Shape-controlled Gold Nanoparticles Research Articles

Surface topography and free energy regulate osteogenesis of stem cells: effects of shape-controlled gold nanoparticles.

ABSTRACTThe surface free energy of a biomaterial plays an important role in the early stages of cell–biomaterial interactions, profoundly influencing protein adsorption, interfacial water accessibility, and cell attachment on the biomaterial surface. Although multiple approaches have been developed to engineer the surface free energy of biomaterials, systematically tuning their surface free energy without altering other physicochemical properties remains challenging. In this study, we constructed an array of chemically-equivalent surfaces with comparable apparent roughness through assembly of gold nanoparticles adopting various geometrically-distinct shapes but all capped with the same surface ligand, (1-hexadecyl)trimethylammonium chloride, on cell culture substrates. We found that bone marrow stem cells exhibited distinct osteogenic differentiation behaviours when interacting with different types of substrates comprising shape-controlled gold nanoparticles. Our results reveal that bone marrow stem cells are capable of sensing differences in the nanoscale topographical features, which underscores the role of the surface free energy of nanostructured biomaterials in regulating cell responses. The study was approved by Institutional Animal Care and Use Committee, School of Medicine, University of South Carolina.

A rapid and convenient screening method for detection of restricted monensin, decoquinate, and lasalocid in animal feed by applying SERS and chemometrics

The surface-enhanced activities of size- and shape-controlled gold nanoparticles (AuNPs) with superior chemical stability were investigated to explore a possible development of a simple and non-destructive spectroscopic method to help the regulatory agency's analytical services for rapid detection and characterization of selected antimicrobials in animal feeds. Feed samples spiked at different concentration ranges of antimicrobials were evaluated using AuNPs as a surface-enhanced Raman spectroscopy (SERS) agent. The collected SERS spectra were mathematically preprocessed for further analysis. The classification models obtained 100% predictive accuracy with zero or little misclassification. The first two canonical variables (p = 0.001) could explain >95% of the variability in preprocessed spectral data. Most chemometric models for predicting MON, DEC, and LAS concentrations showed a high predictive accuracy (r2 > 0.90), lower predictive error (<20 mg/kg), and satisfactory regression quality (slope close to 1.0). The statistical results showed no statistically significant difference between the reference and SERS predicted values (p > 0.05). The findings and implications from the study indicate that SERS would be a powerful and efficient technique possessing a great potential serving as an excellent monitoring and screening tool for antimicrobial contaminated samples in the on-site analysis.

Shape-Controllable Gold Nanoparticle-MoS2 Hybrids Prepared by Tuning Edge-Active Sites and Surface Structures of MoS2 via Temporally Shaped Femtosecond Pulses.

Edge-active site control of MoS2 is crucial for applications such as chemical catalysis, synthesis of functional composites, and biochemical sensing. This work presents a novel nonthermal method to simultaneously tune surface chemical (edge-active sites) and physical (surface periodic micro/nano structures) properties of MoS2 using temporally shaped femtosecond pulses, through which shape-controlled gold nanoparticles are in situ and self-assembly grown on MoS2 surfaces to form Au-MoS2 hybrids. The edge-active sites with unbound sulfurs of laser-treated MoS2 drive the reduction of gold nanoparticles, while the surface periodic structures of laser-treated MoS2 assist the shape-controllable growth of gold nanoparticles. The proposed novel method highlights the broad application potential of MoS2; for example, these Au-MoS2 hybrids exhibit tunable and highly sensitive SERS activity with an enhancement factor up to 1.2 × 107, indicating the marked potential of MoS2 in future chemical and biological sensing applications.

Plasmonic Octahedral Gold Nanoparticles of Maximized Near Electromagnetic Fields for Enhancing Catalytic Hole Transfer in Solar Water Splitting

Due to their localized surface plasmon resonances in visible spectrum, noble metal nanostructures have been considered for improving the photoactivity of wide bandgap semiconductors. Improved photoactivity is attributed to localized surface plasmon relaxations such as direct electron injection and resonant energy transfer. However, the details on the plasmonic solar water splitting through near electromagnetic field enhancement have not been fully understood. Here, the authors report that shape-controlled gold nanoparticles on wide bandgap semiconductors improve the water-splitting photoactivity of the semiconductors with over-bandgap photon energies compared to sub-bandgap photon energies. It is revealed that hot hole injection into the oxygen evolution reaction potential is the rate-limiting step in plasmonic solar water splitting. The proposed concept of photooxidation catalysts derived from an ensemble of gold nanoparticles having sharp vertices is applicable to various photocatalytic semiconductors and provides a theoretical framework to explore new efficient plasmonic photoelectrodes.

Shape-controlled gold nanoparticles supported on MoS₂ nanosheets: synergistic effect of thionine and MoS₂ and their application for electrochemical label-free immunosensing.

Herein, a facile approach for shape-controlled gold nanoparticle (AuNP) decorated thionine-MoS2 nanocomposites (AuNP-Thi-MoS2) had been reported by using the synergistic effect of MoS2 and Thi. Thi was not only used as an electrochemical indicator, but also as a reducing agent to tune the resulting morphologies of AuNPs. With the ratio of MoS2/Thi decreasing, the shapes of AuNPs changed from spherical, triangle, clover-like to flower-like nanostructures. TEM, XRD and XPS were employed to characterize the formation and chemical composition of AuNP-Thi-MoS2 nanocomposites. On the basis of synthesis, a MoS2-based label-free electrochemical immunosensor had been designed to detect carcino-embryonic antigen (CEA). The proposed immunosensor could detect as low as 0.52 pg mL(-1) CEA with excellent selectivity. Moreover, the expected immunosensor showed high stability and excellent reproducibility, which could detect CEA in human serum with satisfactory results. Therefore, the AuNP-Thi-MoS2 nanocomposites may be considered as a candidate sensing platform for fabrication of simple, label-free and ultrasensitive electrochemical sensors.

A minor lipid component of soy lecithin causes growth of triangular prismatic gold nanoparticles

Reduction of bromoauric acid by ascorbic acid in the presence of crude soybean lecithin produced a mixture of spherical and triangular prismatic nanoparticles while higher purity phosphatidylcholine (PC) produced only spherical nanoparticles. The triangular prismatic nanoparticles made with lecithin had an average edge length of 90 nm and a localized surface plasmon resonance between 700 and 1050 nm, depending on the synthetic conditions used. Although crude soy lecithin is composed of 75% PC and phosphatidylethanolamine, additional lipids and other small molecules are present. Preparatory gel electrophoresis was used to separate the different nanoparticle shapes and phosphatidic acid (PA) was identified as bound to the triangular prismatic nanoparticles by mass spectrometry of the gel-purified nanoprisms. Furthermore, PA proved essential to the asymmetric growth. When bromoauric acid was reduced by ascorbic acid using a mixture of pure PA and pure PC, triangular prismatic gold nanoparticles also resulted, confirming the role of PA and providing a second route to these near infrared active nanoparticles. Nanoparticles prepared in soy lecithin or PA–PC mixtures exhibited extended stability with no aggregation after months of storage, in contrast to nanoparticles prepared in pure PC. These nanoparticles were prepared without the use of the alkyl ammonium salts that have limited in vivo applications with other asymmetric gold nanoparticles. This is a versatile synthetic method providing stable, shape-controlled gold nanoparticles using a mild reducing agent and soy lecithin as an environmentally benign ligand source.

Antimicrobial and Anticancer Activity of Gold Nanoparticles Synthesized from Grapes Fruit Extract

Bio-inspired gold nanoparticles are rapidly synthesized at room temperature using grapes fruit extract. A green and low cost synthesis is effective in the formation of stable crystalline gold nanoparticles in the solution. Polyphenols which is present in the grapes fruit extract function as reducing as well as stabilizing agent to produce shape controlled gold nanoparticles. Surface plasmon resonance confirmed the formation of gold nanoparticles in UV-Visible spectra at 500 nm. The Fourier transform infrared spectroscopy (FTIR) analysis was carried out to identify and study the functional groups responsible for the bio-reduction of gold ion. High resolution transmission electron microscopy (HRTEM) images showed the spherical crystalline gold nanoparticles. Thermogravimetric analysis (TGA) measures the weight loss of gold nanoparticles as a function of temperature under a controlled atmosphere. The synthesized gold nanoparticles showed excellent antimicrobial activity towards most of the tested fungal and bacterial culture. It showed good anticancer activity against HeLa cell lines.

Scanning electrochemical microscopy for studying electrocatalysis on shape-controlled gold nanoparticles and nanorods

The electrocatalytic activity for the oxygen reduction reaction (ORR) of different shape-controlled gold nanoparticles (NPs) and nanorods has been studied by scanning electrochemical microscopy (SECM). TEM images and lead underpotential deposition (UPD) voltammetric profiles were used to physically and electrochemically characterize all gold particles studied here, providing information on the shape and surface structure of the different NPs and nanorods. The SECM results demonstrate that cubic gold NPs are the most active towards ORR in 0.1 M NaOH, followed by the spherical gold NPs and, finally, by the short gold nanorods. These results are in agreement with previous studies using conventional electrochemical techniques with gold NPs and single crystal electrodes, since they established that higher ratio of (1 0 0) domains provide higher catalytic activity for ORR.

Application of a conproportionation reaction to a synthesis of shape-controlled gold nanoparticles

Synthesis of gold nanoparticles with multiple shapes by a modified seeding growth method is reported. The optical extinction spectra of a mixture of the seed and growth solutions indicate that the seed particle size decreases during stirring the mixture by a conproportionation reaction of Au metal with Au(III) ions. This conproportionation reaction is used to investigate the effects of variation in seed particle size on the resultant gold nanoparticle shape. When single crystalline and multiply twinned particles are used as the seed particles, they grow into gold nanorods and nanobipyramids, respectively. By letting the seed particles experience the conproportionation reaction before the particle growth to decrease the size, the surface of resultant nanoparticles roughens. Increasing the conproportionation reaction time up to 5 min, multi-branched gold nanoparticles with many lattice defects grow from both of the seed particles. This indicates that the conproportionation reaction is useful to generate lattice defects during the particle growth, which lead to the formation of gold nanoparticles with complex shapes.

CTAB-Assisted Synthesis of Size- and Shape-Controlled Gold Nanoparticles in SDS Aqueous Solution

Variously shaped gold nanoparticles were hydrothermally prepared by adding the cationic surfactant cethyltrimetylammonium bromide (CTAB) into the anionic surfactant sodium dodecyl sulfonate (SDS) in aqueous solution at 180°C without reducing agents and/or templates. Nanoparticle size and shape were controlled by the surfactant mixing ratio CTAB:SDS = x CTAB:(1 − x CTAB) and reaction time. Increasing CTAB concentration from x = 0.01 to x = 0.07 changes the nanoparticle shape from icosahedron to triangle or ellipse. The influence of the cationic/anionic ratio is presumably due to the differing catanionic micelle structures.

A New Route to Obtain High-Yield Multiple-Shaped Gold Nanoparticles in Aqueous Solution using Microwave Irradiation

A highly effective, very fast microwave method is described to synthesize shape controlled gold nanoparticles in the presence of 2,7-dihydroxy naphthalene (2,7-DHN) as a new reducing agent under microwave heating for 60-90 s. The growth of the particles with different shapes (spherical, polygonal, rod, and triangular/prisms) was directed by the surfactant to metal ion molar ratios and the concentration of 2,7-DHN. The evolved nanorods and nanoprisms are fairly small in diameter, and the particle size and shape were successfully tuned just by varying the molar ratios of the reactants. The process presented here can be extended to the synthesis of other nanomaterials with desired size and shape and might find a variety of applications in wide areas, such as catalysis, clinical and diagnostic medicine, and nanoelectronics.

A new route to obtain shape-controlled gold nanoparticles from Au(III)-beta-diketonates.

Ligands with a beta-diketone skeleton have been employed for the first time as reductant to produce ligand stabilized gold nanoparticles of different shapes from aqueous HAuCl(4) solution. Evolution of stable gold nanoparticles follows first order (k approximately equal to 10(-2) min(-1)) kinetics with respect to Au(0) concentration. Growth of particles of different shapes (spherical or triangular or hexagonal) goes hand in hand under the influence of different beta-diketones, which have excellent capping and reducing properties. Chlorine insertion was observed to take place in the beta-diketone skeleton.

A Novel Ultraviolet Irradiation Technique for Shape-Controlled Synthesis of Gold Nanoparticles at Room Temperature

Shape-controlled gold nanoparticles were synthesized using a novel ultraviolet irradiation technique at room temperature. The very slow ultraviolet irradiation photoreduction process may favor the formation of the shaped gold nanoparticles. It was found that not only the concentration of gold cations and the irradiation time but also the concentration and the species of polymer capping materials play important roles in the morphology control of the gold nanoparticles.