Optical Fiber Ball Resonator Sensor Spectral Interrogation through Undersampled KLT: Application to Refractive Index Sensing and Cancer Biomarker Biosensing

Abstract

Optical fiber ball resonators based on single-mode fibers in the infrared range are an emerging technology for refractive index sensing and biosensing. These devices are easy and rapid to fabricate using a CO2 laser splicer and yield a very low finesse reflection spectrum with a quasi-random pattern. In addition, they can be functionalized for biosensing by using a thin-film sputtering method. A common problem of this type of device is that the spectral response is substantially unknown, and poorly correlated with the size and shape of the spherical device. In this work, we propose a detection method based on Karhunen−Loeve transform (KLT), applied to the undersampled spectrum measured by an optical backscatter reflectometer. We show that this method correctly detects the response of the ball resonator in any working condition, without prior knowledge of the sensor under interrogation. First, this method for refractive index sensing of a gold-coated resonator is applied, showing 1594 RIU−1 sensitivity; then, this concept is extended to a biofunctionalized ball resonator, detecting CD44 cancer biomarker concentration with a picomolar-level limit of detection (19.7 pM) and high specificity (30–41%).

Spatial-Division Multiplexing Approach for Simultaneous Detection of Fiber-Optic Ball Resonator Sensors: Applications for Refractometers and Biosensors

“…By setting the hereby reported values for target diameter and motion speed, we can achieve a BR sensor that appears as a good trade-off between a spherical shape and sufficient back-reflected power, which enables the spectral interrogation. The obtained spectra of BR sensors each appear as a quasi-random spectrum with a dependence on the refractive index, as outlined in previous works [ 35 , 40 ].…”

Highly Sensitive Zinc Oxide Fiber-Optic Biosensor for the Detection of CD44 Protein

“…The 557–551 µm optical fiber is found for CD44 protein detection, while the 514–519 µm and 525–521 µm optical fibers are used for prostate-specific antigen (PSA) protein measurement control and CD44 protein negative control measurement, respectively. The values of absolute and relative power, rotation speed and feeding speed to obtain the spherical tip sensors of diameters 557–551 µm, 525–521 µm, 514–519 µm are shown in Table S1 [ 39 ].…”