Au@SiO2核壳纳米粒子的制备及其表面增强拉曼光谱

采用柠檬酸钠还原氯金酸法制备金溶胶, 以正硅酸乙酯(TEOS)为硅源, 氨水作催化剂, 制备以金为核, 二氧化硅为壳的核壳纳米粒子. 金纳米粒子的粒径可以通过柠檬酸钠和氯金酸的比例控制, 通过调节TEOS的量和反应的时间可以控制二氧化硅壳层的厚度. 以苯硫酚为探针分子研究了核壳结构纳米粒子的表面增强拉曼散射(SERS)效应与二氧化硅壳层厚度之间的关系. 研究结果表明, 金内核电磁场增强效应随着二氧化硅壳层厚度的增加逐渐减弱, 且其衰减速度比具有相同尺度的双金属核壳结构纳米粒子的慢. 此外, 探针分子主要以物理作用吸附在二氧化硅的表面, 可通过洗涤方法将探针分子除去, 从而可使该复合结构基底用于循环SERS分析.     

基础实验:金纳米粒子的制备及其光学性质

围绕金纳米粒子前沿内容,设计了一个简易的本科生基础实验,利用柠檬酸钠还原氯金酸法制备分散性好的金纳米粒子溶液,讨论了其尺寸与颜色的关系,探究了不同电解质和非电解质对金纳米粒子团聚及其颜色的影响,初步了解金纳米粒子的光学特性和探针效应基本原理。     

聚苯胺包裹的金纳米粒子的合成和表征及初步应用

用苯胺作还原剂还原氯金酸合成了金纳米结构. TEM实验表明, 苯胺还原氯金酸能生成苯胺齐聚物或其聚合物包裹的金球形纳米粒子. XPS分析表明, 金纳米粒子包覆的聚合物层带正电荷. 该纳米粒子能用于电极表面纳米结构组装及氧化还原性的生物大分子的电化学研究, 实现了超氧化物歧化酶(SOD)在这种带正电荷的金纳米粒子表面的直接电子转移.     

藤茶干粉提取液还原制备金纳米粒子

用藤茶干粉提取液生物还原氯金酸溶液实现了金纳米粒子绿色制备,通过紫外-可见分光光度计、透射电子显微镜和粒度分布等技术手段对金纳米粒子形态等物性进行了表征,运用控制变量法探究了金纳米粒子生物合成的规律。研究发现,金纳米粒子的粒径、粒径分布、形状和稳定性受反应体系pH值、温度以及氯金酸的用量影响。pH6.47或藤茶干粉提取液过量时会引起纳米金的团聚;温度升高,金纳米粒子平均粒径会减小。通过变量控制,可以实现金纳米粒子绿色合成的有效控制。     

金纳米粒子组装体的连续离散型纳米结构控制

采用柠檬酸钠还原氯金酸的方法,制备出粒径均一的金纳米粒子(AuNPs),通过加入二水合双(对-磺酰苯基)苯基膦化二钾盐(BSPP),增强了AuNPs体系的分散性与稳定性.选用直径为15和40nm的AuNPs,用不同序列巯基修饰的单链DNA连接到其表面,通过DNA链的杂交,形成不同结构的金纳米粒子组装体.通过改变加入DNA延长连接单元的比例,可以控制金纳米粒子组装体具有连续离散型的1∶1,2∶1和3∶1纳米结构.     

半导体纳米粒子与金纳米粒子间荧光共振能量转移研究

采用水相法合成的CdTe半导体纳米粒子作为能量给体, 通过Schiff碱反应将单链DNA连接到表面. 采用柠檬酸钠还原氯金酸法制取的Au纳米粒子作为能量受体, 通过Au—S键将单链DNA连接到表面. 通过DNA链间的杂交, 构建了荧光共振能量转移体系(FRET). 测定了CdTe-DNA、 探针体系和探针体系+目标DNA的荧光强度. 结果表明, 探针体系的荧光强度最弱, 加入目标DNA后, 体系荧光增强, 表明该体系的构建是成功的.     

以C60为媒介的网状金纳米粒子聚集体的构筑

通过全甲基化环糊精和卟啉之间的"Click"反应,合成了一种不对称环糊精修饰的卟啉衍生物,并对其结构进行了表征.该化合物与氯金酸作用可以形成平均粒径为5 nm的水溶性金纳米粒子,该金纳米粒子进一步与C60作用形成网状纳米聚集体,并通过紫外光谱和透射电子显微镜验证了聚集体的结构.     

反相微乳液中憎水性纳米金的原位还原法合成

利用十八胺(C18NH2)/正丁醇/正庚烷/HAuCl4(aq)W/O型微乳液体系,在常温的碱促进条件下由正丁醇原位还原氯金酸合成了具有高度单分散的憎水性金纳米粒子。由C18NH2稳定的金纳米颗粒运用紫外可见光谱(UV-vis)、透射电镜(TEM)和X射线衍射(XRD)等分别进行了表征和分析,并探讨了微乳液体系各组分对形成金纳米粒子形貌、尺寸和单分散性的影响。结果显示,随十八胺/氯金酸摩尔比的增加,金粒子的尺寸逐渐减小而单分散性逐渐提高。在正丁醇原位慢还原氯金酸的过程中,实验所选W/O型微乳液模板和表面活性剂十八胺分子对憎水性金纳米粒子的形貌和尺寸仍具有良好的控制作用。     

纳米金比色法测定多西环素和土霉素

采用柠檬酸钠还原法合成粒径约13nm的纳米金粒子.采用紫外-可见分光光度计、荧光分光光度计研究了纳米金粒子与多西环素/土霉素分子的相互作用;通过改变缓冲溶液、纳米金粒子用量、反应时间确定了比色法测定的最优反应条件.结果表明:在弱酸溶液中,多西环素/土霉素分子中的氨基官能团(-NH_2)得到电子成为带电基团(-NH_3~+)并通过静电引力与纳米金粒子结合,使得纳米金粒子发生聚集,导致纳米金吸收光谱发生红移和展宽,颜色由酒红色变成蓝色;在盐酸-柠檬酸钠的缓冲溶液中加入2mL纳米金,反应时间为10min的条件下测得多西环素和土霉素的线性范围分别为0.06~0.66mg·L~(-1)和0.59~8.85 mg·L~(-1),检出限(3σ)分别为0.008 6、0.083 8mg·L~(-1).该方法前处理简单、灵敏、可靠,有望应用于食品分析和临床分析等领域.     

在SDS-PVP团簇软模板中自组装多脚状金纳米粒子

利用十二烷基硫酸钠(SDS)与聚乙烯吡咯烷酮(PVP)组成的团簇为软模板, 在微波辅助下以柠檬酸钠为还原剂快速还原氯金酸生成金晶并自组装成多脚状金纳米粒子. TEM结果显示, 得到回转直径约为50 nm的多脚状纳米结构, 电子衍射(ED)证实其为多晶结构. XRD结果表明, 该多脚状金纳米结构主要沿(111)晶面生长, 构成该纳米结构的晶粒尺寸约为12.7 nm. SDS与PVP组成的团簇结构对金纳米粒子的形貌有显著影响, 固定PVP浓度时, 随着SDS浓度增大, 金纳米粒子的形貌由球形向多脚状转变, 同时还原产物水溶液的UV-Vis光谱在800 nm附近的吸收逐渐增强.     

二苯胺磺酸钠还原法制备粒径可控的金纳米粒子

采用二苯胺磺酸钠还原四氯合金酸的方法,在室温条件下,用SDS(十二烷基硫酸钠)、SDBS(十二烷基苯磺酸钠)作表面活性剂,成功地合成了金纳米粒子.分别讨论了还原剂二苯胺磺酸钠、表面活性剂(SDS、SDBS)及四氯台金酸的浓度等对金纳米粒子的粒径和形貌的影响.通过控制反应条件,可以合成出平均粒径大约为10、14、30、36nm的金纳米粒子.利用透射电镜(TEN)、紫外-可见(UV-Vis)吸收光谱对金纳米粒子进行了表征.研究结果表明不同的SDS或SDBS/HAuCl4的摩尔比,对金纳米粒子的尺寸大小有影响.     

PyDDP修饰的金纳米颗粒的制备及其吸收红移机制

用柠檬酸三钠还原四氯化金制备了金纳米颗粒,并用双十八烷氧基二硫代磷酸吡啶盐（PyDDP）对其进行修饰. 红外吸收光谱表明PyDDP与金颗粒表面以共价键方式结合；透射电子显微镜（TEM）的结果表明, 所得到的PyDDP修饰的纳米金颗粒尺寸与修饰前基本相同; PyDDP修饰的金纳米粒子表面等离子吸收发生了较大幅度的红移.利用偶极子模型结合配位理论解释了PyDDP修饰的金纳米颗粒发生红移的机制.     

Kinetically controlled seeded growth synthesis of citrate-stabilized gold nanoparticles of up to 200 nm: size focusing versus Ostwald ripening

Monodisperse citrate-stabilized gold nanoparticles with a uniform quasi-spherical shape of up to ～200 nm and a narrow size distribution were synthesized following a kinetically controlled seeded growth strategy via the reduction of HAuCl(4) by sodium citrate. The inhibition of any secondary nucleation during homogeneous growth was controlled by adjusting the reaction conditions: temperature, gold precursor to seed particle concentration, and pH. This method presents improved results regarding the traditional Frens method in several aspects: (i) it produces particles of higher monodispersity; (ii) it allows better control of the gold nanoparticle size and size distribution; and (iii) it leads to higher concentrations. Gold nanoparticles synthesized following this method can be further functionalized with a wide variety of molecules, hence this method appears to be a promising candidate for application in the fields of biomedicine, photonics, and electronics, among others.     

A biologically friendly single step method for gold nanoparticle formation

There has been a keen interest for developing a biologically friendly approach for the preparation of gold nanoparticles for their application reasons. A biocompatible, quick and single step method is established for the preparation of gold nanoparticles in lecithin (Egg phosphatidylcholine)/water systems where lecithin itself acts as a reductant for hydrogen tetrachloro aurate (HAuCl(4)) to form the gold nanoparticles. Small gold nanoparticles (5-7 nm in diameter) were prepared in lamellar phases formed by lecithin within 6-7h of HAuCl(4) addition. Sonication of aqueous mixture of lecithin/HAuCl(4) reduces the time of reduction process to seconds when a sonicator with probe (100 W) is used. Most of the particles are found attached to lecithin structures and are comparatively large in size. Some 10nm particles are found attached to small lecithin vesicles (～100 nm) formed during sonication. The nanoparticles formed were stabilized by an anionic surfactant sodium dodecylsulfate (SDS) which proved to be a good stabilizer, the nanoparticles being stable up to six months. To the best of our knowledge, this is the first report where a biological surfactant lecithin itself has acted as a reductant and no other chemical reductants were required for the gold nanoparticle formation. Particles were characterized by Uv-vis spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering (DLS). Lamellar phases were characterized by a polarizing microscope.     

Morphology-selective synthesis of polyhedral gold nanoparticles: what factors control the size and morphology of gold nanoparticles in a wet-chemical process

Polyhedral gold nanoparticles below 100 nm in size were fabricated by continuously delivered HAuCl(4) and PVP starting solutions into l-ascorbic acid aqueous solution in the presence of gold seeds, and under addition of sodium hydroxide (NaOH). By continuously delivered PVP and HAuCl(4) starting solutions in the presence of gold seed, the size and shape of polyhedral gold were achieved in relatively good uniformity (particle size distribution=65-95 nm). Morphological evolution was also attempted using different growth rates of crystal facets with increasing reaction temperature, and selective adsorption of PVP.     

Monodisperse sub-10 nm gold nanoparticles by reversing the order of addition in Turkevich method--the role of chloroauric acid

The Turkevich method for synthesizing gold nanoparticles, using sodium citrate as the reducing agent, is renowned for its ability to produce biocompatible colloids with mean size >10 nm. Here we show that monodisperse gold nanoparticles in the 5-10 nm size range can be synthesized by simply reversing the order of addition of reactants, i.e. adding chloroauric acid to citrate solution. Kinetic studies and electron microscopic characterization revealed that the reactivity of chloroauric acid, initial molar ratio of citrate to chloroauric acid (MR), and reaction mixture pH play an important role in producing monodisperse gold nanoparticles. Reversing the order of addition also enhanced the stabilization of nanoparticles at high MR values. Remarkably, the system exhibits a 'memory' of the order of addition, even when the timescale of mixing is much shorter than the timescale of synthesis.     

Surfactantless photochemical deposition of gold nanoparticles on an optical fiber core for surface-enhanced Raman scattering

Surface-enhanced Raman scattering (SERS) probes based on gold nanoparticles modifying the core of the optical fiber were made by a surfactantless photochemical deposition method. The growth kinetics and shape evolution of gold nanoparticles depending on different experimental conditions were studied. It was found that, under the condition of detectable gold nanoparticle deposition, increasing the concentration of chloroauric acid (HAuCl(4)) was not conducive to the deposition whereas increasing the concentration of sodium citrate (Na(3)Ct) would speed up the deposition. By controlling the concentration of the reaction solution and irradiation time, we obtained fused spherical-like, spherical, and flowerlike gold nanoparticles. To test the SERS activity of the probes, the SERS spectra of a rhodamine 6G aqueous solution were recorded in direct detection mode and remote mode. We have also developed a new approach to improving the SERS sensitivity when detecting in remote mode.     

Size control of gold nanocrystals in citrate reduction: the third role of citrate

Growth kinetics and temporal size/shape evolution of gold nanocrystals by citrate reduction in boiling water were studied systematically and quantitatively. Results reveal that the size variation and overall reaction mechanism were mostly determined by the solution pH that was in turn controlled by the concentration of sodium citrate (Na3Ct) in the traditional Frens's synthesis. This conclusion was further confirmed by the reactions with variable pH but fixed concentrations of the two reactants, HAuCl4 and Na3Ct. Two substantially different reaction pathways were identified, with the switching point at pH = 6.2-6.5. The first pathway is for the low pH range and consists of three overlapping steps: nucleation, random attachment to polycrystalline nanowires, and smoothing of the nanowires via intra-particle ripening to dots. The second pathway that occurred above the pH switching point is consistent with the commonly known nucleation-growth route. Using the second pathway, we demonstrated a new synthetic route for the synthesis of nearly monodisperse gold nanocrystals in the size range from 20 to 40 nm by simply varying the solution pH with fixed concentrations of HAuCl4 and Na3Ct. The switching of the reaction pathways is likely due to the integration nature of water as a reaction medium. In the citrate reduction, the solution pH was varied by changing the initial HAuCl4/Na3Ct ratio. Consequently, when pH was higher than about 6.2, the very reactive [AuCl3(OH)]- would be converted to less reactive [AuCl2(OH)2]- and [AuCl(OH)3]-.