Gold Nanohole Arrays Research Articles

Impact of ordering of gold nanohole arrays on refractive index sensing

Gold nanohole arrays of various hole sizes with fixed thickness are fabricated using colloidal lithography. The degree of ordering of gold nanohole arrays was obtained by using a pair correlation function and a bond-orientation order parameter. Reflectance studies show signatures of surface plasmon polaritons and their coupling with localized surface plasmon resonance (LSPR). These optical responses are found to be dependent on the hole size variations and their ordering. The spectral resolution of resonances is evaluated and found to improve with long-range ordering and a higher bond-orientational order parameter of nanohole arrays. Based on order quantification and optical response, the optimal sample exhibiting coupling of LSPR and surface plasmon polaritons is chosen for refractive index sensing, yielding sensitivity of 470.49 nm/RIU and figure of merit of 14.42.

Effects of Silver Nanoparticles on Plasmon Resonance of Imprinted Gold Nanohole Array

Effects of Silver Nanoparticles on Plasmon Resonance of Imprinted Gold Nanohole Array

Nanoparticle-Enhanced Plasmonic Biosensor for Digital Biomarker Detection in a Microarray.

Nanoplasmonic devices have become a paradigm for biomolecular detection enabled by enhanced light-matter interactions in the fields from biological and pharmaceutical research to medical diagnostics and global health. In this work, we present a bright-field imaging plasmonic biosensor that allows visualization of single subwavelength gold nanoparticles (NPs) on large-area gold nanohole arrays (Au-NHAs). The sensor generates image heatmaps that reveal the locations of single NPs as high-contrast spikes, enabling the detection of individual NP-labeled molecules. We implemented the proposed method in a sandwich immunoassay for the detection of biotinylated bovine serum albumin (bBSA) and human C-reactive protein (CRP), a clinical biomarker of acute inflammatory diseases. Our method can detect 10 pg/mL of bBSA and 27 pg/mL CRP in 2 h, which is at least 4 orders of magnitude lower than the clinically relevant concentrations. Our sensitive and rapid detection approach paired with the robust large-area plasmonic sensor chips, which are fabricated using scalable and low-cost manufacturing, provides a powerful platform for multiplexed biomarker detection in various settings.

Emission Rate Modification and Quantum Efficiency Enhancement of Er3+ Emitters by Near-Field Coupling with Nanohole Arrays

The control of the spontaneous emission properties of quantum emitters with limited losses by near-field coupling with plasmons-supporting nanostructures is one of the keys for next-generation high-efficiency and high-coherence plasmonic devices. In the present work, gold nanohole arrays are demonstrated to be an effective plasmonic system for controlling radiative rate and quantum efficiency of the 1540 nm emission of Er3+ ions embedded in silica. Finite element method electrodynamic simulations were used to describe the interaction between dipolar Er3+ emitters and the nanohole arrays. The results are in agreement with those of photoluminescence measurements performed in different coupling configurations. Particularly, we demonstrated that owing to the combination of strong emission enhancement and low level of ohmic losses in the metal, nanohole arrays are able to enhance the far-field photon yield up to 74%. This in turn is related to an extremely high far-field quantum efficiency: more than 90% of th...

Large-area gold nanohole arrays fabricated by one-step method for surface plasmon resonance biochemical sensing.

Surface plasmon resonance (SPR) nanosensors based on metallic nanohole arrays have been widely reported to detect binding interactions in biological specimens. A simple and effective method for constructing nanoscale arrays is essential for the development of SPR nanosensors. In this work, we report a one-step method to fabricate nanohole arrays by thermal nanoimprinting in the matrix of IPS (Intermediate Polymer Stamp). No additional etching process or supporting substrate is required. The preparation process is simple, time-saving and compatible for roll-to-roll process, potentially allowing mass production. Moreover, the nanohole arrays were integrated into detection platform as SPR sensors to investigate different types of biological binding interactions. The results demonstrate that our one-step method can be used to efficiently fabricate large-area and uniform nanohole arrays for biochemical sensing.

Nanomeshes at Liquid Interfaces: From Free‐Standing Hole Arrays toward Metal–Insulator–Metal Architectures

AbstractThe superior optical properties of metamaterials often rely on hierarchical structures in the sub‐wavelength regime comprising stacks of individually patterned layers. For the fabrication of metamaterials in the visible regime, specific top‐down lithographic methods have been developed. These techniques, however, have several inherent drawbacks such the lack of scalability and low production speeds. Here, a simple and modular approach for the construction of multilayer metal–insulator–metal structures based on the transfer of metal nanohole arrays via liquid interfaces is demonstrated. Gold nanohole arrays are used as model systems that are prepared via nanosphere lithography on a zinc oxide sacrificial layer. Exploiting an interface mediated method, the prepared nanohole arrays are subsequently transferred onto arbitrary hydrophilic or hydrophobic substrates without compromising the high quality of the nanomeshes. Two approaches to stack such nanostructured layers with nanometer precision in a rapid way are demonstrated. Finally, the high mechanical stability of only 100 nm thick gold nanohole arrays allows for the preparation of free‐standing nanomeshes in the order of several hundreds of square‐micrometers.

Tungsten Disulfide-Gold Nanohole Hybrid Metasurfaces for Nonlinear Metalenses in the Visible Region.

Recently, nonlinear hybrid metasurface comes into an attractive new concept in the research of nanophotonics and nanotechnology. It is composed of semiconductors with an intrinsically large nonlinear susceptibility and traditional plasmonic metasurfaces, offering opportunities for efficiently generating and manipulating nonlinear optical responses. A high second-harmonic generation (SHG) conversion efficiency has been demonstrated in the mid-infrared region by using multiquantum-well (MQW)-based plasmonic metasurfaces. However, it has yet to be demonstrated in the visible region. Here, we present a new type of nonlinear hybrid metasurfaces for the visible region, which consists of a single layer of tungsten disulfide (WS2) and a phased gold nanohole array. The results indicate that a large SHG susceptibility of ∼10-1 nm/V at 810 nm is achieved, which is 2-3 orders of magnitude larger than that of typical plasmonic metasurfaces. Nonlinear metalenses with the focal lengths of 30, 50, and 100 μm are demonstrated experimentally, providing a direct evidence for both generating and manipulating SH signals based on the nonlinear hybrid metasurfaces. It shows great potential applications in designing of integrated, ultrathin, compacted, and efficient nonlinear optical devices, such as frequency converters, nonlinear holography, and the generation of nonlinear optical vortex beams.

Surface-enhanced Raman scattering active gold nanoparticle/nanohole arrays fabricated through electron beam lithography

Effective surface-enhanced Raman scattering (SERS)-active substrates from gold nanoparticle and gold nanohole arrays were successfully fabricated through electron beam lithography with precise computer-aided control of the unit size and intergap distance. Their SERS performance was evaluated using 4-mercaptobenzoic acid (4-MBA). These gold arrays yielded strong SERS signals under 785 nm laser excitation. The enhancement factors for 4-MBA molecules on the prepared gold nanoparticle and nanohole arrays maxed at 1.08 × 107 and 8.61 × 106, respectively. The observed increase in SERS enhancement was attributed to the localized surface plasmon resonance (LSPR) wavelength shifting toward the near-infrared regime when the gold nanohole diameter increased, in agreement with the theoretical prediction in this study. The contribution of LSPR to the Raman enhancement from nanohole arrays deposited on fluorine-doped tin oxide glass was elucidated by comparing SERS and transmission spectra. This simple fabrication procedure, which entails employing electron beam lithography and the controllability of the intergap distance, suggests highly promising uses of nanohole arrays as functional components in sensing and photonic devices.

Emission Efficiency Enhancement of Er3+ Ions in Silica by Near‐Field Coupling With Plasmonic and Pre‐Plasmonic Nanostructures

Plasmonic nanostructures have been the object of strong scientific interest in the last decade for their linear and nonlinear optical properties. The present work is focused on the capability to control and enhance the Er3+ emission efficiency in silica by near‐field coupling with plasmonic and pre‐plasmonic nanostructures. The results shows that more than one order of magnitude Er3+ PL enhancement can be obtained with ultra‐small pre‐plasmonic Ag clusters synthesized by ion implantation and thermal annealing. Moreover, resonantly coupled extended plasmonic nanostructures in the form of gold nanohole arrays can efficiently interact with the Er ions, leading to a 20‐fold increase of their radiative emission at 1.54 μm.

Flexible Nanoholey Patches for Antibiotic-Free Treatments of Skin Infections.

Despite the availability of different antibiotics, bacterial infections are still one of the leading causes of hospitalization and mortality. The clinical failure of antibiotic treatment is due to a general poor antibiotic penetration to bacterial infection sites as well as the development of antibiotic-resistant pathogens. In the case of skin infection, the wound is covered by exudate, making it impermeable to topical antibiotics. The development of a flexible patch allowing a rapid and highly efficient treatment of subcutaneous wound infections via photothermal irradiation is presented here. The skin patch combines the near-infrared photothermal properties of a gold nanohole array formed by self-assembly of colloidal structures on flexible polyimide films with that of reduced graphene oxide nanosheets for laser-gated pathogen inactivation. In vivo tests performed on mice with subcutaneous skin infection and treated with the photothermal skin patch show wound healing of the infected site, while nontreated areas result in necrotic muscular fibers and bacterial infiltrate. No loss in efficiency is observed upon multiple use of these patches during in vivo experiments because of their robustness.

Localized surface plasmon resonance sensing structure based on gold nanohole array on beveled fiber edge

This paper proposes a simple, stable, sensitive, and angle-dependent localized surface plasmon resonance (LSPR) sensing structure based on multi-mode optical fiber. We adopted the template transfer method to integrate a nanohole array onto a fiber tip with beveled angle. Experimental results indicated that beveled angle structured probe sensor outperform the flat optical fiber tip structured LSPR sensor in our experiment. We tested the sensitivity and the figure of merit (FOM) of the probe beveled angle from 5°–22°, with refractive index ranging from 1.333–1.385, to find that sensitivity and FOM were optimal at fiber tip bevel angle of 7°, reaching 487 nm/RIU and 29 respectively.

Fabrication of Hierarchical Nanostructures for Surface-Enhanced Raman Scattering Biosensors

Biosensors are novel devices for offering fast, point of care results in healthcare fields. Nanostructures can improve the performance of biosensors. For example, plasmonic gold nanohole arrays have been demonstrated to amplify the surface-enhanced Raman scattering (SERS) signal in biosensors because of their unique optical properties and highly tunable localized surface plasmon resonance (LSPR). However, it remains a challenge to fabricate nanostructures such as nanohole arrays. Herein a gold nanohole array-silica spacer-gold nanodisk array has been fabricated based on nanosphere lithography. The SERS effect is considerably improved due to the plasmonic coupling between the gold nanohole array and the nanodisk array separated by a small silica gap (~10 nm). Ultraviolet-visible spectroscopy, Raman spectroscopy, and finite-difference time domain simulations have been used to characterize the performance. The plasmonic nanostructure obtained can be potentially integrated into microfluidic devices for healthcare and environmental monitoring.

Multimode Coherent Hybrid States: Ultrafast Investigation of Double Rabi Splitting between Surface Plasmons and Sulforhodamine 101 Dyes

A multimode coherent hybrid system formed by strongly coupled surface plasmons in gold nanohole arrays and excitons in sulforhodamine 101 dyes is investigated by using both a steady‐state spectroscopic method and a femtosecond transient absorption spectra approach. A double Rabi splitting up to 255 meV and 188 meV is observed in steady‐state transmission measurements. Furthermore, the dynamics of the multimode coherent hybrid system are studied under upper band resonant excitation. It is found that the bleaching signal associated with uncoupled sulforhodamine 101 molecules completely disappears. Instead, two distinctive bleaching signals corresponding to the middle and lower bands are formed, thus highlighting the presence of coherent hybrid states. Finally, a remarkebly long lifetime for the lower band is observed, even longer than the bleaching recovery of the uncoupled dyes, in perfect agreement with the non‐Markovian regime. These peculiar features can provide new perspectives for coherent energy transfer and mode‐selective chemistry, thus enriching the tools available in the chemical reaction landscape.

Surface plasmon-enhanced fluorescence on Au nanohole array for prostate-specific antigen detection.

Localized surface plasmon (LSP) has been widely applied for the enhancement of fluorescence emission for biosensing owing to its potential for strong field enhancement. However, due to its small penetration depth, LSP offers limited fluorescence enhancement over a whole sensor chip and, therefore, insufficient sensitivity for the detection of biomolecules, especially large molecules. We demonstrate the simultaneous excitation of LSP and propagating surface plasmon (PSP) on an Au nanohole array under Kretschmann configuration for the detection of prostate-specific antigen with a sandwich immunoassay. The proposed method combines the advantages of high field enhancement by LSP and large surface area probed by PSP field. The simulated results indicated that a maximum enhancement of electric field intensity up to 1,600 times can be achieved under the simultaneous excitation of LSP and PSP modes. The sandwich assay of PSA carried out on gold nanohole array substrate showed a limit of detection of 140 fM supporting coexcitation of LSP and PSP modes. The limit of detection was approximately sevenfold lower than that when only LSP was resonantly excited on the same substrate. The results of this study demonstrate high fluorescence enhancement through the coexcitation of LSP and PSP modes and pave a way for its implementation as a highly sensitive bioassay.

Plasmonic nanohole array biosensor for label-free and real-time analysis of live cell secretion.

Cell secretion dynamics plays a central role in physiological and disease processes. Due to its various temporal profiles, it is essential to implement a precise detection scheme for continuous monitoring of secretion in real time. The current fluorescent and colorimetric approaches hinder such applications due to their multiple time-consuming steps, molecular labeling, and especially the 'snapshot' endpoint readouts. Here, we develop a nanoplasmonic biosensor for real-time monitoring of live cell cytokine secretion in a label-free configuration. Our nanoplasmonic biosensor is composed of gold nanohole arrays supporting extraordinary optical transmission (EOT), which enables sensitive and high-throughput analysis of biomolecules. The nanobiosensor is integrated with an adjustable microfluidic cell module for the analysis of live cells under well-controlled culture conditions. We achieved an outstanding sensitivity for the detection of vascular endothelial growth factor (VEGF) directly in complex cell media. Significantly, the secretion dynamics from live cancer cells were monitored and quantified for 10 hours while preserving good cell viability. This novel approach of probing cytokine secretion activity is compatible with conventional inverted microscopes found in a common biology laboratory. With its simple optical set-up and label-free detection configuration, we anticipate our nanoplasmonic biosensor to be a powerful tool as a lab-on-chip device to analyze cellular activities for fundamental cell research and biotechnologies.

Highly sensitive deep-silver-nanowell arrays (d-AgNWAs) for refractometric sensing

Large-area deep-silver-nanowell arrays (d-AgNWAs) for plasmonic sensing were manufactured by combining colloidal lithography with metal deposition. In contrast to most previous studies, we shed light on the outstanding sensitivity afforded by deep metallic nanowells (up to 400 nm in depth). Using gold nanohole arrays as a mask, a silicon substrate was etched into deep silicon nanowells, which acted as a template for subsequent Ag deposition, resulting in the formation of d-AgNWAs. Various geometric parameters were separately tailored to study the changes in the optical performance and further optimize the sensing ability of the structure. After several rounds of selection, the best sensing d-AgNWA, which had a Ag thickness of 400 nm, template depth of 400 nm, hole diameter of 504 nm, and period of 1 μm, was selected. It had a sensitivity of 933 nm·RIU–1, which is substantially higher than those of most common thin metallic nanohole arrays. As a proof of concept, the as-prepared structure was employed as a substrate for an antigen-antibody recognition immunoassay, which indicates its great potential for label-free real-time biosensing.

Dynamics of Strong Coupling between CdSe Quantum Dots and Surface Plasmon Polaritons in Subwavelength Hole Array.

We have investigated the strong coupling interaction between excitons of CdSe quantum dots (QDs) and surface plasmon polaritons (SPPs) of gold nanohole array by steady-state spectroscopic method and transient absorption measurements. Numerical and experimental steady-state measurements demonstrate that the SPP-QD system can indeed undergo strong coupling, characterized by a Rabi splitting up to 220 meV. In particular, it is found that in the transient absorption spectra, under resonant excitation, the 1S transition bleaching band from uncoupled CdSe QDs is completely separated into two distinctive bleaching bands, remarkably fingerprinting the hybrid SPP-QD state. It was also found that the lifetime of these hybrid bands is just slightly shorter than the lifetime of bare CdSe QDs, possibly caused by the phonon bottleneck effect due to the large Rabi splitting. These results could open a new avenue toward the development of novel nanoplasmon devices with strong SPP-QD interaction.

Enhancing angular sensitivity of plasmonic nanostructures using mode transition in hexagonal gold nanohole arrays

We presented a surface plasmon resonance (SPR) sensor with an angular sensitivity up to 440 deg/RIU by using (±1,∓1) mode on a hexagonal gold nanohole array. The large-area gold nanohole arrays were fabricated by thermal-annealing template-stripping method with 180-nm-hole diameter and 600-nm period. A flat dispersion curve deviated from Bragg condition for (±1,∓1) mode occurred when incident angle was larger than 20°. The finite-difference time-domain calculations verified that plasmonic mode changed from surface plasmon mode to cavity mode in nanoholes. Such mode transition resulted in the large change of dispersion curve. The angular sensitivity of the (±1,∓1) mode near the transition band was 6.2 times higher than surface plasmon mode under Bragg condition and 4.5 times higher than prism-based SPR sensors at 850nm wavelength. Biosensing experiments for antigen-antibody interactions verified the surface binding sensitivity was higher than prism-based SPR machine.

Graphene-enhanced plasmonic nanohole arrays for environmental sensing in aqueous samples

The label-free nature of surface plasmon resonance techniques (SPR) enables a fast, specific, and sensitive analysis of molecular interactions. However, detection of highly diluted concentrations and small molecules is still challenging. It is shown here that in contrast to continuous gold films, gold nanohole arrays can significantly improve the performance of SPR devices in angle-dependent measurement mode, as a signal amplification arises from localized surface plasmons at the nanostructures. This leads consequently to an increased sensing capability of molecules bound to the nanohole array surface. Furthermore, a reduced graphene oxide (rGO) sensor surface was layered over the nanohole array. Reduced graphene oxide is a 2D nanomaterial consisting of sp2-hybridized carbon atoms and is an attractive receptor surface for SPR as it omits any bulk phase and therefore allows fast response times. In fact, it was found that nanohole arrays demonstrated a higher shift in the resonance angle of 250–380% compared to a continuous gold film. At the same time the nanohole array structure as characterized by its diameter-to-periodicity ratio had minimal influence on the binding capacity of the sensor surface. As a simple and environmentally highly relevant model, binding of the plasticizer diethyl phthalate (DEP) via π-stacking was monitored on the rGO gold nanohole array realizing a limit of detection of as low as 20 nM. The concentration-dependent signal change was studied with the best performing rGO-modified nanohole arrays. Compared to continuous gold films a diameter-to-periodicity ratio (D/P) of 0.43 lead to a 12-fold signal enhancement. Finally, the effect of environmental waters on the sensor was evaluated using samples from sea, lake and river waters spiked with analytically relevant amounts of DEP during which significant changes in the SPR signal are observed. It is expected that this concept can be successfully transferred to enhance the sensitivity in SPR sensors.

Surface-Enhanced Raman Scattering on Gold Nanohole Arrays in Symmetrical Dielectric Environments Exhibiting Electric Field Extension

The electromagnetic enhancement in surface-enhanced Raman scattering (SERS) caused by localized surface plasmon resonance is a near-field effect, often limiting the practicality of SERS in many applications. However, no attempts have been made to investigate field extension through symmetrical refractive index modulation in a SERS-based system. Here, we report the development and characterization of refractive index-matched SERS substrates supporting electric field extension to realize what is termed “long-range SERS” (LR-SERS). Finite-difference time-domain simulations were employed to tune the plasmonic responses and investigate electric field distributions of gold nanohole arrays (NHAs) as a function of the dielectric environment and geometric parameters. SERS substrates supporting long-range behavior were compared against “conventional” substrates without long-range behavior. SERS intensities from rhodamine 6G (R6G) aqueous solutions of 2.0 × 103 and 1.5 × 102 counts s–1 mW–1 were produced by the LR-S...