Size-dependent interaction of gold nanoparticles with transport protein: A spectroscopic study

Gold nanoparticles of different sizes have been synthesized using sodium citrate as a reducing agent for tetrachloroauric (III) acid. The formed gold nanoparticles have been characterized by the UV-visible and transmission electron microscopy (TEM) measurements. The different sized gold nanoparticles have been used to study the interaction with model transport protein, bovine serum albumin (BSA). Experimental results reveal that BSA molecules adsorbed on the metallic surfaces, suffer strong quenching of their fluorescence and the rate of quenching efficiency is different for different particle size. The analysis of the quenching results has been performed in terms of the Stern-Volmer equation. The mechanism of quenching of fluorescence has been explained. The extent of adsorption of BSA on the gold nanoparticles has been estimated.     

Adsorption kinetics of alkanethiol-capped gold nanoparticles at the hexane–water interface

The pendant drop technique was used to characterize the adsorption behavior of n-dodecane-1-thiol and n-hexane-1-thiol-capped gold nanoparticles at the hexane–water interface. The adsorption process was studied by analyzing the dynamic interfacial tension versus nanoparticle concentration, both at early times and at later stages (i.e., immediately after the interface between the fluids is made and once equilibrium has been established). A series of gold colloids were made using nanoparticles ranging in size from 1.60 to 2.85 nm dissolved in hexane for the interfacial tension analysis. Following free diffusion of nanoparticles from the bulk hexane phase, adsorption leads to ordering and rearrangement of the nanoparticles at the interface and formation of a dense monolayer. With increasing interfacial coverage, the diffusion-controlled adsorption for the nanoparticles at the interface was found to change to an interaction-controlled assembly and the presence of an adsorption barrier was experimentally verified. At the same bulk concentration, different sizes of n-dodecane-1-thiol nanoparticles showed different absorption behavior at the interface, in agreement with the findings of Kutuzov et al. (Phys Chem Chem Phys 9:6351–6358, 2007). The experiments additionally demonstrated the important role played by the capping agent. At the same concentration, gold nanoparticles stabilized by n-hexane-1-thiol exhibited greater surface activity than gold nanoparticles of the same size stabilized by n-dodecane-1-thiol. These findings contribute to the design of useful supra-colloidal structures by the self-assembly of alkane-thiol-capped gold nanoparticles at liquid–liquid interfaces.     

Positronium decay and formation in paraffin wax from polarized and unpolarized positrons

Summary Ps formation and decay in heterogeneousn-alkane samples (paraffin waxes) have been studied both in the solid and in the liquid phase; then, in the solid phase, the positron's residual degree of polarization was measured at the instant of Ps formation. Differently from what is already known in homogeneousn-alkane samples, Ps shows, many degrees below the melting point, a mean lifetime longer than that typical of the liquid phase; furthermore, the mean lifetime's values pertaining to the transition between solid and liquid do not show a sharp variation across the melting temperature but gradually decrease over a range of temperatures of several degrees. Positronium decay in static magnetic fields indicates that o-Ps magnetic quenching in liquid phase is regular, and corresponds to a contact density value α=|ψ(0)|²/|ψ(0)|_vac ²=0.79±0.07; instead, in the solid phase, o-Ps magnetic quenching shows anomalous behaviour for fields weaker than 7kG. Positrons' residual polarization measurements do not reveal the presence of depolarization effects during the whole slowing-down process until Ps is formed.     

不同粒径金纳米微粒对荧光素钠的猝灭效应研究

采用柠檬酸盐合成法制备了不同粒径的金纳米微粒,用吸收光谱和透射电镜对金纳米微粒进行了表征。研究了不同粒径金纳米微粒与荧光素钠分子的相互作用。发现金纳米微粒对荧光素钠具有荧光猝灭效应, 并且其荧光猝灭程度与金纳米微粒的粒径大小有关。随着金纳米微粒粒径的减小,荧光猝灭程度增大。探讨了金纳米微粒对荧光素钠荧光猝灭的机理,表明该荧光猝灭为动态猝灭。     

L-半胱氨酸修饰的金纳米粒子与牛血清白蛋白相互作用的荧光光谱研究

采用荧光猝灭光谱和同步荧光光谱研究了L-半胱氨酸修饰的金纳米粒子(Cys-GNPs)与牛血清白蛋白(BSA)间的相互作用。根据荧光猝灭相关方程计算了Cys-GNPs与BSA相互作用的结合常数和结合位点数,探讨了其荧光猝灭机制为静态猝灭,并且根据热力学参数确定了二者间的作用力类型,推断出Cys-GNPs和BSA间主要靠疏水作用力结合。同步荧光光谱表明,二者的相互作用没有导致牛血清白蛋白的构象及色氨酸残基的微环境发生明显变化。     

不同表面结构的金纳米粒子荧光性质.

"研究了具有不同表面结构的金纳米粒子：裸金纳米粒子、三苯基膦修饰的金纳米粒子、巯基丙酸表面取代的金纳米粒子的荧光性质,及其对CdSe纳米粒子的荧光猝灭作用．发现不同的金纳米粒子荧光信号受粒子表面一价金离子与配体分子之间相互作用的影响,其荧光强度对其表面分子具有强烈的敏感性;具有不同表面结构的金纳米粒子对CdSe纳米粒子的荧光猝灭作用不同,与其吸收光谱和CdSe纳米粒子发射光谱的重叠程度相关."     

Gold nanoparticles having dipicolinic acid imprinted nanoshell for Bacillus cereus spores recognition

Taking into account the recognition element for sensors linked to molecular imprinted polymers (MIPs), a proliferation of interest has been witnessed by those who are interested in this subject. Indeed, MIP nanoparticles are theme which recently has come to light in the literature. In this study, we have proposed a novel thiol ligand-capping method with polymerizable methacryloylamidocysteine (MAC) attached to gold nanoparticles, reminiscent of a self-assembled monolayer. Furthermore, a surface shell by synthetic host polymers based on molecular imprinting method for recognition has been reconstructed. In this method, methacryloyl iminodiacetic acid-chrome (MAIDA–Cr(III)) has been used as a new metal-chelating monomer via metal coordination–chelation interactions and dipicolinic acid (DPA) which is the main participant of Bacillus cereus spores has been used as a template. Nanoshell sensors with templates produce a cavity that is selective for DPA. The DPA can simultaneously chelate to Cr(III) metal ion and fit into the shape-selective cavity. Thus, the interaction between Cr(III) ion and free coordination spheres has an effect on the binding ability of the gold nanoparticles nanosensor. The interactions between DPA and MIP particles were studied observing fluorescence measurements. DPA addition caused significant decreases in fluorescence intensity because they induced photoluminescence emission from Au nanoparticles through the specific binding to the recognition sites of the crosslinked nanoshell polymer matrix. The binding affinity of the DPA imprinted nanoparticles has been explored by using the Langmuir and Scatchard methods and the analysis of the quenching results has been performed in terms of the Stern–Volmer equation.     

Rydberg states in the condensed phase studied by fluorescence depletion spectroscopy

Higher Rydberg states of NO trapped in rare gas matrices have been studied by inducing Rydberg-Rydberg transitions from the lowest Rydberg state and detecting its fluorescence depletion. This technique unravels Rydberg states, which cannot be accessed by ground state absorption. However, no clear cut Rydberg series show up. The data show a compression of the n-(n + 1) splittings between Rydberg states, as well as of the splittings. The results are rationalised in terms of the quantum defect model and the lack of extended Rydberg series is due to the compression of high-n Rydberg states in a tiny energy region below the ionisation potential. Finally, fluorescence depletion data of NO trapped in amorphous sites (the so-called red sites) of solid Ar can be interpreted in terms of the gas phase NO-Ar van der Waals data. A general discussion on the fate of Rydberg states in van der Waals complexes, in liquids, and in solids is presented in an attempt to relate the data in these different media. Received 28 July 1999 and Received in final form 8 November 1999     

Fluorescence quenching using plasmonic gold nanoparticles

This communication describes the study of fluorescence quenching in a new fluorescent laser dye ADS680HO is attached to gold nanoparticles of size 4-12 nm. Photo physical properties confirms that it is due to size, shape, coupling between nanoparticles with laser dye ADS680HO, and energy transfer between dye and nanoparticles. Fluorescence quenching leads to advancement in biomolecular labeling and fluorescence patterning.     

Quenched Emission of Fluorescence by Ligand Functionalized Gold Nanoparticles

A fluorescence-based detection scheme that uses ligand functionalized gold nanoparticles is proposed. The transduction scheme is based on the strong quenching of the fluorescence emission exerted by metallic surfaces on fluorophores positioned in their immediate vicinity (< 5 nm). Binding of fluorophore-labeled anti-biotin to biotinylated gold nanoparticles resulted in decreased fluorescence emission intensity. Subsequent competitive dissociation of labeled anti-biotin with D-biotin resulted in increased fluorescence emission intensity. These interactions occurred by means of specific molecular recognition because when the binding sites of anti-biotin were saturated with D-biotin prior to interaction with the gold nanoparticles; changes in the fluorescence emission intensity were not observed.     

Determining the mechanism of interaction between molecules of porphyrin and fullerene and gold nanoparticles,based on luminescence spectroscopy data

Gold nanoparticles are synthesized via laser ablation of a gold target in a liquid. The constants that characterize the efficiency of porphyrins and fullerenes bonding with gold nanoparticles are determined using a modified Stern–Volmer equation. The results from luminescence quenching measurements are presented. It is found that the efficiency of bonding depends on whether there are functional groups in the molecular fragments. Porphyrin containing para-bromphenyl groups at the meso positions of the porphyrin core has the highest affinity for the surfaces of gold nanoparticles.     

Rhodamine B-Coated Gold Nanoparticles as Effective “Turn-on” Fluorescent Sensors for Detection of Zinc II Ions in Water

We designed a fluorescence resonance energy transfer system consisting of fluorophore Rhodamine B and gold nanoparticles for sensing of zinc ions in aqueous solution. The electrostatic attraction between positively charged N-atoms in Rhodamine molecules and negatively charged citrate corona of gold nanoparticles led to substantial fluorescence quenching. However, the quenching is switched off in the presence of zinc ions and therefore the system can be used as an effective “turn-on” fluorescence sensor. UV-Vis absorption, fluorescence spectroscopy, and transmission electron microscopy were used for sensor evaluation. The approach of “turn-on” fluorescence has real potential for sensing metallic ions in water.     

Dynamic fluorescence quenching and the highest excited states of molecules

The dynamic fluorescence quenching in organic molecules, or quenching of the second kind according to Vavilov’s classification, is an efficient method of investigating excited states in solutions and is widely used in various fields. The effect of quenching on the intensity of the fluorescence from the first and higher singlet states of organic molecules is studied. The results may serve as a basis for determining the nature of the short-wavelength luminescence and can be used to distinguish the S _n fluorescence from the comparably intense luminescence of impurities, which is a very important problem when investigating such emissions. A method for obtaining dynamic quenching by specially chosen quenchers is proposed. The method is based on an experimentally found strong increase in the constants of bimolecular collisions of luminophore and quencher molecules when the luminophore is excited through the highest singlet states.     

Desaktivierung angeregter He-Atome (31P1, 31S0, 41S0, 51S0, 61S0) durch Rb-Atome

Total collisional depopulation rates for He(n¹S₀) (3 ≦ n ≦ 6), He(3¹P¹) in thermal collisions with Rb have been measured using the transient-decay method. The measured quenching cross-sections increase from 4.3 · 10^?10 cm² to 24 · 10^?14 cm² with increasing n from 3 to 6. Comparison of experimental results with theoretical estimations shows that the main processes of quenching depend on n. He-atoms in the n = 3, 4 states are mainly quenched by Penning ionisation and higher excited states by collisional l-mixing.     

Effect of gold nanoparticle size on acoustic cavitation using chemical dosimetry method

When a liquid is irradiated with high intensities of ultrasound irradiation, acoustic cavitation occurs. Acoustic cavitation generates free radicals from the breakdown of water and other molecules. Cavitation can be fatal to cells and is utilized to destroy cancer tumors. The existence of particles in liquid provides nucleation sites for cavitation bubbles and leads to decrease the ultrasonic intensity threshold needed for cavitation onset. In the present investigation, the effect of gold nanoparticles with appropriate amount and size on the acoustic cavitation activity has been shown by determining hydroxyl radicals in terephthalic acid solutions containing 15, 20, 28 and 35 nm gold nanoparticles sizes by using 1 MHz low level ultrasound. The effect of sonication intensity in hydroxyl radical production was considered.The recorded fluorescence signal in terephthalic acid solutions containing gold nanoparticles was considerably higher than the terephthalic acid solutions without gold nanoparticles at different intensities of ultrasound irradiation. Also, the results showed that the recorded fluorescence signal intensity in terephthalic acid solution containing finer size of gold nanoparticles was lower than the terephthalic acid solutions containing larger size of gold nanoparticles. Acoustic cavitation in the presence of gold nanoparticles can be used as a way for improving therapeutic effects on the tumors.     

Quenching of metastable antiprotonic helium atoms in collisions with deuterium molecules

Quenching of metastable antiprotonic helium atoms in collisions with deuterium molecules has been studied using laser spectroscopy at CERN's new Antiproton Decelerator facility. The quenching cross-sections of the states (n, l )= (39, 36), (39, 37), and (39, 38) were determined from the decay rates of the states which were observed using the “deuterium-assisted inverse resonance” (DAIR) method. The results revealed a similar (n, l )-dependence of the quenching cross-sections as in the case of hydrogen but the values were smaller by a factor of ∼1.5. Received 6 July 2001     

Spectral Criterion of the State of Thermodynamic Equilibrium of Molecular Excimers

Using the excimer fluorescence of crystalline pyrene and its liquid solution in n-hexane as an example, we show that the difference between the excimer fluorescence spectra of the systems in a stable and metastable equilibrium states can be characterized by a single parameter calculated from the normalized spectral distribution of intensity in the excimer fluorescence band.     

Spectral Investigations on N-(2-Methylthiophenyl)-2-Hydroxy-1-Naphthaldimine by Silver Nanoparticles: Quenching

The photo—physical properties of N-(2-methylthiophenyl)-2-hydroxy-1-naphthaldimine (NMTHN) on silver nano particles have been investigated using optical absorption and fluorescence emission techniques. Silver nanoparticles of different sizes have been prepared by two different methods. The increases in size of the silver nanoparticles cause a decrease in the quenching of fluorescence of NMTHN. Stern–Volmer quenching constants and the association constants have also been calculated.     

Determination of the Constants of Binding of Acridine Dyes with Micelles of Sodium Dodecyl Sulfate Using the Quenching of Delayed Fluorescence by Heavy Atoms

The constants of binding dye molecules with the micelles of sodium dodecyl sulfate are determined using quenching of delayed fluorescence of acridine dyes by sodium iodide in aqueous–micellar solutions. Kinetic equations have been composed that describe the processes of deactivation of the excited states of dyes. By solving these equations at the concentration of the quencher sodium iodide corresponding to the minimum lifetime of triplet states and at the concentration of micelles corresponding to the least value of the delayed fluorescence quenching rate constants, we obtained the constants of binding dyes with micelles equal to 1.3·10⁷, 2.9·10⁷, and 3.1·10⁷ M^–1 for trypaflavine, acridine orange, and acridine yellow, respectively. We calculated the rate constants of quenching of the triplet states of the molecules of dyes by iodide ions (I ^–) that decreased in transition from trypaflavine to acridine orange and acridine yellow.     

Single-molecule measurements of gold-quenched quantum dots

We report the study of the quenching of quantum dots (CdSe) by gold nanoparticles at the single-molecule level. Double-stranded DNA is used as a rigid spacer to tune the distance between the two nanoparticles. The width of the fluorescent intensity distribution, monitored at different interparticle distances, reflects both the nanoparticle heterogeneity and the fluorescence intermittency of the quantum dot. The fluorescence distribution emitted by single CdSe nanocrystals can easily be distinguished from the fluorescence of partially quenched CdSe. Our results show that the distance-dependence quenching is compatible with a F?rster-type process.