Gold Nanorods In Solution Research Articles

All-fiber phase shifter based on hollow fiber interferometer integrated with Au nanorods

We propose and demonstrate a novel all-fiber phase shifter by integrating a microstructured hollow fiber (MHF) and gold nanorods (GNRs) with photothermal effect. There are two cores and a central hole in the MHF. One core is suspended on the inner surface of the central hole, which serves as the sensing arm. The other one located in the cladding is as the reference arm. A Mach-Zehnder interferometer (MZI) can be fabricated simply through splicing multimode fiber-single mode fiber structures at both ends of the MHF. In this device, the center hole of MHF is filled with the solution of GNRs. The GNRs around the sensing arm is excited by near infrared light in the core via the evanescent interaction and the released heat because of the photothermal effect. Then, the refractive index around the sensing arm is modulated and the interference dips can be reversibly shifted. Experimental results show that spectral shift efficiency about -37.5 pm/mW near 1560 nm can be obtained under an excitation laser at the wavelength of 805 nm. This all-optical device based on MHF and GNRs has great potentials in integrated all-fiber signal controlling.

Probing the Dynamics and the Atomic Structure of Gold Nanorods in Solution with Liquid-Cell TEM

Probing the Dynamics and the Atomic Structure of Gold Nanorods in Solution with Liquid-Cell TEM

A simple paper-based surface enhanced Raman scattering (SERS) platform and magnetic separation for cancer screening

Early and precise diagnosis of cancer is critical for a better prognosis. Here, we describe a simple and cost-effective plasmonic paper as a surface enhanced Raman scattering (SERS) substrate in combination with magnetic separation for cancer screening. The plasmonic paper was fabricated by immersing plain filter paper into gold nanorod solution and the SERS property of the paper was evaluated using 4-mercaptobenzoic acid (4-MBA) and rhodamine 6 G (R6 G), which showed an enhancement factor (EF) in the range of 106–108. HT-29, a colorectal cancer cell line that highly expresses epithelial cell adhesion molecule (EpCAM), served as the target cells; non-EpCAM-expressing cells, namely fibroblasts and red blood cells (RBCs), were used as negative controls. Intrinsic SERS spectra of the target and control cells showed distinctive patterns on the plasmonic paper due to differences in their structure and components. A combination of principal component analysis (PCA) and k-nearest-neighbor algorithm (k-NN) was employed to analyze and distinguish the acquired HT-29 and fibroblast SERS spectra, demonstrating a diagnostic sensitivity and specificity of 84.8% and 82.6%, respectively, whereas the differentiation between HT-29 and RBCs SERS spectra showed a sensitivity and specificity of 96.4% and 100%, respectively. The magnetic separation was applied to capture the target cells from cell mixtures followed by PCA and k-NN analysis. The identification of the captured cells as cancerous cells from the HT-29 and fibroblast mixture indicated an accuracy of 83.7%, while that from a mixture of HT-29 and RBCs was 98.2%. Thus, the simple paper-based SERS substrate with the assistance of magnetic enrichment and multivariate analysis offers a potent new platform for cancer cell detection and screening.

Estimation of the aspect-ratio distribution in chemically synthesized gold nanorods solution using UV-visible absorption spectroscopy

A rapid and ubiquitous method to characterize samples of chemically synthesized Gold Nano Rods (GNRs) is by measuring their UV-visible spectra. The presence of transverse and longitudinal surface plasmon resonance peaks in UV-visible spectra indicate the presence of GNRs. However, the quality of the synthesised sample, and thus their performance in various sensor applications, depends on the geometrical variations of the GNRs present in the solution. As a result, an algorithm has been developed to estimate the Aspect Ratio (AR) variation of the GNRs present by theoretically fitting to the longitudinal surface plasmon resonance peak of the UV-visible spectrum. After numerically benchmarking has been undertaken, the developed algorithm has been used to calculate the mean and standard deviation of the ARs in two synthesized samples, showing that this method offers a fast and cost-effective alternative to Transmission Electron Microscopy.

The Effect of Gold Nanorods Clustering on Near-Infrared Radiation Absorption

In this paper, the plasmonic resonant absorption of gold nanorods (GNRs) and GNR solutions was studied both numerically and experimentally. The heat generation in clustered GNR solutions with various concentrations was measured by exposing them to Near Infrared (NIR) light in experiment. Correspondingly, calculations based on the discrete-dipole approximation (DDA) revealed the same relationship between the maximum absorption efficiency and the nanorod orientation for the incident radiation. Additionally, both the plasmonic wavelength and the maximum absorption efficiency of a single nanorod were found to increase linearly with increasing aspect ratio (for a fixed nanorod volume). The wavelength of the surface plasmonic resonance (SPR) was found to change when the gold nanorods were closely spaced. Specifically, both a shift and a broadening of the resonance peak were attained when the distance between the nanorods was set to about 50 nm or less. The absorbance spectra of suspended nanorods at various volume fractions also showed that the plasmonic wavelength of the nanorods solution was at 780 ± 10 nm, which was in good agreement with the computational predictions for coupled side-by-side nanorods. When heated by NIR light, the rate of increase for both the temperature of solution and the absorbed light diminished when the volume fraction of suspended nanorods reached a value of 1.24×10−6. This matches with expectations for a partially clustered suspension of nanorods in water. Overall, this study reveals that particle clustering should be considered to accurately gauge the heat generation of the GNR hyperthermia treatments.

Reversible Tuning the Aspect Ratio and Plasmonic Shift of Gold Nanorods in Alkaline Environment: Growth, Etching and Rebuilding

The well-developed seed-mediated growth of gold nanorods (GNRs) is under the weakly acidic condition, and the aggregation of the GNRs usually takes place when the pH value is increased to alkalinity. In this study, GNRs have been successfully prepared in the alkaline environment using the reducibility of H2O2 under the alkaline condition (pH = 10), and the longitudinal localized surface plasmon resonance (LSPR) could be fine tuned within a wider wavelength range of 600 ~ 1050 nm by changing the concentration of silver ion. On the other hand, by using the strong oxidizability of the H2O2 under the acidic condition (pH = 3), the prepared GNRs could be etched completely, and the chloroauric acid, as the important raw material of preparing GNRs, could be retrieved. The recovered materials could be reused as the growth solution of GNRs, and the re-prepared GNRs have longer aspect ratio and stronger LSPR. This research reflects the cyclic utilization of noble metal along with preparation of GNRs in the weak alkaline environment.

Chiral Plasmonic Nanochains via the Self-Assembly of Gold Nanorods and Helical Glutathione Oligomers Facilitated by Cetyltrimethylammonium Bromide Micelles.

Gold nanorods are excellent anisotropic building blocks for plasmonic chiral nanostructures. The near-infrared plasmonic band of nanorods makes them highly desirable for biomedical applications such as chiral bioimaging and sensing, in which a strong circular dichroism (CD) signal is required. Chiral assemblies of gold nanorods induced by self-associating peptides are especially attractive for this purpose as they exhibit plasmonic-enhanced chiroptical activity. Here, we showed that the presence of cetyltrimethylammonium bromide (CTAB) micelles in a gold nanorod solution promoted the self-association of l-/d-glutathione (GSH) and significantly enhanced the chirality of the resulting plasmonic nanochains. Chiroptical signals for the ensemble in the presence of CTAB micelles were 20 times greater than those obtained below the critical micelle concentration of CTAB. The strong optical activity was attributed to the formation of helical GSH oligomers in the hydrophobic core of the CTAB micelles. The helical GSH oligomers led the nanorods to assemble in a chiral, end-to-end crossed fashion. The CD signal intensities were also proportional to the fraction of nanorods in the nanochains. In addition, finite-difference time-domain simulations agreed well with the experimental extinction and CD spectra. Our work demonstrated a substantial effect from the CTAB micelles on gold nanoparticle assemblies induced by biomolecules and showed the importance of size matching between the inorganic nanobuilding blocks and the chiral molecular templates (i.e., the GSH oligomers in the present case) in order to attain strong chiroptical activities.

Ultraviolet Analysis of Gold Nanorod and Nanosphere Solutions

The localized surface plasmon resonances of gold nanoparticles have been widely studied at visible and near-infrared frequencies but less so in the ultraviolet. The spectral extinction measurements of gold nanospheres at UV wavelengths reported here closely match calculated spectra down to 200 nm using the measured dielectric function of gold. The nanosphere volume attenuation coefficient, αv, is size-dependent in the 200–300 nm wavelength range where the dielectric function follows the Drude free electron model (as it does for wavelengths larger than 500 nm). In the interband transition region, the extinction is more closely proportional to mass and therefore has a value of αv that is largely independent of size. Gold nanorod solutions exhibit very strong UV extinction below 220 nm due to charge transfer to solvent (c.t.t.s.) excitations of the bromide counterion to the cationic surfactant. The gold nanorod UV properties depend on the alignment between the optical polarization and nanorod structure. For ...

Optoacoustic response of gold nanorods in soft phantoms using high-power diode laser assemblies at 870 and 905 nm.

In the present paper we show the optoacoustic (OA) response of two solutions of gold nanorods dispersed in distilled water (0.8 mg/ml) and hosted in tissue-like phantoms by using small arrays of high-power diode lasers [corrected] at 870 and 905 nm as excitation sources. The high-power diode lasers [corrected] are coupled to a 7-to-1 optical fiber bundle with output diameter of 675 μm. Each solution of gold nanorods exhibits an absorption peak close to the operating wavelength, i.e. ~860 nm and ~900 nm, respectively, to optimize the generation of OA signals. The phantoms are made of agar, intralipid and hemoglobin to simulate a soft biological tissue with reduced properties of scattering. Three 3-mm diameter tubes done in the phantoms at different depths (0.9 cm, 1.8 cm, and 2.7 cm) have been filled with gold nanorods. In this way, OA signals with appreciable SNR are generated at different depths in the phantoms. The high OA response exhibited by gold nanorods suggests their application in OA spectroscopy as exogenous contrast agents to detect and monitor emerging diseases like metastasis and arteriosclerotic plaques.

A Fast and Efficient Replacement of CTAB with MUA on the Surface of Gold Nanorods Assisted by a Water-Immiscible Ionic Liquid.

The synthesis and surface modification of gold nanorods (GNRs) is one of the most important and basic issues in nanoscience. Most of the widely investigated GNRs are coated with a cetyltrimethylammonium bromide(CTAB) bilayer. Here, a highly efficient method is proposed to replace CTAB from the surface of GNRs with a bifunctional 11-mercaptoundecanoic acid in order to decrease the possible toxicity caused by CTAB. This ligand exchange is achieved in a biphasic mixture of an aqueous solution and a water-immiscible ionic liquid (IL), [BMIM][Tf2 N]. That is, by mixing IL, mercaptoundecanoic acid (MUA)/IL (200 × 10-3 m) and a concentrated aqueous solution of GNRs together, followed by vortex stirring for 90 s, CTAB-capped GNRs with varying aspect ratios can be turned into corresponding MUA-capped GNRs with the same aspect ratio. Furthermore, the formed MUA-capped GNRs can be obtained in a large quantity and stored as powders for easy use. The MUA-capped GNRs with improved biocompatibility and colloidal stability are well suited for further biological functionalization and potential applications. This IL-assisted ligand exchange can reverse the surface charge, enhance the stability of GNRs, and suppress its cytotoxicity.

Tissue-Like Phantoms as a Platform for Inserted Fluorescence Nano-Probes.

Tissue-like phantoms are widely used as a model for mimicking the optical properties of live tissue. This paper presents the results of a diffusion reflection method and fluorescence lifetime imaging microscopy measurements of fluorescein-conjugated gold nanorods in solution, as well as inserted in solid tissue-imitating phantoms. A lack of consistency between the fluorescence lifetime results of the solutions and the phantoms raises a question about the ability of tissue-like phantoms to maintain the optical properties of inserted contrast agents.

Bending Gold Nanorods with Light.

V-shaped gold nanoantennas are the functional components of plasmonic metasurfaces, which are capable of manipulating light in unprecedented ways. Designing a metasurface requires the custom arrangement of individual antennas with controlled shape and orientation. Here, we show how highly crystalline gold nanorods in solution can be bent, one-by-one, into a V-shaped geometry and printed to the surface of a solid support through a combination of plasmonic heating and optical force. Significantly, we demonstrate that both the bending angle and the orientation of each rod-antenna can be adjusted independent from each other by tuning the laser intensity and polarization. This approach is applicable for the patterning of V-shaped plasmonic antennas on almost any substrate, which holds great potential for the fabrication of ultrathin optical components and devices.

High-resolution contrast-enhanced optical coherence tomography in mice retinae.

Optical coherence tomography (OCT) is a noninvasive interferometric imaging modality providing anatomical information at depths of millimeters and a resolution of micrometers. Conventional OCT images limit our knowledge to anatomical structures alone, without any contrast enhancement. Therefore, here we have, for the first time, optimized an OCT-based contrast-enhanced imaging system for imaging single cells and blood vessels in vivo inside the living mouse retina at subnanomolar sensitivity. We used bioconjugated gold nanorods (GNRs) as exogenous OCT contrast agents. Specifically, we used anti-mouse CD45 coated GNRs to label mouse leukocytes and mPEG-coated GNRs to determine sensitivity of GNR detection in vivo inside mice retinae. We corroborated OCT observations with hyperspectral dark-field microscopy of formalin-fixed histological sections. Our results show that mouse leukocytes that otherwise do not produce OCT contrast can be labeled with GNRs leading to significant OCT intensity equivalent to a 0.5 nM GNR solution. Furthermore, GNRs injected intravenously can be detected inside retinal blood vessels at a sensitivity of ∼0.5 nM, and GNR-labeled cells injected intravenously can be detected inside retinal capillaries by enhanced OCT contrast. We envision the unprecedented resolution and sensitivity of functionalized GNRs coupled with OCT to be adopted for longitudinal studies of retinal disorders.

Surface Plasmon Enhanced Emission Rate in Silicon Quantum Dot-Decorated Gold Nanorods in Solution

Surface Plasmon Enhanced Emission Rate in Silicon Quantum Dot-Decorated Gold Nanorods in Solution

Application of Gold Nanorods for Photothermal Therapy in Ex Vivo Human Oesophagogastric Adenocarcinoma.

Gold nanoparticles are chemically fabricated and tuned to strongly absorb near infrared (NIR) light, enabling deep optical penetration and therapy within human tissues, where sufficient heating induces tumour necrosis. In our studies we aim to establish the optimal gold nanorod (GNR) concentration and laser power for inducing hyperthermic effects in tissues and test this photothermal effect on ex vivo human oesophagogastric adenocarcinoma. The ideal GNR concentration and NIR laser power that would elicit sufficient hyperthermia for tumour necrosis was pre-determined on porcine oesophageal tissues. Human ex vivo oesophageal and gastric adenocarcinoma tissues were incubated with GNR solutions and a GNR-free control solution with corresponding healthy tissues for comparison, then irradiated with NIR light for 10 minutes. Temperature rise was found to vary linearly with both the concentration of GNRs and the laser power. Human ex vivo oesophageal and gastric tissues consistently demonstrated a significant temperature rise when incubated in an optimally concentrated GNR solution (3 x 10(10) GNRs/ml) prior to NIR irradiation delivered at an optimal power (2 W/cm2). A mean temperature rise of 27 degrees C was observed in tissues incubated with GNRs, whereas only a modest 2 degrees C rise in tissues not exposed to any GNRs. This study evaluates the photothermal effects of GNRs on oesophagogastric tissue examines their application in the minimally invasive therapeutics of oesophageal and gastric adenocarcinomas. This could potentially be an effective method of clinically inducing irreversible oesophagogastric tumour photodestruction, with minimal collateral damage expected in (healthy) tissues free from GNRs.

Colloidal stability of gold nanorod solution upon exposure to excised human skin: Effect of surface chemistry and protein adsorption

In this study, we evaluated the colloidal stability of gold nanorods (with positive, negative and neutral surface charge) in solution upon contact with excised human skin. UV–vis absorption, plasmon peak broadening index (PPBI%) and transmission electron microscope analysis were used to follow nanoparticles aggregation in solution. Our results show that positively charged gold nanorods aggregate extensively upon exposure to excised human skin compared to negatively and neutrally charged gold nanorods. Skin-induced aggregation of cationic gold nanorods was linked to the adsorption of proteins released from the dermis layer to the surface of gold nanorods. Protein adsorption significantly screen nanorod’s effective surface charge and induce their aggregation. Moreover, we demonstrate that the presence of polyethylene glycol polymer on the surface of cationic gold nanorods minimize this aggregation significantly by providing steric repulsion (non-electrostatic stabilization mechanism). This work highlights the importance of evaluating the colloidal stability of nanoparticles in solution upon contact with skin, which is a “usually overlooked” parameter when studying the nanoparticle-skin interaction.

Gold Nanoparticle Patterning on Planar Type MEA for Selective Inhibition of Cultured Neuronal Network Using NIR Photothermal Effect

Event Abstract Back to Event Gold Nanoparticle Patterning on Planar Type MEA for Selective Inhibition of Cultured Neuronal Network Using NIR Photothermal Effect Gu-Haeng Lee1* and Yoonkey Nam2 1 Korea Advanced Institute of Science and Technology, Dept. of Bio and Brain Engineering, Korea 2 Korea Advanced Institute of Science and Technology, Dept. of Bio and Brain Engineering, Korea 1. Motivation MEA (multi-electrodes array) is a powerful tool to research about dissociated neuronal culture activities. There are several methods to control neuronal networks like electrical stimulation, drug stimulation and cell patterning. Especially, limited methods are used to inhibit neurons using drug or optogenetic method. Inhibition method using the photothermal effect of gold nanoparticles is recently shown [1]. In this work, we tried to combine photothermal inhibition and patterning method for selective inhibition that is hard to achieve using conventional electrical stimulation. 2. Material and Methods GNR (gold nanorod) was PEGylated by SH-PEG-NH2(+) to stabilize and modify the surface property. Substrates were planar type MEAs.with the surface of silicon nitride or ONO(Oxide/Nitride/Oxide). After one minute of air plasma treatment on substrates, GNR solution was loaded on the substrate for 12~24 hours. Then, substrates were rinsed with distilled water and dried by an airgun. A PDMS stamp was treated with air plasma for one minute and it was brought in contact with the GNR coated substrates for one minute. After peeling off stamp carefully, we can see the lift-up result. 3. Results Figure1(left). SEM image of the lift-up result on the cover glass. GNRs remain on the bright part. Size of single dot is 3 ¥ìm Figure 2(right). Modified phase contrast image of MEA with GNR(dark) pattern. Distance between center of electrodes is 200 ¥ìm For the lift-up result, the removal ratio of GNR on the substrate was changed to the different condition, like property of GNR, GNR loading time, time after GNR coating, plasma treatment time on PDMS. We saw consistent results from a cover glass substrate that was not necessary to align pattern. There were no limits of pattern shape similar to micro contact printing and achieve circle shape 3-¥ìm size pattern to smallest pattern. We performed lift-up from two kinds of surface condition and GNR charge property. 4. Discussion Lift-up soft lithography can be used in a large area, so it is good for controlling large size network. Cell patterning using micro contact printing or micro-molding in the capillary can be added, because GNR patterning does not affect to network morphology. 5. Conclusion We show GNR micro patterning using lift-up soft lithography was operating well on MEA surface. We may selectively inhibit cultured neuronal network by GNR patterning which is relatively easy compared to light patterning or optogenetic methods. We expect this work helps research about neuronal network by controlling network activities.

Assembling gold nanorods on a poly-cysteine modified glassy carbon electrode strongly enhance the electrochemical reponse to tetrabromobisphenol A

Cysteine (Cys) was electrochemically deposited on a glassy carbon electrode (GCE) by cyclic voltammetry. The poly-Cys modified electrode was placed in a solution of gold nanorods (GNRs) to induced self-assembly of the GNRs. The GNRs/poly-Cys/GCEs were characterized by scanning electron microscopy and electrochemical impedance spectroscopy. A voltammetric study on tetrabromobisphenol A (TBBPA) with this GCE showed the current response to be enhanced by a factor of 11 compared to a non-modified GCE. Based on these findings, a square wave voltammetric assay was worked out. Under optimized conditions, a linear relationship between the oxidation peak current and TBBPA is found for the 10 nM to 10 μM concentration range. The detection limit is 3.2 nM (at an S/N ratio of 3). The electrode was successfully applied to the determination of TBBPA in spiked tap water and lake water samples.

Dynamic microscale temperature gradient in a gold nanorod solution measured by diffraction-limited nanothermometry

We quantify the dynamic microscale temperature gradient in a gold nanorod solution using quantum-dot-based microscopic fluorescence nanothermometry. By incorporating CdSe quantum dots into the solution as a nanothermometer, precise temperature mapping with diffraction-limited spatial resolution and sub-degree temperature resolution is achieved. The acquired data on heat generation and dissipation show an excellent agreement with theoretical simulations. This work reveals an effective approach for noninvasive temperature regulation with localized nanoheaters in microfluidic environment.

Probing the Structure, Composition, and Spatial Distribution of Ligands on Gold Nanorods.

The structure and size of ligands attached to the surfaces of gold nanorods, such as adsorbed surfactants or grafted polymers, are important considerations that facilitate the use of such nanoparticles in the human body, in advanced materials for energy harvesting, or in devices for single molecule detection. Here, we report small-angle neutron scattering (SANS) measurements from surfactant or poly(ethylene glycol) (PEG) coated gold nanorods in solution, which quantitatively determine the location, structure, and composition of these surface layers. In addition, by synthesizing gold nanorods using seed crystals which are coated with deuterated cetyltrimethylammonium bromide (dCTAB), we are able to exploit the isotopic sensitivity of SANS to study, for the first time, the retention of surfactant from the seed crystals to the final gold nanorod product, finding that very little exchange of the deuterated with hydrogenated surfactant occurs. Finally, we demonstrate that, when Au NRs are PEGylated using standard techniques, the surfactant bilayer remains intact, and while mass spectrometry detects the presence of both surfactant and PEG, the composition as measured from SANS is predominantly that of the surfactant. These measurements not only provide new insight into the synthesis and functionalization of gold nanorods but provide a quantitative picture of the structure of grafted polymer and surfactant layers on gold nanorod surfaces which has implications for the fabrication of plasmonic and biomedical materials.