Hierarchical modeling of diffusive transport through nanochannels by coupling molecular dynamics with finite element method

We present a successful hierarchical modeling approach which accounts for interface effects on diffusivity, ignored in classical continuum theories. A molecular dynamics derived diffusivity scaling scheme is incorporated into a finite element method to model transport through a nanochannel. In a 5 nm nanochannel, the approach predicts 2.2 times slower mass release than predicted by Fick’s law by comparing time spent to release 90% of mass. The scheme was validated by predicting experimental glucose diffusion through a nanofluidic membrane with a correlation coefficient of 0.999. Comparison with experiments through a nanofluidic membrane showed interface effects to be crucial. We show robustness of our discrete continuum model in addressing complex diffusion phenomena in biomedical and engineering applications by providing flexible hierarchical coupling of molecular scale effects and preserving computational finite element method speed.     

Influence of size and surface capping on photoluminescence and cytotoxicity of gold nanoparticles

Hydrophilic and homogeneous sub-10 nm blue light-emitting gold nanoparticles (NPs) functionalized with different capping agents have been prepared by simple chemical routes. Structure, average, size, and surface characteristics of these NPs have been widely studied, and the stability of colloidal NP solutions at different pH values has been evaluated. Au NPs show blue PL emission, particularly in the GSH capped NPs, in which the thiol-metal core transference transitions considerably enhance the fluorescent emission. The influence of capping agent and NP size on cytotoxicity and on the fluorescent emission are analyzed and discussed in order to obtain Au NPs with suitable features for biomedical applications. Cytotoxicity of different types of gold NPs has been determined using NPs at high concentrations in both tumor cell lines and primary cells. All NPs used show high biocompatibility with low cytotoxicity even at high concentration, while Au-GSH NPs decrease viability and proliferation of both a tumor cell line and primary lymphocytes.     

Colorimetric quantitative sensing of alkali metal ions based on reversible assembly and disassembly of gold nanoparticles

A novel and simple method for the colorimetric quantitative sensing of individual alkali metal ions (Li⁺, Na⁺, K⁺, and Rb⁺) based on the reversible properties of self-assembled aggregates and individual gold nanoparticles (Au NPs) is described. This paper demonstrates reversible self-assembly processes where the degree of assembly and disassembly is dependent on the individual alkali metal ion concentration, nanoparticle size, and alkali metal ionic radii. The color changes of the colloidal Au NPs with metal ion concentrations in colloidal NP solutions occur reversibly. Below a certain concentration of alkali metal ions, the aggregates of Au NPs are redispersed. As the Au NP diameters and the alkali metal ionic radii increase, the critical concentration decreases.     

Dielectrophoretically Modulated Optical Spectroscopy of Colloidal Nanoparticle Solutions in Microfluidic Channels

Optical spectroscopic techniques (e.g., extinction, scattering, and fluorescence spectroscopies) are important for the analysis of colloidal solutions of nanoparticles (NPs). They are routinely applied to plasmonic and quantum-dot NP samples assuming that these contain a single population of particles with modest size and shape dispersity. However, these spectroscopic techniques become less effective when the sample is a mixture of particles with different sizes, shapes, or composition. Here, an original microfluidic method is proposed for the optical spectroscopic analysis of colloidal NP solutions that combines periodic trapping of NPs by dielectrophoresis (DEP) with in situ optical extinction spectroscopy. The periodic trapping leads to modulation of the continuously monitored optical spectrum depending on the DEP properties of the NPs. DEP-modulated spectroscopy is demonstrated using colloidal gold NPs as small as 40 nm diameter. It is found that the DEP modulation is significantly enhanced when employing suitable microfluidic flow over a multielectrode array. Finally, it is shown that the method can identify and characterize the NP species simultaneously present in a mixture of 40 and 80 nm gold NPs, opening the way toward optical spectroscopic analysis of higher complexity NP mixtures through the combination of the DEP-modulated spectroscopy with chemometric methods.     

Encapsulation of a proteasome inhibitor with gold-polysaccharide nanocarriers

Groundwater remediation using iron oxide and zero-valent iron nanoparticles (NPs) can be effective, but is limited in many applications due to the NP strong retention in groundwater-saturated porous media after injection, the passivation of the porous surface, and the high cost of nanomaterials versus macro scale iron. In this study, we investigated transport of bare and polymer-coated 2-line ferrihydrite NPs (30–300 nm) in saturated aquifer sediments. The influence of poly(acrylic acid) (PAA) polymer coatings was studied on the colloidal stability and transport in sediments packed column tests simulating groundwater flow in saturated sediments. In addition, the influence of calcium cations was investigated by transport measurements using sediments with calcium concentrations in the aqueous phase ranging from 0.5 (typical for most sediments) to 2 mM. Measurements were also made of zeta potential, hydrodynamic diameter, polymer adsorption and desorption properties, and bio-availability of PAA-coated NPs. We found that NP transport through the saturated aquifer sediments was improved by PAA coating and that the transport properties could be tuned by adjusting the polymer concentration. We further discovered that PAA coatings enhanced NP transport, compared to bare NPs, in all calcium-containing experiments tested, however, the presence of calcium always exhibited a negative effect on NP transport. In tests of bioavailability, the iron reduction rate of the coated and bare NPs by Geobacter sulfurreducens was the same, which shows that the PAA coating does not significantly reduce NP Fe(III) bioavailability. Our results demonstrate that much improved transport of iron oxide NP can be achieved in saturated aquifer sediments by introducing negatively charged polyelectrolytes and optimizing polymer concentrations, and furthermore, these coated NPs retain their bioavailability that is needed for applications in bio-environmental remediation.     

尺寸效应对微通道内固液界面温度边界的影响

采用非平衡分子动力学方法模拟不同浸润性微通道内液体的传热过程,分析了尺寸效应对固液界面热阻及温度阶跃的影响.研究结果表明,界面热阻随微通道尺寸的变化可分为两个阶段,即小尺寸微通道的单调递增阶段和大尺寸微通道的恒定值阶段.随着微通道尺寸的增加,近壁区液体原子受对侧固体原子的约束程度降低,微通道中央的液体原子自由移动,固液原子振动态密度近似不变,使得尺寸效应的影响忽略不计.上述两种阶段的微通道尺寸过渡阈值受固液作用强度与壁面温度的共同作用:减弱壁面浸润性,过渡阈值向大尺寸区域迁移;相较于低温壁面,高温壁面处的过渡阈值更大.增加微通道尺寸,固液界面温度阶跃呈单调递减趋势,致使壁面温度边界和宏观尺度下逐渐符合.探讨尺寸效应有助于深刻理解固液界面能量输运及传递机制.     

纳米尺度下毛细流动的分子动力学模拟

采用分子动力学模拟研究纳米尺度下壁面润湿性对毛细流动的影响,主要考虑纳米通道两侧壁面润湿性相同与不同两种情况。研究表明：两侧壁面润湿性相同条件下,毛细流动随着壁面润湿性增强而加快, 毛细高度随时间的变化早期偏离Lucas-Washburn理论,但后期与其预测符合。在纳米通道两侧壁面润湿性不同的情况下,液面会发生振荡,两侧壁面毛细高度也不相等,且液面振荡的幅度和两侧壁面毛细高度差都随着两侧壁面润湿性差异的增大而增大。基于能量转化分析,提出两侧壁面湿润性不同情况下纳米通道中毛细流动发生的条件以及毛细流动快慢的判别依据。研究结果加深了对纳米尺度下毛细流动机理的认识,并为相关工程应用提供理论参考。     

Effect of serum proteins on polystyrene nanoparticle uptake and intracellular trafficking in endothelial cells

The physico-chemical properties of nanoparticles (NPs), such as small dimensions, surface charge and surface functionalization, control their capability to interact with cells and, in particular, with sub-cellular components. This interaction can be also influenced by the adsorption of molecules present in biological fluids, like blood, on NP surface. Here, we analysed the effect of serum proteins on 49 and 100 nm red fluorescent polystyrene NP uptake in porcine aortic endothelial (PAE) cells, as a model for vascular transport. To this aim, NP uptake kinetic, endocytic pathway and intracellular trafficking were studied by monitoring NPs inside cells through confocal microscopy and multiple particle tracking (MPT). We demonstrated that NPs are rapidly internalized by cells in serum-free (SF) medium, according to a saturation kinetic. Conversely, in 10% foetal bovine serum-enriched (SE) medium, NP uptake rate results drastically reduced. Moreover, NP internalization depends on an active endocytic mechanism that does not involve clathrin- and caveolae-mediated vesicular transport, in both SE and SF media. Furthermore, MPT data indicate that NP intracellular trafficking is unaffected by protein presence. Indeed, approximately 50–60% of internalized NPs is characterized by a sub-diffusive behaviour, whereas the remaining fraction shows an active motion. These findings demonstrate that the unspecific protein adsorption on NP surface can affect cellular uptake in terms of internalization kinetics, but it is not effective in controlling active and cellular-mediated uptake mechanisms of NPs and their intracellular routes.     

Effect of shape,height,and interparticle spacing of Au nanoparticles on the sensing performance of Au nanoparticle array

The effect of shape,height,and interparticle spacing of Au nanoparticles(NPs) on the sensing performance of Au NP array is systematically investigated. Lengthening the major axis of elliptical NPs with the minor axis kept constant will cause the redshift of the local surface plasmon(LSP) resonance mode,enhance the sensitivity,and widen the resonance peaks. Larger height corresponds to smaller LSP resonance wavelength and narrower resonance peak. With each NP size unchanged,larger interparticle spacing corresponds to larger resonance wavelength and smaller full-width at half-maximum(FWHM) . Moreover,duty cycle is important for sensitivity,which is largest when the duty cycle is 0.4.     

Deliberate Introduction of Particle Anisotropy in Helical Gold Nanoparticle Superstructures

Helical nanoparticle (NP) superstructures are an important class of chiral NP assemblies. The nature of the constituent NPs (size and shape) within these assemblies dictates their optical properties. However, the construction of helical NP superstructures consisting of various anisotropic NPs remains challenging. Here, a set of cetyltrimethylammonium bromide derivatives is employed to transform constituent spherical gold NPs (≈3 nm) within a chiral single‐helical assembly into gold nanoprisms (edge length ? 10 nm). Careful optimization of this strategy may lead to designed chiral NP architectures with tunable optical properties.     

Enhanced effect of dimension of receptor-ligand complex and depletion effect on receptor-mediated endocytosis of nanoparticles

We present an extended analytical model including the depletion effect and the dimension of ligand-receptor complex,aiming to elucidate their influences on endocytosis of spherocylindrical nanoparticles(NPs). It is found that the dimension of ligand-receptor complex(δ) and the depletion effect interrelatedly govern the optimal conditions of NP endocytosis. The endocytosis phase diagram constructed in the space of NP radius and relative aspect ratio indicates that the endocytosis of NP is enhanced evidently by reducing the optimal radius and the threshold radius of endocytosed NP. Meanwhile, through thermodynamic and kinetic analysis of the diffusion of receptors, the dependence of diffusion length on depletion effect and the dimension of ligand-receptor complex can be identified in great detail. For small aspect ratio, diffusion length decreases with increasing concentration c of small bioparticles in cellular environment. Endocytosis speed corresponding to large radius R and high concentration c of small bioparticles strongly depends on the increasing(2 r-δ). These results may show some highlights into the conscious design of NPs for diagnostic agents and therapeutic drug delivery applications.     

An integrated approach for the systematic evaluation of polymeric nanoparticles in healthy and diseased organisms

Innovative strategies that utilize nanoparticles (NPs) for a better delivery of drugs and to improve their therapeutic efficacy have been widely studied in many clinical fields, including oncology. To develop safe and reliable devices able to reach their therapeutic target, a hierarchical characterization of NP interactions with biological fluids, cells, and whole organisms is fundamental. Unfortunately, this aspect is often neglected and the development of standardized characterization methods would be of fundamental help to better elucidate the potentials of nanomaterials, even before the loading of the drugs. Here, we propose a multimodal in vitro/in vivo/ex vivo platform aimed at evaluating these interactions for the selection of the most promising NPs among a wide series of materials. To set the system, we used non-degradable fluorescent poly(methyl-methacrylate) NPs of different sizes (50, 100, and 200 nm) and surface charges (positive and negative). First we studied NP stability in biological fluids. Then, we evaluated NP interaction with two cell lines of triple-negative breast cancer (TNBC), 4T1, and MDA-MB231.1833, respectively. We found that NPs internalize in TNBC cells depending on their physico-chemical properties without toxic effects. Finally, we studied NP biodistribution in terms of tissue migration and progressive clearance in breast-cancer bearing mice. The use of highly stable poly(methyl-methacrylate) NPs enabled us to track them for a long time in cells and animals. The application of this platform to other nanomaterials could provide innovative suggestions for the development of a systematic method of characterization to select the most reliable nanodrug candidates for biomedical applications.     

Antibacterial activity of silver and zinc oxide nanoparticles produced by spark discharge in deionized water

Inorganic antibacterial agents such as metal nanoparticles (NPs) are very important in biomedical and pharmaceutical areas. There are many methods of synthesizing these NPs, but all of them have their own disadvantages. In this study, ultrasonic‐assisted spark discharge is employed to produce colloidal silver (Ag) and zinc oxide (ZnO) NPs which are stable without using any stabilizers or surfactants. Different tests such as X‐ray diffraction, field emission scanning electron microscopy, and ultraviolet–visible absorption spectroscopy are used for the characterization of the quantity and quality of these NPs, and their antibacterial activity is evaluated by the disk diffusion method and determination of the minimum inhibitory concentrations against Escherichia coli . The results show that the overall antibacterial activity of Ag NPs is higher than that of ZnO NPs.     

Layer reduction in driven 2D-colloidal systems through microchannels

The transport behavior of a system of gravitationally driven superparamagnetic colloidal particles is investigated. The motion of the particles through a narrow channel is governed by magnetic dipole interactions, and a layered structure forms parallel to the walls. The arrangement of the particles is perturbed by diffusion and the motion induced by gravity leading to a density gradient along the channel. Our main result is the reduction of the number of layers. Experiments and Brownian dynamics simulations show that this occurs due to the density gradient along the channel.     

棱形石墨烯纳米孔道内离子传输性能的分子动力学模拟

纳米通道的尺寸、结构和表面化学对其内部溶液的分布结构和输运性质有着重大影响.本文研究了一种全新的菱形石墨烯纳米通道.这种理想的通道与最近被广泛研究的金属有机框架材料(MOF)的内部结构类似,有着与传统的碳纳米管截然不同的内部结构.本文使用分子动力学模拟的方法研究在不同尺寸的菱形石墨烯纳米通道内的KCl溶液的性质,并将其与同尺寸的单壁碳纳米管进行了比较.研究结果表明在小孔道内(<20?)其内部的溶液结构呈现若干个密度极高的聚集区域,即出现了结晶化的趋势．这一研究结果,将为MOF的结构设计提供思路,从而有望实现类似于生物离子通道的高选择性和高传输能力.     

Synergistic Action of Alginate Chemical Reduction and Laser Irradiation for the Formation of Au Nanoparticles with Controlled Dimensions

Freestanding natural polymeric films with homogeneous dispersion of gold nanoparticles (Au NPs) are obtained via in situ reduction of gold(III) chloride trihydrate by sodium alginate (SA) biopolymer matrix, during water evaporation without the use of additional reducing agents. The size and size distribution of the prepared Au NPs can be tuned by changing the concentration of the precursor and/or the procedure of the films’ preparation. The nanocomposite films after preparation are stable in ambient conditions and can be used without the need of further processing, or can be redissolved in water. In the case of water dissolution, the aqueous solutions are irradiated with UV laser pulses turning the previously formed Au NPs into smaller ones with narrow size distributions through photofragmentation. This technique is proposed as a green way of synthesizing Au NPs of tunable size in aqueous solution of alginate, or incorporated in alginate freestanding polymeric films, that due to their biocompatibility can be used as passive labels or active sensors in biomedical applications.     

Nucleation and Growth of Magnetron-Sputtered Ag Nanoparticles as Witnessed by Time-Resolved Small Angle X-Ray Scattering

Kinetic aspects of the synthesis of Ag nanoparticles (NPs) by magnetron sputtering are studied by in situ and time-resolved small angle X-ray scattering (SAXS). Part of the NPs are found to become confined within a capture zone at 1–10 mm from the surface of the target and circumscribed by the plasma ring. Three regimes of the NP growth are identified: 1) early growth at which the average NP diameter rapidly increases to 90 nm; 2) cycling instabilities at which the SAXS signal periodically fluctuates either due to expelling of large NPs from the capture zone or due to the axial rotation of the NP cloud; and 3) steady-state synthesis at which stable synthesis of the NPs is achieved. The NP confinement within the capture zone is driven by the balance of forces, the electrostatic force being dominant. On reaching the critical size, large NPs acquire an excessive charge and become expelled from the capture zone via the electrostatic interactions. As a result, significant NP deposits are formed on the inner walls of the aggregation chamber as well as in the central area of the target.     

Transport of engineered nanoparticles in saturated porous media

Engineered nanoparticles (NPs) can be released into soils as emerging groundwater contaminants because many of them show toxic effects to the ecosystems; however, their fate and transport in soils are largely unknown. The present work examined the transport behavior of two NPs, silver nanoparticles (AgNPs) and carbon nanotubes (CNTs), in saturated porous media. Sodium dodecylbenzene sulfonate (SDBS), an anionic surfactant, was used to disperse the engineered NPs to enhance their stabilities in water. The solubilized NPs were then applied to laboratory columns packed with two types of water-saturated quartz sand to obtain their breakthrough curves. The experimental results showed that the surfactant-solubilized NPs were highly mobile in the saturated porous media. The transport of CNTs in the column was similar to that of colloidal montmorillonite and their recovery rates were around 100%. Less than 15% of the AgNPs were retained in the saturated column during the breakthrough experiments. However, most of the retained AgNPs were released when a SDBS-free water pulse was used to flush the sand column. The Derjaguin–Landau–Verwey–Overbeek (DLVO) theory and a colloid transport model were used to simulate the fate and transport of the engineered NPs in the sand columns. The DLVO theory worked well with AgNPs, but failed to represent the interactions between CNTs and the two sand media. Predictions of the transport model matched the experimental breakthrough data of the two engineered NPs well. Our results indicate that theories and models of colloid transport in porous media may be applicable to describe the fate and behavior of engineered NPs under certain circumstances.     

In situ spectroscopic determination of the activation energies for the growth of silver nanoparticles in silica nanofilms in nitrogen atmosphere

An in situ non-destructive optical microspectroscopy investigation of the growth of Ag nanoparticles (NPs) embedded in SiO₂ nanofilms deposited on soda-lime glass has been conducted during thermal processing under a nitrogen atmosphere. The time variation in Ag NP size was monitored by fitting the surface plasmon resonance with spectra calculated by Mie theory. The spectroscopic data was analyzed in the context of crystal growth theory and the atmosphere/film/substrate physicochemical interactions. The Ag NPs were indicated to grow first through a diffusion-based process and subsequently via Ostwald ripening. The analysis of a set of time-dependent isotherms has allowed for estimating the activation energies for silver diffusion at 2.5 eV for the initial growth stage and 3.2 eV for the ripening.