Effect of surfactant concentration on the size of coated ferromagnetic nanoparticles

We demonstrate that the average size of the coated ferromagnetic Fe₂O₃ nanoparticles is controlled by the surfactant concentration in the coating solution. Magnetization as a function of this ratio first increases and then decreases exhibiting a peak. Surface area of the coated material shows inverse behavior, i.e. first decreases and then increases. Both curves have extrema at the same ratio of surfactant/substrate. We explain these features in terms of competition between surface and volume contribution to the total energy, where surface contribution is determined by the bonding energy between the surfactant SH-group and Fe₂O₃. We support our conclusions by employing transmission electron microscopy and elemental analysis.     

Physicochemical properties of lipid nanoparticles: effect of lipid and surfactant composition

Understanding the effect of lipid and surfactant composition on particle size and colloidal stability plays a pivotal role in designing lipid nanoparticles (LN) for drug delivery. With respect to our long-term goal, LN for brain delivery, formulations containing lipids and surfactants suitable for intravenous (i.v.) application were selected for the current formulation screening study. LN were prepared by hot high pressure homogenization (HPH) and were characterized during 1 year in terms of macroscopic appearance, particle size by photon correlation spectroscopy (PCS) and optical single particle sizing (OSPS), zeta potential (ZP), as well as physical state and polymorphism by differential scanning calorimetry (DSC). The LN dispersions showed a wide variability in macroscopic appearance, mean size and colloidal stability. Influence factors were the type and concentration of both, the lipid and surfactant component used. The most promising LN showed a small mean size (< 200 nm), a low polydispersity index (PI), (< 0.25) absence of particles in the several-micron range, and a slightly negative ZP (> -12 mV); DSC revealed that some represented supercooled liquids; such LN may be stable at room temperature for at least 1 year. The obtained results are regarded helpful for defining the design space for LN delivery systems, i.e., identifying possible designs and design parameters within the given HPH technology to be applied during future formulation development studies.     

Synthesis of magnetic nanoparticles in bicontinuous microemulsions. Effect of surfactant concentration

Precipitation was accomplished at 80 °C for magnetic nanoparticles in bicontinuous microemulsions that were stabilized with different concentrations of a surfactants mixture of dodecyltrimethylammonium bromide/didodecyldimethylammonium bromide (3/2, w/w). These nanoparticles were characterized by X-ray Diffraction, Scanning Transmission Electronic Microscopy (STEM), and Vibrating Sample Magnetometry (VSM), which demonstrated that they were composed of magnetite or a mixture of magnetite-maghemite. The particles were found to have average diameters between 6.9 and 7.9 nm with relatively narrow particle size distribution and showed possible superparamagnetic behavior. In addition, we observed an inverse dependence of particle size on surfactant concentration. Yields obtained in these precipitation reactions were found to be up to three times higher than those typically reported in specialized literature about precipitation of magnetic nanoparticles in reverse microemulsions.     

MnO2包覆Co纳米颗粒的制备与表征

采用化学还原方法制备出具有纳米尺度的Co颗粒,并在其表面包覆1层MnO2膜,从而制备出具有核/壳结构的Co/MnO2颗粒。应用热处理手段,制备出3种不同类型的核/壳样品,分别通过XRD、TEM、SEM测量手段,对它们进行结构分析。并同时对这种铁磁/反铁磁的核壳结构样品进行磁性研究,发现包覆热处理后的Co颗粒具有可观的交换偏置现象。     

Green synthesis of superparamagnetic magnetite nanoparticles: effect of natural surfactant and heat treatment on the magnetic properties

A facile and eco-friendly synthetic approach was employed to synthesize superparamagnetic magnetite (Fe₃O₄) nanoparticles with cubic lattice structure. Zucchini and pomegranate peel-extracts were used as natural stabilizer and surfactant. The X-ray diffraction patterns revealed that the green synthetic technique was successful in formation of highly distributed Fe₃O₄ nanoparticles using both of the above extracts. The infrared (IR) analysis further confirmed the phase formation and the binding of extracts with Fe₃O₄ nanoparticles. Based on UV–Vis analysis, the samples showed the characteristic of surface plasmon resonance in the presence of Fe₃O₄ nanoparticles. The as-synthesized samples were heated at 550 °C for 2 h. It was found that the particles however grew, their sizes remained in nanoscale regime, indicating their thermal stability. The VSM analysis indicated that the as-synthesized samples have a saturation magnetization of 21.4 emu/g (using zucchini peel extract) and 13.3 emu/g (using pomegranate peel extract), which increased respectively to 45.8 emu/g and 38.1 emu/g after the heating process. A negligible coercivity in the samples with the particle sizes of less than 10 nm suggests superparamagnetic behavior of the samples.     

Photoluminescent properties of ZnS:Mn nanoparticles with in-built surfactant

Mn-doped ZnS nanoparticles, having average diameter 3–5 nm, have been synthesized using chemical precipitation technique without using any external capping agent. Zinc blende crystal structure has been confirmed using the X-ray diffraction studies. The effect of various concentrations of Mn doping on the photoluminescent properties of ZnS nanoparticles has been studied. The time-resolved photoluminescence spectra of the ZnS:Mn quantum dots have been recorded and various parameters like lifetimes, trap depths, and decay constant have been calculated from the decay curves at room temperature. The band gap was calculated using UV–Visible absorption spectra.     

Intrinsic effect of anionic surfactant on the morphology of hydroxyapatite nanoparticles and its structural and biological properties

This paper describes the potential effect of anionic surfactant on the morphology of hydroxyapatite (HA) nanostructures during hydrothermal synthesis. Sodium dodecyl sulfate (SDS) was used as an anionic surfactant. Various concentrations of SDS were used to study morphological changes in HA due to the presence of the surfactant. The final morphology, after treatment by a hydrothermal method, revealed that the anionic surfactant induced growth in one direction (a-axis) and inhibited growth in the other (c-axis) based on the charge distribution on the crystal faces of HA. Further structural analysis (by X-ray diffraction) confirmed this growth along the a-axis. In-vitro cellular analysis revealed that the plate-like nanoparticles possess better bioactivity than their bulk counterparts. Therefore, HA nanoplates could be used for applications that include controlled drug delivery and bone mineralization.     

Eu3+ concentration effect on luminescence properties of YAG:Eu3+ nanoparticles

Nanocrystalline Eu³⁺-doped YAG powders were prepared by modified Pechini method. The structural properties were investigated with XRD, SEM and Raman spectroscopy. XRD pattern indicated that the phase-pure YAG:Eu³⁺ crystallites were obtained without the formation of any other phases. Raman spectrum revealed good homogeneity and crystallinity of synthesized nanopowders. The luminescent properties were studied by measurement of excitation and emission spectra, quantum yields and decay curves. The effect of Eu³⁺ concentration on ⁵D₀ level lifetime was studied. The processes resulting in the relaxation of excited state (⁵D₀ level) were discussed and the probabilities of radiative and nonradiative processes were calculated using the model of f–f transition intensities. It was found that the observed shortening of ⁵D₀ level lifetime with Eu concentration is caused by increase of nonradiative process probability.     

纳米氧化锌表面包覆改性及其表征

采用液相沉积法对纳米氧化锌进行表面包覆SiO2和SiO2/Al2O3改性,并用XRD、TEM、TG-DSC对其表面结构进行了表征,借助Zeta电位测定仪、静态沉降实验等分析手段考察了改性前后纳米氧化锌在水体系中的分散稳定性.结果表明,在ZnO表面形成的包覆物是以非晶态形式存在的,通过表面包覆SiO2和SiO2/Al2O3改性后明显提高了氧化锌的表面羟基含量,有效改变了氧化锌的等电点,显著提高了纳米氧化锌在水中的分散稳定性.     

Influence of surfactant concentration on nanohydroxyapatite growth

Nanohydroxyapatite particles with different morphologies were synthesized through a microwave coupled hydrothermal method using CTAB as a template. A successful synthesis of nanosized HAP spheres, rods and fibres is achieved through this method by controlling the concentration of the surfactant. The concentration of the surfactant was tuned in such a way that the desired HAP nanostructures were obtained. The resultant powders were sintered at 900 °C in order to obtain phase pure HAP particles. The results obtained by Fourier transform infrared spectroscopy (FT–IR), X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques have substantiated the formation of nanosized HAP spheres and fibres.     

The role of surfactant in the miniemulsion polymerization of biodegradable polyurethane nanoparticles

The influence of surfactant type and concentration on particle size, formulation yield and stability of the polyurethane (PUR) nanoparticles synthesized by miniemulsion polymerization was investigated. SDS, Tween 80 and Pluronic F68 were employed as surfactants in concentration ranging from 5 to 20% (vs monomer concentration). The surfactant SDS was found not efficient in our system, resulting in a low formulation yield (about 53%), two particle size distributions and zeta potential equal to − 52.3mV. On the other hand, the nonionic surfactants gave monomodal particle size distribution, good yields (> 85%) and zeta potential around to− 24mV. The particles synthesized with Tween 80 or Pluronic F68 were very similar to each other in terms of efficiency, particle size distribution and zeta potential. For instance, the particle diameter slightly decreases from 292nm to 261nm as the amount of Tween 80 surfactant increases from 5 to 20wt.% vs monomer. Moreover, we have observed that a concentration of at least 5wt. % of Tween 80 was necessary to favor particle stability and therefore to avoid aggregation.     

Preparation and tunable luminescent characteristics of SiO2 coated ZnO:LiAc nanoparticles

ZnO:LiAc nanopaticles were successfully synthesized though a colloidal-sol technique in nonaqueous solution under ultrasonic irradiation. The luminescent characteristics from blue to red can be tunable by varying [Li]/[Zn] ratios. The possible reason of tunable luminescent characteristics can be attributed to the increase of density of oxygen vacancies caused by Li+ adsorbed in the surface of magic-sized ZnO nanocrystals based on XRD, zeta potential and XPS results. What's more, it is found that SiO2 shell coated on ZnO:LiAc nanoparticles can improve the surface property of ZnO nanoparticles and enhance the PL emission intensity and optical stability. Due to its excellent luminescent characteristic and optical stability, as-prepared SiO2 coated ZnO:LiAc nanoparticles may be a promising candidate for some applications in high-efficiency low-voltage phosphor, solar cells and biological luminescent labels.     

Subharmonic emissions from microbubbles: effect of the driving pulse shape

The aims of this work are to investigate the response of the ultrasonic contrast agents (UCA) insonified by different arbitrary-shaped pulses at different acoustic pressures and concentration of the contrast agent focusing on subharmonic emission. A transmission setup was developed in order to insonify the contrast agent contained in a measurement chamber. The transmitted ultrasonic signals were generated by an arbitrary wave generator connected to a linear power amplifier able to drive a single-element transducer. The transmitted ultrasonic pulses that passed through the contrast agent-filled chamber were received by a second transducer or a hydrophone aligned with the first one. The radio frequency (RF) signals were acquired by fast echographic multiparameters multi-image novel apparatus (FEMMINA), which is an echographic platform able to acquire ultrasonic signals in a real-time modality. Three sets of ultrasonic signals were devised in order to evaluate subharmonic response of the contrast agent respect with sinusoidal burst signals used as reference pulses. A decreasing up to 30 dB in subharmonic response was detected for a Gaussian-shaped pulse; differences in subharmonic emission up to 21 dB were detected for a composite pulse (two-tone burst) for different acoustic pressures and concentrations. Results from this experimentation demonstrated that the transmitted pulse shape strongly affects subharmonic emission in spite of a second harmonic one. In particular, the smoothness of the initial portion of the shaped pulses can inhibit subharmonic generation from the contrast agents respect with a reference sinusoidal burst signal. It also was shown that subharmonic generation is influenced by the amplitude and the concentration of the contrast agent for each set of the shaped pulses. Subharmonic emissions that derive from a nonlinear mechanism involving nonlinear coupling among different oscillation modes are strongly affected by the shape of the ultrasonic driving pulse.     

Dissolution properties of BaTiO3 nanoparticles in aqueous suspensions

Dissolution of barium ion from aqueous suspensions of commercial nano-sized barium titanate powders (BaTiO₃) has been studied at various pH values, solids loading, different time intervals and different electrolyte concentrations. Zeta potential measurements at various pH values and Fourier transform infrared spectroscopy study were also carried out to know the surface behaviour. Dissolution of Ba²⁺ depends on the suspension pH and stirring time period. The iso-electric points were found at 3.4 and 12.2 for as-received BaTiO₃ powder and 2.3 for the leached BaTiO₃. The Ba²⁺-leached BaTiO₃ suspension retards further leaching of Ba²⁺ ions at different pH values, which favours the achievement of stable suspension.     

低频低能量超声联合微泡对前列腺细胞的影响

目的:采用原子力声显微镜及透射电镜观察低频低能量超声联合微泡对前列腺癌细胞DU145及正常前列腺上皮细胞RWPE-1的作用。方法:两种细胞均分为对照组、单纯超声组、超声联合微泡组。对照组加入一定比例的生理盐水,不进行超声辐照;单纯超声组加入相同比例的生理盐水,用发射频率为21 k Hz的低频超声辐照,辐照2 min,占空比30%;超声联合微泡组加入同前相同比例的微泡造影剂悬浊液,用与单纯超声组相同的超声辐照。处理过的细胞立即用原子力声显微镜观察其形貌并计算其杨氏模量。同时,对同一处理方式的对照组及超声联合微泡组细胞继续培养24 h后,用透射电镜观察细胞。结果:单纯超声组的DU145细胞及RWPE-1细胞的细胞形态与对照组无明显变化;超声联合微泡组的DU145细胞及RWPE-1细胞形态呈类圆形,细胞表面可见放射状显微丝状结构,细胞膜表面可见多个大孔状结构;超声联合微泡组的DU145细胞的弹性模量较RWPE-1细胞大,且与对照组相比,两种细胞的弹性模量均变大,DU145细胞尤甚。透射电镜观察结果示对照组的两种细胞未见细胞自噬,而超声联合微泡组两种细胞都出现自噬现象,其中DU145细胞中可见凋亡现象。结论:低频低能量超声联合微泡可引起前列腺癌DU145细胞及正常前列腺上皮RWPE-1细胞的细胞膜出现孔状结构,并诱导其自噬,且对DU145细胞的损伤大于RWPE-1细胞。     

Bioactivity of gelatin coated magnetic iron oxide nanoparticles: in vitro evaluation

Current research explores formation of bone like apatite on gelatin coated magnetic iron oxide nanoparticles (GIOPs) to evaluate the bioactivity of the material. The GIOPs were soaked in simulated body fluid (SBF) and the apatite formation on the surface was investigated in regular interval of time. Fourier transform-infrared (FT-IR) and x-ray diffraction spectroscopic (XRD) analyses were done to investigate the chemical changes and field emission-scanning electron microscopic (FE-SEM) analysis was done to investigate the morphological changes occurring on the surface of the GIOPs after soaking in different time intervals. The kinetic studies of the apatite growth in SBF suggest that initially calcium and phosphorous ions were deposited to the surface of the GIOPs from the SBF leading to formation of amorphous Ca/P particles. Later, after 9 days of the incubation the amorphous particles were fused to form needle and blade like crystalline structures of bone like apatite.     

Photochemical synthesis of biopolymer coated Aucore-Agshell type bimetallic nanoparticles

Spherical Au nanoparticles have been prepared in the presence of a biopolymer, sodium alginate using UV-photoactivation technique. The particles are sodium alginate coated and are extremely stable. These Au nanoparticles have been used as seed for the synthesis of Aucore-Agshell type bimetallic nanoparticles. Sodium alginate is a carbohydrate-based biopolymer. In this synthesis it acts both as a reducing agent and a stabilizer for the evolved particles. Therefore, no extra capping agent is required from outside to make the generated particle stable. By varying the seed to silver ion ratios and using photoactivation technique Aucore-Agshell type bimetallic nanoparticles with various sizes and compositions have been synthesized. The method is very simple and reproducible and does not need any manipulative skill. Characterizations of these bimetallic nanoparticles have been done from their UV-visible spectroscopy, TEM/EDX, and AFM results. UV-visible extinction spectra reveal that the seed particles have an absorption maxima approximately 527 nm, attributed to the surface plasmon of the pure gold nanoparticles. From the TEM images the particle size of the gold seed particles was calculated to be 8.6 nm. The growth of bimetallic nanoparticles with time has been monitored. The finally evolved bimetallic Aucore-Agshell nanoparticles have a size in the range between approximately 10-14 nm. The particles are very stable and may have the potential for biological and catalytic applications.