共查询到20条相似文献,搜索用时 523 毫秒
1.
Dipannita Parial Hirak K. Patra Piya Roychoudhury Anjan Kr. Dasgupta Ruma Pal 《Journal of applied phycology》2012,24(1):55-60
Intracellular bioconversion of auric ion (Au3+) to gold nanorod (Au0) by the cyanobacterium Nostoc ellipsosporum has been observed for the first time in laboratory condition. The nanorods were produced within the cell after exposing the
healthy growing filaments to 15 mg L−1 gold (III) solution (pH 4.5) for 48 h at 20°C. The gold nanoparticles were extracted with sodium citrate solution and were
subjected to UV–Visible spectroscopy. The characteristic surface-multiple plasmon bands at 560, 610, and 670 nm were observed.
The nature and size of the particles were determined by transmission electron microscopy (TEM), dynamic light scattering (DLS),
X-ray diffraction (XRD), and zeta potential studies. The nanorod size ranged from 137 to 209 nm in length and 33 to 69 nm
in diameter. DLS study revealed the average hydrodynamic size as 435 nm and XRD study indicated the reduction of Au3+ to Au0. Methods of extraction and preservation of gold nanorod particles have also been studied. 相似文献
2.
ChaoLing Du YuMeng You Tao Chen Yan Zhu HaiLong Hu DaNing Shi HongYu Chen ZeXiang Shen 《Plasmonics (Norwell, Mass.)》2011,6(4):761-766
We have investigated the polarization-dependent surface-enhanced Raman scattering (SERS) of an individual Ag nanowire (AgNW)
dimer, which contains two parallel closely packed AgNWs with very different lengths. Similar cos2
θ dependence of signal intensities with respect to the polarization angle θ of the incident laser was observed from the dimeric part and the parts of the body as well as the tip of the longer AgNW.
The dimeric part was demonstrated to exhibit the strongest SERS effect. The results agree well with our numerical simulations
of the electric field distributions using finite element method. The SERS enhancement mechanisms at different parts of the
dimer were also discussed which are different in origin. 相似文献
3.
Multilayer gold surface-enhanced Raman scattering (SERS) substrates, which consist of continuous gold films that are separated
by self-assembled monolayers (SAMs) and cast over 430-nm diameter silica nanospheres on a glass slide, have been evaluated
as a means of further enhancing the SERS signals produced from conventional metal film over nanostructure substrates. Evaluation
of the effect of various SAMs, with different terminal functional groups, on the SERS enhancement factor were measured and
compared to conventional single-layer gold film over nanostructure substrates, revealing relative enhancements as great as
22.4-fold in the case of 2-mercapto-ethanol spacer layers. In addition to evaluation of the effect of different terminal functionalities,
the effect of spacer length was also investigated, revealing that the shorter chain length alcohols provided the greatest
signals. Employing the optimal SERS multilayer geometry, SERS nanoimaging probes were fabricated and the SERS enhancement
factor and variability in enhancement factor were measured over the SERS active imaging area, providing absolute enhancements
similar to previous silver-based SERS nanoimaging probes (i.e., 1.2 × 108). Varying the size of the multilayer gold islands that were deposited on the tip of the SERS active nanoimaging probe, it
is possible to tune the optimal SERS excitation wavelength accurately and predictably over the range of approximately 450
to 600 nm, without coating the entire surface of the probe and significantly reducing the transmission and resulting signal-to-noise
ratio of the images obtained. 相似文献
4.
Subramanian Balamurugan Kathryn M. Mayer Seunghyun Lee Steven A. Soper Jason H. Hafner David A. Spivak 《Journal of molecular recognition : JMR》2013,26(9):402-407
A localized surface plasmon resonance (LSPR) sensor surface was fabricated by the deposition of gold nanorods on a glass substrate and subsequent immobilization of the DNA aptamer, which specifically bind to thrombin. This LSPR aptamer sensor showed a response of 6‐nm λmax shift for protein binding with the detection limit of at least 10 pM, indicating one of the highest sensitivities achieved for thrombin detection by optical extinction LSPR. We also tested the LSPR sensor fabricated using gold bipyramid, which showed higher refractive index sensitivity than the gold nanorods, but the overall response of gold bipyramid sensor appears to be 25% less than that of the gold nanorod substrate, despite the approximately twofold higher refractive index sensitivity. XPS analysis showed that this is due to the low surface density of aptamers on the gold bipyramid compared with gold nanorods. The low surface density of the aptamers on the gold bipyramid surface may be due to the effect of shape of the nanostructure on the kinetics of aptamer monolayer formation. The small size of aptamers relative to other bioreceptors is the key to achieving high sensitivity by biosensors on the basis of LSPR, demonstrated here for protein binding. The generality of aptamer sensors for protein detection using gold nanorod and gold nanobipyramid substrates is anticipated to have a large impact in the important development of sensors toward biomarkers, environmental toxins, and warfare agents. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
5.
Gerald Rosen 《Bulletin of mathematical biology》1974,36(5-6):589-593
Differential inequality methods are developed for establishing upper and lower bounds on the total particle numberN(t)=∫θ(x,t) d3
x associated with solutions to nonlinear reaction-diffusion equations of the form ∂θ/∂t=D∇2θ+fθ-gθ
n+1
, whereD(>0),n(>0),f andg are constant parameters. If finite in a neighborhood oft=0,N(t) is bounded below for allt≥0 by a certain derived function oft for equations withg≥0. An upper bound onN(t) is obtained for equations withn=1,f<0 andg<0. These results provide general preservation and extinction criteria for the total particle number. 相似文献
6.
The leaf lamina ofLavatera cretica L. exhibits a diaphototropic response that discriminates between two opposite, constant vectorial excitations by white light
beams whose fluence rates differ by as little as 10% (50 versus 45 μmol·m−2·S−1). The relationship between the response (angular velocity of laminar reorientation) and the fluence-rate ratio is linear.
The lamina similarly discriminates between two such excitations by polarized light, one with the electrical vector transverse
to the plane of the two beams (θ) and the opposite one with the vector parallel to that plane (⪙). When two such beams were
of equal fluence rate, the lamina reoriented towards the ⪙ beam. When the fluence rate of the θ beam was maintained at 50
μmol·m−2·s−1 and that of the ⪙ beam was reduced, the response to the latter (angular velocity of laminar reorientation) was reduced progressively.
Further reduction in the fluence rate of the ⪙ polarized beam eventually resulted in reorientation in the opposite direction
(towards the θ beam) and the response to the latter increased progressively with the reduction in fluence rate. The equilibrium
was at a ⪙/θ ratio of 0.62. Measurements of reflectance of oblique beams of ⪙ and θ polarized light from the upper laminar
surface, and of transmittance of such light ghrough the lamina, eliminated the possibility that optical dichroism of the lamina
contributed significantly to these results. The implications of this action dichroism to the postulated mechanism of perception
of vectorial excitation by these leaves is discussed.
Dedicated to the 60thbirth day of Professor Hans Mohr 相似文献
7.
Takuro Niidome Akira Ohga Yasuyuki Akiyama Kazuto Watanabe Yasuro Niidome Takeshi Mori Yoshiki Katayama 《Bioorganic & medicinal chemistry》2010,18(12):4453-4458
Gold nanorods exhibit strong absorbance of light in the near infrared region, which penetrates deeply into tissues. Since the absorbed light energy is converted into heat, gold nanorods are expected to act as a contrast agent for in vivo bioimaging and as a thermal converter for photothermal therapy. To construct a gold nanorod targeted delivery system for tumor a peptide substrate for urokinase-type plasminogen activator (uPA), expressed specifically on malignant tumors, was inserted between the PEG chain and the surface of the gold nanorods. In other words, we constructed PEG–peptide-modified gold nanorods. After mixing the gold nanorods with uPA, the PEG chain was released from the surface of the gold and subsequently nanorod aggregation took place. The formation of the aggregation was monitored as a decrease in light absorption at 900 nm. Tumor homogenate induced a significant decrease in this absorption. Larger amount of the PEG–peptide-modified gold nanorods bound to cells expressing uPA in vitro compared with control gold nanorods, which had scrambled sequence of the peptide. The PEG–peptide-modified gold nanorods showed higher accumulation in tumor than the control after they were injected intravenously into tumor-bearing mice, however, the density of the peptide on the surface of the gold nanorods was a key factor of their biodistributions. This targeted delivery system, which responds to uPA activity, is expected to be a powerful tool for tumor bioimaging and photothermal tumor therapy. 相似文献
8.
Nocturnal increases in water potential (ψ) and water content (θ) in the upper soil profile are often attributed to root water efflux, a process termed hydraulic redistribution
(HR). However, unsaturated liquid or vapor flux of water between soil layers independent of roots also contributes to the
daily recovery in θ (Δθ), confounding efforts to determine the actual magnitude of HR. We estimated liquid (J
l) and vapor (J
v) soil water fluxes and their impacts on quantifying HR in a seasonally dry ponderosa pine (Pinus ponderosa) forest by applying existing datasets of ψ, θ and temperature (T) to soil water transport equations. As soil drying progressed, unsaturated hydraulic conductivity declined rapidly such that
J
l was irrelevant (<2E−05 mm h−1 at 0–60 cm depths) to total water flux by early August. Vapor flux was estimated to be the highest in upper soil (0–15 cm),
driven by large T fluctuations, and confounded the role of HR, if any, in nocturnal θ dynamics. Within the 15–35 cm layer, J
v contributed up to 40% of hourly increases in nocturnal soil moisture. While both HR and net soil water flux between adjacent
layers contribute to θ in the 15–65 cm soil layer, HR was the dominant process and accounted for at least 80% of the daily
recovery in θ. The absolute magnitude of HR is not easily quantified, yet total diurnal fluctuations in upper soil water content
can be quantified and modeled, and remain highly applicable for establishing the magnitude and temporal dynamics of total
ecosystem water flux. 相似文献
9.
The transverse mode electron oscillations contribute to most of the surface-enhanced Raman scattering (SERS) intensity from
the nanorod array substrates. To enhance the transverse mode electron oscillation and improve the SERS enhancements, the local
electric field distribution of the orthogonal-nanorod structures, composed of two parallel horizontal nanorods in between
two parallel vertical nanorods, has been studied. The local electric fields of the longitudinal mode along the horizontal
nanorods act as the excitation for the transverse mode electron oscillations in vertical nanorods, leading to the cascade
enhancements of the electric fields around the vertical nanorods. In addition, the plasmon peaks of the longitudinal modes
can be tuned by changing the lengths and the widths of the horizontal nanorods and the separations between horizontal and
vertical nanorods. These results would be much helpful to engineer SERS substrates to obtain larger SERS enhancements. 相似文献
10.
Rapid detection of food- and waterborne bacteria using surface-enhanced Raman spectroscopy coupled with silver nanosubstrates 总被引:1,自引:0,他引:1
Development of rapid and sensitive methods to detect pathogens is important to food and water safety. This study aimed to
detect and discriminate important food- and waterborne bacteria (i.e., Escherichia coli O157:H7, Staphylococcus epidermidis, Listeria monocytogenes, and Enterococcus faecelis) by surface-enhanced Raman spectroscopy (SERS) coupled with intracellular nanosilver as SERS substrates. An in vivo molecular
probing using intracellular nanosilver for the preparation of bacterial samples was established and assessed. Satisfactory
SERS performance and characteristic SERS spectra were obtained from different bacterial samples. Distinctive differences were
observed in SERS spectral data, specifically in the Raman shift region of 500–1,800 cm−1, and between bacterial samples at the species and strain levels. The detection limit of SERS coupled with in vivo molecular
probing using silver nanosubstrates could reach the level of single cells. Experiments with a mixture of E. coli O157:H7 and S. epidermidis for SERS measurement demonstrate that SERS could be used for classification of mixed bacterial samples. Transmission electron
microscopy was used to characterize changes of morphology and cellular composition of bacterial cells after treatment of intracellular
nanosilver. The results indicate that SERS coupled with intracellular silver nanosubstrates is a promising method for detection
and characterization of food- and waterborne pathogenic and non-pathogenic bacterial samples. 相似文献
11.
By the absorption spectroscopy method, optical properties of gold nanorods (10 × 38 nm) and their interaction with globular protein bovine hemoglobin and bovine serum albumin were investigated. Nanorod behavior was studied in water solution and in solution of 97 mM NaCl under ultrasound action during 90 min and results were then compared. In water solutions, nanorod coagulation (aggregation) was observed with reduced optical density of the longitudinal plasmon band widening at λ > 800 nm. In NaCl solution, absorption spectra evolution had a complex character and was in some degree analogous to the result that was obtained for two-dimensional grids of gold nanoparticles when changing the distance between them. By interacting with serum albumin, stabilization of colloid solution and dissociation of nanorod aggregates were observed. 相似文献
12.
T. Kakitani 《European biophysics journal : EBJ》1979,5(4):293-312
Using the twisted conformations of the chromophores for visual pigments and intermediates which were theoretically determined
in the previous paper, energy surfaces of the pigment at −190‡ C were obtained as functions of the torsional anglesθ
9–10 andθ
11–12 or of the torsional anglesθ
9–10 andθ
13–14. In these calculations, the existence of specific reaction paths between rhodopsin (R) and bathorhodopsin (B), between isorhodopsin
I (I) and bathorhodopsin, and between isorhodopsin II (I′) and bathorhodopsin were assumed. It was shown that the total energy
surfaces of the excited states had minimaC
1 atθ
9–10 ∼ −10‡ andθ
11–12 ∼ −80‡,C
2 atθ
9–10 ∼ −85‡ andθ
11–12 ∼ −5‡, andC
3 atθ
9–10 ∼ 0‡ andθ
13–14 ∼ −90‡. These minima are considered to correspond to the thermally barrierless common states as denoted by Rosenfeld et al.
Using the total energy surfaces in the ground and excited states, the molecular mechanism of the photoisomerization reaction
was suggested. Quantum yields for the photoconversions among R, I, I′ and B were related to the rates of vibrational relaxations,
radiationless transitions and thermal excitations. Some discussion was made of the temperature effect on the quantum yield.
Similar calculations of the energy surfaces were also made at other temperatures where lumirhodopsin or metarhodopsin I is
stable. Relative energy levels of the pigments and the intermediates were discussed. 相似文献
13.
Nordin Félidj Guillaume Laurent Johan Grand Jean Aubard Georges Lévi Andreas Hohenau Franz R. Aussenegg Joachim R. Krenn 《Plasmonics (Norwell, Mass.)》2006,1(1):35-39
The surface plasmon fields of gold nanorods with a diameter of 100 nm and lengths of 1–5 m are imaged by using far-field Raman scattering of methylene blue adsorbed on the rods. When optically exciting the nanorods under total internal reflection with wave vector and electric field vector orientations along the rod axis, the plasmon field intensity along this axis is observed to be periodically modulated. This modulation is attributable to a beating of the exciting light wave and the nanorod plasmon mode. The plasmon wavelength deduced from the beat frequency is 379 nm, which is considerably smaller than the exciting laser wavelength of 647 nm. In general, Raman imaging is shown to be a powerful technique to probe local plasmon fields using far-field spectroscopy. 相似文献
14.
Tahereh Makiabadi Audrey Bouvrée Victor Le Nader Hélène Terrisse Guy Louarn 《Plasmonics (Norwell, Mass.)》2010,5(1):21-29
Generally, the immobilization of two-dimensional nanoparticles in immersion procedures is time-consuming (over 24 h). In this
paper, we report a very effective and simple method to fabricate two-dimensional gold nanoparticle patterns over large areas
with high regularity for surface-enhanced Raman scattering (SERS). We achieved a highly sensitive SERS colloid surface by
optimizing temperature and immersion time. The surfaces were characterized by X-ray photoelectron spectroscopy, UV–Vis, atomic
force microscopy, and scanning electron microscopy. The SERS activity of surfaces was compared by using two techniques: “dip”
and “dip and dry” in an aqueous solution of 10−6 M crystal violet. The influence of the morphology of the surface was investigated with both the dip and dip and dry techniques. 相似文献
15.
Numerical simulations of surface plasmon resonance system for monitoring DNA hybridization and detecting protein-lipid film interactions 总被引:1,自引:0,他引:1
This paper presents a simple method to extract information about thin organic films from surface plasmon resonance (SPR)
spectra. From numerical simulations it was found that a shift (Δθ
SPR) of an absorption peak in the SPR spectrum was directly proportional to the product of the thin organic film thickness and
the refractive index difference between the thin organic film and a buffer soaking the sample. It was also found that Δθ
SPR was not sensitive to the thin organic film support of a gold film and a glass cover slip. Relationships between Δθ
SPR and distributions of macromolecule structures, in the thin organic films were theoretically established. Formulae were derived
for a homemade SPR system to calculate length, transverse area, density and surface concentration of macromolecules in the
thin organic film. The validity of these treatments was checked by precisely measuring the size of a single distearoylphosphatidylcholine
molecule on a gold-supported phospholipid film; by quantitatively monitoring hybridization of synthesized oligonucleotides
strands based on a biotin/avidin system; and by quantitatively detecting the steric hindrance of rabbit C-reactive protein
specifically bound to phospholipid monolayers composed of synthesized lipids.
Received: 4 May 1998 / Revised version: 27 July 1998 / Accepted: 27 August 1998 相似文献
16.
Biological regulatory systems can be described in terms of non-linear differential equations or in logical terms (using an
“infinitely non-linear” approximation). Until recently, only part of the steady states of a system could be identified on
logical grounds. The reason was that steady states frequently have one or more variable located on a threshold (see below);
those steady states were not detected because so far no logical status was assigned to threshold values. This is why we introduced
logical scales with values 0,1θ, 12θ, 2, ..., in which1θ,2θ, ... are the logical values assigned to the successive thresholds of the scale. We thus have, in addition to the regular
logical states,singular states in which one or more variables is located on a threshold. This permits identifyingall the steady states on logical grounds. It was noticed that each feedback loop (or reunion of disjointed loops) can be characterized
by a logical state located at the thresholds at which the variables of the loop operate. This led to the concept ofloop-characteristic state, which, as we will see, enormously simplifies the analysis.The core of this paper is a formal demonstration that among the singular states of a system, only loop-characteristic states
can be steady. Reciprocally, given a loop-characteristic state, there are parameter values for which this state is steady; in this case,
the loop is effective (i.e. it generates multistationarity if it is a positive loop, homeostasis if it is a negative loop).
This not only results in the above-mentioned radical simplification of the identification of the steady states, but in an
entirely new view of the relation between feedback loops and steady states. 相似文献
17.
York J Spetzler D Hornung T Ishmukhametov R Martin J Frasch WD 《Journal of bioenergetics and biomembranes》2007,39(5-6):435-439
The abundance of E. coli F1-ATPase molecules observed to rotate using gold nanorods attached to the γ-subunit was quantitated. Individual F1 molecules were determined to be rotating based upon time dependent fluctuations of red and green light scattered from the
nanorods when viewed through a polarizing filter. The average number of F1 molecules observed to rotate in the presence of GTP, ATP, and without nucleotide was ∼50, ∼25, and ∼4% respectively. In some
experiments, the fraction of molecules observed to rotate in the presence of GTP was as high as 65%. These data indicate that
rotational measurements made using gold nanorods provide information of the F1-ATPase mechanism that is representative of the characteristics of the enzyme population as a whole.
Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.
This work was supported by National Institutes of Health grant GM50202 to W.D.F. 相似文献
18.
Nondegenerate pump probe differential transmission experiments on gold nanorods with varying longitudinal surface plasmon resonance have revealed a new phenomenon where the polarity of the transient transmission signal can be reversibly switched between photo bleaching and photo-induced absorption by controlling probe fluence. Under the usual case where probe fluences are nominal, photo bleaching effect is observed for the nanorods with longitudinal surface plasmon resonance energy smaller than the probe photon energy. The laser-induced melting of the nanorods or change in their shape is ruled out for the observed optical switching effect. A quantitative understanding of the results is attempted by invoking a cascaded two-photon absorption dominant beyond a threshold probe fluence of ~75 μJ/cm2. 相似文献
19.
A sensitive SERS quantitative analysis method for Ni2+ by the dimethylglyoxime reaction regulating a graphene oxide nanoribbon catalytic gold nanoreaction
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The nanogold reaction between HAuCl4 and trisodium citrate (TCA) proceeded very slowly at 60°C in a water bath. The as‐prepared graphene oxide nanoribbons (GONRs) exhibited strong catalysis during the reaction to form gold nanoparticles (Au NPs) and appeared as a strong surface‐enhanced Raman scattering (SERS) peak at 1616 cm?1 in the presence of the molecular probe Victoria blue 4R (VB4r). With increase in GONR concentration, the SERS peak increased due to increased formation of Au NPs. Upon addition of dimethylglyoxime (DMG) ligand, which was adsorbed onto the GONR surface to inhibit GONR catalysis, the SERS peak decreased. When Ni2+ was added, a coordination reaction between DMG and Ni2+ took place to form stable complexes of [Ni (DMG)2]2+ and the release of free GONR catalyst that resulted in the SERS peak increasing linearly. A SERS quantitative analysis method for Ni2+ was therefore established, with a linear range of 0.07–2.8 μM, and a detection limit of 0.036 μM Ni2+. 相似文献
20.
Emerging nanoplasmonics utilizing asymmetric core-shell architectures present opportunities to precisely control the plasmon position and signal amplification within a single particle. In particular, asymmetric gold nanorods, assembled into a “matryoshka” structure (gold nanorod core, silica spacer shell, and outer gold shell) have the unique ability to enhance and precisely manipulate the plasmonic signature when compared to single gold nanorods via the generation of hybridized plasmonic modes. Currently, the fundamental understanding of the impact of the gold nanorod matryoshka dimensional parameters on the subsequent resonance behavior is incomplete. In this work, we elucidate the structural-hybridized resonance relationship of gold nanorod nanomatryoshka designs by experimentally varying the key geometrical properties; including silica spacer thickness, gold nanorod core size, and gold shell thickness/continuity. 相似文献