Enhanced Fluorescence from Periodic Arrays of Silver Nanoparticles

Electron beam lithography was used to fabricate silver nanoparticle arrays and study the effects of geometrical properties of particles on metal-enhanced fluorescence. Nanoparticle size, shape, interparticle spacing, and nominal thickness were varied in a combinatorial pattern for investigation of the particle plasmon resonance effect on enhancement of fluorescence from three different fluorophores; Fluorescein, Cy3, and Cy5. A specific geometric property for optimal enhancement from each fluorophore was determined. For interparticle spacings greater or equal to 270 nm, the enhancement matched what is expected for a single-particle model. For those particles smaller than 210 nm, the enhancement was lower than for the larger spacing in the range studied. Triangular-shaped particles gave similar enhancement to those of square-shaped particles. This combinatorial pattern by e-beam lithography was found to be useful for studying how individual parameters enhance the fluorescence that are important for rational design of enhanced fluorescence sensors.     

Morphological Effect on Fluorescence Behavior of Silver Nanoparticles

Effect of Silver nanoparticles (AgNPs) morphology on their fluorescence behavior is reported. AgNPs sol stabilized by Ethylene Diamine Tetra Acetic-Acid (EDTA) was prepared by chemical reduction method. Morphology of the AgNPs was tuned through changing the Ag⁺ ion concentration and P^H of reaction mixture. Additional peaks observed in surface Plasmon resonance spectra suggest the an-isotropic nature of AgNPs. Actual morphology was judged by Transmission Electron Microscopy. Emission spectra recorded using Spectrofluoremeter suggest the fluorescent nature of AgNPs, which also influenced by morphology of AgNPs and attributed to the variation in surface structure of an-isotropic AgNPs.

纳米银与表面吸附荧光素的荧光性能的影响

研究了纳米银粒子对表面吸附荧光素(fluorescein,Fl)的荧光性能的影响。Fl溶液中加入纳米银粒子,Fl分子包覆在纳米银粒子表面形成Fl_n-Ag复合物使纳米银相互桥连形成类似网络的结构,且Fl分子吸收峰随着纳米银浓度的增加发生红移。纳米银通过产生的强局域场将能量传输给Fl发光中心,实现了Fl的荧光增强,荧光增强效率随着纳米银浓度的增加具有最大值。较大粒径的纳米银使Fl获得最大荧光增强效率所需浓度较低且最大荧光增强效率值较高。研究结果表明,纳米银与Fl间的能量传输主要由Fl分子附近局域电磁场增强和分子到金属表面无辐射跃迁能量转移过程所决定并与纳米银的浓度、尺寸密切相关。     

银纳米粒子对抗生素诺氟沙星的荧光猝灭效应

以β-环糊精(β-CD)为稳定剂,葡萄糖为还原剂,采用"绿色化学方法"合成了平均粒径约为31nm的类球形银纳米粒子。研究了其对水溶液中痕量诺氟沙星荧光行为的影响,实验结果表明,制得的银纳米粒子对诺氟沙星具有较强的荧光猝灭效应,且随着加入银纳米粒子量的增加荧光猝灭效果逐渐增强。初步探讨了银纳米粒子对诺氟沙星的荧光猝灭机理。     

银纳米颗粒对胆固醇荧光的增强效用研究

在传统荧光光谱技术的基础上,结合金属纳米颗粒的增强荧光技术,探索提高荧光光谱技术检测人全血溶液中胆固醇含量的精度和分辨率的方法。实验研究方面,采用波长为407 nm的激光作为激发光,照射加入一定量银纳米颗粒作为荧光增强剂的人全血溶液,研究了银纳米颗粒对人全血溶液在可见光波段的荧光增强作用。结果表明,胶体状态的银纳米颗粒可以显著增强低浓度的人全血溶液荧光光谱的强度,且不同位置荧光发射峰的荧光增强效率随银胶加入量的增加均呈现先增后减的趋势,但不同峰位置的最强增强效率对应的银胶加入量不同。理论分析方面,根据实验结果及胆固醇分子和银纳米颗粒在溶液中的分布情况,建立了分子间距模型,并根据模型计算得出胆固醇分子和银纳米粒子之间的最佳增强荧光效果间距在12.19～25 nm范围内,这个结果和其他文献中的理论值吻合较好。综上所述,使用银纳米颗粒可实现全血溶液荧光的增强,研究结果为提高检测血液中多种物质的灵敏度和精度提供了有价值的参考作用。     

Fluorescent Flavin/PVP-Coated Silver Nanoparticles: Design and Biological Performance

A red-emitting fluorescent Riboflavin (RF)/Polyvinylpyrrolidone (PVP)-coated silver nanoparticles system, λ_em?=?527 nm, Φ?=?0.242, with a diameter of the metallic core of 27.33 nm and a zeta potential of ? 25.05 mV was prepared and investigated regarding its biological activity. We found that PVP has a key role in RF adsorption around the SNPs surface leading to an enhancement of antioxidant properties (～70%), low cytotoxicity (> 90% cell viability, at 50 µL/mL, after 48 h of incubation) as well as to an efficient process of its cellular uptake (～ 60%, after 24 h of incubation) in L929 cells. The results are relevant concerning the involvement of RF and its coenzymes forms in SNPs - based systems, in cellular respiration as well as for future studies as antioxidant marker system on tumoral cells for viewing and monitoring them, by cellular imaging.

     

Sensitized Fluorescence of Silver Nanoparticles in the Presence of Pyrene

The fluorescence of pyrene adsorbed onto the surface of the cetyltrimethylammonium-coated silver nanoparticles was studied. Pyrene molecules adsorbed on freshly prepared silver particles were found to be in close proximity to silver surface thus providing the possibility of energy transfer from excited pyrene to silver cores of the particles. In that case along with the expected fluorescence of pyrene we observed the fluorescence of the silver nanoparticles induced by the excited pyrene molecules. In due course the restructuring of the cetyltrimethylammonium layer resulted in moving of pyrene molecules away from silver surface and simultaneous disappearance of the silver nanoparticles fluorescence band. These data strongly support the recent hypothesis of fluorophore-plasmon coupled emission.     

On the Fluorescence of Luminol in a Silver Nanoparticles Complex

The photophysical properties of luminol in a silver nanoparticles complex have been studied by steady-state and time resolved fluorescence spectroscopy. The effect of the serum albumin on the luminol fluorescence in the silver nanoparticles has been also investigated. It was found that the fluorescence quantum yield value of luminol in a silver nanoparticles complex is ??=?0.00407. The decrease of the average fluorescence lifetime value of the luminol in the silver nanoparticles complex was found to be low, <τ>?=?1.712 ns. The luminol does not bind to the serum albumins in the presence of silver nanoparticles. The formation of a new species of luminol on silver nanoparticles is discussed. The results have influence regarding the use of luminol as an assay for bio-analytical applications.     

纳米银组装结构上罗丹明B的表面增强荧光效应

采用表面自组装技术,在玻璃表面构筑银纳米粒子的二维组装结构。银纳米粒子组装结构的表面等离子共振光谱中偶极子表面等离子体共振对组装结构更为敏感而表现出较大位移。组装银纳米粒子可极大增强罗丹明B的荧光。荧光的表面增强效应主要来自银纳米粒子对荧光分子所处区域的局部电磁场增强,银纳米粒子的表面分子修饰对其表面增强效应有较大的影响。     

Donor-Acceptor Compound Based on Rhodanineacetic Acid-Pyrene Derivative: Red-Light Emitting Fluorescent Organic Nanoparticles

A donor-acceptor compound based on Rhodanineacetic acid-pyrene derivative (RAAP), which emits weak yellow-green fluorescence in the methanol solution, was investigated. RAAP nanoparticles with a mean diameter of 50–60 nm were prepared by a simple reprecipitation method without surfactants. The observation of RAAP nanoparticles were undertaken through SEM and TEM method. The emission spectra of RAAP nanoparticles are red-shifted (Δ λ_em = 86 nm) to red region and the intensity is 40-fold higher than that in the methanol solution. Both the J-aggregation and aggregation-induced intramolecular planarization are considered to be the probable mechanism of strong emission for RAAP nanoparticles. The excellent sensibility toward organic vapor which profits from its fluorescence switching behavior is well demonstrated by vapor experiment.     

A Novel Fluorescent Biosensor for Detection of Silver Ions Based on Upconversion Nanoparticles

In this paper, we report a simple and sensitive fluorescent biosensor for the quantitative analysis of silver ions (Ag⁺) by using NaYF₄:Yb³⁺, Tm³⁺ upconversion nanoparticles (UCNPs). Ag⁺ could oxidize o-phenylenediamine (OPD) to the oxidized OPD (oxOPD) directly. The fluorescence of UCNPs can be significantly quenched by oxOPD through inner filter effects (IFE). Under the optimized conditions, the Ag⁺ concentration is proportional to the changes of the fluorescence intensity of UCNPs. The proposed method shows high selectivity and Ag⁺ could be quantitatively detected in the range of 0 to 0.5 mM with a low detection limit of 33 nM for Ag⁺. The selectivity and sensitivity of the detection can also be satisfactory. More importantly, this method has potential in practical application to detect Ag⁺ in real samples without interference.     

A Brief Review on Fluorescent Copper Sensor Based on Conjugated Organic Dyes

The design and development of the fluorescence reporting molecules for the trace recognition of the metallic ions in the aqueous, mixed organic aqueous media, environmental specimen, living things e.g., body fluids, serum, urine etc is the evergreen research area. Among several methodologies utilized for these purposes, the fluorescent techniques have wonderful impact in the era of metal sensor development due to their acclamatory features of non-invasive detection process and appreciable sensitivity. The utilization of small organic molecules for the sensation of metallic ions through the fluorescent techniques harvested the wonderful results having some interesting features of chromogenic response on metal binding, robustness in the preparation and applicability to establish the metallic accumulation level inside the live cells via bioimaging studies. The detailed knowledge and background about the several reported chemosening strategies have the utmost importance in order to understand or to design the novel molecules for metal sensing purposes. The objective of the presents review was to compile the best ever used copper sensing strategies via fluorescent means in the running decade. We have summarized the values of optical positions of the spectral lines, spectral shifting upon metal binding, binding/association/dissociation constants, chromogenic changes in the reaction mixture, proposed complexation mechanism of the ligand with the copper, ligand sensitivities toward the copper recognition, binding stoichiometries and the detailed bioimaging results where applicable.     

Voltage-Gated Metal-Enhanced Fluorescence II: Effects of Fluorophore Concentration on the Magnitude of the Gated-Current

In this letter we report further findings on the ability of an applied direct current to modulate Metal-Enhanced Fluorescence (MEF). Fluorophores in close-proximity to just-continuous silver films (JCS) show significantly enhanced fluorescence intensities. However, when a current is applied to the films, the enhanced fluorescence can be gated in a manner that depends on both the fluorophore concentration, the magnitude of the applied current and the extent of the protein mono to multi-layer surface coverage. Our results are consistent and indeed further support our previous hypothesis and model that fluorophore-metal near-field interactions can be influenced by an applied direct current.     

Enhancement of Fluorescence and Raman Scattering in Cyanine-Dye Molecules on the Surface of Silicon-Coated Silver Nanoparticles

A method of formation of a composite structure based on silver nanoparticles and a thin protective silicon film (AgNPs/Si) is developed. Enhancement of the fluorescence and Raman scattering in cyaninedye molecules deposited onto the formed nanostructure is observed. The optical properties and morphology stability of particles that are in contact with cyanine-dye solutions in organic solvents are studied. It is shown that the AgNPs/Si composite structure can be multiply used as an SERS-active surface.     

有机分子隔离层对机械抛光金属银表面的罗丹明6G荧光增强效应的影响

采用物理吸附法,在机械抛光纯银表面引入对巯基苯胺(p-Amiothiophenol,PATP)分子充当隔离层,运用激光光谱学方法研究隔离层对位于银表面附近的罗丹明6G(Rh6G)分子的荧光增强效应影响。实验结果表明,未经PATP分子修饰的机械抛光金属衬底对Rh6G分子表现为猝灭效应,而经过PATP分子修饰后的银表面对Rh6G分子的荧光发射具有增强效应。根据局域表面等离子共振及辐射能量转移模型对实验观测所得结果进行了分析研究,结果表明,PATP有机分子隔离层的引入有效地减小了荧光分子与金属衬底之间的无辐射能量速率,提高了荧光辐射强度。     

Fluorescence Quenching of 1,4-Dihydroxy-2,3-Dimethyl-9,10-Anthraquinone by Silver Nanoparticles: Size Effect

Size effect of silver nano particles on the photophysical properties of 1,4-dihydroxy-2,3-dimethyl-9,10-anthraquinone (DHDMAQ) have been investigated using optical absorption and fluorescence emission techniques. Silver nanoparticles of different sizes have been prepared by Creighton method using magnetic stirrer and ultrasonic field. Quenching of fluorescence of DHDMAQ has been found to increase with decrease in the size of the silver nanoparticles. Stern–Volmer quenching constants have also been calculated.     

三聚氰胺-铜(Ⅱ)配合物抑制AT-双链铜纳米颗粒合成荧光检测三聚氰胺

基于三聚氰胺与铜离子配位反应并抑制A T-双链铜纳米颗粒合成,构建了一种新型的"turn-off"策略检测三聚氰胺.当三聚氰胺存在时,与铜离子发生配位反应,使得后期合成铜纳米颗粒的铜离子浓度不够,导致铜纳米颗粒荧光减弱.在最优化实验条件下,对三聚氰胺检测的线性范围为1~150μmol·L-1,检出限达0.5μmol·L-1.此外,该方法还可以检测牛奶样品中的三聚氰胺,回收率良好.     

纳米银胶中PVP和Alq3的荧光猝灭研究

本文通过湿法化学还原法合成了平均粒径为4.42nm、标准差为0.98nm的球形银纳米颗粒,并研究了在不同反应时间后获得的银纳米颗粒对PVP和Alq3的荧光猝灭效应。通过深入研究发现,PVP的荧光猝灭效应主要由于其分子链上的酮基与Ag颗粒之间发生了静电吸附,进而导致处在激发态的PVP分子与银颗粒之间产生电子或者能量转移(即非辐射弛豫),猝灭了PVP的荧光发光;而Alq3的荧光猝灭效应则主要归因于银纳米颗粒的欧姆损耗。通过采用时域有限差分法进行模拟发现,溶液中随机分布的银纳米颗粒,不仅能够吸收激发电磁波,削弱激发场强度,而且能够吸收荧光分子辐射的电磁波,进而猝灭了Alq3分子的荧光效应。这些研究成果将有利于了解金属纳米颗粒与PVP及Alq3分子荧光发光之间的关系,为调控荧光发光提供指导。     

具有荧光传感器性能的稀土配合物制备和性能研究

以氯化铕、2-噻吩甲酰三氟丙酮(HTTA)和硅酸钠为原料制备了新型的检测二氯甲烷中乙醇含量的稀土配合物。通过在溶有所制备的稀土配合物的二氯甲烷溶液中滴加无水乙醇,发现溶液的荧光强度逐渐增强,而且具备一定的规律性。所制备的新型稀土配合物通过高分辨质谱分析表明,其结构属于多核稀土配合物。在二氯甲烷溶液中加入乙醇会改变溶液的极性,使多核稀土配合物发生解离从而增强荧光强度。这种稀土配合物可以作为荧光传感器检测有机溶剂中乙醇的含量。     

Influence of pH on the Spectral-Luminescent Characteristics of the Soft Protein Crown of Silver Nanoparticles

Journal of Applied Spectroscopy - The spectral and fluorescent characteristics of bovine serum albumin (BSA) molecules in the soft crown of silver nanoparticles (Ag-NPs) were studied at various pH...