Flower-like Gold Nanostructures Research Articles

A sensitive electrochemical sensor based on graphene quantum dots/hierarchical flower-like gold nanostructures for determination of cytostatic drug flutamide

Using an electrochemical sensor with high sensing capability and manufacturing simplicity, flutamide (FLU) can be quantitatively measured. A glassy carbon electrode is modified with graphene quantum dots (GQDs) and hierarchical flower-like gold nanostructures (HFGNs). Combining GQDs and HFGNs enhanced the electrode surface and electron transfer rate, improving the signal's intensity and sensitivity. Nanostructure characterization, electrochemical characterization, and detection studies indicated the high performance of the platform in terms of sensitivity, selectivity, reproducibility, and stability. With these improvements, linear correlations were achieved between 0.01 and 400 µM, with a detection limit of 6.2 nM (based on 3Ssb/m). Pharmaceuticals and complex biological samples along with interfering agents have been successfully analyzed with this platform.

Sensitive detection of folate receptor-positive circulating tumor cells based on intracellular uptake of the PbS nanoparticle cluster-loaded phospholipid micelles decorated with folic acid in combination with E-DNA sensor

Developing methods for the circulating tumor cells (CTCs) detection is important for noninvasive cancer diagnosis. A sensitive method for homogeneous electrochemical detection of CTCs was developed based on the affinity of folic acid (FA) for folate receptor (FR), which is overexpressed on the CTC surface. The PbS nanoparticle cluster-loaded phospholipid micelles decorated with FA were prepared and used as a nanoprobe. The specific binding of FA to FR-positive CTCs leads to the uptake of the nanoprobes into the CTCs. Cellular imaging assay showed the excellent biocompatibility and selectivity of nanoprobes. After separation of intracellular nanoprobes and the residual free nanoprobes in the solution by centrifugation, nanoprobes in the cell were dissolved using acid. The amount of the target cells was quantified by the electrochemical detection of Pd2+ using the electrochemical DNA (E-DNA) sensor, which was fabricated based on the self-assembly of probe DNA on the flowerlike gold nanostructures modified the screen-printed carbon electrode (SPCE). Because of the large quantities of detectable Pd2+ contained in the nanoprobes, the signal amplification effect was achieved. The developed electrochemical assay allows the detection of ∼5 cells from 1 mL of sample. Studies with both healthy individuals and cancer patient blood samples demonstrate that the assay is sensitive and FR-positive CTCs specific.

Flower-like biogenic gold nanostructures for improved catalytic reduction of 4-nitrophenol

In this study, novel flower-like biogenic gold nanostructures were prepared using gallnut extract and HAuCl4. Gallnut extract is a rich source of phytochemicals such as tannic acid, gallic acid, and polyphenol antioxidants. The process involves the reduction of gold ions in the presence of gallnut main constituents that act as a reducing and shape directing agent for Au. The formation of gold nanoflowers (AuNFs) was confirmed by UV–visible spectroscopy at 629 nm. The absorbance broadened over time, confirming that the size of the nanoparticles increased, resulting in a flower-like framework. Transmission electron microscope analysis showed that gold nanoparticles (AuNPs) with an average size of 8.02 nm self-assemble and grow into nanoflowers with an average diameter of 60.6 nm. In addition, the catalytic behavior of AuNPs and AuNFs was compared for the reduction of 4-nitrophenol to 4-aminophenol. AuNFs showed up to 1.57 times higher catalytic activity towards 4-nitrophenol than AuNPs. The conversion yield of 4-nitrophenol to 4-aminophenol for AuNFs was determined to be 98.1% using high performance liquid chromatography. AuNFs synthesized using green process can be applied in catalysts, wastewater treatment, and sensors.

Gold nanoflowers grown in a porous Si/SiO2 matrix: The fabrication process and plasmonic properties

Highly branched metal nanostructures are of great interest for creating highly sensitive sensors of various molecules through the use of surface-enhanced Raman scattering. However, the method of manufacturing such nanostructures is often complex and difficult to reproduce. Herein, we report a simple, one-pot synthesis of flower-like gold nanostructures (AuNFs) in a porous Si/SiO2 matrix for potential surface enhanced Raman spectroscopy (SERS) applications. Templates covered with 500-nm diameter AuNFs with rough coral-like petals were obtained through a simple electroless reduction of gold(III) chloride salt in diluted hydrofluoric acid inside pores in the Si/SiO2 layer, which were obtained by swift heavy ion track technology. Detailed SERS analysis showed that single nanoflowers are capable of enhancing Raman signals and can be used as independent nanosensors. Having a few AuNFs in close proximity to each other enables more “hot spots” to be formed with an even greater increase in signal intensity. Using such substrates, reliable detection of 4-mercaptopyridine could be achieved down to 0.01 µM concentration. Finally, we theoretically demonstrate that the AuNFs are characterized by a wide-band plasmonic mode as well as by hot spots in the electromagnetic near-field distribution, which can result in a high enhancement factor for Raman scattering.

An electrochemical aptasensing platform for carbohydrate antigen 125 based on the use of flower-like gold nanostructures and target-triggered strand displacement amplification.

An electrochemical aptasensing method is described for the determination of the biomarker CA125. It combines aptamer recognition and target-triggered strand displacement amplification. Flower like gold nanostructures were electrodeposited on a screen-printed carbon electrode to increase the sensor surface, to assemble more toehold-containing hairpin probe 1 (Hp1), and to improve the accessibility for DNA strands. Under the optimal conditions, this assay has a linear response in the 0.05 to 50ng•mL-1 CA125 concentration range, with a low detection limit of 5.0pg•mL-1. This method is specific and stable. It was successfully applied to the detection of CA125 in spiked biological samples, with recoveries between 82.5% and 104.1%. Graphical abstract.

Synthesis of multi-branched gold nanostructures and their surface-enhanced Raman scattering properties of 4-aminothiophenol

Abstract

On-Electrode Synthesis of Shape-Controlled Hierarchical Flower-Like Gold Nanostructures for Efficient Interfacial DNA Assembly and Sensitive Electrochemical Sensing of MicroRNA.

The performance for biomolecular detection is closely associated with the interfacial structure of a biosensor, which profoundly affects both thermodynamics and kinetics of the assembly, binding and signal transduction of biomolecules. Herein, it is reported on a one-step and template-free on-electrode synthesis method for making shape-controlled gold nanostructures on indium tin oxide substrates, which provide an electrochemical sensing platform for ultrasensitive detection of nucleic acids. Thus-prepared hierarchical flower-like gold nanostructures (HFGNs) possess large surface area that can readily accommodate the assembly of DNA probes for subsequent hybridization detection. It is found that the sensitivity for electrochemical DNA sensing is critically dependent on the morphology of HFGNs. By using this new strategy, a highly sensitive electrochemical biosensor is developed for label-free detection of microRNA-21 (miRNA-21), a biomarker for lung cancers. Importantly, it is demonstrated that this biosensor can be employed to measure the miRNA-21 expression level from human lung cancer cell (A549) lysates and worked well in 100% serum, suggesting its potential for applications in clinical diagnosis and a wide range of bioanalysis.

Flower-like gold nanostructures electrodeposited on indium tin oxide (ITO) glass as a SERS-active substrate for sensing dopamine

Flower-like gold nanostructures (so called gold nanoflowers) were electrodeposited on indium tine oxide (ITO) glass and served as a SERS-active substrate for sensing dopamine. A double-potential method was applied for the deposition of gold nanostructures on the glass. The density, size, and morphology of the gold nanostructures were controlled by adjusting parameters such as deposition potentials, duration, and concentrations of gold precursors. The particle density on the glass was controlled by changing the overvoltage potentials, while the size and morphology were controlled by changing the concentration of gold precursors and growth times of Gold crystal seeds. The intensity of the Raman spectrum of dopamine was distinctly enhanced on the gold nanostructures with unique flower-like topography, thereby demonstrating the utility of this SERS-active substrate that is facilely obtained by the double-potential deposition method without supporting electrolytes.

Facile synthesis of hydrangea flower-like hierarchical gold nanostructures with tunable surface topographies for single-particle surface-enhanced Raman scattering.

The physicochemical properties of noble metal nanocrystals depend strongly on their size and shape, and it is becoming clear that the design and facile synthesis of particular nanostructures with tailored shape and size is especially important. Herein a novel class of hydrangea flower-like hierarchical gold nanostructures with tunable surface topographies and optical properties are prepared for the first time by a facile, one-pot, seedless synthesis using ascorbic acid (AA) to reduce hydrogen tetrachloroaurate (HAuCl4) in the presence of (1-hexadecyl)trimethylammonium chloride (CTAC). The morphologies of the synthesized gold nanoflowers are controlled and fine-tuned by varying the synthetic conditions such as the concentration of reagents and the growth temperature. Due to their unique hierarchical three-dimensional (3D) structures with rich hot spots, these gold nanoflowers exhibit an efficient performance in single-particle surface-enhanced Raman scattering (SERS). The work stands out as an interesting approach for anisotropic particle synthesis and morphological control, and the proposed novel, hierarchical gold nanoflowers have a number of exciting potential applications in SERS-based sensors.

One-step synthesis of dendritic gold nanoflowers with high surface-enhanced Raman scattering (SERS) properties

A facile method to synthesize flower-like gold nanostructures showing multiple tips with dendritic structures is developed through a one-step reduction of HAuCl4 with dopamine at room temperature. The gold nanoflowers clearly increase the surface enhanced Raman scattering (SERS) effect, demonstrate promising biocompatibility, and could be internalized by cancer cells, indicating their potential for biomedical applications.

Ultrafast growth of dendritic gold nanostructures and their applications in methanol electro-oxidation and surface-enhanced Raman scattering

A simple and rapid solution-phase synthesis of dendritic gold nanostructures with hyperbranched architecture is demonstrated in this report. Further investigations revealed that the morphology of the synthesized sample depended on proper parameters such as reagent concentration, reaction temperature, reagent addition sequence and stir. Moreover, the dendritic gold nanostructures exhibited a good electrocatalytic activity toward methanol electro-oxidation. When compared with sea-urchinlike and flowerlike gold nanostructures which were prepared by varying the parameters of experiment, dendritic gold nanostructures showed the highest surface-enhanced Raman scattering (SERS) sensitivity using 4-aminothiophenol (4-ATP) as probe molecules. The dendritic gold nanostructures may find potential applications in catalysis, SERS and biosensor.

Switching of hydrophilic to ultra hydrophilic properties of flower-like gold nanostructures

Flower-like morphologies of gold nanostructures were obtained via chemical method by controlling molar concentration ratio of reducing agent and precursor. Chloroauric acid was used as a metal precursor while tri-sodium citrate as the reducing agent. These flower-like structures were characterized by UV–vis spectroscopy, Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD) techniques. The basic crystallite size calculated via XRD measurement was found to be ∼10 nm and remain unaffected by the different concentration ratios. The coating of these structures was made over clean glass substrate and analyzed for wettability by measuring their water contact angles. Our analysis indicates that the coatings of hierarchical flower-like structures of gold are able to provide ultra hydrophilic properties to glass substrate.

Electrochemical growth of flowerlike gold nanoparticles on polydopamine modified ITO glass for SERS application

A functional biopolymer – polydopamine (Pdop) layer was easily modified on the surface of indium tin oxide substrates by spontaneous oxidative polymerization in a dopamine solution. The Pdop layer functions as a novel and promising protector for electrochemical growth of flowerlike gold nanostructures (AuNFs). Electrochemical investigations and SEM results demonstrate that Pdop coating is favored to rapid gold nucleation. The application of AuNFs in surface-enhanced Raman scattering is investigated by using rhodamine 6G as probe molecule. Its detection limit reaches as low as 10 −12 M. Pdop coating as a functional platform to prepare AuNFs is promising for potential applications in sensitive optical chemical sensors.

Synthesis of different gold nanostructures by solar radiation and their SERS spectroscopy

AbstractIn this article, a simple and novel photochemical synthesis of different gold nanostructures is proposed using solar radiation. This method is rapid, convenient and of low cost, and can be performed under ambient conditions. By adjusting the concentration of sodium acetate (NaAc), different morphologies of the products can be easily obtained. Without NaAc, the products obtained are mainly polyhedral gold particles; lower concentration of NaAc (0.05 and 0.1 M) accelerates the formation of flowerlike gold nanostructures; while higher concentration of NaAc (0.5 M) facilitates the formation of a variety of gold nanowires and nanobelts. It is found that the morphology change of gold nanaostructures is the result of the synergistic effect of poly(diallyl dimethylammonium) chloride (PDDA), Ac− ions, and the pH value. In addition, the different gold nanostructures thus obtained were used as substrates for surface‐enhanced Raman scattering (SERS) with p‐aminothiophenol (p‐ATP) as the probe molecule. In comparison, the flowerlike gold nanostructures show stronger SERS effect than the other gold nanostructures, which is associated with their unique geometrical shapes providing highly localized electromagnetic (EM) field for the optical enhancement to the probe molecules. These gold nanostructures, with different geometrical shapes, might have potential applications in the areas of photonics, optoelectronics and optical sensing. Copyright © 2009 John Wiley & Sons, Ltd.

Growth Mechanism of Flowerlike Gold Nanostructures: Surface Plasmon Resonance (SPR) and Resonance Rayleigh Scattering (RRS) Approaches to Growth Monitoring

A facile method is proposed for the room-temperature synthesis of flowerlike gold nanostructures (AuNFs) with a size of 50−115 nm by reducing HAuCl4 with ascorbic acid (AA) in the presence of chitosan. It was found that the concentration of chitosan controlled the size, while that of AA influenced the morphology of as-prepared AuNFs. With higher concentration of AA flowerlike nanostructures were produced, whereas with lower concentration of AA quasi-spherical nanoparticles were formed. Time-dependent surface plasmon resonance (SPR) absorption spectroscopy and the resonance Rayleigh scattering (RRS) technique were used to monitor the growth processes. According to the temporal evolutions of SPR maximum absorption wavelength and RRS intensity, a second growth mechanism is proposed to explain the effect of AA concentration on the morphology and the effect of chitosan concentration on the size of obtained gold nanostructures. In order to determine whether or not the present method is suitable for synthesis of...

Chitosan-Luminol Reduced Gold Nanoflowers: From One-Pot Synthesis to Morphology-Dependent SPR and Chemiluminescence Sensing

By reducing HAuCl4 with chemiluminescent (CL) reagent luminol in the presence of hydrophilic polymer chitosan, three-dimensional flowerlike gold nanostructures (AuNFs) were synthesized via a convenient one-pot method. As-prepared stable and monodisperse AuNFs were consisted of smaller-sized nanodots according to subsequent characterizations by high-resolution transmission electron microscopy, scanning electron microscopy, and powder X-ray diffraction. The size and morphology of AuNFs could be tailored by varying the amount of luminol or chitosan, which further influenced their surface plasmon resonance (SPR) properties in both visible and near-infrared regions. On the basis of the characterizations, a chitosan-assisted second-growth mechanism was proposed to explain their formations and morphology evolutions with the amount of reactants. Moreover, an electromagnetic simulation method, discrete dipole approximation, was introduced to calculate the morphology-dependent extinction spectra of geometrically ir...