Evaluation of gold layer configuration for plasmonic fiber grating biosensors

Abstract

Gold-coated fiber Bragg gratings (FBGs) are nowadays a mature technology for lab-on-fiber sensing based on surface plasmon resonance (SPR) excitation. Tilted FBGs bring valuable assets such as easy light injection, remote operation in very small volumes of analytes and immunity to temperature fluctuations. Different gold configurations have been reported to date, without considering their relative performances in terms of biochemical sensing. In this work, we experimentally study the impact of the gold coating on the cladding mode distribution in the tilted FBG amplitude spectrum and subsequently on its sensitivity to cytokeratins used as biomarkers for cancer diagnosis. Some relevant configurations of gold coatings are produced and tested, relying on both the sputtering and electroless plating (ELP) processes. The obtained results confirm that the coating thickness and its roughness drive the biosensing performances. The experimental limit of detection for cytokeratins 17 sensing reaches 14 fM for the most sensitive configurations.

Multimodal plasmonic optical fiber grating aptasensor

“…This signal shift reflects the binding of molecules at the biosensor surface. Figure 11 depicts the change observed for a 10 −6 g/ml concentration of HER2 compared to PBS and to the same concentration of cytokeratins 17 (CK17), a potential lung cancer biomarker already used in our previous works [19,20,38]. These observations confirm that a very good selectivity was achieved, since the response obtained with CK17 is only 5% of the shift recorded with the same concentration of HER2.…”

“…In practice, for standard FBG interrogators in the C + L wavelength bands, two TFBGs in MMF could be wavelength multiplexed and interrogated simultaneously while only one can be used when dealing with SMF and solutions with a RI close to the one of water. In case of bare TFBG sensor, assessment of sensitivity value is achieved by tracking the cut-off mode, as done in [38] (Figs. 1(b) and 1(d)).…”

“…4(a) and 4(c)). To demodulate gold-coated TFBGs refractometers, we rely on the classical approach, already reported in [38] and the vast majority of papers involving TFBG refractometers and biosensors. Indeed, the most sensitive mode of the SPR signature cannot be tracked accurately, due to its strong attenuation in the amplitude spectrum and noisy nature.…”

“…The tracking is therefore based on another cladding mode resonance, located on the shoulder of the SPR envelope (Figs. 4(b) and 4(d)) [38]. This mode is typically located between the SPR signature (characterized by a pinch in the spectrum) and the cut-off mode (the mode to the left of the SPR signature with the largest peak-to-peak amplitude, whose effective refractive index value is slightly above the one of the surrounding medium) [39].…”

The Simulation of a Surface Plasmon Resonance Metallic Grating for Maximizing THz Sensitivity in Refractive Index Sensor Application

“…e metal thickness t m is an important factor for improving a sensor performance depending on the coupling configuration and structure. For example, the Au thickness affects the sensitivity of a SPR fiber grating biosensor [40]. In this study, measuring in a reflection mode, t m is set to be 100 nm, which is larger than the skin depth of Au (l s,Au � 74 nm) in the frequency of interest [41].…”