Gold Nanoplates Research Articles

Triangular gold nanoplates integrated microgel-based sensor for urinary tract infection and glucosuria detection

A glucose-responsive photonic crystal integrated optical sensor that can detect glucosuria and urinary tract infection was designed by comprehensive numerical analysis. We showed a comparative study of nanoparticle shapes and materials and discussed the performance parameters of the sensor, such as the signal-to-noise ratio, the sensitivity, and the detection limit for various pH levels. Normally distributed nanoparticles were embedded within a functionalized microgel matrix in this proposed structure, and the theoretical study was conducted using the finite element method. Gold was selected as a photonic crystal material due to its nontoxicity and better sensing performance, and triangular-shaped nanoplates were chosen due to their better surface plasmon resonance performance. The sensor showed improved sensitivity of <85.65 nm/mM for pH 7.4, and <110.60 nm/mM for pH 8.0. It depicted a lower detection limit of >0.34 mM for pH 7.4 and >0.30 mM for pH 8.0 than those of previously reported glucose sensor studies. Moreover, the proposed glucose sensor exhibited a practicable signal-to-noise ratio and sensor resolution range. This label-free sensor manifested additional features such as reusability of the sensor, high sensing reversibility, and being readily usable at point-of-care medical facilities.

Shape- and Size-Dependent Refractive Index Sensing and SERS Performance of Gold Nanoplates.

Plasmonic sensors are promising for ultrasensitive chemical and biological analysis. Gold nanoplates (Au NPLs) show unique geometrical structures with high ratios of surface to bulk atoms, which display fascinating plasmonic properties but require optimization. This study presented a systematic investigation of the influence of different parameters (shape, aspect ratio, and resonance mode) on localized surface plasmon resonance properties, refractive index (RI, n) sensitivities, and surface-enhanced Raman scattering (SERS) enhancement ability of different types of Au NPLs through finite-difference time-domain (FDTD) simulations. As a proof of concept, triangular, circular, and hexagonal Au NPLs with varying aspect ratios were fabricated via a three-step seed-mediated growth method by the experiment. Both FDTD-simulated and measured experimental results confirm that the RI sensitivities increase with the aspect ratio. Furthermore, choosing a lower order resonance mode of Au NPLs benefits higher RI sensitivities. The SERS enhancement abilities of Au NPLs also predicted to be highly dependent on the shape and aspect ratio. The triangular Au NPLs showed the highest SERS enhancement ability, while it drastically decreased for circular Au NPLs after the rounding process. The SERS enhancement ability gradually became more intense as the hexagonal Au NPLs overgrown on circular Au NPLs with increasing volumes of HAuCl4 solution. The results are expected to help develop effective biosensors.

Gold triangular nanoplates with edge effect for reaction monitoring under dark-field microscopy

True morphology imaging of individual nanoprobes with high sensitivity and in situ dynamic response is crucial in the dark-field microscopy imaging analysis. However, the geometry and orientation of the probes are experimentally challenging to visualize as their physical dimensions are usually below the diffraction limit. In this work, two-dimensional triangular gold nanoplates (AuNPLs) with the edge length > 600 nm and the thickness ~25 nm displayed clear triangular-shaped far-field scattering patterns (TFSPs) under a dark-field imaging system owing to the strong electrical field strength around the sharp edges and tips. Thus, their actual shape and orientation specific scattering image are directly visualized only by dark-field microscopy and furtherly applied to real-time monitor the etching and alloying progress of AuNPLs. The results showed that the reactive sites of AuNPLs are located at their vertices and sharp edges owing to the sensitive edge effect. This work provides a new perspective to directly monitor the conformation and dynamics of chemical reaction at the single particle level.

Biological imaging applications using colloidal quantum dots with enhanced photoluminescence intensity

The combination of colloidal quantum dots (QDs) and metals yields plasmonic effects, which is promising for application in bio-imaging. On increasing the contact area between CdSe QDs and gold, the PL enhancement ratio increases because of enhanced coupling between the excitons of CdSe QDs and the surface plasmon fields of gold nanoplates; furthermore, a 1.5 times larger PL enhancement factor is observed. These results indicate the correlation between the surface plasmonic effective areas and enhancement ratio of PL, which can help identify a condition for the maximized enhancement of PL intensity for designing more efficient future bio-imaging devices.

Identification of plasmon-driven nanoparticle-coalescence-dominated growth of gold nanoplates through nanopore sensing

The fascinating phenomenon that plasmon excitation can convert isotropic silver nanospheres to anisotropic nanoprisms has already been developed into a general synthetic technique since the discovery in 2001. However, the mechanism governing the morphology conversion is described with different reaction processes. So far, the mechanism based on redox reactions dominated anisotropic growth by plasmon-produced hot carriers is widely accepted and developed. Here, we successfully achieved plasmon-driven high yield conversion of gold nanospheres into nanoplates with iodine as the inducer. To investigate the mechanism, nanopore sensing technology is established to statistically study the intermediate species at the single-nanoparticle level. Surprisingly, the morphology conversion is proved as a hot hole-controlled coalescence-dominated growth process. This work conclusively elucidates that a controllable plasmon-driven nanoparticle-coalescence mechanism could enable the production of well-defined anisotropic metal nanostructures and suggests that the nanopore sensing could be of general use for studying the growth process of nanomaterials.

Observation of the plasmon mode transition from triangular to hexagonal nanoplates.

The geometrical shape of a metal nanostructure plays an essential role in determining the optical functionality of plasmonic cavity modes. Here, we investigate the geometrical modification effect on plasmonic cavity modes induced in two-dimensional gold nanoplates. We perform near-field transmission measurements on triangular and tip-truncated triangular nanoplates and reveal that the plasmonic cavity modes are qualitatively consistent with each other as long as the snipping size is not significant. To elucidate the tip-truncation effect on plasmonic cavity modes in detail, we carry out numerical simulations for nanoplates with various snipping sizes and find that tip truncation affects not only the optical selection rules but also the energy relation for the plasmonic cavity modes. These findings provide a foundation for the rational design of plasmonic cavities with desired optical functionality.

Improving the Efficiency of the Concentrating Solar Power Plants Using Heat Transfer Nanofluids with Gold Nanoplates: An Analysis from Laboratory to Industrial Scale

Improving the Efficiency of the Concentrating Solar Power Plants Using Heat Transfer Nanofluids with Gold Nanoplates: An Analysis from Laboratory to Industrial Scale

Triangular gold nanoplates/two-dimensional nano mica platelets with a 3D lightning-rod effect as flexible nanohybrid substrates for SERS bacterial detection.

Triangular gold nanoplates (TAuNPs) were prepared by a one-step rapid growth method and then reduced and stabilized on two-dimensional nano mica nanoplatelets (NMPs). We also prepared TAuNP/NMP nanohybrids with a three-dimensional lightning-rod effect by oxidative etching. The surface of the delaminated NMPs (only 1 nm thick) is highly charged and can provide a large specific surface area; thus, it can be used as a substrate for the stable growth of gold nanoplates. In addition, by controlling relevant synthesis parameters, the edge length of the TAuNPs can be easily adjusted in the range of 30-90 nm. During reduction of the TAuNPs, the cationic surfactant cetyltrimethylammonium chloride was added as a protective agent to surround the TAuNPs; consequently, the surface was positively charged, which facilitates adsorption for detecting molecules with negative charges. When nanohybrids were used in surface-enhanced Raman spectroscopy (SERS) to detect adenine molecules, the limit of detection concentration was 10-9 M. The Raman enhancement factor was 5.7 × 107, and the relative standard deviation (RSD) was 9.8%. Finally, this method was applied to the biological detection of Staphylococcus aureus, and the surface charge and hydrophilic properties of the material significantly improved the SERS signal of S. aureus. The limit of detection concentration was 102 CFU mL-1, and the RSD was 11.2%. The TAuNP/NMP nanohybrids can provide very rapid and sensitive SERS detection of biomolecules.

Synthesis of Hexagonal Gold Nanoparticles and Study of its Optical and Near-field Distribution Properties by Discrete Dipole Approximation

Anisotropic nanostructures with unique physical and chemical properties have been widely applied in optical, electronic, magnetic, and catalytic fields. This paper described the synthesis of hexagonal gold nanoplates (HAuNPs) by trisodium citrate and ascorbic acid. The optical and near-field distribution properties of hexagonal gold nanoplates were studied by discrete dipole approximation method. Simulation results showed that due to the shape anisotropy of HAuNPs, the optical properties of HAuNPs were significant differences between the horizontal orientation and vertical orientation.

The role of positively charge poly-L-lysine in the formation of high yield gold nanoplates on the surface for plasmonic sensing application.

An anisotropic structure, gold (Au) nanoplates was synthesized using a two-step wet chemical seed mediated growth method (SMGM) directly on the substrate surface. Prior to the synthesis process, poly-l-lysine (PLL) as a cation polymer was used to enhance the yield of grown Au nanoplates. The electrostatic interaction of positive charged by PLL with negative charges from citrate-capped gold nanoseeds contributes to the yield increment. The percentage of PLL was varied from 0% to 10% to study the morphology of Au nanoplates in term of shape, size and surface density. 5% PLL with single layer treatment produce a variety of plate shapes such as hexagonal, flat rod and triangular obtained over the whole substrate surface with the estimated maximum yield up to ca. 48%. The high yield of Au nanoplates exhibit dual plasmonic peaks response that are associated with transverse and longitudinal localized surface plasmon resonance (TSPR and LSPR). Then, the PLL treatment process was repeated twice resulting the increment of Au nanoplates products to ca. 60%. The thin film Au nanoplates was further used as sensing materials in plasmonic sensor for detection of boric acid. The anisotropic Au nanoplates have four sensing parameters being monitored when the medium changes, which are peak position (wavelength shift), intensity of TSPR and LSPR, and the changes on sensing responses. The sensor responses are based on the interaction of light with dielectric properties from surrounding medium. The resonance effect produces by a collection of electron vibration on the Au nanoparticles surface after hit by light are captured as the responses. As a conclusion, it was found that the PLL treatment is capable to promote high yield of Au nanoplates. Moreover, the high yield of the Au nanoplates is an indication as excellent candidate for sensing material in plasmonic sensor.

Spatially Resolved Spectroscopic Characterization of Nanostructured Films by Hyperspectral Dark-Field Microscopy.

Nanostructured films have been widely used for preparing various advanced thin-film devices because of their unique electrical, optical, and plasmonic characteristics associated with the nano-size effect. In situ, nondestructive and high-resolution characterization of nanostructured films is essential for optimizing thin-film device performance. In this work, such thin-film characterization was achieved using a hyperspectral dark-field microscope (HSDFM) that was constructed in our laboratory by integrating a hyperspectral imager with a commercial microscope. The HSDFM allows for high-resolution (Δλ = 0.4 nm) spectral analysis of nanostructured samples in the visible-near-infrared region with a spatial resolution as high as 45 nm × 45 nm (corresponding to a single pixel). Four typical samples were investigated with the HSDFM, including the gold nanoplate array, the self-assembled gold nanoparticle (GNP) sub-monolayer, the sol-gel nanoporous titanium dioxide (TiO2) film, and the layer-stacked molybdenum disulfide (MoS2) sheet. According to the experimental results, the plasmon resonance scattering bands for nanoplate clusters are identical with those for individual gold nanoplates, indicating that the gap between adjacent nanoplates is too large to allow plasmonic coupling between them. A different case was observed with the self-assembled GNP sub-monolayer in which the aggregated clusters with the internal plasmonic interaction show a considerable red-shift of the plasmon resonance band relative to the isolated single GNP. In addition, the protein adsorption on the nanoporous TiO2 film was observed to be inhomogeneous on the microscale, and the stepped boundaries of the MoS2 sheet were clearly observed. A quasi-linear dependence of the single-pixel light intensity on the step height was obtained by combining the HSDFM with atomic force microscopy. The minimum thickness detectable by the present HSDFM is 6.5 nm, corresponding to the 10-layer MoS2 film. The work demonstrated the outstanding applicability of the HSDFM for nanostructured film characterization.

Fabrication of a surface-enhanced Raman spectroscopy-based analytical method consisting of multifunctional DNA three-way junction-conjugated porous gold nanoparticles and Au-Te nanoworm for C-reactive protein detection.

C-Reactive protein (CRP) is a biomarker of inflammatory responses and an index for assessing the risk of cardiovascular disease and estimating prognosis. In this study, we constructed a surface-enhanced Raman spectroscopy (SERS) biosensor composed of a multifunctional DNA three-way junction (DNA 3WJ), porous gold nanoplates (pAuNPs), and an Au-Te nanoworm structure for detection of CRP. The pAuNP and Au-Te nanostructures were synthesized by galvanic replacement reactions, and the morphology was confirmed by transmission electron microscopy, scanning electron microscopy, and dynamic light scattering (DLS). To generate the SERS signal, the Au-Te nanostructure was immobilized on an indium-tin oxide substrate, and the thiol-modified CRP aptamer was then self-assembled onto the modified substrate for CRP recognition. To amplify the SERS signal and identify the Raman tag, the multifunctional DNA 3WJ was conjugated with the pAuNPs, and each fragment of 3WJ was functionalized to biotin (pAuNP conjugation), methylene blue (Raman reporter), and CRP aptamer (target binding). The results were confirmed by gel electrophoresis. For conjugation between pAuNPs and DNA 3WJ, avidin was encapsulated in pAuNPs, and the conjugation structure was confirmed by DLS. The fabricated SERS biosensor showed detection limits of 2.23 pM in phosphate-buffered saline and 3.11 pM in diluted human serum. Overall, the proposed biosensor may have potential applications as a SERS biosensor platform.

Crown monitoring: Trace the dynamic changes of caspase-3 and H2O2 in real-time imaging based on FRET/SERS

Caspase-3 and hydrogen peroxide (H2O2) are closely associated with numerous diseases, both of them are vital in different physiological and pathological conditions. They are closely related and also can act independently. The selective and accurate determination of caspase-3 and H2O2 simultaneously to determine their state of being in different situations is of great significance for further study of their molecular mechanisms and the elucidation of their biological functions. In our latest research, a AuNPL-crown nanoprobe was obtained by attaching (4-aminosulfonylphenyl) boronic acid (4-APBA) and peptide-FITC (NH2-Asp-Glu-Val-Asp (DEVD)-FITC) to gold nanoplates (AuNPLs). The fabricated AuNPL-crown nanoprobe was used for dual-channel and real-time tracking of the dynamic changes in caspase-3 and H2O2 based on fluorescence resonance energy transfer (FRET)/surface-enhanced Raman spectroscopy (SERS) technology. The AuNPL-crown nanoprobe not only provides synergy but can also achieve noninterference, making the results more reliable and repeatable. This study simultaneously traced the dynamic changes of caspase-3 and H2O2 on a single probe, which provides a potential new platform for the analysis of caspase-3 and H2O2 in the biological environment with high accuracy, sensitivity, convenience, and efficiency. In summary, we develop a new strategy for the simultaneous detection of different substances on a single probe.

Strain-Induced Modulation of Localized Surface Plasmon Resonance in Ultrathin Hexagonal Gold Nanoplates.

Anisotropic gold nanoplates (NPLs) have raised the interesting possibility that their reduced geometrical symmetry allows fine tuning of their optical properties associated with the excitation of localized surface plasmon resonances (LSPRs). Recent developments have greatly improved LSPR tunability by utilizing the spatial distribution of LSPR modes. However, the nanoscale interplay between defect-induced mechanical strain and the spatial variation of LSPR modes remains poorly understood. In this work, the combination of high spatial- and spectral-resolution mapping of LSPR modes and nanoscale strain mapping using aberration-corrected transmission electron microscopy are applied to investigate the nanoscale distribution of LSPR modes in an ultrathin single hexagonal gold NPL and the effect of defect-induced strains on its LSPR properties. The electron energy-loss spectral maps reveal four distinct LSPR components and intensity distributions of all LSPR modes in a hexagonal gold NPL. Furthermore, the strain maps provide experimental evidence that the tensile strain field induced by a Z-shaped faulted dipole is responsible for the asymmetric distribution of LSPR intensity in a hexagonal gold NPL.

Triangular gold nanoplates as saturable absorber for passively Q-switched fiber laser at 1.56 μm

Wideband pulsed fiber lasers have been realized by using gold nanomaterials as saturable absorber (SAs). Compared to other morphologies, triangle gold nanoplates (TGNs) have multiple localized surface plasmon resonance peaks, which means that it can be used for construct wideband pulse laser. In this work, we propose and demonstrate an all-fiber passively Q-switched fiber laser at 1.56 μm by using TGNs as SA. The modulation depth and saturation intensity of the TGNs SA measured at 1560 nm are 7.1% and 13.8 MW cm−2, respectively. By putting the TGN SA into the laser cavity pumped by a 980 nm laser diode, stable passively Q-switched laser at 1568 nm was achieved for a threshold pump power of 40 mW. The pulse duration decreases from 11.4 μs to 4.2 μs and the repetition rate increases from 12.5 kHz to 20 kHz with the increasing of the pump power from 40 mW to 75 mW. Our results indicate that the TGNs is a type of versatile broadband SA material for construct pulse lasers.

Epitaxially aligned single-crystal gold nanoplates formed in large-area arrays at high yield

Epitaxially aligned single-crystal gold nanoplates formed in large-area arrays at high yield

Selective Formation of Lotus Leaf‐ and Donut‐Like Gold Nanoplates via Seeded Growth

AbstractWe report a seeded growth of gold (Au) nanoplates with two distinct morphologies, which are similar to a lotus leaf and a donut, respectively. The success of this synthesis relies on the use of flat Au nanoplates in high purity as seeds, followed by a controlled deposition. In particular, the presence of Ag+ led to the deposition of Au atoms preferentially occurred at the central part of one face of the nanoplate and thus the formation of lotus leaf‐like shape. In contrast, when Ag+ was absent, the growth mainly occurred to the edge region. Then, cold‐welding of newly‐formed branches and further diffusion of Au atoms created holes in the nanoplate, resulting in the formation of donut‐like shape. The Au nano‐lotus leaves with tunable sizes exhibited absorbance in near‐infrared region and enhanced chemical activities in electrochemical measurements. The current strategy is extended to fabricate Au−Ag nanoplates with a similar lotus leaf‐like morphology, which also exhibited strong absorbance in near‐infrared region in UV‐vis extinction spectra. The current work allows the fabrication of two‐dimensional Au‐based nanomaterials with concave shape and three‐dimensional architecture and could be potentially extended to other noble metals and alloys.

Enhancement of Optical Nonlinearity in the Triangular Gold Nanoplates on Indium Tin Oxide

The nonlinear optical materials with small footprint, low operating energy, ultrafast and large nonlinear optical response are highly required for the signal processing. Here, we investigated the broadband optical nonlinear response of the triangular gold nanoplates on indium tin oxide (ITO) coated glass, and obtained a large optical nonlinear enhancement at its localized surface plasmon resonance (LSPR) region at the wavelength of 780 nm, far from the ENZ (epsilon-near-zero) region of ITO. The measured nonlinear refractive index and nonlinear absorption coefficient can reach up to 8.39×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-15</sup> m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /W and 5.81×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-8</sup> m/W, respectively. The experimental results highlight the noble metals' potential for nonlinear optics and nanophotonics.

Mass transport through a sub-10 nm single gold nanopore: SERS and ionic current measurement

Sub-10 nm single gold nanopore was fabricated at the tip of a glass nanopipette. SERS spectrum of R6G and ionic current blockage of lambda-DNA through the plasmonic nanopore were observed. • The chemically synthesized single gold nanopore with high SERS activity. • Both ionic current and dynamic SERS spectrum were obtained on a plasmonic nanopore. • The present study proved that single molecule transport is quite possibly be detected using the sub-10 nm gold nanopore. Gold nanopore is promising to be used in single molecule sequencing by measuring surface enhanced Raman scattering (SERS) spectrum. To achieve this goal, fabrication of small and size-controllable single gold nanopore is in urgent need. We synthesized gold nanoplates with a sub-10 nm single nanopore at the center, which was then successfully attached at the tip of a glass nanopipette using sulfhydryl silane. The transport of about 1.4 × 10 3 rhodamine 6G molecules was detected using SERS. The current blockage caused by single lambda DNA passing through the nanopore was also observed. The translocation time of lambda DNA through the gold nanopore was much longer than that of lambda DNA through the bare glass nanopipette, revealing the strong DNA-gold nanopore interaction affected the transport behavior of lambda DNA. The observed result further shows that the time resolution of SERS (~ms) may match the transport time of DNA through plasmonic nanopore. The sub-10 nm gold nanopore is possible to be used in single molecule transport detection with the improvement of the nanopore attachment.

Imaging Plasmons with Sub-2 nm Spatial Resolution via Tip-Enhanced Four-Wave Mixing.

Four-wave mixing at plasmonic tip-sample nanojunctions may be used to visualize plasmonic fields with sub-2 nm spatial resolution under ambient laboratory conditions. We illustrate the latter using a gold-coated atomic force microscopy probe irradiated with a pair of near-infrared femtosecond laser pulses and used to image plasmonic gold nanoplates and silver nanocubes. Through diagnostic polarization-dependent tip-only measurements, we illustrate that the four-wave mixing signal is localized to the tip apex. The apex-bound signal is further enhanced when the tip is located at specific locations near plasmonic nanoparticles. Overall, this work paves the way for visualizing chemical transformations as well as coherent electronic and vibrational dynamics with joint femtosecond temporal and few-nanometer spatial resolution under ambient conditions.