Plasmonic platforms are a promising solution for the next generation of low-cost, integrated biomedical sensors. However, fabricating these nanostructures often requires lengthy and challenging fabrication processes. Here we exploit the peculiar features of Focused Ion Beam milling to obtain single-step patterning of a plasmonic two-dimensional (2D) array of truncated gold nano-pyramids (TNP), with gaps as small as 17 nm. We describe the formation of plasmonic bandgaps in the arrangement of crossed tapered grooves that separate the nano-pyramids, and we demonstrate refractive index sensing via dark field imaging in patterned areas of 30 $μ$m $\times$ 30 $μ$m.
Surface plasmon resonance (SPR) is a novel optical sensing technique with a unique ability to monitor molecular binding in real-time for biological and chemical sensor applications. Interferometry is an excellent tool for accurate measurement of SPR changes, the measurement and comparison is made for the sensitivity, dynamic range and resolution of the different analytes using interferometry techniques. SPR interferometry can also employ phase detection in addition to the amplitude of the reflected light wave, and the phase changes more rapidly compared with other approaches, i.e., intensity, angle and wavelength. Therefore, the SPR phase interferometer offers the advantages of spatial phase resolution and high sensitivity. This work discusses the advancements in interferometric SPR methods to measure the phase shifts due to refractive index changes. The main application areas of SPR sensors are demonstrated, i.e., the Fabry-Perot interferometer, Michelson interferometer and Mach-Zehnder interferometer, with different configurations. The three interferometers are discussed in detail, and solutions are suggested to enhance the performance parameters that will aid in future biological and chemical sensors.
In this work, we demonstrate the modulation in optical response at visible wavelengths of a dielectric grating structure under a thermal stimulus. The grating structure is coated with a thin layer of vanadium dioxide (VO2) which undergoes a phase transition from an insulator to a metal at a temperature of ~ 68°C. We report on the design, simulations, and characterization of the proposed structure. Measured optical response through experiments finds a good agreement with the predictions made by numerical simulations.
Creating plasmonic nanoparticles on a tapered optical fiber tip enables a remote SERS sensing probe, ideal for challenging sampling scenarios like biological tissue, specific cells, on-site environmental monitoring, and deep brain structures. However, nanoparticle patterns fabricated from current bottom-up methods are mostly random, making geometry control difficult. Uneven statistical distribution, clustering, and multilayer deposition introduce uncertainty in correlating device performance with morphology. Here, we employ a tunable solid-state dewetting method to create densely packed monolayer Au nanoislands (NIs) with varied geometric parameters, directly contacting the silica TF surface. These patterns exhibit analyzable nanoparticle sizes, densities, and uniform distribution across the entire taper surface, enabling a systematic investigation of particle size, density, and analyte effects on the SERS performance of the through-fiber detection system. The study is focused on the SERS response of a widely employed benchmark Rhodamine 6G molecule and Serotonin, a neurotransmitter with high relevance for the neuroscience field. The numerical simulations and limit of detection (LOD) experiments on R6G show that the increase of the total near-field enhancement volume promotes the SERS sensitivity of the probe. However, for serotonin we observed a different behavior linked to its interaction with the nanoparticle's surface. The obtained LOD is as low as 10-7 M, a value not achieved so far in a through-fiber detection scheme. Therefore, we believe our work offers a strategy to design nanoparticle-based remote SERS sensing probes and provide new clues to discover and understand the intricate plasmonic-driven chemical reactions.
Photovoltaic (PV) panels are subject to partial shading in many practical situations due to nearby obstacles like trees, buildings and the adjacent PV panels. Multiple peaks can exist on the resulting power-voltage (P-V) characteristics of the PV panel under partial shading conditions. This may disturb the efficient maximum power point tracking (MPPT) operation as many existing MPPT methods can converge to local peaks. In this paper, effects of different shading conditions on the characteristics of the PV panel have been investigated. Based on the results and observations, a simple MPPT technique is proposed to circumvent the trappings into the local peaks. The proposed method is based on several critical observations under common shading conditions. The proposed method uses variable step approach which considerably reduces the time to track the global peak. Effectiveness of the proposed method has been verified by computer simulations and experimental results.
The ability to fabricate plasmonic structures on the distal facet of an optical fiber has led to a diverse range of minimally invasive sensors. However these applications have been hindered by the inherent turbidity of the fiber and complex transmission properties of the nanostructures. We propose to use a wavefront shaping technique to pre-shape light prior to transmission through the nanostructed fiber to control the coupling between the guided modes of the fiber and the plasmonic nanostructures. We show that the sensing resolution of a plasmonic fiber optic can achieve a sub-cellular spatial resolution in biological applications. In this work, a broad range of plasmonic structures are explored as candidates for spatially resolved plasmonic sensing including periodic nanostructures for extraordinary optical transmission and sub-diffraction beam formation as well as nanoislands fabricated by a solid-state dewetting procedure for surface enhanced Raman spectroscopy.
This paper provided a general study of Wireless Body Area Network (WBAN) in health monitoring system as well as the study of the application of wearable and implanted Bio-Medical-Sensors (BMS) which are used to monitor the vital signs of a patient in early detection. Energy efficiency is a significant issue in WBAN which can be achieved by reducing the overhead of control packets, prioritizing sensor-nodes and sink-node selection. Moreover, uncertainty in network topologies, such as distance and link affect between sensor-nodes occurs due to the mobility of human. In this research, we propose a scheme to reduce the overhead of control packets and prioritizing the threshold values of vital signs by assigning low and high transmission power with enhanced IEEE802.15.6 CSMA/CA as well as introduce a Mobility Link Table (MLT) for selecting a sink-node to communicate with the coordinator. Compare it with existing IEEE802.15.6 CSMA/CA technique and results shows the proposed techniques regarding mean power consumption, network delay, network throughput.
Creating plasmonic nanoparticles on a tapered optical fiber (TF) tip enables a remote surface-enhanced Raman scattering (SERS) sensing probe, ideal for challenging sampling scenarios like biological tissues, site-specific cells, on-site environmental monitoring, and deep brain structures. However, nanoparticle patterns fabricated from current bottom-up methods are mostly random, making geometry control difficult. Uneven statistical distribution, clustering, and multilayer deposition introduce uncertainty in correlating device performance with morphology. Ultimately, this limits the design of the best-performance remote SERS sensing probe. Here we employ a tunable solid-state dewetting method to create densely packed monolayer Au nanoislands with varied geometric parameters in direct contact with the silica TF surface. These patterns exhibit analyzable nanoparticle sizes, densities, and uniform distribution across the entire taper surface, enabling a systematic investigation of particle size, density, and analyte effects on the SERS performance of the through-fiber detection system. The study is focused on the SERS response of a widely employed benchmark molecule, rhodamine 6G (R6G), and serotonin, a highly relevant neurotransmitter for the neuroscience field. The numerical simulations and limit of detection (LOD) experiments on R6G show that the increase of the total near-field enhancement volume promotes the SERS sensitivity of the probe. However, we observed a different behavior for serotonin linked to its interaction with the nanoparticle's surface. The obtained LOD is as low as 10–7 M, a value not achieved so far in a through-fiber detection scheme. Therefore, our work offers a strategy to design nanoparticle-based remote SERS sensing probes and provides new clues to discover and understand intricate plasmonic-driven chemical reactions.
Plasmonic fiber optics have attracted considerable research interest from perspectives ranging from fundamental physics to biomedical optics. However, across all fields, researchers face two distinct but strongly connected challenges. First, a nanofabrication challenge: integrating nanostructures on a substrate fiber; second, a photonic problem: engineer the interaction between the plasmonic structures and the modal patterns of light propagation. In this work we aim to show how both state-of-the-art fabrication approaches and optical techniques may be used to resolve these issues for plasmonic endoscopy in both deep and shallow brain regions. By applying wavefront shaping, we show that either a sub-region or entire plasmonic structure on a flat fiber facet can be holographically activated. We have applied this method to a wide range of plasmonic structures including periodic nanostructures for EOT and sub-diffraction beam formation and nanoislands for Surface Enhanced Raman Spectroscopy (SERS), resulting in a multifunctional plasmonic endoscope targeted at shallow brain regions. Alternatively, we show how a tapered optical fiber can also be used as a substrate of plasmonic structures targeted at detection of neurotransmitters in deep brain regions.
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