重力对金纳米颗粒在生物膜表面吸附影响的荧光研究

纳米颗粒在生物膜表面的吸附行为是纳米生物技术领域的重要问题. 采用正、倒置实验, 通过荧光显微镜定量研究了重力对金纳米颗粒在支撑磷脂膜表面吸附的影响. 研究发现, 颗粒尺寸决定其在顶或底层支撑膜表面吸附的差异性. 吸附量的差异与颗粒的沉淀速率和扩散速率之比的对数呈线性关系. 粒径小于14 nm时, 不考虑重力在吸附时的影响; 粒径大于176 nm时, 重力在吸附中占主导地位. 为药物载体研究和理解颗粒－生物膜相互作用提供参考.     

重力对金纳米颗粒在生物膜表面吸附影响的荧光研究

纳米颗粒在生物膜表面的吸附行为是纳米生物技术领域的重要问题.采用正、倒置实验,通过荧光显微镜定量研究了重力对金纳米颗粒在支撑磷脂膜表面吸附的影响.研究发现,颗粒尺寸决定其在顶或底层支撑膜表面吸附的差异性.吸附量的差异与颗粒的沉淀速率和扩散速率之比的对数呈线性关系.粒径小于14 nm时,不考虑重力在吸附时的影响;粒径大于176 nm时,重力在吸附中占主导地位.为药物载体研究和理解颗粒-生物膜相互作用提供参考.     

表面活性剂单体引起的细胞膜失稳

表面活性剂常用于细胞裂解、脂质体外排与膜组分搜集等.但在临界成胶束浓度以下,它如何以单体状态与生物膜作用的机制与调控仍存在很多疑问.本文研究了表面活性剂带电性对膜失稳的影响.石英电子微天平检测发现非离子型Triton X-100产生了最显著的磷脂膜结构三维再组装.荧光显微观测表明膜表面生成了非稳的出芽微泡,在机械扰动下可发生解离.该表面活性剂溶液环境中的体外细胞也出现了活力丧失.但是,离子型CTAB与SDS却无法触发相似的膜失稳与细胞失活效应.分析认为,由于不存在后两者体系中的单体间静电排斥, Triton X-100更易高效地插入生物膜,从而诱导膜结构再组装.研究深化了表面活性剂与生物膜作用机制的理解,对表面活性剂在生物医药、膜组分萃取等领域的深化应用提供了指导与帮助.     

重力场下生物膜表面的金纳米棒吸附

纳米颗粒在生物膜表面的吸附对其生物医学应用至关重要.在本研究中,采用正置与倒置石英电子微天平及耗散系数测量实验,表征了不同溶液高度的支撑膜表面金纳米棒的吸附动力学.发现金棒在重力场下产生溶液浓度不均性.长宽比增大能够提高金棒的流体力学尺寸,延缓金棒的不均再分布过程,从而维持不同溶液高度生物膜表面吸附量的一致.同时,由于浓度不均程度差异,短棒、中棒、长棒在不同溶液高度的吸附量排序关系也是变化的.在溶液底层短棒的吸附量最大,在溶液顶层中棒的吸附量最大.研究深化考察了调控纳米颗粒在生物膜表面吸附的物理因素,为纳米材料的医学应用提供了参考.     

SERS光谱表征类生物膜

跨膜蛋白与配体间的相互作用研究对于探索细胞内信号转导的分子机制具有重要意义。拉曼光谱能够提供精细的蛋白质和脂类的结构信息,贵金属表面增强拉曼散射(SERS)基底上组装磷脂构建类生物膜可为表征脂类和跨膜蛋白的结构提供便利。研究制备了金纳米粒子-类生物膜结构,并获得了磷脂的SERS光谱,为研究跨膜蛋白-配体间相互作用提供了界面支持。     

金纳米棒的单光束光操纵及其散射谱的测量

利用波长为800nm的单光束飞秒激光对水溶液中的金纳米棒颗粒进行了稳定地二维光捕获.通过测量金纳米棒的散射谱研究了光阱中金纳米棒之间的耦合相互作用.比较光阱中只有单个金纳米棒被捕获和两个金纳米棒同时被捕获时的散射谱.结果表明,当两个金纳米棒同时被光阱捕获时,金纳米棒之间相互排斥,存在一定的间隔,该间隔使得两个金纳米棒之间没有发生表面等离子耦合相互作用.该实验结果为金纳米棒的光操纵及其在生物分子探测等领域的研究提供技术指导及实验参考.     

tBid蛋白引发磷脂膜透化过程的研究

Bid蛋白是仅有BH3结构域的Bcl-2家族蛋白,在溶酶体膜透化以及线粒体外膜透化引发的细胞凋亡过程中起着非常重要的调控作用,但是Bid蛋白与生物膜之间的相互作用导致脂膜透化的确切机制尚不十分清楚.本文利用激光扫描共聚焦显微成像技术及基于氧化石墨烯表面诱导荧光衰逝的单分子荧光技术,分别从单囊泡及单分子水平对tBid蛋白与磷脂膜之间的相互作用进行了系统的研究.结果表明,tBid蛋白在膜上聚集后可引起脂膜的透化,且脂膜透化的发生源于聚集体中一些tBid蛋白更深入地插入了脂膜中.     

包膜颗粒的表面磷脂重排对细胞内吞的影响

在纳米颗粒表面包裹生物膜可以增强体系的生物相容性、靶向性、内含物释放的可控性,但包膜颗粒与细胞膜作用的机制仍不清楚.在本研究中,我们考察了不同侧向流动性的负电性磷脂膜包裹的多孔硅纳米颗粒的体外细胞内吞行为.发现,高流动的液态磷脂包被产生了较高的内吞效率,并且它的内吞方式也与低流动的凝胶态磷脂包被情况存在差异.Derjaguin-Landau-Verway-Overbeek理论分析表明,前者的磷脂空间重排能够促进生物膜与细胞膜的融合与粒子内吞,而后者在膜融合过程中存在高能量势垒,因此只能以胞饮的方式被动地进入细胞.我们的研究深化了包膜粒子内吞过程的认识,为后续设计复杂的纳米载药体提供了新的思路和参考.     

包膜颗粒的表面磷脂重排对细胞内吞的影响

在纳米颗粒表面包裹生物膜可以增强体系的生物相容性、靶向性、内含物释放的可控性,但包膜颗粒与细胞膜作用的机制仍不清楚.在本研究中,我们考察了不同侧向流动性的负电性磷脂膜包裹的多孔硅纳米颗粒的体外细胞内吞行为.发现,高流动的液态磷脂包被产生了较高的内吞效率,并且它的内吞方式也与低流动的凝胶态磷脂包被情况存在差异.Derjaguin-Landau-Verway-Overbeek理论分析表明,前者的磷脂空间重排能够促进生物膜与细胞膜的融合与粒子内吞,而后者在膜融合过程中存在高能量势垒,因此只能以胞饮的方式被动地进入细胞.我们的研究深化了包膜粒子内吞过程的认识,为后续设计复杂的纳米载药体提供了新的思路和参考.     

金纳米棒标记HepG2人肝癌细胞的荧光成像及其AFM探测

金纳米棒具有独特的光学性质,在生物医学领域有着广泛而重要的应用前景.本文制备了长径比为8∶1的金纳米棒,其在480 nm波长激发下,在560 nm和707 nm波长处有两个荧光发射峰.基于金纳米棒的荧光性质,将其标记于HepG2人肝癌细胞表面,利用激光扫描共聚焦显微镜对标记后的细胞进行荧光成像.在488 nm激发下,获...     

Structure and switching of single-stranded DNA tethered to a charged nanoparticle surface

Using a molecular theory, we investigate the temperature-dependent self-assembly of single-stranded DNA(ss DNA)tethered to a charged nanoparticle surface. Here the size, conformations, and charge properties of ss DNA are taken into account. The main results are as follows: i) when the temperature is lower than the critical switching temperature, the ss DNA will collapse due to the existence of electrostatic interaction between ss DNA and charged nanoparticle surface; ii)for the short ss DNA chains with the number of bases less than 10, the switching of ss DNA cannot happen, and the critical temperature does not exist; iii) when the temperature increases, the electrostatic attractive interaction between ss DNA and charged nanoparticle surface becomes weak dramatically, and ss DNA chains will stretch if the electrostatic attractive interaction is insufficient to overcome the elastic energy of ss DNA and the electrostatic repulsion energy. These findings accord well with the experimental observations. It is predicted that the switching of ss DNA will not happen if the grafting densities are too high.     

Combined effects of headgroup charge and tail unsaturation of lipids on lateral organization and diffusion of lipids in model biomembranes

Lateral organization and dynamics of lipids in plasma membranes are crucial for several cellular processes such as signal transduction across the membrane and still remain elusive.In this paper,using coarse-grained molecular dynamics simulation,we theoretically study the combined effects of headgroup charge and tail unsaturation of lipids on the lateral organization and diffusion of lipids in ternary lipid bilayers.In neutral ternary lipid bilayers composed of saturated lipids,unsaturated lipids,and cholesterols,under the conditions of given temperature and components,the main factor for the phase separation is the unsaturation of unsaturated lipids and the bilayers can be separated into liquid-ordered domains enriched in saturated lipids and cholesterols and liquid-disordered domains enriched in unsaturated lipids.Once the headgroup charge is introduced,the electrostatic repulsion between the negatively charged lipid headgroups will increase the distance between the charged lipids.We find that the lateral organization and diffusion of the lipids in the(partially) charged ternary lipid bilayers are determined by the competition between the headgroup charge and the unsaturation of the unsaturated lipids.In the bilayers containing unsaturated lipids with lower unsaturation,the headgroup charge plays a crucial role in the lateral organization and diffusion of lipids.The headgroup charge may make the lipid domains unstable and even can suppress phase separation of the lipids in some systems.However,in the bilayers containing highly unsaturated lipids,the lateral organization and diffusion of lipids are mainly dominated by the unsaturation of the unsaturated lipids.This work may provide some theoretical insights into understanding the formation of nanosized domains and lateral diffusion of lipids in plasma membranes.     

Molecular dynamics study of the infiltration of lipid-wrapping C60 and polyhydroxylated single-walled nanotubes into lipid bilayers

Because of the many potential medical applications of nanoparticles, considerable research has been conducted on the interactions between nanoparticles and biomembranes. We employed coarsegrained molecular dynamics simulations to study the infiltration of lipid-wrapping C₆₀ and polyhydroxylated single-walled nanotubes. Diffusion coefficients and scaling factors are adopted to quantify the diffusivity of the biomembranes, and the rupture tension is used to measure the lateral strength of the lipid bilayer. According to our simulations, all wrapped nanoparticles, except those wrapped by dipalmitoyl-glycero-phosphoglycerol, can be inserted into the bilayers. Our simulations also reveal that the bilayers remain in free diffusion after the nanoparticle insertions while their diffusion coefficient can be altered significantly. The polyhydroxylated single-walled nanotubes lead to significant changes to the lateral strength of biomembranes and this effect depends on the quantity of the inserted nanoparticles. The simulations demonstrate the feasibility of using these methods to deliver nanoparticles while some suggestions are given for choosing the appropriate lipids for wrapping. The results also suggest that the functionalized nanoparticles could be applied in strengthening or weakening the lateral strength of biomembranes for specific purposes.     

Role of surface ligands in nanoparticle permeation through a model membrane: a coarse-grained molecular dynamics simulations study

How nanoparticles interact with biological membranes is of significant importance in determining the toxicity of nanoparticles as well as their potential applications in phototherapy, imaging and gene/drug delivery. It has been shown that such interactions are often determined by nanoparticle physicochemical factors such as size, shape, hydrophobicity and surface charge density. Surface modification of the nanoparticle offers the possibility of creating site-specific carriers for both drug delivery and diagnostic purposes. In this work, we use coarse-grained molecular dynamic simulations to explore the permeation characteristics of ligand-coated nanoparticles through a model membrane. We compare permeation behaviors of ligand-coated nanoparticles with bare nanoparticles to provide insights into how the ligands affect the permeation process. A series of simulations is carried out to validate a coarse-grained model for nanoparticles and a lipid membrane system. The minimum driving force for nanoparticles to penetrate the membrane and the mechanism of nanoparticle–membrane interaction were investigated. The potential of the mean force profile, nanoparticle velocity profile, force profile and density profiles (planar and radial) were obtained to explore the nanoparticle permeation process. The structural properties of both nanoparticles and lipid membrane during the permeation, which are of considerable fundamental interest, are also studied in our work. The findings described in our work will lead to a better understanding of nanoparticle–lipid membrane interactions and cell cytotoxicity and help develop more efficient nanocarrier systems for intracellular delivery of therapeutics.     

Interaction between α-actinin and negatively charged lipids membrane investigated by surface plasmon resonance and electrochemical methods

α-Actinin has been shown to be capable of interacting with some special membrane phospholipids directly, which is important for its function. In this study, hybrid bilayer membranes composed of negatively charged lipids are constructed on the surface plasmon resonance gold substrate and on the gold electrode, respectively, and the interaction between α-actinin and negatively charged lipids membrane is investigated by surface plasmon resonance, cyclic voltammetry and electrochemical impedance spectroscopy methods. α-Actinin is proved to be able to interact with the negatively charged lipids membrane directly. It can also insert at least partly into the membrane or lead to some defect or lesion in the membrane, which increase the permeability of the membrane. This study would bring some insight on the interaction between the α-actinin and the cell membranes in vivo.     

多聚赖氨酸诱导的负电性磷脂巨囊泡形变

利用荧光显微技术表征了多聚赖氨酸诱导的负电性磷脂巨囊泡的动力学响应行为.研究发现,多聚赖氨酸可吸附至二油酰磷脂酰胆碱和二油酰磷脂酸混合磷脂巨囊泡的表面,诱导其发生粘连、出"绳"及破裂现象.分析认为,在低盐环境中,膜形变由多聚赖氨酸吸附于二油酰磷脂酸富集区引起的膜两叶应力不对称,以及静电相互作用等因素产生.研究结果对基于聚合物-巨囊泡体系的药物输运控释、细胞形变、微控反应和基因治疗等方面的研究提供有价值的支持.     

Coarse-grained simulations on interactions between spectrins and phase-separated lipid bilayers

Spectrin, the principal protein of the cytoskeleton of erythrocyte, plays a crucial role in the stability and flexibility of the plasma membrane of erythrocyte. In this work, we investigate the interactions between spectrins and phase-separated lipid bilayers using coarse-grained molecular dynamics simulation. We focus on the preference of spectrins with different lipids, the effects of the anionic lipids and the residue mutation on the interactions between spectrins and the lipid bilayers. The results indicate that spectrins prefer to contact with phosphatidylethanolamine (PE) lipids rather than with phosphatidylcholine (PC) lipids, and tend to contact with the liquid-disordered (Ld) domains enriched in unsaturated PE. Additionally, the anionic lipids, which show specific interaction with the positively charged or polar amino acids on the surface of the spectrins, can enhance the attraction between the spectrins and lipid domains. The mutation leads to the decrease of the structural stability of spectrins and increases the curvature of the lipid bilayer. This work provides some theoretical insights into understanding the erythrocyte structure and the mechanism of some blood diseases.     

Nano-meter-sized domain formation in lipid membranes observed by small angle neutron scattering

Using a contrast matching technique of small angle neutron scattering (SANS), we have investigated a phase separation to liquid-disordered and liquid-ordered phases on ternary small unilamellar vesicles (SUVs) composed of deuterated-saturated, hydrogenated-unsaturated phosphatidylcholine lipids and cholesterol, where the equilibrium size of these domains is constrained to less than 10nm by the system size. Below a miscibility temperature, we observed characteristic scattering profiles with a maximum, indicating the formation of nano-meter-sized domains on the SUVs. The observed profiles can be described by a multi-domain model rather than a mono-domain model. The nano-meter-sized domain is agitated by thermal fluctuations and eventually ruptured, which may result in the multi-domain state. The kinetically trapped nano-meter-sized domains grow to a mono-domain state by decreasing temperature. Furthermore, between the miscibility and disorder-order transition temperature of saturated lipid, the integrated SANS intensity increased slightly, indicating the formation of nano-meter-sized heterogeneity prior to the domain nucleation.     

Adsorption of model charged proteins on charged surfaces with grafted polymers

The adsorption of model charged proteins on charged surfaces with and without grafted polymers is studied using a molecular approach. The ability of the polymer layer to reduce the amount of proteins adsorbed on top of the surface (primary adsorption) and at the same time to increase the adsorption of the proteins on top of the polymer layer (secondary adsorption) is presented. It is found that charging the free ends of the chains can result in an efficient way to enhance adsorption at the tip of the brush. Increasing the surface coverage of the polymers with charged free ends enhances the amount of proteins adsorbed at the tip of the polymer layer, while at the same time strongly reduces the number of proteins adsorbed directly onto the surface. The interplay between the attractive van der Waals protein-surface interactions, the steric polymer-protein interactions and the effect of the electrostatic interactions in determining the final adsorption is discussed. The manipulation of solution conditions to tune the amount of secondary adsorption is presented.     

1H-13C polarization transfer in membranes: a tool for probing lipid dynamics and the effect of cholesterol

Phospholipid bilayers with over 20% cholesterol can form a liquid-ordered (l(o)) phase, which can be found in lateral domains, called rafts, in biomembranes. We show here that high-resolution (13)C and (1)H solid-state NMR are well suited to explore this phase, intermediate between gel and fluid. This approach can be applied to artificial or natural membranes, with no isotopic enrichment and with the help of magic-angle spinning (MAS), taking advantage of the high resolution and sensitivity of these nuclei. The sensitivity of magnetization transfer schemes to different lipid states has allowed us here to discriminate between various phases. We show that the phase composed of unsaturated phospholipids and cholesterol differs, in terms of lipid dynamics, both from the previously described l(o) phase and from the liquid-disordered phase.