Plasma desorption mass spectroscopy of thiol-passivated gold nanoparticles

Plasma desorption mass spectrometry has been applied to characterization of dodecanthiol-passivated gold nanoparticles. An overview of the experimental set-up and mass analyses for the nanoparticles prepared in different conditions are shown. Mass distributions were found to shift to higher mass regions with increasing reaction temperature and reaction period. The results are consistent with those of transmission electron microscopy observations, UV-visible absorption spectra and also with a reported laser desorption mass spectrometry.     

Cavity ring-down spectroscopy of metallic gold nanoparticles

The optical properties of supported gold nanoparticles with sizes of 1.3 nm, 1.6 nm, 2.5 nm, and 2.9 nm have been studies by using cavity ring-down spectroscopy in the photon energy range between 1.8 eV and 3.0 eV. The obtained results show the possibility to obtain optical information of nanoassembled materials with high sensitivity. The experimental findings are compared to calculations using Mie-Drude theory. Whereas the broadening of the surface plasmon resonance with decreasing size is well described by this model, the observed blue-shift of the surface plasmon resonance contradicts the predictions of the Mie-Drude theory. The latter effect can be explained by the presence of a skin region with decreased polarizability typical for coinage metal particles. Furthermore, it is found that the supported gold nanoparticles are robust under ambient conditions, an important issue when using these materials for optical applications.     

Molecular histology analysis by matrix-assisted laser desorption/ionization imaging mass spectrometry using gold nanoparticles as matrix

Gold nanoparticles (AuNPs) were applied and optimized as matrix for matrix-assisted laser desorption/ionization mass spectrometry analysis of animal tissues, and enabled histological analysis of animal tissues at molecular level by imaging mass spectrometry (IMS). AuNPs were coated on animal tissue in a solvent-free manner via argon ion sputtering. Metabolites, including neurotransmitters, fatty acids and nucleobases, were directly detected from mouse brain tissue. Based on region-specific chemical profiles, fine histological features of mouse brain tissue and heterogeneous regions of tumor tissue were both revealed.     

Near-field spectroscopy of surface plasmons in flat gold nanoparticles

We use near-field interference spectroscopy with a broadband femtosecond, white-light probe to study local surface plasmon resonances in flat gold nanoparticles (FGNPs). Depending on nanoparticle dimensions, local near-field extinction spectra exhibit none, one, or two resonances in the range of visible wavelengths (1.6-2.6 eV). The measured spectra can be accurately described in terms of interference between the field emitted by the probe aperture and the field reradiated by driven FGNP surface plasmon oscillations. The measured resonances are in good agreement with those predicted by calculations using discrete dipole approximation. We observe that the amplitudes of these resonances are dependent upon the spatial position of the near-field probe, which indicates the possibility of spatially selective excitation of specific plasmon modes.     

Raman spectroscopy of gold nanoparticles in polycrystalline LiF film

Results of the Raman spectroscopy analysis of a new composite material based on a thin polycrystalline LiF film containing gold nanoparticles are presented. The formation of spherical gold nanoparticles in the film has been confirmed by the X-ray structural analysis and observation of the optical plasmon resonance absorption spectrum with a maximum at 534 nm. The obtained composite layers have been subjected to annealing by ruby laser (λ = 694 nm) in the spectral region on a descending long-wavelength wing of the plasmon absorption band of gold nanoparticles. Raman spectroscopy has been applied for the first time to the investigation of the modification of the shape of gold nanoparticles in LiF during laser annealing. The experimental Raman spectra are compared with calculated modes of in-phase bending vibrations generated in gold nanoparticles.     

Diffusion-controlled synthesis of gold nanoparticles: nano-liposomes as mass transfer barrier

Lipid vesicles and other types of amphiphilic materials are of great interest in the size-controlled synthesis of metal nanoparticles. In this study, we prepared nano-sized liposomes encapsulating tetrachloroauric acid for the facile synthesis of gold nanoparticles with controlled size over a range of 2–5 nm at room temperature. The semi-permeable character of the lipid membrane to the varying concentrations of reducing agent—sodium borohydride-regulated the particle formation kinetics. Diffusion of the reducing agent through the liposomal membrane in a controlled manner resulted in ultrasmall nanoparticles of a narrow size distribution with less aggregation as compared to the solution-based preparation method.     

Detection and spectroscopy of gold nanoparticles using supercontinuum white light confocal microscopy

We combine confocal microscopy using supercontinuum laser illumination and an interferometric detection technique to identify single nanoparticles of diameter below 10 nm. Spectral analysis of the signal allows us to record the plasmon resonance of a single nanoparticle. Our results hold great promise for fundamental studies of the optical properties of single metal clusters and for their use in biophysical applications.     

Silver nanoparticles as matrix for laser desorption/ionization mass spectrometry of peptides

Silver nanoparticle synthesized from chemical reduction has been successfully utilized as a matrix in matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) of peptides. Acting as a substrate to adsorb analytes, as well as a transmission medium for UV laser, silver nanoparticle was found to assist in the desorption/ionization of peptides with little or no induced fragmentation. The size of the nanoparticle was typically in the range of 160 ± 20 nm. One of the key advantages of silver nanoparticle for peptides analysis is its simple step for on-probe sample preparation. In addition, it also minimizes the interferences of sodium dodecyl sulfate (SDS) surfactant background signal, resulting in cleaner mass spectra and more sensitive signal, when compared to α–cyano-4-hydroxycinnamic acid (CCA) matrix.     

Experimental study using optoacoustic spectroscopy (OAS) on spherical gold nanoparticles

In this paper a spectroscopic characterisation method based on the optoacoustic technique has been used to investigate the optical properties of two separate spherical gold nanoparticle (SGNP) solutions where an absorption peak located at 520 nm has been observed. This analysis has been carried out over the visible wavelength range from 410 to 650 nm using a Q-switched Nd:YAG pumped optical parametric oscillator (OPO). To verify the reliability of optoacoustic spectroscopy (OAS), the results obtained have been compared to those from more standard and limited spectrophotometer and reference collimated optical transmission schemes, where good agreement is shown. The experimental procedure presented here demonstrates the potential of this technique for integration along with optoacoustic imaging methods to identify physiological information for non-destructive in-vivo applications.     

Brownian diffusion of gold nanoparticles in an optical trap studied by fluorescence correlation spectroscopy

The effect of thermal-induced Brownian motion on gold nanoparticles (Au NPs) in optical traps is studied by fluorescence correlation spectroscopy (FCS) method. The Brownian motion and optical trapping potential are investigated by the decay time of the FCS curve and the laser power. It is shown that that the probability of finding a gold nanoparticle in the trap depends on the ratio of the optical energy of the particle to its thermal energy. A power threshold is observed by the decay time as a function of laser power. The experimental studies show that the temperature rise does not seriously affect the average number of particles in the focal spot, but the average residence time is more sensitively affected by the temperature.     

Raman spectroscopy of combinatory anticancer drug release from gold nanoparticles inside a single leukemia cell

Combinatory anticancer drug release from gold nanoparticles (AuNPs) in K562 human myeloid leukemia cells was performed using Raman spectroscopy. We fabricated the anticancer drug of imatinib as a BCR‐ABL tyrosine kinase inhibitor on AuNP surfaces along with a transferrin (Tf)‐targeting moiety to treat the leukemia cells. DNA topoisomerase I inhibitor topotecan was also assembled to monitor its fluorescence onto AuNPs. The linker group of 4‐carboxylic benzoic acid was used to conjugate to targeting the Tf protein. Our Raman data indicated that the drug molecules were not detached in the cell culture media but released after treatment with glutathione (2 mM). Intracellular distribution and release of the anticancer drug–AuNP conjugates in K562 cells were examined by both fluorescence microscopy and dark‐field microscopy with surface‐enhanced Raman scattering. Copyright © 2013 John Wiley & Sons, Ltd.     

Shape evolution of gold nanoparticles

The tetraoctylammonium bromide-stabilized gold nanoparticles have been successfully fabricated. The shape evolution of these nanoparticles under different annealing temperatures has been investigated using high-resolution transmission electron microscopy. After an annealing at 100 °C for 30 min, the average diameters of the gold nanoparticles change a little. However, the shapes of gold nanoparticles change drastically, and facets appear in most nanoparticles. After an annealing at 200 °C for 30 min, not only the size but also the shape changes a lot. After an annealing at 300 °C for 30 min, two or more gold nanoparticles coalesce into bigger ones. In addition, because of the presence of Cu grid during the annealing, some gold particles become the nucleation sites of Cu₂O nanocubes, which possess a microstructure of gold-particle core/Cu₂O shell. These Au/Cu₂O heterostructure nanocubes can only be formed at a relatively high temperature (≥300 °C). The results can provide some insights on controlling the shapes of gold nanoparticles.     

Ripening of nanowire-supported gold nanoparticles

Gold nanoparticles have applications ranging from catalysts for low temperature oxidation of CO to solar energy capture in the infrared. For all these applications, particle size and shape are critical. In this study, nanoparticle gold formed on GaN nanowires by plasma-enhanced chemical vapor deposition was annealed at temperatures ranging from 150 to 270 °C for 24 h. Particle size was measured before and after annealing using a field emission scanning electron microscope. Ripening of the gold particles was observed even at the lowest annealing temperatures of the study. The particle growth kinetics showed an Arrhenius relationship with activation energy of 27.38 kJ/mol. This value suggests that ripening occurs by particle migration and coalescence rather than adatom diffusion.     

Photothermal desorption spectroscopy with IR lasers

Medium-energy ion scattering on the relaxed GaAs(110) surface measures a value of 29° ± 3° for the rotation of the top Ga-As atomic chains. Measurements in a scattering geometry especially sensitive to the surface-parallel displacements concomitant with such a bond rotation, show that bond-lengths in the relaxed surface remain unchanged.     

Surface-enhanced Raman spectroscopy coupled with gold nanoparticles for rapid detection of amoxicillin residues in duck meat

Antibiotic residues in meat pose serious threats to human beings and animals, and are one of the main food safety concerns all around the world. A novel method based upon surface-enhanced Raman spectroscopy (SERS) coupled with gold nanoparticles was developed in this study for rapid detection of amoxicillin residues in duck meat, one widely used in duck farming. Three different particle sizes of gold nanoparticles were synthesized using 0.3, 0.7, and 1.1?mL 1% trisodium citrate, while 0.7?mL was found to be the optimal volume as Raman enhancement substrate for the detection of amoxicillin residues in duck meat. The amounts of gold nanoparticles (0.5?mL), duck meat extract containing amoxicillin (50?μL), and sodium chloride solution (100?μL), as well as adsorption time (5?min) were optimized by single factor experiments. A calibration curve with the determination coefficient of 0.9661 was established for quantitative analysis of unknown amoxicillin samples. The average recoveries of amoxicillin residues in duck meat extract were 96–139%. This study provided a rapid and simple approach to analyze amoxicillin residues in duck meat in excess of 0.2?mg?L^?1 using SERS coupled with gold nanoparticles, which has the potential for wide applications in the detection of the antibiotic residues in meat.     

基于i-motifDNA构型变化和纳米金紫外-可见吸收光谱的pH测定研究

利用纳米金对DNA构型的区分效应设计了一种快速灵敏可视化的pH计。对i-motif DNA-纳米金体系的紫外可见吸收光谱变化进行了系统研究,考察了盐浓度、i-motif DNA浓度、四重体形成时间以及DNA序列对pH响应的影响。在既定条件下,纳米金的紫外-可见吸收光谱在pH 5.3～7.0范围内呈现规律性变化,在520nm处的吸光度逐渐增大,在700nm处的吸光度逐渐减小,纳米金的颜色逐渐由蓝紫色变化至红色。该pH计具有纳米金无需修饰、可视化、成本低、速度快等特点,有望用于某些pH值发生变化的生命过程的监测。     

Photochemical synthesis of polygonal gold nanoparticles

In this paper, we propose a method to generate gold nanoparticles capable of absorbing near infrared light (NIR) radiation through a photochemical reaction. This approach does not require the use of either surfactants or polymers, reducing the difficulties that may arise in further chemical modifications for the gold nanoparticles. The gold nanoparticles with either triangular or hexagonal shapes were generated using the photo-reduction method, mixing hydrogen tetrachloroaurate with sodium oxalate, a reducing agent, in aqueous solution under illumination of a mercury lamp (λ_max = 306 nm) for more than 10 min. The size of the gold nanoparticles varies from 25 to 200 nm, which mainly depends on the duration of light illumination and the concentration of sodium oxalate. Furthermore, we demonstrate that the presence of the gold nanoparticles in aqueous solutions can effectively elevate the temperature of the solutions under irradiation of NIR light (808 nm) within a few minutes. The gold nanoparticles can be potentially used as suitable photothermal agents for hyperthermia.     

Agglomeration behavior of lipid-capped gold nanoparticles

The current investigation deciphers aggregation pattern of gold nanoparticles (AuNPs) and lipid-treated AuNPs when subjected to aqueous sodium chloride solution with increasing ionic strengths (100–400 nM). AuNPs were synthesized using 0.29 mM chloroauric acid and by varying the concentrations of trisodium citrate (AuNP1 1.55 mM, AuNP2 3.1 mM) and silver nitrate (AuNP3 5.3 μM, AuNP4 10.6 μM) with characteristic LSPR peaks in the range of 525–533 nm. TEM analysis revealed AuNPs to be predominantly faceted nanocrystals with the average size of AuNP1 to be 35?±?5 nm, AuNP2 15?±?5 nm, AuNP3 30?±?5 nm, and AuNP4 30?±?5 nm and the zeta-average for AuNPs were calculated to be 31.23, 63.80, 26.08, and 28 nm respectively. Induced aggregation was observed within 10 s in all synthesized AuNPs while lipid-treated AuNP2 (AuNP2-L) was found to withstand ionic interferences at all concentration levels. However, lipid-treated AuNPs synthesized using silver nitrate and 1.55 mM trisodium citrate (AuNP3, AuNP4) showed much lower stability. The zeta potential values of lipid-treated AuNPs (AuNP1-L-1x/200, ??17.93?±?1.02 mV; AuNP2-L-1x/200, ??21.63?±?0.70; AuNP3-L-1x/200, ??14.54?±?0.90; AuNP3-L-1x/200 ??13.77?±?0.83) justified these observations. To summarize, AuNP1 and AuNP2 treated with lipid mixture 1 equals or above 1x/200 or 1x/1000 respectively showed strong resistance against ionic interferences (up to 400 mM NaCl). Use of lipid mixture 1 for obtaining highly stable AuNPs also provided functional arms of various lengths which can be used for covalent coupling.

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Graphical abstract Agglomeration behavior of gold nanoparticles before and after lipid capping

     

Chemical composition of surface-functionalized gold nanoparticles

The composition of surface-functionalized gold nanoparticles (diameter of the metallic core: 17–20 nm) was determined by elemental analysis (C, H, N, S, Au, Na) after preparation of a larger batch. Gold nanoparticles were prepared and functionalized with citrate according to the classical Turkevich method. The citrate-functionalized nanoparticles contained about 3.1 wt% of organic material (135 ng cm⁻² or 3.1 molecules nm⁻²). A partial exchange of citrate was accomplished by tris(sodium-m-sulfonato-phenyl)phosphine (TPPTS) which led to 2.1 wt% of citrate (90 ng cm⁻² or 2.1 molecules nm⁻²) and 1.4 wt% TPPTS (61 ng cm⁻² or 0.6 molecules nm⁻²). The citrate coating was quantitatively exchanged by poly(N-vinyl pyrrolidone) (PVP) after immersion in solutions with concentrations of 33, 66 and 128 mg L^-1, respectively, leading to contents of 4 to 6 wt% of PVP (171–271 ng cm⁻² or 9–15 PVP monomer units nm⁻²).     

芯帽纳米颗粒的光热性质

贵金属纳米结构中的光热效应在肿瘤光热治疗、光热成像、纳米药物等领域具有重要的应用价值.各向异性的芯帽纳米结构以其丰富的可调结构参数和对激发光偏振态敏感的特性,可灵活地在近红外波段获得理想的光学吸收性质,从而可以实现温度的高效调节.本文基于有限元方法研究了颗粒物纳米结构参数对其光热效果的作用规律,数值结果表明:通过对结构参数的微量改变(包括金壳厚度、芯壳比、芯径、金属表面覆盖率等)可实现温度的显著调整;在偏振态的旋转范围(30?—70?)内可快速地产生大温变光热的准线性调整.其不弱于纳米芯壳和纳米棒结构的光热性能可为纳米光热生医研究提供一种新的选择.