Gold Nanoparticle Arrays Research Articles

Plasmonic properties of gold nanostructures on Hf-doped ZnO film and its application for refractive index sensing with a high figure of merit

This paper reports a systematic study of the plasmonic properties of periodic arrays of gold nanoparticles in contact with a novel transparent conducting oxide (TCO) material - Hafnium-doped zinc oxide (HZO). Resonant coupling of the grating diffraction orders with the propagating surface plasmons along the waveguide film, which can generate large field enhancements, are investigated by FDTD simulations. By tuning the ratio of Hf dopants to ZnO film, the plasmon resonances can be tuned and narrower resonance with FWHM of 2-5 nm are observed. Such plasmonic substrates are shown in this study to have high figure of merit in refractive index sensing applications.

Long-Range Plasmon-Induced Anisotropic Growth of an Organic Semiconductor between Isotropic Gold Nanoparticles.

Plasmon-induced diazonium reduction was used to graft an organic semiconductor, namely oligo(bisthienylbenzene) (BTB), onto square arrays of gold nanoparticles (NPs) of various diameters. Grafting was evidenced by scanning electron microscopy (SEM) measurements by the extinction spectra of the localized surface plasmon resonance, as well as by Raman and energy dispersive X-ray (EDX) spectroscopies. We show that BTB is selectively deposited around the NPs. The thickness of the layer increases with increasing irradiation time and reaches a limit which depends on the size of the NPs with the thicker organic layers being generated for smaller NPs. Under polarized irradiation, BTB growth is strongly anisotropic. Starting from arrays with square gratings and spherical NPs, long-range plasmon-induced anisotropic growth makes it possible to generate in the direction of the polarized light, lines, columns, or lines and columns of NPs connected by an organic semiconductor. These results demonstrate that the growth is due to hot electrons.

Rapid Actuation of Thermo-Responsive Polymer Networks: Investigation of the Transition Kinetics.

The swelling and collapsing of thermo-responsive poly(N-isopropylacrylamide)-based polymer (pNIPAAm) networks are investigated in order to reveal the dependency on their kinetics and maximum possible actuation speed. The pNIPAAm-based network was attached as thin hydrogel film to lithographically prepared gold nanoparticle arrays to exploit their localized surface plasmon resonance (LSPR) for rapid local heating. The same substrate also served for LSPR-based monitoring of the reversible collapsing and swelling of the pNIPAAm network through its pronounced refractive index changes. The obtained data reveal signatures of multiple phases during the volume transition, which are driven by the diffusion of water molecules into and out of the network structure and by polymer chain re-arrangement. For the micrometer-thick hydrogel film in the swollen state, the layer can respond as fast as several milliseconds depending on the strength of the heating optical pulse and on the tuning of the ambient temperature with respect to the lower critical solution temperature of the polymer. Distinct differences in the time constants of swelling and collapse are observed and attributed to the dependence of the cooperative diffusion coefficient of polymer chains on polymer volume fraction. The reported results may provide guidelines for novel miniature actuator designs and micromachines that take advantages of the non-reciprocal temperature-induced volume transitions in thermo-responsive hydrogel materials.

Conformational control of two-dimensional gold nanoparticle arrays in a confined geometry within a vesicular wall

The two-dimensional (2D) assembly of gold nanoparticles (AuNPs) in a confined geometry is a rare phenomenon that has not been experimentally verified for complex systems. In this study, this process was investigated in detail using two types of block copolymers with hydrophobic and hydrophilic blocks and a series of AuNPs of three different sizes protected by hydrophobic ligands. In aqueous solutions, the selected block copolymers self-assembled into vesicular nanostructures with a hydrophobic domain in the wall, which functions as a confined geometrical space for hydrophobic AuNPs (i.e., it exerts a confinement effect and restricts the movement of AuNPs). Small-angle X-ray scattering studies revealed that AuNPs of different sizes assembled differently in the same confined geometry of the vesicular wall. In addition, optimal conditions for the formation of a regular NP array in the hydrophobic domain were determined. The AuNPs successfully self-assembled into a regular 2D lattice structure, forming a shell around the vesicle, when their size matched the thickness of the hydrophobic domain of the vesicular nanostructure. This study provides guidelines for the fabrication of nanoparticle arrays with controlled structures, which could enhance the functionality of materials and their physical properties.

Gold nanoparticle arrays organized in mixed patterns through directed self-assembly of ultrathin block copolymer films on topographic substrates

Controlling complexity in assemblies of metal and semiconductor nanoparticles has the potential to expand the utilization of photonic devices into wavelength regimes that are currently inaccessible. Here we show that casting ultrathin films of asymmetric block copolymers on topographically defined substrates affords four types of mixed patterns through fine control of film thickness. Analysis of top-view and cross-sectional images revealed different morphological behavior of the film in the trench and on the plateau, which was explained by the difference in the type of boundary imposed by each topographic feature. Exposed domains were chemically modified and selectively decorated with gold nanoparticles, giving rise to nanoparticle superstructures with mixed patterns in a controlled fashion. We envisage utilization of such hierarchical superstructures as plasmon waveguides and metasurfaces.

Narrowband Plasmonic Absorber Using Gold Nanoparticle Arrays for Refractive Index Sensing

Here, a design of localized surface plasmon resonance (LSPR)-based sensor using narrowband metamaterial absorber based on a gold nanoparticle array is studied. The LSPR based sensor has found comprehensive applications in clinical analysis and environmental monitoring. The simulation outcomes demonstrate that the proposed structure has an absorption bandwidth (FWHM) of 5.7nm. Sensors with narrow bandwidth can develop efficiency and correctness detection. Furthermore, as a refractive index sensor, the sensitivity is obtained as high as S = 964nm/RIU with large value of figure of merit (FOM = <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.653\times 10$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> ). The proposed design displays polarization independence, which will remove the polarization requirement of equipment. We further demonstrate the array as a biosensor for detecting some viruses, suggesting the applicability for label-free clinical sensing. The device has an extensive performance, such as perfect absorption, polarization insensitivity, high sensitivity, and FOM, appropriate for applied applications.

Enhanced light harvesting in GaAs thin-film solar cells using plasmonic gold (Au) nanoparticle absorbers

Surface texturing methods are often used in thin-film solar cells (SCs) to achieve effective photon trapping. However, such approaches have a detrimental impact on cell performance and are not suitable for thin-films. Plasmonic light trapping using metal nanoparticles (NPs) is one of the promising technique for achieving superior optical absorption in thin-film SCs with less material usage. In this article, to improve the optical performance of GaAs thin-film SCs, a uniformly distributed Gold (Au) nanoparticle (NP) array is introduced at the top of transparent indium-tin-oxide (ITO) electrode. The Au NP array functions as an antireflection layer, increasing light harvesting in active layer for both visible and infrared (IR) wavelength regions. By performing 3-D finite-different time-domain (FDTD) analysis, we have presented a comparative optoelectronic study of the GaAs SCs with and without Au NPs. Photovoltaic parameters such as optical absorption (A (λ)), photogeneration density (Goptical rate), and photocurrent density (Jsc) are used to evaluate performance of the structures. The proposed thin-film SCs with Au NPs achieved an optical absorption of 60% (planar) and 77% (NW array) with a remarkable photocurrent of 22.8 mA/cm2 (planar) and 26.7 mA/cm2 respectively.

Facile Detection and Quantification of Acetamiprid Using a Portable Raman Spectrometer Combined with Self-Assembled Gold Nanoparticle Array

Rapid and facile determination of pesticides is critically important in food and environmental monitoring. This study developed a self-assembled gold nanoparticle array based SERS method for highly specific and sensitive detection of acetamiprid, a neonicotinoid pesticide that used to be difficult in SERS analysis due to its low affinity with SERS substrates. SERS detection and quantification of acetamiprid was conducted with self-assembled gold nanoparticle arrays at the interface of chloroform and water as the enhancing substrate. Since targets dissolved in chloroform (organic phase) also have access to the hot-spots of Au NP array, the developed method exhibited good sensitivity and specificity for acetamiprid determination. Under the optimal conditions, SERS intensities at Raman shifts of 631 cm−1 and 1109 cm−1 displayed a good linear relationship with the logarithm concentration of acetamiprid in the range of 5.0 × 10−7 to 1.0 × 10−4 mol/L (0.11335 ppm to 22.67 ppm), with correlation coefficients of 0.97972 and 0.97552, respectively. The calculated LOD and LOQ of this method were 1.19 × 10−7 mol/L (0.265 ppb) and 2.63 × 10−7 mol/L (0.586 ppb), respectively, using SERS signal at 631 cm−1, and 2.95 × 10−7 mol/L (0.657 ppb) and 3.86 × 10−7 mol/L (0.860 ppb) using SERS signal at 1109 cm−1, respectively. Furthermore, the developed SERS method was successfully applied in determining acetamiprid on the surface of apple and spinach. This method offers an exciting opportunity for rapid detection of acetamiprid and other organic pesticides considering its advantages of simple preparation process, good specificity and sensitivity, and short detection time (within 1 h).

Efficient surface enhanced Raman scattering substrates based on complex gold nanostructures formed by annealing sputtered gold thin films

Surface enhanced Raman scattering (SERS) has attracted great attention of scientists in the last few decades due to its wide range of applications, especially in detecting chemical compounds even at single molecular level. In this research, we combine sputtering and post annealing method to prepare gold nanoparticles with uniform distribution on cover glass substrates, which work as efficient SERS substrates. This work studies the effect of gold thickness on the formation of nanoparticles during annealing process. The effect of size, inter-distance and morphology of gold NPs on plasmon properties was studied by scanning electron microscope and absorption spectroscopy. The enhancement capability of different morphologies was also verified by using Finite Different Time Domain (FDTD) technique. The as-prepared gold nanoparticles arrays are efficient surface enhanced Raman scattering substrates as demonstrated by the ability to detect methylene blue at concentration as low as 10−10 M. The facile, cost-effective fabrication process is convenient to scale up for mass production of high sensitivity surface enhanced Raman substrates.

Centimeter-Scale Gold Nanoparticle Arrays for Spatial Mapping of the Second Harmonic and Two-Photon Luminescence

Fabricating highly homogeneous plasmonic nanostructures over a large area and optically evaluating their structural quality are challenging. Here, we propose an elegant approach to achieve various ...

Microscale Thermophoresis in Liquids Induced by Plasmonic Heating and Characterized by Phase and Fluorescence Microscopies

Thermophoresis denotes the motion of particles along temperature gradients. Insignificant in most daily-life observations, this peculiar effect can become dominant in applications involving nano- and microscale heating in fluids. Recent studies in nanoplasmonics observed significant thermophoresis of molecules and particles, in particular in plasmonic trapping, SERS, and biosensing. Evidencing the presence of thermophoresis is not obvious and quantifying its magnitude is even less accessible considering existing techniques. In this article, we introduce a method capable of quantifying the thermophoresis of particles in the context of nanoplasmonic applications. A gold nanoparticle array under illumination is used to create microscale temperature gradients, and a dual fluorescence-phase microscopy technique is used to map both temperature and concentration in parallel. This association enables the determination of Soret coefficients for a wide range of temperatures from a single image acquisition. This metrology technique paves the way for broader fundamental research in microscale thermophoresis in liquids and better-controlled applications in nanophotonics involving thermoplasmonic effects.

Reconfigurable localized surface plasmon resonance spectrum based on acousto-dynamic coupling in arrays gold nanoparticles induced by shear horizontal vibration

Reconfigurable localized surface plasmon resonance (LSPR) is an essential characteristic for various applications to support Society 5.0. However, many LSPR spectrum have poor reconfigurability. As a novelty, we proposed a reconfigurable LSPR spectrum by acousto-dynamic coupling in arrays of gold nanoparticles (AuNPs) induced by shear-horizontal vibrations. The vibrations were produced by piezoelectric phenomena especially shear horizontal surface acoustic waves (SH-SAWs) on a 36XY-LiTaO3 substrate after applying an electric signal, the ON-condition. The experimental results demonstrated that the ON-condition produced a blueshift effect on the peak position (λP) with an adjustment quality factor compared to the OFF-condition. Moreover, in order to perform the finite-difference time-domain (FDTD) analysis, we reproduced the morphological structure of AuNPs base on scanning electron microscope (SEM) images. The different coupling distances and different arrays structures were utilized as ON-condition approaches for dimer AuNPs and arrays AuNPs, respectively. The FDTD simulation obtained a blueshift effect compared to the initial structure. Finally, the proposed structure successfully combines piezoelectric phenomena with plasmonic phenomena to produce reconfigurable LSPR. The LSPR spectrum can be switched comfortably and reverses easily. The proposed method can be applied for multifunctional sensors with the high possibility of integration into a wireless network.

Accurate and fast modeling of scattering from random arrays of nanoparticles using the discrete dipole approximation and angular spectrum method.

Lens-free microscopes can utilize holographic reconstruction techniques to recover the image of an object from the digitally recorded superposition of an unperturbed plane wave and a wave scattered by the object. Image reconstruction most commonly relies on the scalar angular spectrum method (ASM). While fast, the scalar ASM can be inaccurate for nanoscale objects, either because of the scalar approximation, or more generally, because it only models field propagation and not light-matter interaction, including inter-particle coupling. Here we evaluate the accuracy of the scalar ASM when combined with three different light-matter interaction models for computing the far-field light scattered by random arrays of gold and polystyrene nanoparticles. Among the three models-a dipole-matched transmission model, an optical path length model, and a binary amplitude model-we find that which model is most accurate depends on the nanoparticle material and packing density. For polystyrene particles at any packing density, there is always at least one model with error below 20%, while for gold nanoparticles with 40% or 50% surface coverage, there are no models that can provide errors better than 30%. The ASM error is determined in comparison to a discrete dipole approximation model, which is more computationally efficient than other full-wave modeling techniques. The knowledge of when and how the ASM fails can serve as a first step toward improved resolution in lens-free reconstruction and can also be applied to other random nanoparticle array applications such as lens-based super-resolution imaging, sub-diffraction beam focusing, and biomolecular sensing.

Aptamer-functionalized Au nanoparticles array as the effective SERS biosensor for label-free detection of interleukin-6 in serum

• Homogeneous Au nanoparticles array was fabricated which showed high SERS activity. • The SERS substrate was modified with IL-6 aptamer which could recognized IL-6 specifically. • The aptamer-SERS assay could detect IL-6 in blood in a wide range with lower limit of detection of 1 pM. • Bacterial infection and radiation injure effect on mice could be evaluated based on IL-6 SERS detection. A label-free, highly sensitive, and selective biosensor for detection of interleukin-6 (IL-6), which is an important inflammatory and cancer progression cytokine, has been achieved by combining gold nanoparticles (NPs) array surface-enhanced Raman spectroscopy (SERS) substrate and DNA aptamer. The SERS substrate consisted of Au NPs array is functionalized with the aptamer which is composed of the IL-6 recognition sequence and the output signal reporter. Upon recognition of target IL-6 in serum, the aptamer changes its conformation, resulting in the corresponding change of the output Raman intensity ratio (I 660 /I 736 ), with which the quantitative evaluation of IL-6 in 10 -12 -10 -7 M range can be realized. This SERS approach was employed to detect IL-6 in mice serum for inspecting the effect of drug and bacterial infection, and particularly, the radiation injury in the treated animals. This work therefore exemplifies that the aptamer-based SERS biosensor can serve as a promising tool for quick and convenient medical diagnosis applications.

THE STUDY OF THERMAL STABILITY OF DNA DUPLEX ON NANOPARTICLE-BASED PLATFORMS: A METHOD FOR BIOSENSING APPLICATIONS

In this research, a new method for DNA detection is proposed by studying the thermal stability of DNA duplexes modified on the nanostructured platform. The nanostructures are fabricated by using the block copolymer nanolithography method to form ordered arrays of gold nanoparticles on the silicon substrate. The thermally induced denaturation of the DNA duplex on the sensing part is monitored to determine the heat transfer property (thermal resistance) at the solid-liquid interface. An about 50% change in the thermal resistance during the DNA denaturation has fairly confirmed the feasible working of the sensing platform. The sensitivity, selectivity, and repeatability of the DNA biosensor are also evaluated by analysing the thermal resistance behaviour during thermal induction cycles. For the first time, a label-free, cost-effective, and easy data read-out DNA sensing method is developed in comparison with conventional fluorescence techniques.

Tension–compression behavior in gold nanoparticle arrays: a molecular dynamics study

The mechanical properties of Au nanoparticle arrays are studied by tensile and compressive deformation, using large-scale molecular dynamics simulations which include up to 16 million atoms. Our results show that mechanical response is dominated by nanoparticle size. For compression, strength versus particle size shows similar trends in strength than full-density nanocrystals. For diameters (d) below 10 nm there is an inverse Hall–Petch (HP) regime. Beyond a maximum at 10 nm, strength decreases following a HP d −1/2 dependence. In both regimes, interparticle sliding and dislocation activity play a role. The array with 10 nm nanoparticles showed the same mechanical properties than a polycrystalline bulk with the same grain size. This enhanced strength, for a material nearly 20% lighter, is attributed to the absence of grain boundary junctions, and to the array geometry, which leads to constant flow stress by means of densification, nanoparticle rotation, and dislocation activity. For tension, there is something akin to brittle fracture for large grain sizes, with NPs debonding perpendicular to the traction direction. The Johnson–Kendall–Roberts contact theory was successfully applied to describe the superlattice porosity, predicting also the array strength within 10% of molecular dynamics values. Although this study is focused on Au nanoparticles, our findings could be helpful in future studies of similar arrays with NPs of different kinds of materials.

Macroscopical monolayer films of ordered arrays of gold nanoparticles as SERS substrates for in situ quantitative detection in aqueous solutions.

In this work, macroscopical monolayer films of ordered arrays of gold nanoparticles (MMF-OA-Au NPs) are successfully prepared at the interfaces of toluene-diethylene glycol (DEG) with a water volume fraction of 10% (no more than 25%), which can greatly reduce the electrostatic repulsion among NPs during the self-assembly due to the quick transfer of the remaining citrate ions into the DEG solutions containing water. Thanks to the uniformity in the intensity of SERS signals, the as-prepared MMF-OA-Au NPs transferred onto polydimethylsiloxane (PDMS) as SERS substrates (MMF-OA-Au NP@PDMS) can achieve in situ quantitative detection of the analytes (such as crystal violet and malachite green) in aqueous solutions. Moreover, MMF-OA-Au NP@PDMS as SERS-based pH sensors can directly determine the pH value of the aqueous solution in the range of 3 to 10 by means of the established well-defined linear relationship with the intensity of the peak of νCOO- without any calibration, instead of the intensity ratio of the Raman peaks of νCOO- to ν8a with further calculation. In addition, the as-prepared SERS-based pH sensors can still have excellent long-term durability.

Third-order nonlinear optical response of ion-implanted embedded arrays of plasmonic gold nanoparticles

Abstract Arrays of plasmonic gold nanoparticles, embedded in fused silica plates, were prepared by implanting 2 MeV Au+ ions through a silica particle lithographic mask. The nonlinear optical response of these periodic arrays was experimentally investigated using the z-scan technique at 532 nm with 26 ps pulses from a Nd:YAG laser. The open-aperture z-scan measurements were performed following different linear polarization angles for the incident light beam. A strong saturable absorption and a very clear nonlinear dichroic behavior were determined, the latter indicated by a sinusoidal modulation of the nonlinear absorption coefficient β (up to about 20% of its absolute value) as a function of the polarization angle. This result gives clear evidence of the formation of ordered arrays of embedded Au nanoparticles, corresponding to a honeycomb lattice symmetry with a modulation period of 30°.

Ultrasensitive antibody-aptamer plasmonic biosensor for malaria biomarker detection in whole blood

Development of plasmonic biosensors combining reliability and ease of use is still a challenge. Gold nanoparticle arrays made by block copolymer micelle nanolithography (BCMN) stand out for their scalability, cost-effectiveness and tunable plasmonic properties, making them ideal substrates for fluorescence enhancement. Here, we describe a plasmon-enhanced fluorescence immunosensor for the specific and ultrasensitive detection of Plasmodium falciparum lactate dehydrogenase (PfLDH)—a malaria marker—in whole blood. Analyte recognition is realized by oriented antibodies immobilized in a close-packed configuration via the photochemical immobilization technique (PIT), with a top bioreceptor of nucleic acid aptamers recognizing a different surface of PfLDH in a sandwich conformation. The combination of BCMN and PIT enabled maximum control over the nanoparticle size and lattice constant as well as the distance of the fluorophore from the sensing surface. The device achieved a limit of detection smaller than 1 pg/mL (<30 fM) with very high specificity without any sample pretreatment. This limit of detection is several orders of magnitude lower than that found in malaria rapid diagnostic tests or even commercial ELISA kits. Thanks to its overall dimensions, ease of use and high-throughput analysis, the device can be used as a substrate in automated multi-well plate readers and improve the efficiency of conventional fluorescence immunoassays.

A Simulation Study for Field Enhancement due to Multiresonant Localized Surface Plasmon Excitation in the truncated Octahedral Gold Nanoparticle Arrays

We theoretically demonstrates large field enhancement at the close-packed, truncated octahedral gold nanoparticle array by using a finite difference time domain method. A multiple peak at the visible and near infrared frequency implies the multiple resonance in the nanostructures, corresponding to the dipolar and quadrupolar mode excitation of electric field at the single octahedral particles. The splitting of two adjacent resonant peak as a function of the distance of the particles implies the existence of the significant coupling between the resonant modes of the individual nanoparticles. The electric field profile at the gap between the particles shows the field enhancement due to such mode couplings, where dipolar and quadrupolar mode are simultaneously involved. Such evolution of mode coupling with increasing gap distance confirms the resonant modes excitation and their coupling is the origin of the strong field enhancement. Simulation with different polarization of the incident light denotes the dominant coupling mode is governed by the size of the interaction area. Importantly, electric field at the gap is hugely enhanced up to 17 at the optimal gap distance of 4 nm.