Light-Sheet Skew Ray-Enhanced Localized Surface Plasmon Resonance-Based Chemical Sensing

Abstract

A stronger absorption of pump/probe light is desirable for maximizing the sensitivity to enable accurate measurements of trace chemical elements. We introduce a new sensing technique built on light-sheet excitation of skew rays in a multimode fiber with an additional enhancement of localized surface plasmon resonance (LSPR) and its evanescent-field hotspots between gold nanospheres on the coated fiber. A skewed light-sheet (i.e., a thin plane of light) can exploit the optimum ray group, producing enhanced and uniform interactions between light and matter for higher absorption/sensitivity and higher power threshold. The heightened evanescent field couples to the localized surface plasmon resonant modes to attain even greater sensitivity. We compared this excitation method with the previously demonstrated light-sheet skew ray-based sensor without LSPR and observed an enhancement in normalized attenuation of pump light up to seven orders of magnitude for low-concentration rhodamine B. The improvement in the normalized detection limit is almost three orders of magnitude. This new sensing technique uses a functionalized fiber rather than pairing a passive fiber with added functional particles in the analyte, which offers better area-selectivity. The potentially low-cost chemical sensors can be used on a range of sensing mechanisms such as pump/probe light absorption.

Fiber-Optic Skew Ray Sensors

“…(g) Chen et al [63] compared various fiber excitation methods and showed an improvement in analyte absorption (e.g., Rhodamine B) with light-sheet skew rays (i.e., finer selection) of up to one order of magnitude relative to skew rays and at least three orders of magnitude over nearly normal-incidence rays. Chen et al [64] demonstrated the advantages of light-sheet skew rays further with measurements on the concentration of Rhodamine B, achieving a detection limit of 0.18 ng/mL (180 ppt) within a range of 0.1-10 ng/mL. (h) Chen et al [22] introduced the ability of skew rays to detect microscopic defects in fiber core, cladding or coating.…”

“…It is evident that light-sheet skew rays offer the highest sensitivity under the tested conditions. Chen et al [64] improved upon the base design by introducing localized SPR to light-sheet skew rays, resulting in an enhancement in attenuation (3.08 dB with 0.1 ng/mL and 3 mm length, or 1.18 × 10 8 dB/(mg/mL)/cm) of up to seven orders of magnitude for 0.1 ng/mL of Rhodamine B under similar conditions. The attenuation peaks are visible in Figure 12.…”

“…Attenuation (color depth) induced by 0.1 ng/mL concentration Rhodamine B relative to pure water as a function of launch angle and center offset. Reprinted with permission from[64]. Copyright (2019) American Chemical Society.…”

Highly-Sensitive Polymer Optical Fiber SPR Sensor for Fast Immunoassay

“…C. Li et al [31] proposed the Au/Al 2 O 3 based multilayer composite hyperbolic metamaterial (HMM), graphene thin-film on the D-shaped fiber SPR sensor with the improved sensitivity up to 4 461 nm/RIU. However, the above methods change the external relative refractive index (RI) from the surface of the gold film to make the external effective RI closer to the base RI so as to improve the RI sensitivity of the device [32][33][34][35]. Complex surface modification methods can enhance the base sensitivity of the sensor, but the limited improvement often results in the extra complexity for the subsequent modification of the biochemical sensor.…”

Innovative sensor for refractive index monitoring based on a plastic optical fiber side-polished in a ‘V’-bent structure

“…The use of the evanescent field around an optical fiber provides a simple, and easy to access approach to the characterization of the refractive index (RI) of a range of different chemicals used, for example, in a variety of applications which include healthcare, manufacturing, agriculture and security [1,2]. Plastic optical fibers (POFs) [3,4] are routinely employed in a number of applications (being preferred to the more familiar silica fiber used in communications applications) for both delivering light and detecting local environments in evanescent-wave-based chemical sensors, taking advantage of their robustness, ease of optical coupling to and from the fiber and ready-operability of the sensor based on such fiber.…”