IP-Dip-Based SPR Structure for Refractive Index Sensing of Liquid Analytes

GST plasmonic gap structure investigation as a switch and sensor

In this paper, a plasmonic perfect absorber that consists of a gold rectangular bar with three gaps is investigated as a switch and sensor in the near-infrared region. Phase change material germanium-antimony-tellurium (GST) is utilized in two gaps to perform the switching capability with a high extinction ratio of 18.49 dB. In addition, the sensing performance of the structure for detection of a solution of glucose in water and diagnosis of different cancer cells is studied. The best sensitivity of 1504 nm/RIU is obtained for detection of the PC12 cancer cell, and the figure of merit of the structure is around 17R I U -1.

Recent advances in surface plasmon resonance imaging and biological applications

Surface Plasmon Resonance Imaging (SPRI) is a robust technique for visualizing refractive index changes, which enables researchers to observe interactions between nanoscale objects in an imaging manner. In the past period, scholars have been attracted by the Prism-Coupled and Non-prism Coupled configurations of SPRI and have published numerous experimental results. This review describes the principle of SPRI and discusses recent developments in Prism-Coupled and Non-prism Coupled SPRI techniques in detail, respectively. And then, major advances in biological applications of SPRI are reviewed, including four sub-fields (cells, viruses, bacteria, exosomes, and biomolecules). The purpose is to briefly summarize the recent advances of SPRI and provide an outlook on the development of SPRI in various fields.

Highly Sensitive Plasmonic Structures Utilizing a Silicon Dioxide Overlayer

In this paper, simple and highly sensitive plasmonic structures are analyzed theoretically and experimentally. A structure comprising a glass substrate with a gold layer, two adhesion layers of chromium, and a silicon dioxide overlayer is employed in liquid analyte sensing. The sensing properties of two structures with distinct protective layer thicknesses are derived based on a wavelength interrogation method. Spectral reflectance responses in the Kretschmann configuration with a coupling BK7 prism are presented, using the thicknesses of individual layers obtained by a method of spectral ellipsometry. In the measured spectral reflectance, a pronounced dip is resolved, which is strongly red-shifted as the refractive index (RI) of the analyte increases. Consequently, a sensitivity of 15,785 nm per RI unit (RIU) and a figure of merit (FOM) of 37.9 RIU-1 are reached for the silicon dioxide overlayer thickness of 147.5 nm. These results are in agreement with the theoretical ones, confirming that both the sensitivity and FOM can be enhanced using a thicker silicon dioxide overlayer. The designed structures prove to be advantageous as their durable design ensures the repeatability of measurement and extends their employment compared to regularly used structures for aqueous analyte sensing.

Shallow-Tapered Chirped Fiber Bragg Grating Sensors for Dual Refractive Index and Temperature Sensing

In this work, we present a gold-coated shallow-tapered chirped fiber Bragg grating (stCFBG) for dual refractive index (RI) and temperature sensing. The stCFBG has been fabricated on a 15-mm long chirped FBG, by tapering a 7.29-mm region with a waist of 39 μm. The spectral analysis shows two distinct regions: a pre-taper region, in which the stCFBG is RI-independent and can be used to detect thermal changes, and a post-taper region, in which the reflectivity increases significantly when the RI increments. We estimate the RI and thermal sensitivities as 382.83 dB/RIU and 9.893 pm/°C, respectively. The cross-talk values are low (−1.54 × 10⁻³ dB/°C and 568.1 pm/RIU), which allows an almost ideal separation between RI and thermal characteristics. The stCFBG is a compact probe, suitable for long-term and temperature-compensated biosensing and detection of chemical analytes.