Plasmonic Nanohole Research Articles

Plasmonic Nanohole Sensor for Capturing Single Virus-Like Particles toward Virucidal Drug Evaluation.

A plasmonic nanohole sensor for virus-like particle capture and virucidal drug evaluation is reported. Using a materials-selective surface functionalization scheme, passive immobilization of virus-like particles only within the nanoholes is achieved. The findings demonstrate that a low surface coverage of particles only inside the functionalized nanoholes significantly improves nanoplasmonic sensing performance over conventional nanohole arrays.

Large-Area, Lithography-Free Super Absorbers and Color Filters at Visible Frequencies Using Ultrathin Metallic Films

Plasmonic materials and metamaterials have been widely utilized to achieve spectral transmission, reflection and absorption filters based on localized or delocalized resonances arising from the interaction of photons with nanostructured materials. Realization of visible-frequency, high-performance, large-area, optical filters based on nanoplasmonic materials is rather challenging due to nanofabrication related problems (cost, fabrication imperfection, surface roughness) and optical losses of metals. Here, we propose and demonstrate large-area perfect absorbers and transmission filters that overcome difficulties associated with the nanofabrication using a lithography-free approach. We also utilize and benefit from the optical losses in metals in our optical filter designs. Our resonant optical filter design is based on a modified, asymmetric metal-insulator-metal (MIM) based Fabry-Perot cavity with plasmonic, lossy ultra-thin (~30 nm) metallic films used as the top metallic layer. We demonstrated a narrow bandwidth (~17 nm) super absorber with 97% maximum absorption with a performance comparable to nanostructure/nanoparticle-based super absorbers. We also investigated transmission (color) filters using ultra-thin metallic films, in which different colors can be obtained by controlling the dielectric spacer thickness. With performance parameters of transmission peak intensity reaching 60% and a narrow-band of ~ 40 nm, our color filters exceed the performance of widely studied plasmonic nanohole array based color filters. Proposed asymmetric Fabry-Perot cavities using ultra-thin metallic films could find applications in spectrally selective optical (color and absorber) filters, optoelectronic devices with controlled bandwidth such as narrow-band photodetectors, and light-emitting devices.

Influence of the Evanescent Field Decay Length on the Sensitivity of Plasmonic Nanodisks and Nanoholes

We evaluate and compare the sensitivity of gold nanodisks on silica substrates and nanoholes made in silica-supported gold films, two of the most common sensor structures used in plasmonic biosensing. An alumina overcoat was applied by atomic layer deposition (ALD) to precisely control the interfacial refractive index and determine the evanescent plasmonic field decay length. The results are in good agreement with analytical models and biomolecular binding experiments for the two substrates. We found that nanodisks outperform nanoholes for thin dielectric coatings ( ∼20 nm). The optimum nanoplasmonic transducer element for a given biorecognition reaction can be chosen based on experimentally determined bulk sensitivities/noise levels and theoretically estimated evanescent field decay lengths.

Electrofocusing-enhanced localized surface plasmon resonance biosensors.

Localized surface plasmon resonance (LSPR) biosensors typically suffer from diffusion limited mass transport and nonspecific adsorption upon detection of biomolecules in real biofluids. We employ here a peptide-modified plasmonic gold nanohole (AuNH) array for real-time detection of human troponin I (cTnI). Applying a negative electric bias on the AuNH sensor chip enables us to attract and concentrate cTnI at the sensor surface, while repelling other proteins thus decreasing interferences due to nonspecific adsorption.

Investigating the Fabrication Imperfections of Plasmonic Nanohole Arrays and Its Effect on the Optical Transmission Spectra

We investigate the extraordinary optical transmission spectra of thin gold films perforated with imperfect nanohole arrays using the finite difference time domain (FDTD) method. Exponential shapes for the nanohole sidewalls are used. To the best of our knowledge, such investigation of transmission spectra of imperfect nanohole arrays has not previously been demonstrated. It was found that the asymmetry between the two openings of the circular nanoholes or bending to their sidewalls strongly modifies both the intensity and resonance positions of the transmission spectra. Furthermore, the results of this study assist in explaining the technicality of extraordinary optical transmission phenomenon and why some experimental results on transmission differ from those expected.

High-Brightness Plasmon-Enhanced Nanostructured Gold Photoemitter

Plasmonic nanohole arrays are fabricated in gold thin films by focused ion beam (FIB) lithography. Subsequent heat treatment creates sub 100 nm nanometric structures including tips, rods and flakes, all localized in the nanohole array region. The combined nanohole array and nanostructured surface comprise an efficient photoemitter. High brightness photoemission is observed from this construct using photoemission electron microscopy (PEEM), following 780 nm femtosecond (fs) laser irradiation. By comparing our observables to results of finite difference time domain (FDTD) calculations, we demonstrate that photoemission from the sub-100 nm structures is enhanced in the region of propagating surface plasmons launched from the nanohole arrays. Additionally, by tuning hole diameter and separation in the nanohole array, the photoemission intensity of nanostructured photoemitters can be controlled. We observe a photoemission enhancement of over 108, relative to photoemission from the flat region of the gold substrate at laser intensities well below the ablation threshold.

Extraordinary Optical Transmission in Metallic Nanostructures with a Plasmonic Nanohole Array of Two Connected Slot Antennas

A novel subwavelength transparent metal structure consisting of a periodic connected slot antennas nanohole array in a gold film is proposed in this work. The transmission characteristics of the structure are investigated by the three-dimensional finite-difference time-domain (3D FDTD) method. A broad transmission band with bandwidth more than 300 nm and maximum transmission intensity more than 90 % is achieved via the localized surface plasmons at the edges of nanoholes, the surface plasmon polaritons (SPPs) on the surface of the gold film, and Fabry–Ferot resonances of surface plasmons in the nanoholes. The transmission properties can be tailored by changing the geometrical parameters and dielectric materials filled in the holes. These results indicate that our structure has potential applications in optical devices such as plasmonic filters, sensors, and so on.

A thermal plasmonic sensor platform: resistive heating of nanohole arrays.

We have created a simple and efficient thermal plasmonic sensor platform by letting a DC current heat plasmonic nanohole arrays. The sensor can be used to determine thermodynamic parameters in addition to monitoring molecular reactions in real-time. As an application example, we use the thermal sensor to determine the kinetics and activation energy for desorption of thiol monolayers on gold. Further, the temperature of the metal can be measured optically by the spectral shift of the bonding surface plasmon mode (0.015 nm/K). We show that this resonance shift is caused by thermal lattice expansion, which reduces the plasma frequency of the metal. The sensor is also used to determine the thin film thermal expansion coefficient through a theoretical model for the expected resonance shift.

Template fabricated plasmonic nanoholes on analyte-sensitive substrates for real-time vapor sensing

Plasmonic nanoholes on analyte-sensitive substrates are used for vapor sensing.

Reflection Phase and Amplitude Determination of Short-Range Ordered Plasmonic Nanohole Arrays.

The reflection phase and amplitude of a short-range ordered gold plasmonic nanohole array are measured in the vis-NIR range using an interferometric substrate. The phase flip is observed around the minimum of the reflection amplitude, which is consistent with the resonance of a single oscillator. Above the resonance wavelength, the phase shift roughly follows that of a continuous metal film with the same thickness. Numerical simulation of the corresponding hexagonal long-range ordered nanohole array exhibits similar phase behavior with a sharper phase flip at the amplitude minimum, where the field enhancement is strongest. By changing the refractive index of the surrounding medium, larger phase shifts as well as positive and negative amplitude changes were observed around the resonance wavelength. This interferometric substrate method enables simultaneous broad-band phase and amplitude acquisition on the second time scale.

Plasmon-induced photonic and energy-transfer enhancement of solar water splitting by a hematite nanorod array

Plasmonic metal nanostructures offer a promising route to improve the solar energy conversion efficiency of semiconductors. Here we show that incorporation of a hematite nanorod array into a plasmonic gold nanohole array pattern significantly improves the photoelectrochemical water splitting performance, leading to an approximately tenfold increase in the photocurrent at a bias of 0.23 V versus Ag|AgCl under simulated solar radiation. Plasmon-induced resonant energy transfer is responsible for enhancement at the energies below the band edge, whereas above the absorption band edge of hematite, the surface plasmon polariton launches a guided wave mode inside the nanorods, with the nanorods acting as miniature optic fibres, enhancing the light absorption. In addition, the intense local plasmonic field can suppress the charge recombination in the hematite nanorod photoanode in a photoelectrochemical cell. Our results may provide a general approach to overcome the low optical absorption and spectral utilization of thin semiconductor nanostructures, while further reducing charge recombination losses.

Large-Area Low-Cost Flexible Plastic Nanohole Arrays for Integrated Bio-Chemical Sensing

Detection of plasmonic resonance peak shifts of nano-structured metamaterials is a promising method for sensing bio-chemical binding events. Although the concept is widely demonstrated in the laboratory environment using surface nano-structures machined at low-throughput and high-costs, practical solutions for high-volume production of an integrated sensing device are very limited. We present a concept of an integrated architecture that combines a thin layer of plasmonic nanohole sensing arrays, organic light-emitting diode illumination source, and microfluidic chip, for point-of-care, field, or lab applications. We discuss the fabrication of the sensor components. In particular, we present the improved fabrication of master nano-structure replication stamps, and demonstrate outstanding results for producing singular sheets or scale up to roll-to-roll embossing of nanohole arrays on a 2000 ft production roll. We further demonstrate that nanohole arrays embossed on flexible polyethylene terephthalate plastic sheets, when coated with 100 nm thin Au metal film, are capable of generating average plasmonic resonance shifts of 180 nm refractive index unit. Hence, we report the extraordinary transmission and plasmonic resonance shifts of nanohole arrays fabricated on roll-to-roll plastic sheets for the very first time. Our results show that the embossed nano-structures on plastic are suitable as sensor elements in our proposed integrated sensor architecture, and a promising technology for low-cost disposable applications.

Extraordinary Optical Transmission Property of X-Shaped Plasmonic Nanohole Arrays

Optical transmission properties of periodic X-shaped plasmonic nanohole arrays in a silver film are investigated by performing the finite element method. Obvious peaks appear in the transmission spectra due to surface plasmon polaritons (SPPs) on the top surface of the silver film, to the Fabry–Ferot resonance effect of SPPs in the nanohole, and to the localized surface plasmon resonance of the nanohole. Besides the topologic shape parameters of the X-shaped nanohole, transmission properties strongly depend on incident polarization. The results of this study not only present a tunable plasmonic filter, but also aid in the understanding of the mechanisms of the extraordinary optical transmission phenomenon.

Cytotoxic and genotoxic assessment of Euterpe oleracea fruit oil and Pentaclethra macroloba oil in human peripheral lymphocytes

Rapid and sensitive detections of the growth of bacteria are essential assay procedures in the food industry, water and environment control and clinical diagnosis. Here, we present a plasmonic nanohole sensor for rapid, sensitive and quantitative monitoring of the bacterial growth and antibiotic susceptibility test. The concept is based on extraordinary optical transmission (EOT) phenomenon in plasmonic nanohole and employs Escherichia coli specific antibody for bacteria capturing. The challenge lies in detecting the much larger dimension of E. coli with the smaller penetration depths of the electromagnetic field. The plasmonic nanohole array was fabricated using mask-based deep ultraviolet (DUV) lithography method and characterized for bulk refractive index sensitivity and surface mass sensitivity. After gold-specific surface modification and antibody immobilization, bacteria were effectively captured and grown on the sensor surface. The sensor platform with temperature-controlled environment was successfully tested for monitoring the growth of E. coli. The plasmonic nanohole sensor has immense potential for clinical diagnosis such as rapid determination of pathogen susceptibility test; with bulk refractive index sensitivity of 406.4 nm/RIU and surface mass sensitivity of ~1.802 ng/mm2. We explored the capability of the sensor to provide sensitive monitoring of low bacterial quantity (<100 cells) and rapid detection within 2 h. Finally, the rapid antibiotic susceptibility test (AST) of E. coli was demonstrated with the plasmonic nanohole sensor.

Sensitivity improved plasmonic gold nanoholes array biosensor by coupling quantum-dots for the detection of specific biomolecular interactions

In this paper, we focused on the large-scale fabrication of gold nanoholes array capable of supporting surface plasmonic resonance (SPR) via the developed nanosphere lithography (NSL) technique, which could be used as high performance biosensor for the detection of specific streptavidin–biotin interactions. Direct UV–vis absorption mode measurement was used to monitor the SPR peak shift. For the better immobilization of biotin, the surface of gold nanoholes array was functionalized with 3-mercaptopropyl trimethoxysilane (MPTS) and 3-aminopropyl triethoxysilane (APTES). After the streptavidin binding to the biotin, the SPR peak position showed an 11nm wavelength shift due to the refractive index change caused by the biotin–streptavidin binding. The sealing treatment was performed by using bovine serum albumin (BSA) to eliminate the influences of nonspecific adsorption for more accurate detection. Interestingly, the detection sensitivity of the gold nanoholes array could be further enhanced by coupling the water-soluble CdSe/ZnS quantum dots (QDs), which showed four-fold improvement in detection sensitivity as compared to the gold nanoholes array biosensor without the coupling of QDs. The mechanisms for the enhancement of detection sensitivity were also discussed. This would provide new capabilities for the highly sensitive measurements of biomolecular binding.

Plasmonic nanohole array sensors fabricated by template transfer with improved optical performance

Surface plasmon resonance sensors of the nanohole array type provide a promising platform for label-free biosensing on surfaces. For their extensive use, an efficient fabrication procedure to make nanoscale features on metallic films is required. We develop a simple and robust template-transfer approach to structure periodic nanohole arrays in optically thick Au films on poly(dimethylsiloxane) substrates. This technique significantly simplifies the process of sensor fabrication and reduces the cost of the device. A spectral analysis approach is also developed for improving the sensor performance. The sensitivity of the resulting sensor to refractive index change is 522 nm/RIU (refractive index unit) and the resolution is improved to 2 × 10−5 RIU, which are among the best reported values for localized surface plasmon resonance sensors. We also demonstrate the limit of detection of this sensor for cardiac troponin-I.

Plasmonic nanohole arrays for monitoring growth of bacteria and antibiotic susceptibility test

Rapid and sensitive detections of the growth of bacteria are essential assay procedures in the food industry, water and environment control and clinical diagnosis. Here, we present a plasmonic nanohole sensor for rapid, sensitive and quantitative monitoring of the bacterial growth and antibiotic susceptibility test. The concept is based on extraordinary optical transmission (EOT) phenomenon in plasmonic nanohole and employs Escherichia coli specific antibody for bacteria capturing. The challenge lies in detecting the much larger dimension of E. coli with the smaller penetration depths of the electromagnetic field. The plasmonic nanohole array was fabricated using mask-based deep ultraviolet (DUV) lithography method and characterized for bulk refractive index sensitivity and surface mass sensitivity. After gold-specific surface modification and antibody immobilization, bacteria were effectively captured and grown on the sensor surface. The sensor platform with temperature-controlled environment was successfully tested for monitoring the growth of E. coli. The plasmonic nanohole sensor has immense potential for clinical diagnosis such as rapid determination of pathogen susceptibility test; with bulk refractive index sensitivity of 406.4nm/RIU and surface mass sensitivity of ~1.802ng/mm2. We explored the capability of the sensor to provide sensitive monitoring of low bacterial quantity (<100cells) and rapid detection within 2h. Finally, the rapid antibiotic susceptibility test (AST) of E. coli was demonstrated with the plasmonic nanohole sensor.

Actively transporting virus like analytes with optofluidics for rapid and ultrasensitive biodetection

Effective analyte delivery is essential to achieve rapid and sensitive biodetection systems. In this article, we present an actively controlled fluidic system integrated with a suspended plasmonic nanohole sensor to achieve superior analyte delivery efficiency and ultrafast sensor response, as compared to conventional fluidic systems. 70 nm sized virus like analyte solution is used to experimentally demonstrate the system performance improvements. Sensor response time is reduced by one order of magnitude as compared to the conventional methods. A seven orders of magnitude dynamic concentration range from 10(3) to 10(9) particles mL(-1) is quantified, corresponding to a concentration window relevant to clinical diagnosis and drug screening. Our non-destructive detection system, by enabling efficient analyte delivery, fast sensing response and minimal sample volume, opens up opportunities for sensitive, rapid and real-time virus detection in infectious disease control and point-of-care applications.

Chemoselective gas sensors based on plasmonic nanohole arrays

We have demonstrated a binary chemoselective gas sensor using a combination of plasmonic nanohole arrays and a voltage-directed assembly of diazonium chemistry. The employment of a voltage-directed functionalization allows for the realization of a multiplexed sensor. The device was read optically and was fabricated using a combination of electron-beam and conventional lithography; it contains several regions each electrically isolated from each other. We used calibrated gas dosage delivery to confirm the selectivity of the sensor and observed reversible spectral shifts of several nm upon gas exposure. The resulting spectral shift indicates the potential for use in chemical arrayed detection for low concentration gas sensing

Large-scale fabrication of plasmonic gold nanohole arrays for refractive index sensing at visible region

We present the design and fabrication of large-scale gold nanohole arrays based on the versatile nanosphere lithography technique. The gold nanohole arrays exhibit two surface plasmonic resonance related transmission peaks and show a sensitive response to refractive index. The working wavelength and sensitivity can be tuned by changing the hole diameter and hole depth. A sensitivity of 125 nm/refractive index unit is obtained in the visible region. Our quasi-infinite gold nanohole arrays film can serve as an optical enhancing component while also can serve as a transparent conductive electrode for the opto-electric devices.