based nanoparticle preparation. For this purpose, diethyleneglycol coating of gadolinium oxide (Gd₂O₃-DEG) was performed using new supervised polyol route, and small particulate gadolinium oxide (SPGO) PEGylation was obtained with methoxy-polyethylene-glycol-silane (550 and 2,000 Da) coatings as SPGO-mPEG-silane550 and 2,000, respectively. Physicochemical characterization and magnetic properties of these three contrast agents in comparison with conventional Gd-DTPA were verified by dynamic light scattering transmission electron microscopy, Fourier transform infrared spectroscopy, inductively coupled plasma, X-ray diffraction, vibrating sample magnetometer, and the signal intensity and relaxivity measurements were performed using 1.5-T MRI scanner.As a result, the nanoparticle sizes of Gd₂O₃-DEG, SPGO-mPEG-silane550, and SPGO-mPEG-silane2000 could be reached to 5.9, 51.3, 194.2 nm, respectively. The image signal intensity and longitudinal (r₁) and transverse relaxivity (r₂) measurements in different concentrations (0.3 to approximately 2.5 mM), revealed the r₂/r₁ ratios of 1.13, 0.89, 33.34, and 33.72 for Gd-DTPA, Gd₂O₃-DEG, SPGO-mPEG-silane550, and SPGO-mPEG-silane2000, respectively.The achievement of new synthesis route of Gd₂O₃-DEG resulted in lower r₂/r₁ ratio for Gd₂O₃-DEG than Gd-DTPA and other previous synthesized methods by this and other groups. The smaller r₂/r₁ ratios of two PEGylated-SPGO contrast agents in our study in comparison with r₂/r₁ ratio of previous PEGylation (r₂/r₁ = 81.9 for mPEG-silane 6,000 MW) showed that these new three introduced contrast agents could potentially be proper contrast enhancers for cellular and molecular MR imaging.     

Size dependence of the magnetic properties of Ni nanoparticles prepared by thermal decomposition method

By means of thermal decomposition, we prepared single-phase spherical Ni nanoparticles (23 to 114 nm in diameter) that are face-centered cubic in structure. The magnetic properties of the Ni nanoparticles were experimentally as well as theoretically investigated as a function of particle size. By means of thermogravimetric/differential thermal analysis, the Curie temperature T_C of the 23-, 45-, 80-, and 114-nm Ni particles was found to be 335°C, 346°C, 351°C, and 354°C, respectively. Based on the size-and-shape dependence model of cohesive energy, a theoretical model is proposed to explain the size dependence of T_C. The measurement of magnetic hysteresis loop reveals that the saturation magnetization M_S and remanent magnetization increase and the coercivity decreases monotonously with increasing particle size, indicating a distinct size effect. By adopting a simplified theoretical model, we obtained M_S values that are in good agreement with the experimental ones. Furthermore, with increase of surface-to-volume ratio of Ni nanoparticles due to decrease of particle size, there is increase of the percentage of magnetically inactive layer.     

One-step hydrothermal synthesis of a TiO2-Ti3C2Tx nanocomposite with small sized TiO2 nanoparticles

A TiO₂-Ti₃C₂T_x nanocomposite was prepared using a simple and facile one-step hydrothermal method. The small sized TiO₂ nanoparticles were synthesized and assembled on the surface of Ti₃C₂T_x nanosheets using Ti₃C₂T_x itself as titanium source by in-situ technique. The microstructure of TiO₂-Ti₃C₂T_x nanocomposite was characterized by means of XRD、FESEM、TEM、XPS and Raman, respectively. The effects of ethanol and hydrothermal holding time on the size of TiO₂ nanoparticles were investigated. The results show that adding proper amount of ethanol into pure water results in decrease of the size of TiO₂ nanoparticles. Under ethanol-water mixed solution, increasing the time of hydrothermal treatment results in growth and even aggregation of TiO₂ nanoparticles. The TiO₂ nanoparticles with average particle size of 30 nm were obtained when the hydrothermal treatment was conducted in ethanol-water mixed solution at 200 ℃ for 12 h.     

Preparation and characterization of nanosized nickel oxide

Nanosized nickel oxide was synthesized by a simple liquid-phase process to obtain the hydroxide precursor and then calcined to form the oxide. The precursor and the nickel oxide were characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), thermal analysis (TG) and temperature-programmed reduction (TPR). The results indicated that the particle size of nickel oxide was controlled by the calcined temperature (T_C). Mixed phases of nickel oxide and nickel hydroxide were present as the T_C was lower than 300 °C. Non-stoichiometric nickel oxide (NiO_x, x = 1.2) was formed between 250 °C and 400 °C and a pure nickel oxide was formed as the T_C arrived 500 °C. The particle size of nickel oxide changed as the calcined temperature was controlled under 250 °C, 300 °C, 400 °C and 500 °C, the order was 5.6 nm, 6.5 nm, 11 nm and 17 nm, respectively.     

High-temperature synthesis of composite materials based on (Cr,Mn, V)–Al–C MAX phases

Composite materials based on (Cr, Mn, V)–Al–C MAX phases were obtained by self-propagating high-temperature synthesis (SHS). Regularities of synthesis of composite materials from mixtures containing chromium (III) oxide, manganese (IV) oxide, vanadium (V) oxide, calcium (IV) oxide, aluminum, and carbon powders were studied. The synthesis of 30-g blend was carried out in an SHS reactor with a volume of 3 l under Ar pressure (5 MPa). Variation in the amount of the starting reagents markedly affected the process parameters, phase composition, and microstructure of combustion products. The combustion products were characterized by XRD, SEM, and EDS analysis. For Cr–Al–C system, MAX Cr₂AlC phase in addition to chromium aluminide Cr₅Al₈ and chromium carbides (Cr₇C₃, Cr₃C₂) was detected. SEM studies showed that Cr₂AlC has a laminated structure with layer thickness varying from 3 to 20 nm. XRD pattern of Mn–Cr–Al–C composite material were found to have signals belonging (Cr_xMn_1–x)₂AlC solid solution, Mn₃AlC, and Cr₂Al. It was shown that V–Al–C composite material contains nano-layered MAX V₂AlC phase and particles VC_х, VAl₃.     

Advanced synthesis for monodisperse polymer nanoparticles in aqueous media with sub-millimolar surfactants

Highly monodisperse polystyrene nanoparticles with mean diameters of less than 100 nm are synthesized via aqueous emulsion polymerization using an amphoteric initiator (VA-057) in the presence of sub-millimolar concentrations of anionic surfactant. Since the net charge on the initiator is almost zero at neutral pH, the resultant latex particle size is mainly determined by surfactant adsorption. Polymerizations were performed in the presence of a range of anionic surfactants with differing critical micelle concentrations (CMC) by varying the concentrations of surfactant, initiator and monomer, and also the ionic strength. Sodium dodecyl benzene sulfonate (SDBS), sodium hexadecyl sulfate (SHS), and sodium octadecyl sulfate (SOS) have relatively low CMCs and so enable formation of highly monodisperse nanoparticles at relatively low (sub-millimolar) surfactant concentrations, C_S (i.e. below the CMC in each case). Empirically, it was found that the particle number, N_p, and coefficient of variation of the particle size, C_V, were strongly dependent on the C_S/CMC ratio: N_p increased almost in proportion with the square of this ratio, while the C_V exhibited a minimum at approximately C_S/CMC = 0.20. Higher ionic strength reduced the particle size, which is consistent with the above relationship because the addition of salt lowers the CMCs of ionic surfactants. Polymer latex particles produced using such formulations form highly regular, close-packed colloidal arrays.     

Preparation and electrochemical studies of electrospun TiO2 nanofibers and molten salt method nanoparticles

The TiO₂ nanofibers and nanoparticles are prepared by electrospinning and molten salt method, respectively. The materials are characterized by X-ray diffraction scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and a thermal analysis. The SEM and TEM studies showed that fibers were of average diameter ∼100 nm and composed of nanocrystallites of size 10-20 nm. Electrochemical properties of the materials are evaluated using cyclic voltammetry, galvanostatic cycling and electrochemical impedance spectroscopy. Cyclic voltammetric studies show a hysteresis (ΔV) between the cathodic and the anodic peak potentials for TiO₂ nanofibers and nanoparticles (sizes ∼15-30 nm) are in the range, 0.23-0.30 V and a redox couple Ti^4+/3+ around ∼1.74/2.0 V. Electrochemical cycling results revealed that the TiO₂ nanofibers have lower capacity fading compared to that of the nanoparticles. The capacity fading for 2-50 cycles was ∼23% for nanofibers, which was nearly one-third of that of corresponding nanoparticles (∼63%). We discussed the effect of particle size on hysteresis and cycling performance of TiO₂ nanoparticles. Impedance analysis of TiO₂ nanofibers and nanoparticles during first discharge cycle is analyzed and interpreted.