A Review of 2D and 3D Plasmonic Nanostructure Array Patterns: Fabrication, Light Management and Sensing Applications

Abstract: This review article discusses progress in surface plasmon resonance (SPR) of two-dimensional (2D) and three-dimensional (3D) chip-based nanostructure array patterns. Recent advancements in fabrication techniques for nano-arrays have endowed researchers with tools to explore a material’s plasmonic optical properties. In this review, fabrication techniques including electron-beam lithography, focused-ion lithography, dip-pen lithography, laser interference lithography, nanosphere lithography, nanoimprint lithography, and anodic aluminum oxide (AAO) template-based lithography are introduced and discussed. Nano-arrays have gained increased attention because of their optical property dependency (lightmatter interactions) on size, shape, and periodicity. In particular, nano-array architectures can be tailored to produce and tune plasmonic modes such as localized surface plasmon resonance (LSPR), surface plasmon polariton (SPP), extraordinary transmission, surface lattice resonance (SLR), Fano resonance, plasmonic whisperinggallery modes (WGMs), and plasmonic gap mode. Thus, light management (absorption, scattering, transmission, and guided wave propagation), as well as electromagnetic (EM) field enhancement, can be controlled by rational design and fabrication of plasmonic nano-arrays. Because of their optical properties, these plasmonic modes can be utilized for designing plasmonic sensors and surfaceenhanced Raman scattering (SERS) sensors

Novel Functionalized Nanopores for Plasmonic Sensing

Nanoplasmonic sensors offer a label-free platform for real-time monitoring of biomolecular interactions by tracking changes in refractive index through optical spectroscopy. However, other surface sensitive techniques such as conventional surface plasmon resonance offer similar capabilities with equal or even better resolution in terms of surface coverage. Still, plasmonic nanosensors provide unique possibilities when the nanoscale geometry itself is of interest. By taking the advantage of nanofabrication technology, it is possible to engineer nanostructures with controllable dimensions, curvature and optical properties to study nanometer-sized biomolecules, such as proteins.\ua0 This thesis presents different types of nanoplasmonic sensing platforms, each with a unique geometry in which biomolecules can be probed through plasmonic read out. Two of the structures were fabricated by short-range ordered colloidal self-assembly and etching of the solid support underneath a nanohole array. The structures are denoted as ‘nanocaves’ and ‘nanowells’ depending on the degree of anisotropy. By suitable surface functionalization, the geometry of the plasmonic nanocavities was utilized for location-specific detection of proteins. In addition, nanowells were employed to investigate curvature-dependent biomolecular interactions.\ua0 We have also developed subwavelength apertures in optically thin silicon nitride membranes covered with continuous metal films, referred to as solid-state ‘nanopores’. Plasmonic nanopores in suspended metal-insulator-metal films were fabricated in short-range ordered and long-range ordered arrays using short-range ordered colloidal self-assembly and electron beam lithography, respectively. Both methods prevent the metal from ending up on the silicon nitride walls which is of paramount importance for plasmonic properties and selective chemical functionalization. Preparing nanopores with identical structure but different aperture ordering provides the opportunity to understand how aperture ordering influences plasmonic response, particularly with respect to the nature of far field spectral features. Long-range ordered vs. short-range ordered nanopores exhibit similar optical properties with only a few differences in the plasmonic response.\ua0 By appropriate material-specific modification (thiol and trietoxysilane chemistry) plasmonic nanopores were employed for detection of average sized proteins (~ 60 kg/mol) inside the pores. In addition to nanoplasmonic sensing, we could also construct a credible mimic (in terms of geometry) of nuclear pore complexes, when the size of the solid state nanopores approaches ~ 50 nm. The unique geometry and size of nanopores (diameter ~ 50 nm) opens up the possibility to mimic the geometry of biological nanomachines with integrated optical sensing capabilities

Large Area Nanohole Arrays for Sensing Fabricated by Interference Lithography

Several fabrication techniques are recently used to produce a nanopattern for sensing, as focused ion beam milling (FIB), e-beam lithography (EBL), nanoimprinting, and soft lithography. Here, interference lithography is explored for the fabrication of large area nanohole arrays in metal films as an efficient, flexible, and scalable production method. The transmission spectra in air of the 1 cm2 substrate were evaluated to study the substrate behavior when hole-size, periodicity, and film thickness are varied, in order to elucidate the best sample for the most effective sensing performance. The efficiency of the nanohole array was tested for bulk sensing and compared with other platforms found in the literature. The sensitivity of ~1000 nm/RIU, achieved with an array periodicity in the visible range, exceeds near infrared (NIR) performances previously reported, and demonstrates that interference lithography is one of the best alternative to other expensive and time-consuming nanofabrication methods

Engineering Plasmonic Nanostructures for Light Management and Sensing

The two major global problems are to provide health safety and to meet energy demands for ever growing population on a large scale. The study of light interaction with nanostructures has shown a promising solution in improving the fields of bio-sensor and solar energy devices which addresses above mentioned two major global problems. Nanostructures have tunable physicochemical properties such as light absorption, electrical and thermal properties unlike bulk materials, which gives an advantage in applications like bio-sensing and energy harvesting devices. The development of nanofabrication techniques along with the discovery of Surface Enhanced Raman Scattering (SERS) and Plasmon Enhanced Fluorescence (PEF), led to the development of Point of Care (POC) sensing devices. The fundamental understanding of light path in a nanostructured material led to the improvement in solar energy harvesting performance. For both of these applications, engineering nanostructures is the key to improving performance. In this work, different plasmonic nanostructures were designed, fabricated and analyzed for biosensor and light management applications. A new fabrication route, which combines nanosphere lithography with silicon-based clean-room microfabrication processes, has been developed to produce large-area long-range ordered gold nanoring array patterns in a controllable fashion. The developed nanoring structure has SERS enhancement of 2*109 and is used for miRNA detection. A novel pyramid array on gold film 3D plasmonic nanostructure is designed to convert plasmonic light scattering to confined light absorption. This structure generates a cavity mode by hybridization of fundamental modes, which creates a strong electric and magnetic field with a large mode volume. Due to its unique properties pyramids coupled film structure is used for both solar light management device and in Metal Enhanced Fluorescence (MEF). The fabricated structure is used to demonstrate plexiton (plasmon – exciton coupling) generation and is very effective in light trapping in the gap mode. In MEF, the sandwich nanostructure is used for Metal Organic Framework (MOF) fluorescence enhancement and the enhancement factor is around 5*102. With the plasmonic metal nanostructure optimization, the performance of a specific application is improved. However, the metals used for plasmonic applications are noble metals like gold and silver to support strong localized surface plasmon resonance (LSPR), which are expensive. Two-dimensional semiconductor materials have shown plasmon resonance in the visible region, having a lot of applications in sensing and photonics. Heavily doped semiconductors could replace expensive metals without compromising the performance. LSPR in metals is tuned by shape, size and refractive index of surroundings. This restricts plasmon resonance tuning over a narrow wavelength range and need to choose a different metal to exceed the rage of application. In contrast, LSPR in plasmonic semiconductors can be tuned with parameters like carrier density, annealing temperature and doping. This gives an advantage of tuning the plasmon peak over a broad range including visible, Near Infrared (NIR) and Infrared(IR) regions. This is because, for semiconductor materials, the carrier concentration can be varied over a large range. Herein, the molybdenum oxide thin films were directly deposited and nitrogen annealed which showed a tunable localized surface plasmon resonance (LSPR). A chip based 2D semiconductor material is fabricated to study the structural and size dependent plasmon resonance. This work establishes a way to fabricate chip based ordered semiconductor nanostructures, which helps in a systematic study of plasmon properties on nanostructures

A Study of the Analytical and Diagnostic Potential of Fibre-Optic Surface Plasmon Resonance-Extraordinary Optical Transmission Biosensors

A fibre-optic surface plasmon resonance-extraordinary optical transmission (SPR-EOT) biosensor is developed based on a conventional SPR biosensor, utilising optical fibres and extraordinary optical transmission to miniaturise the biosensor for point-of-care diagnosis and real-time online analysis. The SPR biosensor is a well-established biosensing platform based on surface plasmon and it has been commercialised to study the binding kinetics of biomolecules. The EOT biosensor is based on enhanced light transmission when it goes through a metallic periodic array of subwavelength nanoholes. A fibre-optic SPR-EOT biosensor is fabricated by transferring a thin gold film with a nanohole matrix to a tip of an optical fibre. The portability and practicability of the EOT biosensor are significantly enhanced thanks to this fabricating technique. In this thesis, I evaluated the performance of fibre-optic SPR-EOT biosensors in detecting different biomolecules including monoclonal antibodies, toxin B and spike proteins by optimising the fabricating procedure and the sensing surface preparation process. Furthermore, regeneration of the sensing surface was also studied to allow multiple use of these sensors. The fibre-optic SPR-EOT biosensor was evaluated as a process analytical technology tool for detection and measurements of monoclonal antibodies in the bioreactor during the antibody manufacture process. Peaks at 830 nm of light transmission spectra were shifted during the detection. The biosensor detected an antibody concentration as low as 4.4×10-4 mg/mL. Due to the robustness of protein A, the protein A-based biosensor was tested for surface regeneration, and the result demonstrated that the biosensor could withstand up to 10 regenerations using 0.1 M glycine hydrochloride (pH=2.8). The biosensor was also assessed for detection of biomolecules for disease diagnosis at the early phase. It was used to detect toxin B produced from Clostridium Difficile with the limit of detection of 1.4 pg/ml, which was comparable to other novel methods. A procedure of preparing the fabricating materials and the fabrication process were established to ensure a consistent batch-to-batch quality of the biosensor. The potential of using the biosensor for early diagnosis of Clostridium Difficile infection was revealed through three batches of toxin B samples. Finally, the biosensor was tested for rapid detection of the N protein of the SARS-CoV2 virus. The limit of detection was 1.77 μg/mL, which was far above that obtained from other detection methods (ELISA and lateral flow assay for COVID-19 diagnosis) although these methods often take a much longer time than our developed biosensor. The limit of detection could be lowered to 0.046 pg/mL by altering the fabricating method and materials, but the quality of fabricated biosensors would not be consistent. This thesis accentuates the potential of fibre-optic SPR-EOT biosensors for bioapplications, especially for analytical and diagnostic applications. My PhD study has contributed to preparation of the biosensor components, establishment of fabricating techniques, and development of methods of functionalization, which lay a solid foundation for commercialisation of the fibre-optic SPR-EOT biosensor.Thesis (Ph.D.) -- University of Adelaide, School of Chemical Engineering and Advanced Materials, 202