Highly sensitive detection of urinary protein variations using tilted fiber grating sensors with plasmonic nanocoatings

Abstract

Surface plasmon resonance (SPR) optical fiber biosensors can be used as a cost-effective and relatively simple-to-implement alternative to well established bulky prism configurations for high sensitivity biological sample measurements. The miniaturized size and remote operation ability offer them a multitude of opportunities for single-point sensing in hard-to-reach spaces, even possibly in vivo. The biosensor configuration reported in this work uses a tilted fiber Bragg grating (TFBG) in a commercial single mode fiber coated with a nanometer scale silver film. The key point is that by reducing the silver film thickness to around 20-30 nm (rather than 50 nm for optimal SPR excitation), different modes of the TFBG spectrum present very high but opposite sensitivities to refractive index (RI) changes around the TFBG. Experimental results obtained with the coated TFBG embedded inside a microfluidic channel show an amplitude sensitivity greater than 8000 dB/RIU (Refractive Index Unit) and a limit of detection of 10(-5)RIU. Using this device, the effect of different concentrations of protein in rat urine was clearly differentiated between healthy samples, nephropatic samples and samples from individuals under treatment, with a protein concentration sensitivity of 5.5 dB/(mg/ml) and a limit of detection of 1.5 × 10(-3)mg/ml. Those results show a clear relationship between protein outflow and variations in the RI of the urine samples between 1.3400 and 1.3408, pointing the way to the evaluation and development of new drugs for nephropathy treatments. The integration of TFBGs with microfluidic channels enables precise measurement control over samples with sub-microliter volumes and does not require accurate temperature control because of the elimination of the temperature cross-sensitivity inherent in TFBG devices. Integration of the TFBG with a hypodermic needle on the other hand would allow similar measurements in vivo. The proposed optical fiber/microfluidic plasmonic biosensor represents an appealing solution for rapid, low consumption and highly sensitive detection of analytes at low concentrations in medicine as well as in chemical and environmental monitoring.

High resolution fiber optic surface plasmon resonance sensors with single-sided gold coatings

“…This simultaneous presence of the SPR-active hybrid plasmonic modes and well identified cut-off modes provides two independent measurements of the same quantity (the SRI) in a single device. While spectral signatures for SPR and mode cut-off have been observed previously in TFBGs with uniform but too thin coatings, it was at the expense of the figure of merit because of the broadening of the SPR occurring in such cases and the fact that the cut-off modes still had to tunnel across some metal to reach the surrounding medium [26].…”

“…In recent years, the comprehensive working principle, the interrogations techniques, and the optimization methods of SRI sensitivity, for the TFBG-based SPR sensor have been investigated in our group [12][13][14][15][16][17][18][19][20]. As a result, a number of chemical [21] and biomedical [22][23][24][25][26] sensing applications were successfully demonstrated with the TFBG-based SPR platform, as well as probes for the optical properties of nanoscale metal films [27,28].…”

“…The most common methods to deposit the required coatings use physical vapor deposition techniques, such as evaporation (electron beam or thermal) and sputtering, both of which are directional (thicker in the region of the fiber facing the metal source). In order to achieve uniform coatings by these techniques, rotating mechanisms can be used to hold fibers in the deposition tool [5,26], or successive depositions carried out after manually rotating the fiber [22]. In the latter case, the gold coatings are still not absolutely uniform around the TFBG surface with thicker areas facing the vapor deposition directions.…”

Ultrasensitive plasmonic sensing in air using optical fibre spectral combs

“…Fibre SPR refractometers with sensitivities of ∼500 nm RIU −1 in aqueous solutions have been demonstrated17. Biochemical sensors based on the antibody/antigen affinity have also been reported for proteins and cell immunosensing1819202122. They present limits of detection and sensitivities that compete with the most sophisticated plasmonic-based sensing solutions2324.…”

Study of Multi Physical Parameter Monitoring Device Based on FBG Sensors Demodulation System

“…So FBG has huge tremendous value for smart structure monitoring, intelligent oil wells and pipelines, intelligent civil engineering construction, aerospace and voyage engineering [3]. In the field of the airplane Status monitoring, many physics parameters need to be monitored, FBG sensor is an potential solution [4,5]. For cross-sensitivity problem between strain and temperature in FBG, A FBG signal demodulation system is designed to monitor the temperature and strain on the aircraft.…”