信息得自于这里。

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gravity 1.32破解版，下载。把twitter的认证方式改为“proxy/plaintext”即可。“oauth/secure”在我这里测试未通过。

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我的nokia又活了。

作用:

将微弱的光信号(闪烁晶体在射线作用下发出的荧光光子)按比例转换成电子并倍增放大成易于测量的电信号，其放大倍数可高达106～109。

组成：

光电倍增管主要由光阴极、多级倍增极、电子收集极(阳极)组成，整个系统密封在抽成真空状态的玻璃壳内。

原理

射线在晶体中引起的闪烁光打在光阴极上，通过光电效应产生一定数目的光电子。由于光阴极和各级倍增极之间都加有电压(高压电源经分压电阻R供给)，使阴极产生的电子被有效地放大并集中到下一极，最后在阳极形成很大的电子流，通过负载电阻RL即得到易于测量的电压脉冲。此过程产生的电流量与入射在光阴极上的光子数目成正比。因此，输出的脉冲幅度与射线在闪烁体中的能量损失成正比。

圆探头的SPECT机使用光电倍增管一般为37～91个，方形或矩形探头的SPECT机使用光电倍增管一般为55～96个。光电倍增管的形状有圆形和六角形两种。圆形晶体一般通过六角形的光导与晶体紧密相贴。六角形的光电倍增管是圆形光电倍增管的最新改进型，其主要优点是去除光导，直接与晶体相贴，消除探测间隙，提高灵敏度和空间分辨率。这种光电倍增管已经逐渐取代圆形光电倍增管和光导。光电倍增管在探头中呈蜂窝状排列。整体光电倍增管的性能稳定性取决于各个光电倍增管的性能参数是否一致、各个光电倍增管的工作电压是否稳定以及是否有足够长的预热时间，它们直接影响着系统的均匀性、分辨率和线性度。对光电倍增管性能影响最大的是直流高压的稳定性。而高压又是由低压交流电经整流升压获得的，所以SPECT机都要求有稳压电源。在经常停电的地方，还要配备不间断供电电源(UPS)，以保证SPECT机的稳定性和工作的连续性。

全文请猛击这里。

more recent reviews on this subject tend to agree that it is also necessary to consider the size-dependent properties of nanoparticles, which are sometimes referred to as the ‘nanoeffect’. Among these novel properties is an exacerbated surface reactivity that enhances the number of interactions that may occur between nanoparticles and the surrounding medium.

The toxicity of manufactured nanomaterials is strongly influenced by their surface chemistry, and thus their chemical stability, as it determines how the nanomaterial interacts with organisms.

both the dispersion and chemical stabilities of nanoparticles in water are mainly driven by reactions occurring at the solid/liquid interface.

1. General reactions at the solid/liquid & solid/solid interfaces in aqueous system

A distinguishing feature between a nanoparticle and a similarly sized molecule is the persistence of an insoluble segment of the nanometric body, which displays a rigid lattice structure independent of the dispersing solvent and restricts conformational and thermal freedom. In other words, while nanoparticles can form rather stable aqueous dispersions, they do not dissolve in water in the truest sense of the word.

As with other materials, nanoparticle solubility is highly dependent on the properties of the solvent and the concepts that have been applied to colloids may be equally applied to nanoparticles. However, new considerations based on size-dependent properties must be taken into account, since particle dissolution kinetics and solubility are expected to be higher for nanoparticles. The dissolution rate (k) is indeed proportional to the surface area (A), as shown by the Noyes–Whitney equation.

2. Affinity with water

Affinity with water is determined by the presence of Lewis acid–base (AB) groups on the surface, which may hydrogen bond with water molecules.

Colloids (<1 µm) that are characterized by a hydrophilic surface can easily be dispersed in aqueous media.

The usual terminology that can be used for such a system is ‘suspension’, ‘colloidal dispersion’ or ‘sol’, in opposition to the ‘solution’ obtained with soluble molecules. (注意)

The further stability of such dispersions is dependent on the chemistry and composition of the surrounding medium. This same terminology and understanding may also be extended to nanoparticle dispersions.

3. Dispersion stability

Dispersion stability is influenced by a variety of parameters, including: the intrinsic characteristics of the nanoparticles, and more particularly their surface properties; solution chemistry (e.g., ionic strength, ionic composition, pH and nanoparticle concentration); and the adsorption, either intentionally or unintentionally, of macromolecules to the nanoparticle surface.

The stability of nanoparticle dispersions depends on the collision frequency between nanoparticles and the sticking efficiency of these collisions. Collectively, these parameters may be used to predict the propensity of nanoparticles to aggregate. The interparticle collision frequency results from both the Brownian motion and local mechanical stirring [33,34]. However, in the nanometric size range, the latter has no significant effect and Brownian motion remains the driving contribution.

The sticking efficiency between two particles is determined as the sum of interfacial interactions that exist between colliding particles. When repulsive interactions are dominant, the sticking efficiency is negligible and the particle dispersion is stable. Conversely, attractive interactions result in a relatively high sticking efficiency and induce progressive aggregation (i.e., a destabilized dispersion). This balance has been largely considered and modeled in the literature within the context of the Derjaguin–Landau–Verweey–Overbeek (DLVO) theory and its numerous extensions.

The extended DLVO model accounts for three separate interfacial interaction components: the electrostatic component (UEL ), the van der Waals component (ULW ) and the acid–base component (UAB ). Of these three interaction components, those resulting from acid–base interactions are considered non-DLVO interactions. Electrostatic interactions occur between charged surfaces and the overlapping of electric double layers, which are diffuse clouds of counter and co-ions surrounding charged surfaces in water. The range over which electrostatic interactions occurs decreases exponentially with separation distance and varies inversely with solution ionic strength [37]. Solution pH must also be considered as it influences the protonation and deprotonation state of surface groups and, thus, the magnitude and sign of the surface charge (see metal oxide section). In a homogeneous particle dispersion, UEL is repulsive according to the electric surface potential of the particles.

造成不平衡电子分布的原因即是电子受外力而脱离轨道，这个外力包含各种能量(如动能、位能、热能、化学能……等)在日常生活中，任何两个不同材质的物体接触后再分离，即可产生静电。

The second interaction component accounts for van der Waals interactions, which are constant and fixed by the solid bulk composition. ULW is always attractive and decreases according to a power 6 law when the separation distance increases (i.e., more rapidly than UEL ).

Repulsive UEL and attractive ULW thus compete with each other in determining the stability of a given colloidal dispersion.

The resulting balance mainly depends on the ionic strength, which determines the range over which UEL acts. There is a minimum salt concentration, termed critical coagulation concentration, above which UEL becomes a minor interaction component relative to ULW , which results in a high sticking efficiency.

A limitation in DLVO approach is that it does not take into account the polarity of the approaching surfaces (i.e., electron–acceptor/electron–donor interactions; Lewis acid–base forces, UAB ). However, these may become significant with regard to UEL /ULW balance when hydrophobic or very hydrophilic particles are considered, and more particularly in the case of nanoparticles displaying a high proportion of surface atoms. In these cases, the dispersion stability predictions from DLVO approach are unrealistic and should be complemented by UAB consideration. UAB results from the interaction between surface groups and water (i.e., hydrogen bonding). These interactions are often considered to be short ranged and decay in an exponential fashion with separation distance. UAB is attractive and constant for nonpolar surfaces (hydrophobic), while it is increasingly repulsive with polar ones (hydrophilic).

For nanoparticles, an additional factor not taken into account in these theoretical approaches is their exacerbated surface energy due to high surface tension. According to the Young-Laplace’s equation, the surface tension of a particle is inversely proportional to its radius of curvature (i.e., its size).

where ΔP is the pressure difference, g is interfacial tension, and R1 and R2 are the principal radii of curvature of the particle. With very small nanoparticles (<20–30 nm), this leads to a surface pressure so high that they become thermodynamically unstable. In order to minimize such a pressure jump across the solid surface, nanoparticles may acquire novel properties and/or behaviors that do not exist for larger colloids, even if surface functional groups and their speciation are independent of size. Favored dissolution, phase transformation or crystallographic changes are examples of size-dependent properties that have been reported for nanoparticles. Implicitly, a significant decrease in surface tension (i.e., thermodynamic stabilization) can also be commonly achieved when ultrafine nanoparticles aggregate together into larger and dense clusters. This surface tension effect should thus be considered as an additional attractive interparticle force that exists between small nanoparticles, and may have significant consequences in terms of dispersion stability.

注：热力学不稳定是指对化学反应过程生成的过渡态或者中间体，或者说是生成的一种物质，其能量是较高的，或者说化学位较高，有自发的继续发生反应继续转化的趋势，那么热力学上来说就是不稳定的。

注：表面张力，是液体表面层由于分子引力不均衡而产生的沿表面作用于任一界线上的张力。通常，由于环境不同，处于界面的分子与处于相本体内的分子所受力是不同的。在水内部的一个水分子受到周围水分子的作用力的合力为0，但在表面的一个水分子却不如此。因上层空间气相分子对它的吸引力小于内部液相分子对它的吸引力，所以该分子所受合力不等于零，其合力方向垂直指向液体内部，结果导致液体表面具有自动缩小的趋势，这种收缩力称为表面张力。表面张力(surface tension)是物质的特性，其大小与温度和界面两相物质的性质有关。

将水分散成雾滴，即扩大其表面，有许多内部水分子移到表面，就必须克服这种力对体系做功——表面功。显然这样的分散体系便储存着较多的表面能(surface energy)。

4. Metal oxide nanoparticles

Many metal oxides will hydrolyze in the presence of water to form hydroxide layers at the surface (?M–OH). The polar hydroxyl (-OH) groups may cause the surface to attract and physically adsorb a single or several additional layers of polar water molecules, which confers a hydrophilic character to the oxide. Moreover, amphoteric (?M–OH) sites may become charged by reacting with H+ or OH- ions. At low pH, hydroxide surfaces adsorb protons and become positively charged (?M–OH2+) , whereas at high pH, proton desorption induces a negative surface charge (?M–O?) .

The density of amphoteric sites on a surface, of the order of 1 µmol/m2 is determined by the atomic structure of the surface lattice planes of the oxide. The overall surface charge of the oxide then results from the respective expressions of all the hydroxyl sites according to the pH.

The point of zero charge (PZC) is commonly defined as the pH at which the overall surface charge of a particle is neutralized.

In terms of dispersion, the pH-dependent surface charge implied by these amphoteric sites mainly assumes the interparticle electrostatic repulsions (UEL ) required for stability. Typically, when the solution pH is far from the PZC, the highly charged surface results in a stable dispersion due to high UEL repulsive interactions, whereas when the pH is in the range of the PZC ± 1, the low surface charge results in a high sticking efficiency between surfaces (aggregation).

Titanium dioxide

no correlation could be clearly observed between PZC and IEP of TiO2 and the prevailing size (nano- vs micro-particle) or lattice (rutile vs anatase) characteristics of the particles studied. This large range is probably due to impurity or default effects depending on the respective methods used for nanoparticle synthesis, or to specific ion adsorption from the electrolytes used . The subsequent stability of TiO2 nanoparticles in aqueous suspension, due to UEL forces, like every metal oxide, is mainly governed by solution pH and ionic strength.

Iron oxides

The behavior of iron oxide nanoparticles in aqueous media is largely governed by the size, shape, oxidation state and stability of the iron oxide, all varying according to the specific synthesis procedure and conditions used.

The PZC for iron oxides is generally reported to be between 7.2 and 9.5 (Table 1 for nanoparticles).

In the absence of surface coatings, iron oxides will readily self-aggregate at moderate ionic strengths and/or as the solution pH approaches the PZC. Under these conditions the interfacial interaction between iron oxide particles is governed by attractive van der Waals forces and/or magnetic interactions (e.g., as is the case for magnetite and maghemite).

The type of interaction may play a role in the resulting aggregate structure, which has been described as spherical or chain-like.

其作用是:

1. 把呈六角形排列的光电倍增管通过光藕合剂(一般为硅脂)与NaI(Tl)晶体藕合，
2. 把晶体受γ射线照射后产生的闪烁光子有效地传送到光电倍增管的光阴极上。

注意：如果不加这个东西，就会造成漏光，丢失信号。因为PMT都是圆的。

光导有多种形状，一般其下底面为六角形，紧密地排列在晶体之上；上顶面为圆形，与光电倍增管紧密贴合。这样，当应用圆形光电倍增管时，射入光电倍增管之间间隙内的闪烁光便不会损失。

光导的侧面涂有对荧光反射性能良好的氧化镁涂剂，以便让更多的闪烁光进入光电倍增管，也可以防止光线从光导的侧面透射到其他光电倍增管的光阴极上。

在晶体和光导、光导和光电倍增管之间都充填有光学硅脂，以排除空气，减少闪烁光透过两种光介面时的损失。光导从每次荧光事件中收集闪烁光的能力和正确地把它分配到光电倍增管的能力，影响着SPECT机的空间分辨率、线性度、均匀性和灵敏度。因此，上述措施对提高整机的性能是很重要的。

一般说来，薄的光导提供较好的分辨率，而厚的光导则提供较好的均匀性。

——过程

γ射线进入晶体后，与之发生相互作用，闪烁晶体吸收带电粒子的能量使原子、分子激发，受激发的原子、分子在退激时发射荧光光子。

荧光光子的数目、能量、输出的光脉冲幅度与入射γ射线的能量成正比。入射γ射线的能量越小，所产生的光子能量越小，输出的光脉冲幅度也越小，反之亦然。

利用光导、光反射物质和光藕合剂将荧光光子尽可能收集到光电倍增管的光阴极上，由于光电效应，光子在光阴极上打出光电子。

——晶体特征

目前，大多数SPECT机均采用大直径的碘化钠(铊激活)晶体。NaI(Tl)晶体是含有约0.1%铊的碘化钠单晶体。

• 优点：它的发光效率很高，其最强发射光谱波长为4150 nm左右，能与光电倍增管的光谱响应较好匹配，晶体透明度也很好。NaI晶体的密度较大，ρ=3.67g/cm3，有效原子序数高达50，所以对γ射线的探测效率特别高。
• 主要缺点：是容易潮解，必须在密封条件下保存和使用，而且质脆，容易碎裂，故使用时应避免大的震动和温度的较大变化，一般室内温度要严格控制在15～30℃之间，每小时温差不超过3℃。

——位置及构造

晶体位于准直器和光电倍增管之间。

• 其准直器侧面(入射面)采用铝板密封，既能透过γ射线，又能遮光；
• 其光电倍增管侧面(发光面)用光导玻璃密封，晶体内所产生的闪烁光子能顺利地进入光电倍增管。

——晶体规格

晶体有不同规格的大小和厚度。圆形晶体的直径一般为28～41cm，方形和矩形大视野晶体在SPECT机中也广为使用。

晶体厚度不仅影响SPECT机的灵敏度和空间分辨率，同时也限定了它所接受射线的能量范围。目前常用的晶体厚度为6.4～12.5cm。

一般薄晶体接受的能量偏低，而厚晶体接受的能量则偏高。

——晶体厚度与固有分辨率的关系

薄晶体在SPECT机中使用越来越普遍。它可以提高SPECT机的固有分辨率。最理想的状况是γ射线进入晶体只经过一次相互作用就以闪烁光形式发射出来，这样产生的闪烁点定位准确，分辨率好。但实际情况并非如此，γ射线进入晶体后经过多次相互作用才被光电倍增管所探测，这种闪烁点定位不精确，空间分辨率模糊。对于99Tcm和201Tl等低能放射性核素，大部分γ射线与晶体的相互作用发生在晶体的入射面（靠近准直器）的2～5mm内。对此，如果应用厚晶体，不仅对灵敏度没有明显改善，而且明显降低了空间分辨率。例如，把晶体厚度从12.5mm降至6.5mm，空间分辨率可以提高70％，相应的灵敏度仅损失15％。目前大部分的SPECT机均采用9.4mm厚的晶体，以获得空间分辨率与灵敏度之间较好的匹配。

• ECT: Emission Computed Tomography
• SPECT: Single Photon Emission Computed Tomography
• PET: Positron Emission Tomography
• FBP: Filtered Backprojection
• MIBI: Methoxyisobutyl Isonitrile
• MDP: Methylenediphosphonate
• ECD: Ethylcysteinate Dimer
• PMT: photomultiplier tube 光电二极管
• SMC: summing matrix circuit
• ECG: Electrocardiograph
• GFR: glomerular filtration rate
• ERPF: Effective renal plasma flow
• Space-Bandwidth Product (SBP) of a SPECT system, the SBP depends on 
              1. The effective area of its detectors – the larger the area, the more information can be processed; and            
              2. The intrinsic detector resolution -the finer the pixilation of the detector, the more information can be transferred.
              Therefore, the SBPof amulti-pinhole SPECT system can be expressed as

        
         (M. Kupinski & H. Barrett, Small-Animal SPECT Imaging, 2005 Springer Science Media)

• intrinsic resolution: pixel size *2
• figure of merit (FOM): space-bandwidth-efficiency product, high FOM is another inherent advantage of the large area and high intrinsic resolution of broadband detectors. defined as:

• multi-channel spectral analysis(MCA)

投影图像相对于成像物体放大，当成像物体越靠近针孔时，图像放大愈大。可以利用这种图像放大的特点来有效克服探测器的内在分辨率对系统空间分辨的制约，进而取得高分辨的成像。

屏幕剪辑的捕获时间: 2010-8-30 22:59

针孔材料

当孔深为零时，铅材料针孔的边缘透射份额超过了50％，其它材料(钨合金、高纯金、铂和铀)的针孔边缘透射份额也超过了20％；当孔深为0.5 mm时，针孔边缘透射份额可得到较大的抑制，铅材料针孔的边缘透射份额降至20％以下，其它材料针孔边缘透射份额则可降至10％以下。

孔深厚度

• 点光源

直射部分的效率迅速下降，而透射与直射、散射与直射的比值上升。当丫射线垂直入射时，随着孑L深厚度的增加，直射部分效率基本保持不变，透射、散射的份额则逐渐减小。

• 面光源

对于140.5 keV伽玛射线，当孔深为0.5 mm时，透射与散射部分之和与直射部分的比值达到最小，约0.147，因此，最佳的孑L深厚度约为0.5 mm。

多孔成像的好处

• 放大倍数越小，多针孔的探测效率高于单针孔越明显。

在同样的像距条件下，放大倍数较小意味着物距较大。在物距较大也就是物体离准直器较远的时候，多针孔成像时成像孔由于远离中轴线而引起地对物体所张立体角大小减小，从而使探测效率下降的作用因素趋于弱化，从而使多针孔成像对单针孔的优势更明显的表现出来，探测效率较之于物距小时高于单针孔更明显。

• 物体尺寸与物距的比越大，多针孔的探测效率高于单针孔越明显。

在同样的物距条件下，如果拨成像物体尺寸越大，物体上偏离中轴线的部分越多，单针孔成像对物体边缘探测效率的下降作用越强烈，而此时四孔成像由于成像孔分布在偏离在中轴线一定位置的地方，从而能够一定程度上较好额抑制物体边缘探测效率下降的效应。

准直器最基本的性能指标是灵敏度和分辨率。

1. 所谓准直器灵敏度是指准直器接收来自放射源的放射线的能力。
2. 所谓准直器分辨率(空间分辨率)是指准直器探头鉴别两个紧密相连的放射源的能力，目前多用点源或线源响应曲线最大高度的一半处的全宽度即FWHM(full width at half maximun)表示。分辨率越好，FWHM越小。

灵敏度和分辨率呈相反的关系。

要求有较高的灵敏度，往往要以牺牲分辨率为代价，反之亦然。准直器的设计就是在灵敏度和分辨率之间选择最佳的折衷匹配。因此，它是SPECT影像装置的关键部件。准直器的性能是直接影响系统性能的主要因素。

    3.  准直器的另外一项性能指标是间壁穿透率，它反映准直器小孔之间的间壁屏蔽视野外的与准直器孔角不符的射线的能力，一般要求穿透率≤10％。如果间壁太厚，探测几何效率将会降低；如果太薄，将使影像对比度（分辨率？？？）降低。

准直器有以下几种:

1. 平行孔准直器

最常用的一类准直器。它是由一组垂直于晶体表面的铅孔组成。每个孔仅接收来自它正前方的射线，而防止其他方向上的射线射入晶体。

最接近准直器处的空间分辨率最好，随距离的增加而变差，

而灵敏度随距离的增加却变化不大，因γ光子的空间浓度虽随距离的平方成反比而减少，但晶体暴露于放射源的总面积却按距离的平方成正比而增加。

平行孔准直器的性能由其孔数、孔径、孔长、间壁厚度和准直器的材料所决定。

根据准直器适用的γ光子的能量范围，可将平行孔准直器分为低能（≤150keV）、中能（150～350keV）和高能（≥350keV）3种。根据低能准直器的灵敏度和分辨率可将平行孔准直器分为低能通用型、低能高分辨率、低能高灵敏度3种。

孔径越小，分辨率越好；

间壁厚度减少，灵敏度增加。

影像大小与靶器和准直器之间的距离无关。

2. 针孔准直器

它是单孔准直器，其成像原理与光学中的小孔成像原理相同，像与实物的方向相反。

成像的大小与被检物距离针孔的远近有关，距离越近，成像越大。

其分辨率和灵敏度与其孔径的大小有关，孔径增大，灵敏度提高，分辨率降低，反之亦然。

3. 发散孔准直器

其优点是扩大有效视野10%～20%，且视野随放射源与准直器距离的增加而增大。

其缺点是灵敏度和分辨率较平行孔准直器差。且随放射源与准直器距离的增加而变坏。

利用这种准直器，被测物被缩小，但并不是所有的部分都受到相应的缩小，故产生影像畸变。

4. 聚焦孔准直器

其优点是可以提高灵敏度和分辨率，但也容易出现影像的畸变。主要适用于总计数时间受限的动态研究。

把一个这么简单的事情描述的这么复杂，看的头都晕了。不就是正电荷增加了uptake同时增加了toxicity吗？而且没有给出最佳的正电荷比例。

亮点是第二张图，我觉得这么个办法调整表面电荷挺聪明的。

Nanoparticle penetration into cell membranes is an interesting phenomenon that may have crucial implications on the nanoparticles’ biomedical applications. In this paper, a coarse-grained model for gold nanoparticles (AuNPs) is developed (verified against experimental data available) to simulate their interactions with model lipid membranes. Simulations reveal that AuNPs with different signs and densities of surface charges spontaneously adhere to the bilayer surface or penetrate into the bilayer interior. The potential of mean force calculations show that the energy gains upon adhesion or penetration is significant. In the case of penetration, it is found that defective areas are induced across the entire surface of the upper leaflet of the bilayer and a hydrophilic pore that transports water molecules was formed with its surrounding lipids highly disordered. Penetration and its concomitant membrane disruptions can be a possible mechanism of the two observed phenomena in experiments:

1. AuNPs bypass endocytosis during their internalization into cells and cytotoxicity of AuNPs.
2. It is also found that both the level of penetration and membrane disruption increase as the charge density of the AuNP increases, but in different manners. The findings suggest a way of controlling the AuNP−cell interactions by manipulating surface charge densities of AuNPs to achieve designated goals in their biomedical applications, such as striking a balance between their cellular uptake and cytotoxicity in order to achieve optimal delivery efficiency as delivery agents.

It is clear that the severe disruption on the bilayer is caused by the strong attractions between the terminals of AuNPs’ cationic ligands (ammonium) and the phosphate groups of DPPC and DPPG. In a recent experiment, it is found that highly charged cationic AuNPs are able to generate holes on supported lipid bilayers.These bilayers are supported on a mica surface, which carries negative net charges that provide the bilayer with a similar electric feature to that of a PC/PG bilayer. Although the size of holes observed in the experiment are larger than that the simulation, they both indicate a highly disruptive nature of cationic AuNPs shown to negative bilayers, which shows qualitative agreement to each other.

Both the level of penetration and disruption goes higher as the AuNPs’ surface charge increases but in different manners. At the cationic coverage below 50%, the increase of the penetration is prominent. . The particle is already “inside” the bilayer when the coverage has reached 50%. However, further increase of coverage promotes penetration to a much lesser degree. Even at 100% cationic coverage, the particle still resides in the bilayer interior and does not move downward to breakout the lower leaflet of the bilayer.

By contrast, the disruption on the membrane is not significant until the coverage reaches around 60%. Further increase of coverage results in severe membrane disruption which is clearly visible.

the influence of surface charge density of a AuNP on membrane can be divided into two stages.

1. In the first stage where the AuNPs have lower charge densities, the effect of surface charge mainly contributes to penetration.
2. In the second stage where AuNPs have higher charge densities, the effect of surface charge mainly contributes to membrane disruption since further penetration is not possible. The finding may provide us a clue on how to avoid high toxic effect of AuNPs while achieve certain goal in their biomedical applications.

A recent experimental study showed that the membrane affinity constant of cationic AuNPs is three times greater than that of anionic AuNPs in human cancer cell lines.(Cho, E. C.; Xie, J.; Wurm, P. A.; Xia, Y. Understanding the Role of Surface Charges in Cellular Adsorption versus Internalization by Selectively Removing Gold Nanoparticles on the Cell Surface with a I2/KI Etchant Nano Lett. 2009, 9, 1080– 1084)

cationic AuNPs are, on average, 27 times more toxic than their anionic counterparts in three different cell lines.(Hauck, T. S.; Ghazani, A. A.; Chan, W. C. Assessing the Effect of Surface Chemistry on Gold Nanorod Uptake, Toxicity, and Gene Expression in Mammalian Cells Small 2008, 4, 153– 159)

TOXICITY vs surface charge

1. First, cationic AuNPs have higher adhesion to cell membranes than anionic AuNPs do, which is also a reason for their high uptake;
2. second, their membrane disruption ability is far more significant than that of their anionic counterparts. AuNPs with high cationic surface coating can disrupt a bilayer membrane to a great extent, which subsequently compromises the membrane integrity and thus breach the hydrophobic barrier. The hydrated channel will lead to the exchange of medium between extracellular fluid and cytosol, which may cause acute cytotoxicity.(21)
3. Although not enough to compromise bilayer integrity, anionic AuNPs are capable of altering cell functions by inducing changes on membrane protein properties as well as bilayer properties, which can in turn affect the functioning of membrane proteins (see ref 37 for an in-depth review). Changes on the functioning of membrane proteins are able to alter cell functions substantially, which may be one of the reasons for the observed minor cytotoxicity of anionic AuNPs, since the AuNPs are still able to induce negative effects once inside the cells.(9)