Hollow-Core Negative Curvature Fiber with High Birefringence for Low Refractive Index Sensing Based on Surface Plasmon Resonance Effect

In this paper, a hollow-core negative curvature fiber (HC-NCF) with high birefringence is proposed for low refractive index (RI) sensing based on surface plasmon resonance effect. In the design, the cladding region of the HC-NCF is composed of only one ring of eight silica tubes, and two of them are selectively filled with the gold wires. The influences of the gold wires-filled HC-NCF structure parameters on the propagation characteristic are investigated by the finite element method. Moreover, the sensing performances in the low RI range of 1.20–1.34 are evaluated by the traditional confinement loss method and novel birefringence analysis method, respectively. The simulation results show that for the confinement loss method, the obtained maximum sensitivity, resolution, and figure of merit of the gold wires-filled HC-NCF-based sensor are −5700 nm/RIU, 2.63 × 10−5 RIU, and 317 RIU−1, respectively. For the birefringence analysis method, the obtained maximum sensitivity, resolution, and birefringence of the gold wires-filled HC-NCF-based sensor are −6100 nm/RIU, 2.56 × 10−5 RIU, and 1.72 × 10−3, respectively. It is believed that the proposed gold wires-filled HC-NCF-based low RI sensor has important applications in the fields of biochemistry and medicine.

ZnO/ZnS Core/Shell Nanostructures on Biologically Inspired Gold Wires for Uric Acid Sensing

In this work, microwires of gold nanoparticles (Au NPs) were grown using the fungus Aspergillus niger as a biological template. Au NPs were synthesized through the reduction of chloroauric acid using monosodium glutamate (MSG) in an aqueous media. The MSG here, served as a nutritional trigger behind the self-organization of Au NPs on Aspergillus niger apart from being the reducing as well as stabilizing agent. The fungal hyphae coated with gold nanoparticles were spread over the glass slide. The ZnO/ZnS core/shell nanostructures were deposited in a 2 mm gap of gold microwires’ spread. Uric acid sensing behavior of these ZnO/ZnS core/shell nanostructures were studied using the gold microwires as electrode.

Low cost tips for tip-enhanced Raman spectroscopy fabricated by two-step electrochemical etching of 125 µm diameter gold wires

Tip-enhanced Raman spectroscopy (TERS) has become a well-applied technique for nanospectroscopy, allowing for single molecule sensitivity with sub-nanometer spatial resolution. The demand for efficient, reproducible and cost-effective probes for TERS is increasing. Here we report on a new electrochemical etching protocol to fabricate TERS tips starting from 125 µm diameter gold wires in a reproducible way. The process is reliable (50% of the tips have radius of curvature <35 nm, 66% <80 nm), fast (less than 2 min) and 2.5 times cheaper than the etching of standard 250 µm diameter wires. The TERS performance of the tips is tested on dyes, pigments and biomolecules and enhancement factors higher than 105 are observed. TERS mapping with a spatial resolution of 5 nm is demonstrated.