Gold Nanorods In Solution Research Articles

Thin Film Formation of HSA in the Presence of CTAB-Capped Gold Nanorods through Phase Separation.

Phase behavior in protein-nanoparticle systems in light of protein corona formation has been investigated. We report the formation of HSA thin films following the addition of a solid protein to a solution of CTAB-capped gold nanorods (AuNRs) via phase separation. The phase separation behavior was observed through UV-vis spectroscopy, turbidity assays, and DLS studies. UV-vis spectra for the protein-AuNR solution indicated a possible self-assembly formation by CTAB-HSA complexes and AuNR-HSA conjugates. The turbidity was found to increase linearly up to 30-50% v/v for each component. The growth phase slope is proportional to the concentration of the components, AuNRs, and HSA, with no lag phase. Dynamic light scattering (DLS) shows the formation of larger aggregates with time, implying a segregated phase of AuNR-HSA and a CTAB-HSA-AuNR network. ζ-potential values confirm surface modification, implying protein corona formation on nanorods. The thin films were also characterized using SEM, AFM, SAXS, XPS, FTIR, and TGA studies. SEM images show a smooth surface with a reduced number of pores, indicating the compactness of the deposited structure. AFM shows two different structural pattern formations with the deposition, indicating possible self-assembly of the protein-conjugated nanoparticles. FTIR studies indicate a change in the hydrogen bonding network and confirm the CTAB-HSA-AuNR complex network formation. The XPS studies indicate Au-S bond formation, along with Au-S-S-Au interactions. SAXS studies indicate the formation of aggregates (oligomers), as well as the presence of dominant attractive intermolecular interactions in the thin films.

Colorimetric sensing of lead ion using gold nanorod with enhanced sensitivity via catalytic etching

AbstractLead, a prevalent heavy metal, poses significant risks to human health through various exposure pathways. Herein, we propose an extremely sensitive assay toward lead ion (Pb2+) using gold nanorods (GNRs) as probes based on its catalytic activity on etching gold in the presence of 2‐mercaptoethanol and sodium thiosulfate. In the presence of Pb2+, etching predominantly occurs at the two ends of GNRs, leading to the reduction of aspect ratio and the corresponding blueshift of the localized surface plasmon resonance (LSPR). With increasing Pb2+ concentration over the range of 0–50 μM, the color of GNR solution lightens, ultimately becoming colorless. The wavelength shift (Δλ) of LSPR is highly dependent on Pb2+ concentration, with a linear regression equation of Δλ = 10.05ln[Pb2+] + 9.59 and an R2 = 0.995. The assay demonstrates high selectivity for Pb2+ over other potentially interfering ions such as Cu2+ because of its special catalytic activity in the etching of GNRs and the complexing ability of 2‐mercaptoethanol and sodium thiosulfate. Validation of the assay was accomplished by analyzing several forest‐derived food samples, affirming the accuracy in real‐world scenarios. The assay we developed holds promise for many applications in environmental protection and food safety.

Defining New Benchmarks of Low CTAB‐Concentration‐Based Gold Nanorod Synthesis: The Underestimated Potential of Polymer‐Directed Anisotropic Growth

AbstractThis work presents new anisotropic growth‐directing copolymers suitable for the seed‐mediated growth of gold nanorods (GNRs). Copolymers with different architectures are studied. They all contain dimethylaminomethyl methacrylate (DMAEMA) functionalized with 1‐bromohexadecane (BHD) as the vital component. For the synthesis of the different copolymers, the photo‐iniferter reversible addition–fragmentation chain transfer (photoRAFT) polymerization is used, where DMAEMA is combined with a lower critical solution temperature (LCST) polymer block for better solubility after the functionalization. The results show that the presented copolymers can induce anisotropic growth of gold nanoparticles. Additionally, the influence of the LCST of the water‐soluble block and the temperature of the growth solution on the GNR synthesis are investigated. Furthermore, the plasmonic behavior of the resulting GNRs solution is investigated at temperatures around the LCST of the copolymer.

Q-switched Er-doped fiber laser using an aqueous solution of gold nanorods and polyvinyl alcohol

Authors reported the generation of Q - Switched pulses in an erbium-ytterbium co-doped fiber laser using an aqueous solution of colloidal gold nanorods (GNRs) and Polyvinyl Alcohol (PVA) as a saturable absorber (SA). The effect of the GNRs and PVA concentrations on the pulses has been explored. Passive Q-Switching is achieved at 1.1 W (1.8 A). Pulses with a minimum width of 9.6 µs having a repetition rate of 21.5 kHz and a maximum energy of 0.15 µJ at 1.56 μm are obtained for a pump current of 2.195 W (3.12 A).

Simulation of the spectral properties and photothermal effects of homogeneously dispersed solution of gold nanorods

The photothermal effect influences the sensing performance of gold nanorods (AuNRs) in solution, mainly in terms of sensitivity and detection accuracy. However, less work has been done to investigate this influence by using numerical simulation methods. A model for calculating the extinction curve of uniformly dispersed AuNRs in aqueous solution was established using the finite element method, and the influence of photothermal effect on the sensing performance of AuNRs solution is investigated by combining with density functional theory (DFT). The sensitivity and detection accuracy of AuNRs solutions were investigated by considering the refractive index change and the thermal expansion effect caused by the photothermal effect. It demonstrated that the refractive index change has a great influence on the sensitivity and detection accuracy, while the thermal expansion effect only affects the detection accuracy. The developed numerical simulation model for the study of the photothermal effect is expected to provide meaningful guidance for the development of the AuNRs solution sensors.

Plasmonic structure of zinc (Zn) and zinc oxide (ZnO) on a tapered optical fiber

The authors developed plasmonic structures of zinc (Zn) and zinc oxide (ZnO) on the surface of a tapered optical fiber using optical tweezing. The powdered Zn or ZnO was added to gold nanorods (GNRs) solution and sonicated before tweezing. The concentration of the mixture was 0.5 µg/µl. The GNRs were present in the cetyltrimethylammonium bromide (CTAB) solution. The authors investigated the plasmonic structures and explored the effect of the tweezing conditions on the distribution of the Zn or ZnO on the tapered fiber surface.

Carbon Nanotubes for the Optical Far-Field Readout of Processes That Are Mediated by Plasmonic Near-Fields

As science progresses at the nanoscopic level, it becomes more and more important to comprehend the interactions taking place at the nanoscale, where optical near-fields play a key role. Their phenomenology differs significantly from the propagative light we experience at the macroscopic level. This is particularly important in applications such as surface-enhanced spectroscopies for single-molecule detection, where often the optimization of the plasmonic structures and surfaces relies on far-field characterizations. The processes dominating in the far-field picture, though, are not the same dominating in the near-field. To highlight this, we resort to very simple metallic systems: Isolated gold nanorods in solution. We show how single-walled nanotubes can be exploited to read out processes occurring at the near-field level around metallic nanoparticles and make the information accessible in the far-field region. This is implemented by monitoring the spectral profile of the enhancement of the photoluminescence and Raman signal of the nanotubes for several excitation wavelengths. Through this excitation-resolved study, we show that the far-field optical read-out detects the transversal and longitudinal dipolar plasmonic oscillations of gold nanorods, whereas the near-field read-out through the nanotubes reveals other mechanisms to dominate. The spectral position of the maximum enhancement of the optical near-field mediated signals are located elsewhere than the far-field bands. This dichotomy between near-field and far-field response should be taken into account when optimizing plasmonic nanostructures for applications such as surface-enhanced spectroscopies.

Facile and robust fabrication of hierarchical Au nanorods/Ag nanowire SERS substrates for the sensitive detection of dyes and pesticides.

Surface enhanced Raman spectroscopy (SERS) has emerged as a promising tool for the rapid and ultrasensitive recognition of trace amounts of environmental pollutants. Hierarchical SERS substrates usually show superior performance to single-component substrates but require complicated preparation protocols. Herein, a facile, robust and low-cost route for the fabrication of hierarchical SERS substrates has been reported, in which no complicated laborious protocols or sophisticated equipment is needed. In the hierarchical SERS substrate, Au nanorods were distributed onto the network of Ag nanowires through evaporation induced self-assembly. The density of the Au nanorods and Ag nanowires could be easily tailored by tuning the number of droplets of gold nanorod solution and the concentration of silver nanowire solution. The nanogaps formed between Au nanorods and Ag nanowires were able to induce a rich enhanced electromagnetic field area via localized surface plasmon resonances and surface plasmon polaritons to achieve amplification of the Raman signal. The as-prepared substrate showed high uniformity and was capable of identifying 10-12 M rhodamine 6G, 10-10 M thiram and 10-10 M crystal violet, with correlation coefficients (R2) all higher than 0.98. This approach can be employed for the detection of trace dyes, pesticides or other environmental pollutants with high sensitivity and uniformity.

Enhanced Delivery of Thermoresponsive Polymer-Based Medicine into Tumors by Using Heat Produced from Gold Nanorods Irradiated with Near-Infrared Light.

Simple SummaryTo establish a therapy targeting scattered tumors throughout the body, we propose a novel drug delivery system using a thermoresponsive polyoxazoline (POZ) as a drug carrier in combination with gold nanorods (GNR), which produce heat when irradiated with near-infrared (NIR) light. After the tumor was irradiated with NIR light, where GNR was accumulated in advance, the radiolabeled POZ was intravenously injected. As a result, a marked tumor uptake was achieved via self-aggregation of POZ by sensing heat yielded from the GNR. Because the POZ would be chemically modified with various anti-tumor drugs including therapeutic radionuclides, remarkable anti-tumor effects can be expected by enhancing delivery of POZ-based medicine into scattered tumors throughout the body.The aim of this study was to establish a drug delivery system (DDS) for marked therapy of tumors using a thermoresponsive polymer, polyoxazoline (POZ). The effectiveness of the following was investigated: (i) the delivery of gold nanorods (GNRs) to tumor tissues, (ii) heat production of GNR upon irradiation with near-infrared (NIR) light, and (iii) high accumulation of an intravenously injected radiolabeled POZ as a drug carrier in tumors by sensing heat produced by GNRs. When the GNR solution was irradiated with NIR light (808 nm), the solution temperature was increased both in a GNR-concentration-dependent manner and in a light-dose-dependent manner. POZ, with a lower critical solution temperature of 38 °C, was aggregated depending on the heat produced by the GNR irradiated by NIR light. When it was intratumorally pre-injected into colon26-tumor-bearing mice, followed by NIR light irradiation (GNR+/Light+ group), the tumor surface temperature increased to approximately 42 °C within 5 min. Fifteen minutes after irradiation with NIR light, indium-111 (111In)-labeled POZ was intravenously injected into tumor-bearing mice, and the radioactivity distribution was evaluated. The accumulation of POZ in the tumor was significantly (approximately 4-fold) higher than that in the control groups (GNR+/without NIR light irradiation (Light–), without injection of GNR (GNR–)/Light+, and GNR–/Light– groups). Furthermore, an in vivo confocal fluorescence microscopy study, using fluorescence-labeled POZ, revealed that uptake of POZ by the tumor could be attributed to the heat produced by GNR. In conclusion, we successfully established a novel DDS in which POZ could be efficiently delivered into tumors by using the heat produced by GNR irradiated with NIR light.

Real-Time Control of Nanoparticle-Mediated Thermal Therapy Using Photoacoustic Imaging.

This work aims to determine whether photoacoustic (PA) thermometry from a commercially available PA imaging system can be used to control the temperature in nanoparticle-mediated thermal therapies. The PA imaging system was interfaced to obtain PA images while scanning ex-vivo tissue. These images were then used to obtain temperature maps in real-time during heating. Validation and calibration of the PA thermometry were done using a fluoroptic thermometer. This thermometer was also used to develop and tune a software-based proportional integral derivative (PID) controller. Finally, a PA-based PID closed-loop controller was used to control gold nanorod (GNR) mediated laser therapy. The use of GNRs substantially enhanced laser heating; the temperature rise increased 7-fold by injecting a GNR solution with a concentration of 0.029 mg/mL. The control experiments showed that the desired temperature could be achieved and maintained at a targeted location in the ex-vivo tissue. The steady-state mean absolute deviations (MAD) from the targeted temperature during control were between 0.16 [Formula: see text] and 0.5 [Formula: see text], depending on the experiment. It was possible to control hyperthermia treatments using a software-based PID controller and a commercial PA imaging system. The monitoring and control of the temperature in thermal-based therapies are important for assuring a prescribed temperature to the target tissue while minimizing the temperature of the surrounding healthy tissue. This easily implemented non-invasive control system will facilitate the realization of a broad range of hyperthermia treatments.

Direct and Plasmonic Nanoparticle‐Mediated Infrared Neural Stimulation: Comprehensive Computational Modeling and Validation

AbstractInfrared neural stimulation techniques have potential applications in the diagnosis and treatment of numerous neurological and psychiatric disorders. There has been little progress in the computational modeling of these techniques and further improvement is needed in this area. In this paper, a comprehensive computational model is presented for simulating the complete mechanism of direct and plasmonic nanoparticle‐mediated infrared neural stimulation techniques in schematic samples of experimental setups. The simulation process involves three phases: 1) Simulating the light transmission and absorption in setups containing pure water or a gold nanorod solution using developed 3D, time‐independent, and time‐dependent Monte Carlo models, 2) calculating the spatiotemporal evolutions of temperature within the setup using the finite difference method and a presented novel method, and 3) simulating the thermally induced responses of lipid membranes using an improved method compared to existing theoretical models. The model is validated by comparing the computational results with existing experimental data. The effect of the laser pulse characteristics, nanofluid properties, and some other related parameters on the thermally induced membrane responses is investigated. The computational results help to optimize the parameters selection and maximize the overall efficiency of the infrared neural stimulation techniques.

Plasmon-Enhanced Perovskite Solar Cells with Efficiency Beyond 21 %: The Asynchronous Synergistic Effect of Water and Gold Nanorods.

Although perovskite films have excellent extinction coefficients, further increase of the light-absorbing capacity by increasing the thickness of the active layer is always required in perovskite solar cells (PSCs). However, to maintain the morphology quality of the perovskite layer, the film thickness is subject to certain restrictions. To increase the light absorbance without significantly inflating the perovskite film while keeping the high quality of the perovskite film, herein, we added an aqueous solution of gold nanorods (AuNRs) to the perovskite precursor solution via a so-called asynchronous synergistic effect (ASE) strategy of water and AuNR. The former improves the quality of the perovskite film during the crystallization process to reduce defect density and enhance carrier mobility. Simultaneously, the latter increases the light absorption of the perovskite layer through the localized surface plasmon resonance (LSPR) effect when the device is exposed to light. We show that the ASE strategy leads to an excellent power conversion efficiency (PCE) of 21.73 % and outstanding long-term stability, which can retain 95 % of its initial PCE after storage for three months in an air atmosphere.

Evaporation-induced self-assembly of silver nanospheres and gold nanorods on a super-hydrophobic substrate for SERS applications

Surface-enhanced Raman scattering (SERS) has drawn attention for broad applications. We successfully fabricated highly effective SERS structures via evaporation-induced self-assembly of blend nanoparticles containing sliver nanospheres (Ag NSs) and gold nanorods (Au NRs) on a super-hydrophobic (SH) substrate. On the SH substrate, the droplets of the mixed aqueous solution of silver nanospheres (Ag NSs), gold nanorods (Au NRs), and probe molecules can preserve their spherical shape during the evaporation process, and the probe molecules (R6G) are confined into extremely small areas after solvent removal due to hydrophobicity-enhanced concentration effects. The Raman enhancement effect of the blend nanoparticles with 40 vol% Ag NSs is far higher than that of the other samples. The structure of the aggregated Ag NSs on the film-like Au NRs greatly enhances the SERS effect of Ag NSs, which is optimal for the blend system with 40 vol% Ag NSs. The SERS structure also displays excellent signal reproducibility (RSD < 10%) and low detection limits (0.5 nM). Thus, this work offers a simple and efficient strategy to fabricate a highly effective SERS structure with broad applications in environmental science, analytical chemistry, etc.

Bubble dynamics of laser-induced cavitation in plasmonic gold nanorod solutions and the relative effect of surface tension and viscosity

Laser-induced cavitation (LIC) bubbles and the shockwaves they form upon collapse are destructive to nearby solid boundaries, making them of interest for biomedical and industrial applications. Furthermore, the LIC bubbles provide spatial control that can be tuned by the bubble size, collapse time and shockwave intensity. The inclusion of plasmonic nanoparticles, such as gold nanoparticles (GNP) in the liquids where LIC bubbles are formed, can further enhance the absorption of light, allowing for bubble formation at lower laser energies. However, the effect of the physical properties of such liquids on LIC bubble dynamics remains unknown. In this study, the dynamics of LIC bubbles in water–ethanol, water-glycerol, and water-GNP solutions were investigated by simultaneous high-speed shadowgraphy and spatial transmittance modulation. The first set of experiments demonstrated that LIC bubbles induced in the GNP solutions led to more efficient cavitation formation with lower fluence compared to solutions without GNPs, thereby producing higher-intensity pressure waves. A second set of experiments was conducted to determine the surface tension of GNP solutions at room temperature and was found to be 70.62 mN/m. With this information, and the corresponding values reported in the literature for ethanol and glycerol, we aimed at discerning the role of surface tension and viscosity on the dynamics of LIC bubbles, apart from the enhanced optical absorption of the GNP solutions. We observed that the optical breakdown threshold for plasma formation was reduced by 18% in GNP solutions as compared to DI water and 10.4% compared to ethanol, and the intensity of initial shockwaves in the GNP solutions was much higher than those in DI water. This enhanced intensity of shockwaves in GNP solutions compared to DI water opens a new avenue for the enhancement of cancer cell treatment and anti-bacterial applications in the biomedical field and the enhancement of the laser ablation technique in the industrial setting.

Tracking the Effects of Ligands on Oxidative Etching of Gold Nanorods in Graphene Liquid Cell Electron Microscopy.

Surface ligands impact the properties and chemistry of nanocrystals, but observing ligand binding locations and their effect on nanocrystal shape transformations is challenging. Using graphene liquid cell electron microscopy and the controllable, oxidative etching of gold nanocrystals, the effect of different ligands on nanocrystal etching can be tracked with nanometer spatial resolution. The chemical environment of liquids irradiated with high-energy electrons is complex and potentially harsh, yet it is possible to observe clear evidence for differential binding properties of specific ligands to the nanorods' surface. Exchanging CTAB ligands for PEG-alkanethiol ligands causes the nanorods to etch at a different, constant rate while still maintaining their aspect ratio. Adding cysteine ligands that bind preferentially to nanorod tips induces etching predominantly on the sides of the rods. This etching at the sides leads to Rayleigh instabilities and eventually breaks apart the nanorod into two separate nanoparticles. The shape transformation is controlled by the interplay between atom removal and diffusion of surface atoms and ligands. These in situ observations are confirmed with ex situ colloidal etching reactions of gold nanorods in solution. The ability to monitor the effect of ligands on nanocrystal shape transformations will enable future in situ studies of nanocrystals surfaces and ligand binding positions.

Gold Nanorod-Optical Fiber for Sensing Biomolecular Interaction

The optical fiber deposits with gold nanorods was successfully accomplished as a biosensor device which sensing to the refractive index change on the surrounding surface. The principle is based on the localized surface plasmon resonance (LSPR) occurs on the metal surface of gold nanorods (AuNRs). The gold nanorods were coated on the glass core fiber surface through the covalent bond. The uncladded area fiber optic was incubated in 5% of (3-Mercaptopropyl) trimethoxysilane (MPTMS) in ethanol for overnight to alter the thiol group on the surface. The gold nanorods with aspect ratio ⁓2.035 was deposited on thiol surface by incubation the optical fiber in gold nanorod solution for 6 hr. The sensor provides the sensitivity of 4.94×104 a.u./RIU. Moreover, antibody for blood grouping was immobilized on the AuNRs-optical fiber to detect the red blood cells. The AuNRs-optical fiber can detect A antigen on the immobilized anti-A surface with Δ%T of 0.98 and can detect B-antigen on the immobilized anti-B surface with Δ%T of 1.78. This work possesses possibility of a simple AuNRs-optical fiber to detect the biomolecular interaction.

Optically enhanced terahertz modulation and sensing in aqueous environment with gold nanorods

Terahertz (THz) technique, with plenty attractive properties such as its prominent detecting ability, non-destruction and non-ionization, has been getting increased attention. THz modulator, enabling efficient manipulation, is crucial for THz devices and sensing applications. However, its practical implementation still remains a challenge because of the small modulation depth, slow modulation rate and difficult operation way. Nanomaterials have been constantly creating possibilities for the advancement of THz technology. Considering their excellent optical and electrical characteristics, gold nanorods (GNRs) are integrated with silicon-based materials to improve the performance for THz modulation, so as to promote the possibility of THz sensing in aqueous environment. In this paper, the modulation ability of THz wave based on bare silicon with/without dried GNR film, liquid cell with GNR solutions, and silicon channel with GNR solutions is systematically investigated. According to the results, a six-time larger modulation depth can be realized with the plasmonic effect of GNRs through infrared laser irradiation, which is employed to increase the protein detection sensitivity up to ppm level in water state. It is anticipated that integrating nanomaterials with THz functional devices is meaningful to improve the performance of THz technology, which could facilitate its wide applications in various fields.

Gold Nanorod-tags in Mucous Membrane of a Zebrafish

Zebrafish were exposed to a gold nanorod solution (0.5 mM) for 10 min. Mucous membranes were collected either on ITO plate or blotting membrane. The adsorption and retention of gold nanorods in mucous membranes were evaluated by mass spectrometry of gold ions desorbed from the nanorods. Nanorods modified with cationic polymers were retained in mucous membranes for at least seven days, while anionic and nonionic polymer-modified nanorods were desorbed within three days. These results demonstrate the feasibility of using gold nanorods as a fish tag.

Determination of the Aspect-ratio Distribution of Gold Nanorods in a Colloidal Solution using UV-visible absorption spectroscopy

Knowledge of the distribution of the aspect ratios (ARs) in a chemically-synthesized colloidal solution of Gold Nano Rods (GNRs) is an important measure in determining the quality of synthesis, and consequently the performance of the GNRs generated for various applications. In this work, an algorithm has been developed based on the Bellman Principle of Optimality to readily determine the AR distribution of synthesized GNRs in colloidal solutions. This is achieved by theoretically fitting the longitudinal plasmon resonance of GNRs obtained by UV-visible spectroscopy. The AR distribution obtained from the use of the algorithm developed have shown good agreement with those theoretically generated one as well as with the previously reported results. After bench-marking, the algorithm has been applied to determine the mean and standard deviation of the AR distribution of two GNRs solutions synthesized and examined in this work. The comparison with experimentally derived results from the use of expensive Transmission Electron Microscopic images and Dynamic Light Scattering technique shows that the algorithm developed offers a fast and thus potentially cost-effective solution to determine the quality of the synthesized GNRs specifically needed for many potential applications for the advanced sensor systems.

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.