Triangular Gold Nanoplates Research Articles

Rational Calibration Strategy for Accurate and Sensitive Colorimetric Detection of Iodide and l-Thyroxine Based on Gold Triangular Nanoplates

We developed a sensitive and accurate colorimetric method to detect iodide (I–) and l-thyroxine by etching gold triangular nanoplates (AuTNPs) in the presence of H2O2. The morphological changes of AuTNPs resulted in vivid color variations of the nanoprism dispersion, accompanied by a blue shift of the in-plane localized surface plasmon resonance (LSPR) peak, enabling visual and photometric sensing. To improve the accuracy and the linear range, the overlapping out-of-plane and in-plane LSPR peaks of the AuTNPs were deconvoluted, and a new calibration model was established by plotting the square of the in-plane LSPR wavelength shift against the concentration of the analytes. Under optimum conditions, the limits of detection (LODs) for iodide reached 1 μM and 50 nM by the naked eye and photometry, respectively, and the corresponding LODs for l-thyroxine were 200 and 13.7 nM. Importantly, improved accuracy and linear range were obtained by the new data processing strategy. The method was applied in detecting ...

Single-particle Correlation Study: Polarization-dependent Differential Interference Contrast Imaging of Two-dimensional Gold Nanoplates

Questions surrounding the optical properties of two-dimensional (2D) triangular single gold nanoplates (AuNPs) remain largely unanswered. Herein, a scanning-electron microscopy-correlated single-particle study was conducted to identify polarization-dependent optical properties of AuNPs under dark-field (DF) and differential interference contrast (DIC) microscopy. AuNPs with an aspect ratio of ∼3 showed a single broad DF scattering spectrum without separation of the two dipole and quadrupole resonance modes present in 2D AuNPs. Polarization-sensitive interference properties of the individual AuNPs were revealed through periodic changes in the intensities and types of DIC images obtained. A dipole resonance mode was found to mainly contribute to the polarization-sensitive interference properties of AuNPs. Furthermore, DIC polarization anisotropy allowed us to track the real-time orientation of a dipole resonance mode of a AuNP rotating on a live cell membrane.

Regioselective DNA Modification and Directed Self-Assembly of Triangular Gold Nanoplates.

As a class of emerging nanoparticles, gold nanotriangles (AuNTs) are characterized by unique structural anisotropy and plasmonic properties. The organization of AuNTs into well-defined architecture potentially promises collective properties that are difficult to produce by individual AuNTs. To date, however, the orientation-controlled self-assembly of AuNTs has been achieved with limited success. Here, we describe an effective and straightforward approach to induce directed self-assembly of AuNTs. By taking advantage of the uneven chemical reactivity of AuNT surfaces, we implement regioselective modification of the edges and the top/bottom surfaces with two different double-stranded DNA (dsDNA) sequences. By means of terminal single base pairing/unpairing, controlled assembly of the dsDNA-modified AuNTs evolves in a face-to-face or edge-to-edge manner based on blunt-end stacking interaction on an intentional region of the AuNTs, along with entropic repulsion by unpaired terminal nucleobases on the other region. This approach could be useful for achieving directed self-assembly of other anisotropic nanoparticles.

Elucidating the contribution of dipole resonance mode to polarization-dependent optical properties in single triangular gold nanoplates

We synthesized triangular gold nanoplates (AuNPs) through a one-pot seedless growth method and characterized their optical properties under dark-field (DF) microscopy at the single particle level. We experimentally demonstrated that the dipole resonance is not completely separated from the quadrupole resonance for single AuNPs with an aspect ratio of ∼5. We further used a defocused orientation and position imaging technique to visualize the spatial scattering field distributions from dipole and quadrupole modes. Their optical properties were mainly dominated by the dipole resonance, which resulted in the polarization-dependent, periodic DF defocused images and intensities of single AuNPs.

Static and Dynamic Near-Field Measurements of High-Order Plasmon Modes Induced in a Gold Triangular Nanoplate.

Precise understanding of the spatiotemporal characteristics of plasmons is essential for the development of applications of plasmonic nanoparticles. In this study, we investigated the spatiotemporal properties of high-order plasmon modes induced in a gold triangular nanoplate by static and dynamic near-field measurements. The near-field transmission measurements revealed that in-plane and out-of-plane polarized plasmon modes were simultaneously excited and these modes spectroscopically and spatially overlapped. The superposition of these modes was visualized in the near-field two-photon excitation image of the nanoplate. We performed time-resolved autocorrelation measurements on the nanoplate and found that the correlation width was broader than the excitation pulse due to the plasmon dephasing process. From the correlation width map of the nanoplate, we experimentally demonstrated that the out-of-plane plasmon mode exhibits a longer dephasing time than the in-plane plasmon mode. These findings indicate that the out-of-plane mode is desirable for improving the performance of plasmons in various applications.

Anti-EGFR Peptide-Conjugated Triangular Gold Nanoplates for Computed Tomography/Photoacoustic Imaging-Guided Photothermal Therapy of Non-Small Cell Lung Cancer.

Non-small cell lung cancer (NSCLC) is difficult to cure because of the high recurrence rate and the side effects of current treatments. It is urgent to develop a new treatment that is safer and more effective than current treatments against NSCLC. Herein, we constructed anti-epidermal growth factor receptor (EGFR) peptide-conjugated PEGylated triangular gold nanoplates (TGN-PEG-P75) as a targeting photothermal therapy (PTT) agent to treat NSCLC under the guidance of computed tomography (CT) and photoacoustic (PA) imaging. The surface of TGNs is successfully conjugated with a novel peptide P75 that has the specific affinity to epidermal growth factor receptor (EGFR). It is found that the EGFR is overexpressed in NSCLC cells. The TGN-PEG-P75 has uniform edge length (77.9 ± 7.0 nm) and neutrally charged surface. The cell uptake experiments demonstrate remarkable affinity of the TGN-PEG-P75 to high EGFR expression cells than low EGFR expression cells (5.1-fold). Thanks to the strong near-infrared absorbance, high photothermal conversion efficiency, and the increased accumulation in tumor cells via the interaction of P75 and EGFR, TGN-PEG-P75 exhibits 3.8-fold superior therapeutic efficacy on HCC827 cells than TGN-PEG. The in vivo CT/PA dual-modal imaging of the TGN-PEG-P75 is helpful in selecting the optimal treatment time and providing real-time visual guidance of PTT. Furthermore, treatments on HCC827 tumor-bearing mouse model demonstrate that the growth of NSCLC cells can be effectively inhibited by the TGN-PEG-P75 through PTT, indicating the great promise of the nanoplatform for treating NSCLC in vivo.

Qiao Zhang.

"My favorite time of day … is the evening when I can spend my time with my family. The energy that my family provides always keeps me moving forward. The secret of being a successful scientist … is to not rely completely on the literature. Sometimes an unconstrained woolgather can help us find new ideas. "This and more about Qiao Zhang can be found on page 319.

Iodine-Mediated Etching of Triangular Gold Nanoplates for Colorimetric Sensing of Copper Ion and Aptasensing of Chloramphenicol.

A colorimetric method for fast, simple, and selective detection of Cu2+ was developed using I--mediated etching of triangular gold nanoplates (AuNPLs). The method was based on our finding that Cu2+ efficiently promoted this etching in the presence of SCN-. The etching process was accompanied by a dramatic color change from blue to red, allowing for visual and spectroscopic detection of Cu2+ with detection limits of 10 and 1 μM, respectively. When molecular recognition by a DNA aptamer was incorporated into this method, visual detection of chloramphenicol was also achieved with a detection limit of 5 μM.

Synthesis and Applications of Triangular Gold Nanoplates

Synthesis and Applications of Triangular Gold Nanoplates

Size Control and Growth Process Study of Au@Cu2O Particles.

Au@Cu2O cuboctahedron with gold triangular nanoplate core and Cu2O shell was synthesized by a chemical method. X-ray diffraction (XRD) and transmission electron microscopy (TEM) tests demonstrated that the as-synthesis samples were consisted of gold triangular nanoplate core and Cu2O shell, and both of them were in good crystallization. The effective size control of the particles could be realized by controlling the amount of Au cores added in the synthetic process and Au@Cu2O particles with different shell thickness could be synthesized. The decrease of Cu2O shell thickness had a great difference in the optical performance, including blue shift of the resonant peaks and enhanced absorption intensity. The growth process from rough sheet structure to cuboctahedron was also explored. The results of photocatalytic degradation experiment showed that Au@Cu2O particles showed much better photocatalytic performance than that of pure Cu2O. The improved photocatalytic property of the Au@Cu2O particles was attributed to the comprehensive effect of the enhanced visible-light absorption and high separation rate of electron-hole pairs.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1603-6) contains supplementary material, which is available to authorized users.

Ultra-Sensitive Detection of AFP Based on Multi-Spectral Information From Face-to-Face Aggregation of Gold Triangular Nanoplates

Ultra-Sensitive Detection of AFP Based on Multi-Spectral Information From Face-to-Face Aggregation of Gold Triangular Nanoplates

Green, Selective, Seedless and One-Pot Synthesis of Triangular Au Nanoplates of Controlled Size Using Bael Gum and Mechanistic Study

A seedless, one pot, green and selective synthesis of triangular gold nanoplates (NPs) by the reduction of chloroauric acid using Aegle marmelos gum (bael fruit derived gum; BG), with control over size is reported. The size of the NPs is found to be dependent critically on the concentration of the BG with triangular, triangular with truncation at the apex and hexagonal plates being the predominant shapes over a wide concentration range, at room temperature. At very high concentration of BG and at room temperature, the shape of the particles is spherical. A fine-tuning of the temperature, at a particular concentration of BG, results in the formation of perfect triangular NPs. Increasing the temperature of reduction to 90 °C and especially above a particular BG concentration, Au nanoparticles that are elongated spheres are obtained as the major product. The possible mechanism for the Au NPs formation is investigated using techniques such as HR-TEM, SEM, XRD and UV–visible spectroscopy. The formation of sing...

Specific detection of carcinoembryonic antigen based on fluorescence quenching of Au-Ag core-shell nanotriangle probe

Gold-silver bimetallic fluorescence quenching nanoprobe has been synthesized based on the gold triangular nanoplate with silver coating. In order to guarantee the specificity of the probe, surface modifications of the triangular nanoplates including carboxyl replacement, carboxyl activation and antibody connection have been carried out. The fluorescence spectral study indicates that the fluorescence intensity of carcinoembryonic antigen (CEA) could be effectively quenched by the silver coated-gold triangular nanoprobe. And the fluorescence quenching ability could be improved by optimizing the interaction time and amount of binding anti-CEA to modified nanoprobe, and the interaction time of binding CEA to anti-CEA. By using this sensing method, the CEA could be detected with an ultra low detection limit of 10pg/mL, and the linear range spans a scope from 20 to 200pg/mL. Interference experiment results show that the influence from the interfering proteins could be neglected in the detection procedure. And the CEA could be specifically detected by using this bimetallic triangular nanoplate probe.

Tuning the Fluorescence Quenching Properties of Plasmonic Ag-Coated-Au Triangular Nanoplates: Application in Ultrasensitive Detection of CEA

By using the fluorescence spectroscopic techniques, the fluorescence quenching abilities of gold triangular nanoplates with silver coating have been studied. Because of the surface plasmon resonance (SPR)-induced nonradiative energy transformation, the fluorescence emission intensity of carcinoembryonic antigen (CEA) could be greatly quenched by the silver-coated-gold triangular nanoplates. By comparing with the bare gold triangular nanoplates, the nanoplates with silver coating exhibit greater fluorescence quenching ability and could be further improved by increasing the coating thickness. The fluorescence quenching effect also depends on the concentration of CEA. For bare gold triangular nanoplates, the quenching ability to CEA is decreased as the CEA concentration is increased. Whereas for silver-coated-gold triangular nanoplates, the quenching ability to CEA is increased as the CEA concentration is increased. By analyzing the intensity quenching of the fluorescence peak, CEA could be detected with an ultra-low detection limit of 5 pg/mL.

Misalign-dependent double plasmon modes “switch” of gold triangular nanoplate dimers

The optical properties of the edge-to-edge gold triangular nanoplate dimers have been studied in theory by discrete dipole approximation method. Two clearly separated plasmon modes (low-energy and high-energy modes) are observed. Each of the double plasmon modes could be selectively turned on or off by modulating the misalign value of the dimer. When the misalign is <60 nm, the low-energy mode plays the dominant role in the spectra. In this case, the electric field intensities at the tips along the polarization direction fade down, whereas the intense electric field in the gap gets more concentrative, as the misalign increases. However, as the misalign is increased to 100 nm, the high-energy mode dominates the spectrum. And the intense electric fields concentrated around the outer tips become stronger as the misalign increases. The “switch” process is also accompanied by the inversion of the field vectors in the gap. In addition, the wavelength separation and positions of the double plasmon modes could be tuned flexibly by adjusting the gap value and the thickness of the dimer, respectively. These findings are promising for the nanophotonic switch, nanomotor, molecular ruler, surface enhanced fluorescence, surface enhanced Raman scattering, dual channel biosensor, and molecular imaging applications.

Close-packed assemblies of discrete tiny silver nanoparticles on triangular gold nanoplates as a high performance SERS probe

An island like array of tiny Ag nanoparticles bounded on triangular Au nanoplates was synthesized as surface-enhanced Raman spectroscopy substrate.

High-yield seedless synthesis of triangular gold nanoplates through oxidative etching.

We demonstrate that monodispersed triangular gold nanoplates with high morphological yield (>90%) can be synthesized through a rapid one-pot seedless growth process. The edge length of triangular Au nanoplates can be readily tuned between 40 and 120 nm by varying the reaction parameters. Systematic studies reveal that distinct from previous hypothesis that the formation of nanoplates is mainly determined by the selective binding of iodide ions, our results show that iodide ions could have dual functions: it can selectively bind to the Au {111} facets and also selectively remove other less stable shape impurities through oxidative etching by forming tri-iodide ions (I(3)(-)), thus facilitating the formation of nuclei with dominant planar structure. This new synthetic route will not only help to better understand the growth mechanism of triangular gold nanoplates but also promote the research in anisotropic noble metal nanostructures.

Morphological effect of gold nanoparticles on the adsorption of bovine serum albumin.

Various properties of gold nanoparticles (GNPs) are found to play crucial roles in their biological activity. Among them, the morphology and surface chemistry are extremely important. This is because of differences in surface energies of various crystal facets arising from a large fraction of edges, corners and vertices. In the present work, we provide a comparative study on the adsorption and binding affinities of bovine serum albumin (BSA) onto triangular gold nanoplates (TGNP) and gold nanorods (GNR). The results were compared with similar size of both CTAB and citrate stabilized spherical GNPs. Our data suggested stronger binding of BSA on citrate stabilized spherical GNPs whereas TGNP shows the weakest binding among all the GNPs. A blue shift of approximately 20 nm in tryptophan fluorescence was observed for all CTAB stabilized GNPs, indicating the local dielectric changes surrounding the tryptophan residue. Loss of the secondary structure was also observed for all CTAB stabilized GNPs. No spectral shift was observed for citrate stabilized spherical GNPs though maximum quenching of fluorescence and minimum structural loss was observed. With the help of molecular simulation recently developed by our group, a binding model is proposed to explain all the above experimental results.

High-yield synthesis of triangular gold nanoplates with improved shape uniformity, tunable edge length and thickness.

We report the synthesis of uniform triangular gold nanoplates by a modified seeded growth method. The concentration of cetyltrimethylammonium bromide (CTAB) in the growth solution and the time interval between multiple steps of growth were important factors which determined the formation of uniform triangular Au nanoplates. In addition, by further isotropic overgrowth, the thickness of triangular Au nanoplates can be finely tuned within a wide range of 10-80 nm, which at present remains a challenge using conventional seeded growth.

Microfluidic platform for continuous flow synthesis of triangular gold nanoplates

A microfluidic platform for the continuous flow synthesis of triangular gold nanoplates with and without surfactants is developed. The temperature profile in the microchannel, residence time and composition have been studied to understand effect of these parameters on the yield of the triangular nanoplates and were optimized for obtaining maximum yield of triangles. The flow synthesis approach has been demonstrated where the Br− ions can be supplied to the reaction mixture either from the surfactant viz. Cetyl trimethylammonium bromide (CTAB) or even from HBr. Apart from the Br− ions, the temperature gradient at the inlet of the continuous flow reactor is one of the key parameter that affects the yield of the triangular nanoplates. Finally we establish that with a right combination of the controlling parameters a better yield of the Au nanotriangles by flow methods can be achieved even in the absence of surfactant.