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%).
Highlights
Published: 10 October 2021Optical fiber biosensors make use of optical fiber waveguides for detecting biological analytes on the fiber surface, using suitable biofunctionalization methods that allow sensors to have excellent sensitivity and high specificity [1], and find important applications as immunosensors [2] in the diagnostic of cancer [2,3], cardiac [4], and urologic biomarkers [5], as well as in modern wearable devices [6]
We presented a method based on the Karhunen−Loeve transform for the interrogation of optical fiber ball resonators used in refractive sensing and biosensing
Optical fiber ball resonators have the advantage of a single-step rapid and reliable fabrication process, which can make a significant step up in terms of volume manufacturing
Summary
Optical fiber biosensors make use of optical fiber waveguides for detecting biological analytes on the fiber surface, using suitable biofunctionalization methods that allow sensors to have excellent sensitivity and high specificity [1], and find important applications as immunosensors [2] in the diagnostic of cancer [2,3], cardiac [4], and urologic biomarkers [5], as well as in modern wearable devices [6] Biosensors base their working principle on refractive index (RI) detection [7]; using a suitable functionalization method, it is possible to convert a refractometer into a biosensor and measure the response to a specific analyte as well as the specificity of detection. SMF-based devices working at infrared wavelengths have
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