SANS and UV-vis spectroscopy studies of resultant structure from lysozyme adsorption on silica nanoparticles

The interaction of lysozyme protein (M.W. 14.7 kD) with two sizes of silica nanoparticles (16 and 25 nm) has been examined in aqueous solution using UV-vis spectroscopy and small-angle neutron scattering (SANS). The measurements were performed on fixed concentration (1 wt %) of nanoparticles and varying concentration of protein in the range 0 to 2 wt %. The adsorption isotherm as obtained using UV-vis spectroscopy suggests strong interaction of the two components and shows an exponential behavior. The saturation values of adsorption are found to be around 90 and 270 protein molecules per particle for 16 and 25 nm sized nanoparticles, respectively. The adsorption of protein on nanoparticles leads to the aggregation of particles and these structures have been studied by SANS. The aggregates are characterized by fractal structure coexisting with unaggregated particles at low protein concentrations and free proteins at higher protein concentrations. Further, contrast variation SANS measurements have been carried out to differentiate the adsorbed and free protein in these systems.     

Small-angle neutron scattering study of adsorbed pluronic tri-block copolymers on laponite

The adsorption of selected poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) tri-block copolymers on synthetic clay particles (laponite) has been investigated. The adsorbed amount and distribution of polymer was determined as a function of relative block composition and size, using the technique of contrast variation small-angle neutron scattering. The pluronic molecules appear to adsorb via a preferential segregation of hydrophobic PPO segments at the surface, with hydrophilic PEO segments dangling into solution. The effect of the PPO segments is substantial with large increases in adsorbed amount and layer thickness as the anchor fraction decreases/PEO chain length increases. This is in direct contrast to the behavior observed for PEO homopolymer adsorption (of much higher molecular weights) where the adsorbed amount and layer thickness are smaller and change little with molecular weight.     

(1)H NMR and small-angle neutron scattering investigation of the structure and solubilization behavior of three-layer nanoparticles

Three-layer nanoparticles were prepared by radiation-induced polymerization of 1-10 g/L of methyl methacrylate dissolved in a 0.1 wt % D(2)O solution of polystyrene-poly(methacrylic acid) (PS-PMA) micelles. According to NMR and small-angle neutron scattering (SANS), most of the poly(methyl methacrylate) (PMMA) is adsorbed at the core-shell interface of the particles. A small fraction of shorter PMMA probably sticks to outer parts of the PMA chains. The absorption kinetics and equilibria of benzene and chloroform were studied by NMR and SANS time-resolved experiments. The diffusion front in the PS core is very narrow but quite broad in the PMMA sheet suggesting, thus, a less compact state of PMMA. According to SANS, the diffusion kinetics is almost independent of the PMMA sheet thickness. In contrast to it, the absorption capacity, reflected by both SANS and NMR, increases markedly with the PMMA content in the particle. The maximum amount of solubilized compound depends on its positive interaction with PMMA (expressed by the chi parameter) but is restricted by the growing interface tension between swollen PMMA and D(2)O. In accordance with this conclusion, a particle saturated with benzene can absorb chloroform only at the expense of a part of benzene expelled into the surrounding medium and vice versa. Starting with 10 g PMMA/L (10 times the weight of the original micelles), the particles become unstable when being swollen with a good solvent.     

Neutron scattering from water adsorbed on an alumina membrane

The pore structure of an alumina membrane was studied by adsorption in conjunction with small-angle neutron scattering (SANS). The effect of an incomplete contrast matching was investigated and simple formulae allowing the calculation of the amount of water adsorbed and the film areas, at various relative pressures, were derived for the ternary system. In the vicinity of the contrast matching point, however, incomplete contrast matching does not introduce a substantial complication to data analysis. The adsorption isotherm was reconstructed from the SANS data and agrees well with the experimental adsorption isotherm. For the alumina membrane, a coordination number of ≈10 was estimated from the SANS determined areas.     

In situ measurement of bovine serum albumin interaction with gold nanospheres

We present in situ observations of adsorption of bovine serum albumin (BSA) on citrate-stabilized gold nanospheres. We implemented scattering correlation spectroscopy as a tool to quantify changes in the nanoparticle brownian motion resulting from BSA adsorption onto the nanoparticle surface. Protein binding was observed as an increase in the nanoparticle hydrodynamic radius. Our results indicate the formation of a protein monolayer at similar albumin concentrations as those found in human blood. Additionally, by monitoring the frequency and intensity of individual scattering events caused by single gold nanoparticles passing the observation volume, we found that BSA did not induce colloidal aggregation, a relevant result from the toxicological viewpoint. Moreover, to elucidate the thermodynamics of the gold nanoparticle-BSA association, we measured an adsorption isotherm which was best described by an anticooperative binding model. The number of binding sites based on this model was consistent with a BSA monolayer in its native state. In contrast, experiments using poly(ethylene glycol)-capped gold nanoparticles revealed no evidence for adsorption of BSA.     

Investigation of confined ionic liquid in nanostructured materials by a combination of SANS, contrast-matching SANS, and nitrogen adsorption

Small-angle neutron scattering (SANS), contrast-matching SANS, and nitrogen adsorption have been utilized to investigate the confined ionic liquid (IL) [bmim][PF(6)] phase in ordered mesoporous silica MCM-41 and SBA-15. The results suggest that the pores of SBA-15 are completely filled with IL whereas a small fraction of the pore volume, the pore "core", of MCM-41 is empty. The contrast-matching SANS measurements confirm the enhanced solubility of water in IL. In addition, they provide strong evidence that water does not enter the empty pore core of MCM-41, possibly because of the preferred orientation of the IL molecules in the adsorbed layer.     

A small-angle neutron scattering study of adsorbed poly(ethylene oxide) on Laponite

The adsorption of poly(ethylene oxide) (PEO) on synthetic anisotropic clay particles (Laponite) has been investigated as a function of the molecular weight. Contrast variation small-angle neutron scattering (SANS) measurements were used to characterize the distribution and adsorbed amount of polymer on the particles. These experiments show not only that polymer is present on the face of the clay particle but that it also extends or "wraps" over the edges. The edge layer was thicker than the face layer for all the molecular weights studied. The polymer layers are unusually thin, with a thickness and adsorbed amount that show little variation with molecular weight.     

Interaction of dissolved proteins with spherical polyelectrolyte brushes

We consider the adsorption of bovine serum albumin (BSA) on spherical polyelectrolyte brushes (SPB). The SPB consist of a solid polystyrene core of 100nm diameter onto which linear polyelectrolyte chains (poly(acrylic acid), (PAA)) are grafted. The adsorption of BSA is studied at a pH of 6.1 at different concentrations of added salt and buffer (MES). We observe strong adsorption of BSA onto the SPB despite the effect that the particles as well as the dissolved BSA are charged negatively. The adsorption of BSA is strongest at low salt concentration and decreases drastically with increasing amounts of added salt. The adsorbed protein can be washed out again by raising the ionic strength. The various driving forces for the adsorption are discussed. It is demonstrated that the main driving force is located in the electrostatic interaction of the protein with the brush layer of the particles. All data show that the SPB present a new class of carrier particles whose interaction with proteins can be tuned in a well-defined manner.     

'Stealth' corona-core nanoparticles surface modified by polyethylene glycol (PEG): influences of the corona (PEG chain length and surface density) and of the core composition on phagocytic uptake and plasma protein adsorption

Nanoparticles possessing poly(ethylene glycol) (PEG) chains on their surface have been described as blood persistent drug delivery system with potential applications for intravenous drug administration. Considering the importance of protein interactions with injected colloidal dug carriers with regard to their in vivo fate, we analysed plasma protein adsorption onto biodegradable PEG-coated poly(lactic acid) (PLA), poly(lactic-co-glycolic acid) (PLGA) and poly(-caprolactone) (PCL) nanoparticles employing two-dimensional gel electrophoresis (2-D PAGE). A series of corona/core nanoparticles of sizes 160–270 nm were prepared from diblock PEG-PLA, PEG-PLGA and PEG-PCL and from PEG-PLA:PLA blends. The PEG Mw was varied from 2000–20 000 g/mole and the particles were prepared using different PEG contents. It was thus possible to study the influence of the PEG corona thickness and density, as well as the influence of the nature of the core (PLA, PLGA or PCL), on the competitive plasma protein adsorption, zeta potential and particle uptake by polymorphonuclear (PMN) cells. 2-D PAGE studies showed that plasma protein adsorption on PEG-coated PLA nanospheres strongly depends on the PEG molecular weight (Mw) (i.e. PEG chain length at the particle surface) as well as on the PEG content in the particles (i.e. PEG chain density at the surface of the particles). Whatever the thickness or the density of the corona, the qualitative composition of the plasma protein adsorption patterns was very similar, showing that adsorption was governed by interaction with a PLA surface protected more or less by PEG chains. The main spots on the gels were albumin, fibrinogen, IgG, Ig light chains, and the apolipoproteins apoA-I and apoE. For particles made of PEG-PLA45K with different PEG Mw, a maximal reduction in protein adsorption was found for a PEG Mw of 5000 g/mole. For nanospheres differing in their PEG content from 0.5 to 20 wt %, a PEG content between 2 and 5 wt % was determined as a threshold value for optimal protein resistance. When increasing the PEG content in the nanoparticles above 5 wt % no further reduction in protein adsorption was achieved. Phagocytosis by PMN studied using chemiluminescence and zeta potential data agreed well with these findings: the same PEG surface density threshold was found to ensure simultaneously efficient steric stabilization and to avoid the uptake by PMN cells. Supposing all the PEG chains migrate to the surface, this would correspond to a distance of about 1.5 nm between two terminally attached PEG chains in the covering ‘brush’. Particles from PEG5K-PLA45K, PEG5K-PLGA45K and PEG5K-PCL45K copolymers enabled to study the influence of the core on plasma protein adsorption, all other parameters (corona thickness and density) being kept constant. Adsorption patterns were in good qualitative agreement with each other. Only a few protein species were exclusively present just on one type of nanoparticle. However, the extent of proteins adsorbed differed in a large extent from one particle to another. In vivo studies could help elucidating the role of the type and amount of proteins adsorbed on the fate of the nanoparticles after intraveinous administration, as a function of the nature of their core. These results could be useful in the design of long circulating intravenously injectable biodegradable drug carriers endowed with protein resistant properties and low phagocytic uptake.     

Adsorption of nanoparticles at the solid-liquid interface

The adsorption of differently charged nanoparticles at liquid-solid interfaces was investigated by in situ X-ray reflectivity measurements. The layer formation of positively charged maghemite (γ-Fe(2)O(3)) nanoparticles at the aqueous solution-SiO(2) interface was observed while negatively charged gold nanoparticles show no adsorption at this interface. Thus, the electrostatic interaction between the particles and the charged surface was determined as the driving force for the adsorption process. The data analysis shows that a logarithmic particle size distribution describes the density profile of the thin adsorbed maghemite layer. The size distribution in the nanoparticle solution determined by small angle X-ray scattering shows an average particle size which is similar to that found for the adsorbed film. The formed magehemite film exhibits a rather high stability.     

Evolution of self-assembled silica-tetrapropylammonium nanoparticles at elevated temperatures

The time evolution of silica nanoparticles in solutions of tetrapropylammonium (TPA) has been studied using a combination of small-angle scattering, conductivity, and pH measurements to provide the first comprehensive analysis of nanoparticle structural and compositional changes at elevated temperatures. We have found that silica-TPA nanoparticles subjected to hydrothermal treatment (70-90 degrees C) grow via an Ostwald ripening mechanism with growth rates that depend on both pH and temperature. Small-angle X-ray (SAXS) and neutron (SANS) scattering confirm that the core-shell structure of the particles, initially present at room temperature, is maintained during heating, but an evolution toward sphericity is evidenced especially at high values of pH. SAXS absolute intensity calculations were utilized to calculate the changes in nanoparticle composition and concentration over time. These changes along with the conductivity and pH measurements and SANS contrast matching studies indicate that, upon heating, TPA becomes embedded in the core of nanoparticles giving rise to more zeolitic-looking nanomaterials.     

Volume transition and internal structures of small poly(N‐isopropylacrylamide) microgels

Monodispersed poly(N‐isopropylacrylamide) (PNIPAM) nanoparticles, with hydrodynamic radius less than 50 nm at room temperature, have been synthesized in the presence of a large amount of emulsifiers. These microgel particles undergo a swollen–collapsed volume transition in an aqueous solution when the temperature is raised to around 34 °C. The volume transition and structure changes of the microgel particles as a function of temperature are probed using laser light scattering and small angle neutron scattering (SANS) with the objective of determining the small particle internal structure and particle–particle interactions. Apart from random fluctuations in the crosslinker density below the transition temperature, we find that, within the resolution of the experiments, these particles have a uniform radial crosslinker density on either side of the transition temperature. This result is in contrast to previous reports on the heterogeneous structures of larger PNIPAM microgel particles, but in good agreement with recent reports based on computer simulations of smaller microgels. The particle interactions change across the transition temperature. At temperatures below the transition, the interactions are described by a repulsive interaction far larger than that expected for a hard sphere contact potential. Above the volume transition temperature, the potential is best described by a small, attractive interaction. Comparison of the osmotic second virial coefficient from static laser light scattering at low concentrations with similar values determined from SANS at 250‐time greater concentration suggests a strong concentration dependence of the interaction potential. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 849–860, 2005     

Modes of conformational changes of proteins adsorbed on a planar hydrophobic polymer surface reflecting their adsorption behaviors

Infrared spectra of hen egg white lysozyme and bovine serum albumin (BSA) adsorbed on a solid poly tris(trimethylsiloxy)silylstyrene (pTSS) surface in D2O solution were measured using attenuated total reflection (ATR) Fourier transform infrared spectroscopy. From the area and shape of the amide I' band of each spectrum, the adsorption amount and the secondary structure were determined simultaneously, as a function of adsorption time. We could show that the average conformation for all the adsorbed lysozyme molecules was solely determined by the adsorption time, and independent of the bulk concentration, while the adsorption amount increased with the bulk concentration as well as the adsorption time. These results suggest that lysozyme molecules form discrete assemblies on the surface, and that the surface assemblies grow over several hours to have a definite architecture independent of the adsorption amount. As for BSA, the extent of the conformational change was solely determined by the adsorption amount, regardless of the bulk concentration and the adsorption time. These differences in the adsorption properties of lysozyme and BSA may reflect differences in their conformational stabilities.     

Association between branched poly(ethyleneimine) and sodium dodecyl sulfate in the presence of neutral polymers

In the present paper, the effect of different neutral polymers on the self-assemblies of hyperbranched poly(ethyleneimine) (PEI) and sodium dodecyl sulfate (SDS) has been investigated at different ionization degrees of the polyelectrolyte molecules. The investigated uncharged polymers were poly(ethyleneoxide), poly(vinylpyrrolidone) and dextran samples of different molecular mass. Dynamic light scattering and electrophoretic mobility measurements demonstrate that the high molecular mass PEO or PVP molecules adsorb considerably onto the surface of the PEI/SDS nanoparticles. At appropriate concentrations of PVP or PEO, sterically stabilized colloidal dispersions of the polyelectrolyte/surfactant nanoparticles with hydrophobic core and hydrophilic corona can be prepared. These dispersions have considerable kinetic stability at high ionic strengths where the accelerated coagulation of the PEI/SDS nanoparticles results in precipitation in the absence of the neutral polymers. In contrast, the addition of dextran does not affect considerably the kinetic stability of PEI/SDS mixtures because of its low adsorption affinity towards the surface of the polyelectrolyte/surfactant nanoparticles.     

Thermoresponsive core-shell microgels with silica nanoparticle cores: size, structure, and volume phase transition of the polymer shell

Core-shell microgels made of the thermoresponsive polymer poly(N-isopropylacrylamide) (PNIPAM) and silica nanoparticles as inorganic cores were investigated by dynamic light scattering (DLS) and small angle neutron scattering (SANS). In order to study the response of the particles upon changes of temperature, experiments were done in a temperature interval close to the volume phase transition temperature of the PNIPAM shell. While DLS probes the hydrodynamic dimensions of the particles, determining their centre of mass diffusion, SANS provides the correlation length xi of the PNIPAM network. Additionally, the composite particles were characterised by electron microscopy as well as atomic force microscopy to reveal the core-shell structure and at the same time the approximate dimensions and the shape of the microgels.     

Electrostatic interaction between chitosan-modified latex particles and bovine serum albumin

Electrostatic interaction between poly(methyl methacrylate) latex particles with different levels of chitosan modification and bovine serum albumin (BSA) was investigated. The critical flocculation concentration is in the range 5–15 nmol dm⁻³ for these latex products toward added BSA. A series of isothermal equilibrium adsorption experiments shows that the adsorption process is divided into two distinct intervals. Adsorption of BSA on latex particles in intervals I and II is primarily controlled by charge neutralization and hydrophobic interaction, respectively. Intervals I and II can be reasonably described by an empirical parabola equation and the Langmuir isotherm model, respectively. The maximum amount of BSA adsorbed per unit weight of polymer particles was observed at pH ≅ 5. A maximum elution yield of about 80% can be achieved using NaSCN as the elution electrolyte, and NaSCN is more effective in inducing desorption of BSA from the particle surface than NaCl. The chitosan content has very little effect on the interaction between latex particles and BSA. By contrast, the influence of the content of 2,2′-azobis(2-amidinopropane) dihydrochloride, a cationic initiator used in preparing the chitosan-modified latex products, on the BSA adsorption process is significant. Received: 26 March 1999 Accepted in revised form: 3 June 1999     

Small-angle neutron scattering study of concentrated colloidal dispersions: the interparticle interactions between sterically stabilized particles

Small-angle neutron scattering (SANS) was used to investigate the interparticle interactions in concentrated dispersions of colloidal silica stabilized either by steric or by electrostatic repulsive interactions. In 10 mM NaCl, an adsorbed PEO layer is required to prevent flocculation, and particles are stabilized by steric repulsions. The adsorbed layer was made invisible to neutrons by contrast matching with the aqueous continuous phase. Dispersions of the same particles at the same concentrations but in the absence of added salt and adsorbed PEO were also studied. In both cases, the SANS spectra of concentrated dispersions show a peak at low Q, which is due to interparticle interactions: a structure factor. The SANS data can be described rather well by a homogeneous spherical form factor and a structure factor based on the Hayter-Penfold/Yukawa potential model. The steric potential was compared to the electrostatic potential obtained by fitting the SANS data of the bare silica dispersions. The steric potential shows a greater dependence on the particle volume fraction, which we ascribe to the penetration and compression of the adsorbed PEO layer as the particles approach.     

聚甲基丙烯酸甲酯-牛血清白蛋白核壳纳米粒子在金表面的吸附过程及在传感器中的应用

利用铜离子引发体系, 制备出核层为聚甲基丙烯酸甲酯(PMMA)壳层为牛血清白蛋白(BSA)的PMMA-BSA核壳纳米粒子. 通过透射电子显微镜(TEM)表征, 直接观察到PMMA-BSA纳米粒子的核壳结构.结合X射线光电子能谱(XPS)测试, 分析PMMA-BSA纳米粒子的表面成分, 证明PMMA-BSA纳米粒子的壳层是BSA. 利用带耗散的石英晶体微天平(QCM-D)研究了PMMA-BSA纳米粒子在金片表面的吸附行为. 频率的迅速下降, 耗散因子的快速上升, 说明PMMA-BSA粒子快速地吸附到金片表面. 利用磷酸盐缓冲液反复冲洗时, 频率和耗散没有变化, 表明PMMA-BSA 纳米粒子在金片上吸附较牢固. 以金电极为基底电极, 吸附PMMA-BSA纳米粒子后, 利用戊二醛修饰粒子壳层, 再通过氨基与醛基的反应来固定葡萄糖氧化酶, 制备出电流型葡萄糖传感器. 电化学测试表明该传感器对葡萄糖具有良好的电流响应, 在0.3 V的工作电位下, 响应电流与葡萄糖浓度在0.20-5.85 mmol·L^-1范围内呈现出较好的线性关系, 相关系数为0.989. 传感器的灵敏度高达28.6 μA·L·mmol^-1·cm^-2, 响应时间仅为11 s. 传感器还具有良好的稳定性, 在25℃下储存30 d, 响应电流仅下降了16%.     

Small-angle neutron scattering on a core-shell colloidal system: a contrast-variation study

Small-angle neutron scattering (SANS) measurements are reported on a sterically stabilized, core-shell colloidal system using contrast variation. Aqueous dispersions of polystyrene particles bearing grafted poly(ethylene glycol) (PEG) have been studied over a large range of particle concentrations and two different solvent conditions for the PEG polymer. SANS data are analyzed quantitatively by modeling the particles as core-shell colloids. In a good solvent and under particle contrast conditions, an effective hard-sphere interaction captures excluded-volume interactions up to high concentrations. Contrast variation, through isotopic substitution of both the core and solvent, expedite a detailed study of the PEG layer, both in the dilute limit and as a function of the particle concentration. Upon diminishing the solvent quality, subtle changes in the PEG layer translate into attractions among particles of moderate magnitude.     

Influence of polyelectrolyte multilayer adsorption on the temperature sensitivity of poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) (PNiPAM) microgels

The electrophoretic mobility and temperature-dependent particle size of poly(N-isopropylacrylamide) (PNiPAM) microgels after alternating adsorption of poly(diallyldimethylammonium chloride) (PDADMAC) and poly(sodium 4-styrenesulfonate) (PSS) have been determined. First a PNiPAM-co-acrylic acid (AAc) shell was added to the PNiPAM microgel, then PDADMAC and PSS were adsorbed alternately. The studies of the electrophoretic mobility revealed charge reversal when a polyelectrolyte (PE) layer was adsorbed. Particle size measurements revealed a strong influence of polyelectrolyte adsorption on the temperature-dependent particle swelling. The strong influence of the adsorbed polyelectrolyte on the particle size is in contrast to polyelectrolyte multilayer adsorption on rigid particles.