Self-assembly Of Gold Nanorods Research Articles

Thiols Modulated Gold Nanorods Self-Assembly: Indirect Hydrophobic Effects Instead of Direct Electrostatic/Hydrogen Bonds Attraction.

For nanocrystals (NCs) self-assembly, understanding the chemical and supramolecular interactions among building blocks is significant for both fundamental scientific interests and rational nanosuperstructure construction. However, it has remained an extreme challenge for many self-assembly systems due to the lack of appropriately quantitative approaches for the corresponding exploration. Herein, by combination of the proposed colorimetric method for cationic surfactant quantitation and all-atom simulations, we manage to present a clear chemical picture for the thiol molecules modulated self-assembly of gold nanorods (GNRs), one of the earliest and most convenient methods for the fabrication of freestanding GNR self-assemblies. It is revealed that the self-assembly of GNRs is driven by the hydrophobic effects of the alkyl chains of the modified cationic surfactants, as their bilayer structure is destroyed by the added thiol molecules. In other words, the actual roles of the thiol molecules for causing GNRs assembly are indirectly inductive effects instead of the previously believed direct electrostatic attraction and/or hydrogen-bond linking effects of the binding thiol molecules. Furthermore, the GNRs exhibit diameter-dependent assembly behaviors: thicker GNRs tend to adopt the end-to-end assembly mode, while thin ones prefer the side-by-side assembly mode, further demonstrating that hydrophobic effects among the build blocks are the driving force for the GNRs assembly.

Au nanorod assembly for sensitive SERS detection of airway inflammatory factors in sputum.

In this paper, we demonstrate a surface-enhanced Raman spectroscopy (SERS) biosensor based on the self-assembly of gold nanorods (AuNRs) for the specific detection of airway inflammatory factors in diluted sputum. The AuNR surface was modified with an antibody that was able to specifically recognize an airway inflammatory factor, interleukin-5 (IL-5), so that a end-to-end self-assembly system could be obtained, resulting in an order of magnitude amplification of the Raman signal and greatly improved sensitivity. Meanwhile, the outer layer of the biosensor was coated with silicon dioxide, which improved the stability of the system and facilitated its future applications. When the detected concentration was in the range of 0.1-50pg/mL, the SERS signal generated by the sensor showed a good linear relationship with the IL-5 concentration. Moreover, it had satisfactory performance in diluted sputum and clinical subjects with asthma, which could achieve sensitive detection of the airway inflammatory factor IL-5. Overall, the developed biosensor based on the SERS effect exhibited the advantages of rapid and sensitive detecting performance, which is suitable for monitoring airway inflammatory factors in sputum.

Self-assembly of Gold Nanorods into a Highly Ordered Sheet via Electrostatic Interactions with Double-stranded DNA

Assemblies of cationic gold nanorods (AuNRs) via electrostatic interactions with double-stranded (ds) DNA were investigated in solution and after evaporation as a cast-film. Interestingly, moderately positively charged AuNRs assembled with dsDNA provided a monolayer sheet with an ordered alignment resembling a two-dimensional (2D) smectic structure during solvent evaporation.

Electrostatically self-assembled gold nanorods with chondroitin sulfate for targeted photothermal therapy for melanoma

BackgroundThe application of gold nanorods (GNRs) in photothermal therapy is a promising avenue for cancer treatment. The aim of this study was to develop a GNR-based targeted photothermal therapy for melanoma. MethodsWe utilized the electrostatic interaction between cationic GNRs and an anionic polymer chondroitin sulfate A (CSA), which has an affinity for binding to melanoma cells, to construct an anionic binary GNR-CSA complex (GNR-CS) at an optimal theoretical charge ratio of the trimethylammonium groups of GNR: carboxyl and sulfate groups of CSA = 1:2.5. The cytotoxicity to normal cells and erythrocyte agglutination activity of GNR-CS were evaluated. After the cellular uptake of GNR-CS by melanoma cells (B16-F10) was investigated, the photothermal performance of GNR-CS against B16-F10 cells was evaluated in vitro. ResultsThe particle size and zeta potential of GNR-CS were approximately 35 nm and -20 mV, respectively. GNR-CS showed little cytotoxicity to normal cells and low erythrocyte agglutination activity, indicating good biocompatibility. Compared with negatively-charged GNR, GNR-CS was highly taken up by B16-F10 cells even if it was negatively charged. Cellular uptake was significantly suppressed upon treatment with excess CSA, suggesting the involvement of a CSA-specific uptake pathway. Furthermore, irradiation of the GNR-CS solution with near-infrared (NIR) light increased its temperature in light-intensity and GNR-concentration dependent manners. GNR-CS exhibited significant and GNR-dose dependent cytotoxicity in melanoma cells in combination with NIR light irradiation. ConclusionGNRs coated with CSA have the potential as a medicine in targeted photothermal therapy for melanoma.

Non-enzymatic colorimetric sensor for cardiac Troponin I (cTnI) based on self-assembly of gold nanorods on heparin

The paper reports a simple enzyme-free colorimetric sensor for the detection of cardiac marker, Troponin I (cTnI) based on the self-assembly of gold nanorods (AuNRs) on heparin. The sensing system consists of a purple colour solution of Hexadecyltrimethylammonium bromide (CTAB) stabilised AuNRs self-assembled in presence of heparin due to the electrostatic interaction resulting in the reduction of surface plasmon absorption (SPR) of AuNRs and hence colour quenching/change of solution from red to blue. However, in the presence of cTnI, the electrostatic balance was disturbed due to the strong complex forming tendency between heparin and cTnI which was attributed due to the stronger complex forming tendency between the sulphate and carboxylate group of glycosaminoglycans and heparin binding proteins present in cTnI. Hence, the AuNRs are left free in the solution and retains the native red colour of the solution. As the concentration of cTnI in the solution was increased, the colour gradually changes from blue to red there by enabling the sensing of cTnI. The above mechanisms were confirmed by transmission electron microscopy. The AuNR aggregation was found to be inversely proportional to the concentration of cTnI. The change in absorbance of AuNRs with different concentrations of cTnI was monitored by UV-Visible spectroscopy. Using this sensor system, cTnI in the range of 0.5–15 ng/mL could be measured with a detection limit of 0.4 ng/mL. The system also showed good selectivity in presence of different competing substances under the same experimental conditions. The method appears to be simple, cost effective, and would be highly be beneficial in rural health care centres where high tech diagnostic aids are inaccessible.

Optimization of gold nanorod arrays for surface enhanced Raman spectroscopy (SERS) detection of atrazine.

Recently, there has been increasing concern over the widespread use of the herbicide atrazine which has been reported to have problematic side effects on local ecosystems. This has highlighted the need for rapid and accurate point-of-need assessment tools for analytical determination of herbicides in ground and surface waters. Surface enhanced Raman spectroscopy (SERS) is a sensitive vibrational spectroscopy technique which has recently been employed for the analysis of a variety of analytes in water, ranging from pharmaceuticals to pesticides. In this work, SERS sensors constructed using gold nanorod (AuNR) arrays are optimized and then utilized for the rapid and sensitive detection of atrazine. In this study, the effect of relative humidity on the self-assembly of gold nanorods into arrays was explored, and the SERS performance was assessed using para-aminothiophenol as a SERS probe. Once the SERS performance of the substrates was deemed optimal, the detection of atrazine was highlighted. This work represents the first time that relative humidity has been explored as an optimization strategy for controlled alignment of gold nanorods for SERS analysis of atrazine.

Electrochemical immunosensor based on self-assembled gold nanorods for label-free and sensitive determination of Staphylococcus aureus

An electrochemical immunosensor based on self-assembled gold nanorods on glassy carbon electrode was developed for label-free and sensitive detection of Staphylococcus aureus (S. aureus). The gold nanorods were firstly assembled on the electrode surface by using poly-(diallyldimethylammonium chloride) (PDDA) and poly-(styrenesulfonate) (PSS) as the linkers, followed by the functionlization of anti-S. aureus antibodies. The immobilized antibodies on self-assembled gold nanorods could efficiently capture S. aureus to the modified electrode by the specific immune reaction, which clearly blocked the electron transfer of electrochemical probes on the electrode surface due to the resistance of S. aureus. Atomic force microscopy and electrochemical impedance spectroscopy were used to verify the stepwise assembly of the immunosensor fabrication. The immunosensor could detect S. aureus in a linear range from 1.8 × 103 to 1.8 × 107 CFU mL−1 with a low detection limit of 2.4 × 102 CFU mL−1. Furthermore, the designed electrochemical immunosensor was successfully used to determine S. aureus in milk samples with acceptable results. The proposed immunosensor could be further expanded to sensitive detect other pathogens with the addition of specific antibodies.

Hierarchical Colloidosomes with a Highly Ordered and Oriented Arrangement of Gold Nanorods via Confined Assembly at the Emulsion Interface

Self-assembly of gold nanorods (AuNRs) into hierarchically ordered superstructures is a prerequisite for the fabrication of functional materials and devices. Although 1D linear and 2D sheetlike ord...

Building vertical gold nanorod arrays to enhance upconversion luminescence of <i>β</i>-NaYF<sub>4</sub>: Yb<sup>3+</sup>/Er<sup>3+</sup> nanocrystals

The plasmon resonance effect is one of the effective ways to enhance the upconversion (UC) luminescence, which is realized by enhancing the electromagnetic field from incident light interacting with free electrons of AuNRs surface. In this work, a series of GVA@SiO<sub>2</sub>@NaYF<sub>4</sub>:Yb<sup>3+</sup>/Er<sup>3+</sup> composite structures with different thickness values of SiO<sub>2</sub> isolation layer is successfully built from self-assembled gold nanorods, steamed SiO<sub>2</sub>, and spin-coating rare-earth nanocrystals. The results of the SEM indicate that the size of gold-nanorods is approximately 22 nm in diameter and 65 nm in length. The X-ray diffraction and transmission electron microscope results demonstrate that the NaYF<sub>4</sub>:Yb<sup>3+</sup>/Er<sup>3+</sup> nanocrystals possess hexagonal-phase structure with a size of about 20 nm. Under 980 nm near-infrared (NIR) excitation, the UC emission characteristics of GVA@SiO<sub>2</sub>@NaYF<sub>4</sub>:Yb<sup>3+</sup>/Er<sup>3+</sup> composite structure are studied by using a confocal microscope spectroscopic test system, and regulated by changing the thickness of SiO<sub>2</sub> isolation layer. The results indicate that the UC emission intensity of NaYF<sub>4</sub>:20%Yb<sup>3+</sup>/2%Er<sup>3+</sup> nanocrystals is enhanced by about 8.8 times, and the enhancement factor of red UC emission intensity is about 16.2. In order to further prove the enhancement effect of the red UC emission, the GVA@SiO<sub>2</sub>@NaYF<sub>4</sub>:40%Yb<sup>3+</sup>/20%Er<sup>3+ </sup>composite structure with red UC emission is constructed in the same way. It can be found that the UC emission intensity of NaYF<sub>4</sub>:40%Yb<sup>3+</sup>/20%Er<sup>3+</sup> nanocrystals is enhanced by 8.7 times and the red UC emission intensity is raised by about 9.7 times under the 980 nm NIR excitation. The corresponding excitation enhancement mechanism is simulated according to the power excitation dependence. And it is found that the rate of UC emission decreases and the R/G ratio also decreases with the excitation pump power increasing. The analysis of the above results shows that the excitation enhancement plays a leading role and is accompanied by emission enhancement. Meanwhile, the study of Er<sup>3+</sup> ion dynamic process indicates that the Er<sup>3+</sup> ion transition rate is accelerated due to the coupling from UC emission peaks and gold nanorod absorption peaks in GVA@SiO<sub>2</sub>@NaYF<sub>4</sub>:40%Yb<sup>3+</sup>/20%Er<sup>3+ </sup>composite structure. The enhancement mechanism of UC emission is also simulated, which further proves that the excitation enhancement is dominant. This kind of composite structure can not only help us to further understand the physics mechanism of the plasmon-enhanced UC luminescence but also promote the applications of rare-earth materials in medical imaging and fingerprint recognition.

Morphologies of self-assembled gold nanorod-surfactant-lipid complexes at molecular level

Gold nanorods (GNRs) have aroused the extensive interest of many researchers in recent years due to their unique physicochemical properties. However, the toxic cetyltrimethylammonium bromide (CTAB) is often introduced into the process of synthesizing GNRs, which hinders the wide-range applications of GNRs in clinical practice. To reduce the toxicity, the CTAB molecules coated on the surface of GNRs should be replaced by nontoxic and biocompatible agents such as phospholipid. Thus the component and morphology of the mixed coating agents on the surface of GNRs affect the physicochemical properties of GNRs. To study the morphology and properties of the coated GNRs at a molecular level, we investigate the self-assembly of GNRs, CTAB, and dimyristoyl phosphatidylcholine (DMPC) by using solvent-free dissipative particle dynamics simulations. Our results show that the morphology of the assembled complex mainly depends on the CTAB/DMPC molar ratio, while neither of the interaction strength between GNRs and the coating agents nor the diameter of GNRs has significant effect on the morphology. At a certain combination of GNRs-coating agent interaction strength with GNRs diameter, the mixture of CTAB and DMPC on the surface of GNRs undergoes a gradual change in morphology as the CTAB/DMPC molar ratio increases, including the forming of intact bilayer membrane, cracked bilayer membrane, long patches of micelles, and short wormlike micelles winding GNRs in spiral shape. The morphology of intact bilayer membrane verifies the experimental guess, while the other three morphologies are brand-new discoveries. We also find that when the GNR’s diameter becomes smaller, or the CTAB/DMPC molar ratio is larger, or the interaction strength is greater, the agents cap the ends of GNRs, meanwhile the membrane thickness becomes thinner. The multiple morphologies of the assembled complexes can be qualitatively explained by the shape energy of a membrane adsorbed on a solid surface. When the surface tension of the membrane (which is proportional to the spontaneous curvature of the membrane) exceeds a critical value (which is equal to the adhesion energy density of the membrane), the membrane dissociates from the solid surface and its shape changes. The change trend is related to the spontaneous curvature of the free membrane. As a result of the synergy and competition among the inherent curvatures of GNRs, the spontaneous curvature of CTAB/DMPC membrane or micelle, as well as the adhesion energy, various interesting morphologies are produced. Our simulations and analyses directly characterize the morphological structures of CTAB and lipid coated GNRs, which allow us to in depth understand the self-assembling behaviors of GNRs at a molecular level. This is also conductive to achieving the controlled assemblies of GNRs.

Synthesis of gold nanorods with varied length-diameter ratios-applications using SERS for the detection of drugs

We herein report the preparation, optical properties, and use of gold nanorods for the detection and analysis of additives and impurities in weight-loss healthcare products. Gold nanorods with different aspect ratios were synthesized by controlling the silver nitrate content. The resulting self-assembled gold nanorods, combined with a portable Raman spectrometer, were used as surface-enhanced Raman scattering substrates to analyze and detect phenolphthalein and sibutramine hydrochloride in a simulated aqueous solution. The obtained results indicate the high sensitivity and stability of this detection method owing to the use of gold nanorod substrates prepared from 100 μL silver nitrate. Therefore, the proposed detection method has potential for promoting the application of Raman spectroscopy in the detection of such drugs.

Salt Mediated Self-Assembly of Poly(ethylene glycol)-Functionalized Gold Nanorods

Although challenging, assembling and orienting non-spherical nanomaterials into two- and three-dimensional (2D and 3D) ordered arrays can facilitate versatile collective properties by virtue of their shape-dependent properties that cannot be realized with their spherical counterparts. Here, we report on the self-assembly of gold nanorods (AuNRs) into 2D films at the vapor/liquid interface facilitated by grafting them with poly(ethylene glycol) (PEG). Using surface sensitive synchrotron grazing incidence small angle X-ray scattering (GISAXS) and specular X-ray reflectivity (XRR), we show that PEG-AuNRs in aqueous suspensions migrate to the vapor/liquid interface in the presence of salt, forming a uniform monolayer with planar-to-surface orientation. Furthermore, the 2D assembled PEG functionalized AuNRs exhibit short range order into rectangular symmetry with side-by-side and tail-to-tail nearest-neighbor packing. The effect of PEG chain length and salt concentration on the 2D assembly are also reported.

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).

A colorimetric sensor for protamine detection based on the self-assembly of gold nanorods on graphene oxide

Here, we report a simple colorimetric detection method for the determination of protamine based on the self-assembly of gold nanorods (AuNRs) on graphene oxide (GO).

Visual colorimetric sensing system based on the self-assembly of gold nanorods and graphene oxide for heparin detection using a polycationic polymer as a molecular probe

Simple colorimetric system based on gold nanorods-graphene oxide self-assembly for heparin detection using a polycationic polymer as a molecular probe is shown here.

Plasmonic microgels of Au nanorods: Self-assembly and applications in chemophotothermo-synergistic cancer therapy

Plasmonic microgels (PMgels) of the self-assembled gold nanorods (Au NRs) with side-by-side piles in ionic liquid microgels were prepared. Transmission electron microscopy (TEM) images revealed unique self-growth and self-arrangement of Au NRs in the microgel systems. The fabrication of PMgels occurs through co-assembling Au NRs and an ionic liquid microgel system, therefore differs from the fabrication of conventional plasmonic hybrid nanocomposites. These PMgels showed strong absorption in the near-infrared window and enhanced photothermal conversion efficiency, up to 52.8%, compared to the Au NRs (22%) as a result of the ordering and dense packing of Au NRs in the microgels. When the PMgels were exposed to a near-IR laser, the doxorubicin hydrochloride (Dox) released from PMgels and the resulting thermal effect can immensely inhibit tumor growth both in vitro and in vivo. The tests demonstrated that no tumor metastasis occurred. This platform of the PMgels with the laser-controlled delivery system could provide chemo-photothermal synergistic therapy for a wide spectrum of diseases.

Femtosecond mode-locking of an ytterbium-doped fiber laser using self-assembled gold nanorods

We experimentally demonstrate the use of a saturable absorber (SA) based on self-assembled gold nanorods (GNRs) for femtosecond mode-locking of an ytterbium-doped fiber-based 1 µm laser. A novel type of SA was made by implementation of an end-to-end GNRs self-assembly technique through hot-air induced rapid drying of the GNRs in a deionized water suspension, which enabled us to enhance optical absorption in the 1.06 µm wavelength region. By incorporating this novel SA into an ytterbium-doped fiber-based ring cavity under dispersion-managed conditions, we were able to readily generate mode-locked, soliton pulses having a temporal width of 840 fs at 1063.9 nm. To the best of our knowledge, this is the first demonstration of the effectiveness of a GNRs-based SA for the generation of femtosecond soliton pulses operating in the 1 µm range.

Towards In Vivo Tumor Detection Using Polarization and Wavelength Characteristics of Self‐Assembled Gold Nanorods

AbstractThis work suggests a novel concept for sensing the back‐reflected and absorbed light at two polarization states and at several wavelengths based on self‐assembled gold nanorods (SGNs). While the SGNs are flowing in the bloodstream, the reflected light has a low degree of polarization at the specific wavelength. In comparison, when the SGNs are not moving, such as when the SGNs are located in a tumor, the reflected light has a high degree of polarization. Impressively, the SGNs structures further display a considerably improved contrast in the diffusion reflection (DR) system. Such characteristics provide a new strategy for possible in vivo detection of a tumor with enhanced resolution.

Light-triggered Assembly of Gold Nanorods based on Photoisomerization of Spiropyrans

The self-assembly of gold nanorods (AuNRs) derivatized with photoisomerizable spiropyran ligands was investigated. Under UV irradiation, the AuNRs that were functionalized on the surface by spiropyran with a dithiolane formed end-to-end assemblies accompanied with isomerization of the spiropyran moiety, simultaneously showing a red-shift of the longitudinal plasmon band and the increase in absorbance resulted from the merocyanine form. The networked structure of AuNRs was ultimately built “on demand” by UV irradiation.

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.