Au NRs Research Articles

Gold nanorods–trypsin biocorona: a novel nano composite for in vitro cytotoxic activity towards MCF-7 and A-549 cancer cells

In the present work, we have synthesized cetyltrimethyl ammonium bromide (CTAB) capped gold nanorods (Au NRs) to evaluate apparent binding affinities for the adsorption of trypsin (TRP).

Preparation and Progress in Application of Gold Nanorods

Gold nanorods (Au NRs) have attracted extensive research interest due to their unique optical properties, adjustable aspect ratio, and easy surface modification in the fields of biosensing, bioimaging, and disease diagnosis and detection. In this review, we present a comprehensive review of various methods for preparing gold nanorods including hard template method, electrochemistry method, photochemistry method, seed-mediated growth method, secondary growth method, and amorphous seed method. The unique optical properties of the gold nanorods and its applications in biomedical, detection, catalysis, and information storage will also be discussed in detail.

Nanostructured sapphire optical fiber embedded with Au nanorods for high-temperature plasmonics in harsh environments.

Sensors for harsh environments must exhibit robust sensing response and considerable thermal and chemical stability. We report the exploration of a novel all-alumina nanostructured sapphire optical fiber (NSOF) embedded with Au nanorods (Au NRs) for plasmonics-based sensing at high temperatures. Temperature dependence of the localized surface plasmon resonance (LSPR) of Au NRs was studied in conjunction with numerical calculations using the Drude model. It was found that LSPR of Au NRs changes markedly with temperature, red shifting and increasing in transmission amplitude as the temperature increases. Furthermore, this variation is highly localized through tunneling by overlapping the near-field of thin cladding and sapphire optical fiber. The NSOF embedded with Au NRs has the potential for sensing in advanced energy generation systems.

Sensitive Multicolor Visual Detection of Exosomes via Dual Signal Amplification Strategy of Enzyme-Catalyzed Metallization of Au Nanorods and Hybridization Chain Reaction.

Exosomes as nanosized vesicles have been recognized as potential noninvasive biomarkers for early cancer diagnosis. Herein, we presented a sensitive multicolor visual method for exosome detection based on enzyme-induced silver deposition on gold nanorods (Au NRs). To achieve highly sensitive determination of exosomes, hybridization chain reaction (HCR) was employed to introduce more alkaline phosphatase (ALP) for signal amplification. First, exosomes were captured by magnetic bead-labeled CD63 aptamer, and, then, cholesterol-modified DNA probes were spontaneously inserted into the exosomal lipid membrane. The ends of the DNA probes act as the initiator to trigger the HCR for signal amplification. Finally, with the help of HCR, increased sites led to enhanced ALP loading and thus boosted the ascorbic acid generation. Silver ions were reduced by ascorbic acid, and silver shells were formed on Au NRs, giving rise to the blue shift of the longitudinal localized surface plasmon resonance peak. Correspondingly, the concentration of exosomes can be obviously distinguished with naked eyes via the vivid color variation. Due to the dual signal amplification of HCR and metallization of Au NRs, highly sensitive detection for exosomes were realized with detection limits as low as 1.6 × 102 particles/μL by UV-vis spectroscopy and 9 × 103 particles/μL by naked eyes. Compared to the reported colorimetric methods for exosome quantification, visualization based on plentiful color tonalities is the most captivating merit of our approach, and HCR-induced signal amplification highlights the virtue of the strategy. The applicability of the method was validated by the analysis of clinical samples.

Controllable synthesis of Au-TiO2 nanodumbbell photocatalysts with spatial redox region

Photocatalytic water splitting has increasingly attracted attention as one of the most useful methods of converting solar energy into chemical fuel. However, the undesirable reverse reaction significantly limits the enhancement of efficiency. Herein, we fabricated an Au nanorods/TiO2 nanodumbbells structure photocatalyst (Au NRs/TiO2 NDs) via a facile synthetic strategy, which has spatially separated oxidation and reduction reaction zones. Owing to the unique structure, the charge separation of these photocatalysts can be significantly improved and the reverse reaction can be efficiently inhibited. The photogenerated electrons were injected from the TiO2 to the Au NRs, and a positively charged TiO2 region and negatively charged Au region were formed under UV irradiation. An enhanced hydrogen production performance was obtained compared with that seen in normal Au-TiO2 heterostructure. Under optimized conditions, the H2-production rate can reach up to 60,264 μmol/g/h, about six times higher than previously reported Au/TiO2 photocatalysts. Besides this, our work also demonstrates the key factors of precise synthesis of the Au NRs/TiO2 NDs structure, which provides a new perspective and experience for the design of similar catalysts.

Highly sensitive and selective visual detection of Cr(VI) ions based on etching of silver-coated gold nanorods

We report a visual detection of Cr(VI) ions using silver-coated gold nanorods (AuNR@Ag) as sensing probes. Au NRs were prepared by a seed-mediated growth process and AuNR@Ag nanostructures were synthesized by growing Ag nanoshells on Au NRs. Successful coating of Ag nanoshells on the surface of Au NRs was demonstrated with TEM, EDS, and UV–vis spectrometer. By increasing the overall amount of the deposited Ag on Au NRs, the localized surface plasmon resonance (LSPR) band was significantly blue-shifted, which allowed tuning across the visible spectrum. The sensing mechanism relies on the redox reaction between Cr(VI) ions and Ag nanoshells on Au NRs. As the concentration of Cr(VI) ions increased, more significant red-shift of the longitudinal peak and intensity decrease of the transverse peak could be observed using UV–vis spectrometer. Several parameters such as concentration of CTAB, thickness of the Ag nanoshells and pH of the sample were carefully optimized to determine Cr(VI) ions. Under optimized condition, this method showed a low detection limit of 0.4 μM and high selectivity towards Cr(VI) over other metal ions, and the detection range of Cr(VI) was tuned by controlling thickness of the Ag nanoshells. From multiple evaluations in real sample, it is clear that this method is a promising Cr(VI) ion colorimetric sensor with rapid, sensitive, and selective sensing ability.

An Efficient Electrochemiluminescence Enhancement Strategy on Bipolar Electrode for Bioanalysis.

This paper develops an efficient electrochemiluminescence (ECL) enhancement strategy on closed bipolar electrode for the detection of prostate specific antigen (PSA). We first synthesized a cyclometalated iridium(III) complex (pq)2Irbza with high ECL efficiency and used as ECL emitter in the anodic cell of BPE. While we introduced a Pt-tipped Au NRs and constructed a sandwich immune structure at the cathodic pole of BPE. Combined the signal amplification strategies of enzyme catalysis and the synergistic catalytic effect of bimetallic structure for the reduction of H2O2, the attached Pt-tipped Au NRs-GOx-Ab2 nanocomplex as both recognition probes and signal amplification units could mediate the ECL signals of (pq)2Irbza/tripropylamine (TPrA) on the anodes of BPE through faradaic reaction due to the charge neutrality of BPE. Therefore, a highly sensitive BPE-ECL sensor for detection of PSA with a detection limit of 0.72 pg/mL and a linear range from 1.0 pg/mL to 10 ng/mL was obtained. This work is expected to broaden the application of iridium complex and bimetallic nanocatalyst in biological detection and could be utilized to detect many other biological molecules.

Size-effect of gold nanorods on modulating the kinetic process of amyloid-β aggregation

Inhibiting the Aβ aggregation and understanding the kinetic process of Aβ fibrillation are very important for exploring possible tactics to treat AD. Here size-effect of Au NRs are reported to modulate the process of Aβ fibrillation. The results indicate that CTAB-stabilized Au NRs could efficiently suppress Aβ fibrillation and the inhibition efficiency of larger Au NRs is better. We calculated the relationship between Aβ aggregation rates and the sizes of Au NRs and found that the rate constant k was a quadratic function of diameters or lengths. This work provides a new strategy for exploring size-effect of nanoparticles on Aβ fibrillation.

Investigation of the LSPR on a wavelength-tunable random laser

A wavelength-tunable random laser is fabricated by a spincoating method, and the film is constructed by Polyvinyl Alcohol, Rhodamine 6G and Au NRs, using a silicon rubber slab as the substrate. The Au NRs provide a plasmonic feedback mechanism, enhancing the photoluminescence of the gain material. The wavelength of the random lasing emission is tuned by a mechanical stretch method, and the rearrangement of Au NRs has a great effect on the wavelength and polarization of the output spectra. This simple approach provides a wavelength-tuneable random laser for applications.

Gold Nanobipyramids: An Emerging and Versatile Type of Plasmonic Nanoparticles.

Gold nanobipyramids (Au NBPs) and gold nanorods (Au NRs) are two types of elongated plasmonic nanoparticles with their longitudinal dipolar plasmon wavelengths synthetically tunable from the visible region to the near-infrared region. Both have highly polarization-dependent absorption and scattering cross sections because of their anisotropic geometries. In terms of their differences, each Au NBP has five equally angularly separated twinning planes that are aligned parallel to the length direction, while the most common Au NRs are single-crystalline. As a result, Au NBPs possess two sharp end tips, while Au NRs have rounded or flat ends, resulting in very different plasmonic properties. In general, Au NBPs exhibit larger local electric field enhancements, larger optical cross sections, narrower line widths, better shape and size uniformity, and higher refractive index sensitivity than Au NRs. With the recent development of reliable methods for the growth of Au NBPs with high purity and uniformity, Au NBPs have been attracting much interest for the investigation of their intriguing plasmonic properties and applications. In this Account, we provide a concise introduction to Au NBPs, including their fascinating plasmonic properties, wet-chemistry growth methods, plasmonic applications, and structure-directing function. The synthesis of uniform Au NBPs with variable sizes is of vital importance to control their plasmonic properties. In the synthesis part, we summarize the recent developments on the synthesis of Au NBPs, with a focus on the role of seeds in the seed-mediated growth of pentatwinned Au NBPs and methods to improve their number purity. The excellent plasmonic properties of Au NBPs make them promising candidates for numerous applications. To further explore the largely improved functionalities of Au NBPs, different types of Au-NBP-based hybrid nanostructures have been prepared. They exhibit synergistic interactions between Au NBPs and the other components. We highlight the widespread plasmonic applications of Au NBPs and Au-NBP-based hybrid nanostructures in the fields of spectroscopy, photocatalysis, sensing, switching, and biomedical technologies. We next turn to the structure-directing function of Au NBPs to demonstrate the Au-NBP-directed growth of metal nanostructures and their applications. The structure-directing function is enabled by the unique pentatwinned crystalline structure of Au NBPs. Finally, we conclude with remarks on the future perspectives and research directions on Au NBPs as well as the remaining challenges. We hope that this Account will act as a platform to offer fascinating opportunities and stimulate fast-growing research on the various aspects of Au NBPs.

Colorimetric adenosine assay based on the self-assembly of aptamer-functionalized gold nanorods.

A colorimetric method is presented for ultrasensitive determination of adenosine. The assay is based on side-by-side self-assembly of aptamer-functionalized gold nanorods (Au NRs). It relies on the fact that the conjugation of the helper DNA predominantly occurs at the terminal ends of the Au NRs rather than at their sides. The adenosine aptamers consist of two pieces of ssDNA (termed C1 and C2) that were individually attached to the sides of Au NRs. In the presence of adenosine, it will be captured by C1 and C2 to form a stable sandwich structure. As a result, a side-to-side assembly of the Au NRs occurs. If the adenosine concentration is increased, the absorbance of the Au NRs at 742nm gradually decreases, and the color changes from brick red to dark brown. Response is linear range in the 10 pM to 5nM adenosine concentration range, and the detection limit is as low as 3.3 pM. Adenosine analogues such as uridine and cytidine do not interfere. The method was used to quantify adenosine in serum samples at concentrations as low as10 pM. Graphical abstractSchematic representation of an effective colorimetric method for adenosine detection based on target adenosine-induced side-by-side self-assembly of gold nanorods (Au NRs).

Studies of Ultrafast Transient Absorption Spectroscopy of Gold Nanorods in an Aqueous Solution.

Herein, ultrafast transient absorption spectroscopy is performed to probe the electron transfer studies between aqueous solution and gold nanorods (Au NRs). The seed-mediated growth method is used to synthesize crystalline cylindrical Au NRs having longitudinal plasmon resonance peak maximum at 825 nm. The as-synthesized Au NRs show average width and length of ∼10 ± 2 and ∼50 ± 2 nm, respectively, with an aspect ratio in the range of ∼5. The time-resolved decay profiles have been studied in a subpicosecond resolution range using pump wavelength at 410 nm excitation and probe wavelengths from visible to near-infrared region. The plasmon dynamics studies of Au NRs depend on the electron heating phenomena, coherent acoustic phonon vibration and electronic transient behavior, i.e., electron–phonon coupling, and homogenous dephasing processes. Thus, the obtained results highlighted that the ultrafast charge transfer dynamics studies in Au NRs could play an important role to elucidate their electronic, photothermal, and optical properties for molecular imaging, photothermal therapy, and optoelectronic and light-harvesting devices.

Plasmonic Au nanorods stabilized within anodic aluminum oxide pore channels against high-temperature treatment

Au nanorods (Au NRs) are promising candidates for sensing applications due to their tunable localized surface plasmon resonance wavelength. At temperatures above 250 °C, however, these structures are morphologically unstable and tend to evaporate. We herein report a novel refractory plasmonic nanocomposite system comprising Au NRs entrapped in anodized aluminum oxide (AAO) scaffolds that are stable up to 800 °C. Au NRs were synthesized in the cylindrical pores of sapphire-supported AAO via in situ electroless deposition on catalytic Au nanoparticles (Au NPs) anchored on the pore walls. The morphological characteristics and surface-enhanced Raman scattering (SERS) functionality of Au NRs before and after heat treatment were evaluated using SEM, XRD and Raman spectroscopy. Compared to unconfined Au NRs that evolved into spherical particles at temperatures below 250 °C and subsequently evaporated from the substrate surface, the morphology of Au NRs in AAO was preserved upon heat treatment at temperatures up to 800 °C. Furthermore, by tuning the AAO scaffolds thickness and pore diameter, the aspect ratio (AR) of the entrapped Au NRs was varied from 2.4 to 7.8. The SERS sensitivity of Au NRs in AAO was found to increase with decreasing AR when the incident light was parallel to the rod longitudinal axis, in close agreement with the calculated fourth power of the local electromagnetic field using the finite-difference time domain method.

Amplification of Raman spectra by gold nanorods combined with chemometrics for rapid classification of four Pseudomonas

This paper demonstrates the application of surface-enhanced Raman scattering (SERS) using positive charged gold nanorods (Au NRs) as an enhancement substrate to classify Pseudomonas spp. coupled with multivariate methods. Four species of Pseudomonas as dominant spoilage bacteria of food were isolated from rotten chicken, namely, Pseudomonas gessardii (P9), Pseudomonas psychrophila (P8), Pseudomonas psychrophila (S2) and Pseudomonas fluorescens (T3). Au NRs were synthesized with positive charge by seed-mediated growth method which can be adsorbed onto the surface of the bacteria by electrostatic adsorption. SERS spectra were collected individually for four types of Pseudomonas and pretreated by mean centering (MC), then principal component analysis (PCA) and hierarchical clustering analysis (LDA) were used to achieve data dimensionality reduction and visualize the result of differentiation for the species of Pseudomonas. Particularly, the classification accuracy of LDA was reached to 100%. Following we applied hierarchical clustering analysis (HCA) to cluster each species of Pseudomonas and the results of HCA consistent with the results of 16S rRNA. This study has shown that SERS combined with LDA and HCA can be used as a reliable method to classify Pseudomonas.

Gold nanorods-based hybrids with tailored structures for photoredox catalysis: fundamental science, materials design and applications

Abstract Gold nanorods (Au NRs) have received extensive attention owing to their extremely attractive applications in photoredox catalysis, plasmon-enhanced spectroscopy, biomedical technologies and optoelectronic devices. Enabled by the unique and tunable surface plasmon resonance (SPR), anisotropic Au NRs can interact with and harvest incident light covering the much of the solar spectrum. As such, they may serve as unusual media to supply energetic hot charge carriers, generate heat, and provide strong local electric field and reactive site for redox reactions through different mechanisms. In this review, we present a comprehensive overview on the burgeoning field of Au NRs-based materials for solar energy conversion. We firstly provide a detailed elucidation of the key underpinning science for plasmonic Au NRs and Au NRs-mediated catalysis. The possible charge transfer processes and corresponding roles of Au NRs played in different photoredox catalysis systems are demonstrated, followed by introducing the latest advances in constructing Au NRs-based hybrids with tailored structure. The applications of the hybrids in photoinduced catalysis, photothermal catalysis and photoelectrochemical catalysis are then discussed. Particularly, the process-intensified engineering strategies to maximize solar energy conversion efficiency are further highlighted based on some typical examples. Finally, the perspectives on future research trends and challenges in rational design and deliberate construction of Au NRs-mediated photoredox catalysis systems in a smart configuration are proposed.

Influence of diffusion and deposition processes on the electrochemical formation of gold amalgam

In this study, gold amalgam was prepared on a gold nanorods (Au Rs) modified ITO electrode through an electrochemical reduction of mercury ions (Hg2+), and the formation of amalgam was explored under steady and non-steady states. Under static system, Hg2+ was preferentially deposited at the tips of the Au NRs, and diffused along the Au NRs, because of the electrodeposition rate of Hg2+ was higher than the diffusion rate of Hg2+ in the electrolyte. Under disturbed condition, based on the continuous supply of Hg2+, mercury was gradually reduced and swelled into the interior of Au NRs leading to the formation of nanospheres. UV–vis absorption spectroscopy, transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) were utilized to demonstrate the reaction processes. This study might be able to provide the experimental basis for the preparation of bimetallic nanoalloys.

A morphology-based ultrasensitive multicolor colorimetric assay for detection of blood glucose by enzymatic etching of plasmonic gold nanobipyramids

An ultrasensitively multicolor colorimetric assay on the basis of enzyme-catalyzed reaction mediated etching of gold nanobipyramids (Au NBPs) is developed for detection of blood glucose with naked eye. This assay depends on the catalytic oxidation of H2O2 (generated from glucose oxidation) by horseradish peroxidase (HRP) to generate hydroxyl radicals (•OH) with strong oxidizability, which can accelerate the Au NBPs etching and accompany with vivid color changes and localized surface plasmon resonance (LSPR) blue shift. On the basis of this, the proposed colorimetric glucose assay accomplishes a dynamic range of 0.05–90 μM with detection limit of 0.02 μM, which is almost three orders of magnitude lower than that (10 μM) based on gold nanorods (Au NRs). Moreover, the approximate glucose levels can be intuitively and conveniently judged by the color changes with naked eye. Most importantly, visually distinguish between healthy people and diabetic patients by naked eye dispense with any sophisticated instrument is the most important highlight of this colorimetric assay, indicating the available potential for diagnosis. To the best of our knowledge, this is the first report of colorimetric assay using Au NBPs as etching substrates for visually analysis of glucose.

Synthesis of porphyrin-conjugated silica-coated Au nanorods for synergistic photothermal therapy and photodynamic therapy of tumor

Synergistic therapy of tumor has attracted the attention of an increasing number of researchers because of its higher efficiency compared to single therapy. Herein, 4-carboxyphenyl porphyrin-conjugated silica-coated gold nanorods (AuNR@SiO2-TCPP) were synthesized. The synergistic treatment of photothermal therapy and photodynamic therapy on A549 cancer was researched in vivo and in vitro. In the AuNR@SiO2-TCPP, Au NRs and TCPP act as photothermal agent and photosensitizer, respectively. The temperature of the AuNR@SiO2-TCPP (0.11 nmol L−1) rises to 56.8 °C for 10 min under the illumination of 808 nm laser (2 Wcm−2). In MTT assays, the viability of A549 cancer cell treated with AuNR@SiO2-TCPP (100 μg ml−1) is only 21%. In animal experiments, the relative tumor volumes in mice receiving AuNR@SiO2-TCPP (5 mg kg−1) with 660 and 808 nm irradiations were significantly inhibited and the average value is decreased to 0.78 while the average value of the control group is increased to 7.2. These results demonstrate that the AuNR@SiO2-TCPP is a potential nanomedicine against tumor for clinical application in the near future.

Construction of FRET biosensor for off-on detection of lead ions based on carbon dots and gold nanorods

Exploring new energy donor/acceptor pairs for constructing FRET system has important research significance. In this study, a FRET assembly by using carbon dots (CDs) as energy donor and gold nanorods (Au NRs) as energy acceptor has been proposed through covalent bond interactions by taking advantage of cysteamine as a bridge. The assembly is characterized by UV–vis absorption spectra, fluorescence spectra, FT-IR spectra and TEM images, revealing that Au NRs successfully absorbed on the surface of CDs. As for the occurrence of FRET process from CDs to Au NRs, the fluorescence signal of CDs-cysteamine-Au NRs assembly quenched significantly. Interestingly, Pb2+ ions could bind completely with cysteamine and disturbed the FRET process, which activated fluorescence signal of the system. Based on these experimental phenomena, CDs-cysteamine-Au NRs assembly was performed as an off-on FRET biosensor for Pb2+ ions. The linear range obtained is from 0 to 155 μM with the detection limit of 0.05 μM. Moreover, the FRET-based sensor exhibited high selectivity to the analyte Pb2+ ions against other interference substances. Furthermore, the present approach was successfully applied to detect Pb2+ ions in real samples, which suggested its potential applications in environmental monitoring.

Smart nanoplatform for sequential drug release and enhanced chemo-thermal effect of dual drug loaded gold nanorod vesicles for cancer therapy

BackgroundThe combination of multiple chemotherapeutics has been used in the clinic for enhanced cancer chemotherapy, however, frequent relapse, chemo-resistance and side effects remains therapeutic hurdles. Thus, the development of co-delivery system with enhanced targeting and synergistic different modal treatments has been proposed as promising strategies for intensive improvement of the therapeutic outcomes.ResultsWe fabricated a nanocarrier based on gold nanorods (Au NRs), cRGD peptide-modified and multi-stimuli-responsive paclitaxel (PTX) and curcumin (CUR) release for synergistic anticancer effect and chemo-photothermal therapy (PTX/CUR/Au NRs@cRGD). The specific banding of cRGD to αvβ3 integrin receptor on the tumor cell surfaces facilitated the endocytosis of PTX/CUR/Au NRs@cRGD, and the near-infrared ray (NIR) further enhanced the drug release and chemotherapeutical efficiency. Compared to single drug, single model treatment or undecorated-PTX/CUR/Au NRs, the PTX/CUR/Au NRs@cRGD with a mild NIR showed significantly enhanced apoptosis and S phase arrest in three cancer cell lines in vitro, and improved drug accumulation in tumor sites as well as tumor growth inhibition in vivo.ConclusionsThe tumor targeted chemo-photothermal therapy with the synergistic effect of dual drugs provided a versatile strategy for precise cancer therapy.