Abstract
A new fiber-optic pH sensor based on a thin-core fiber modal interferometer with electrostatic self-assembled nanocoating is presented. After inserting a segment of thin-core fiber into a standard single-mode fiber, high-order cladding modes are excited and interfere with the core mode to form an in-fiber modal interferometer. The side surface of the sensor is then deposited with poly(allylamine hydrochloride) and poly(acrylic acid) nanocoating by electrostatic self-assembly technique. A fast and linear response is obtained in either acid or alkali solution (in the pH range 2.5 to 10) with resolution of 0.013 pH unit.
Highlights
Optical biochemical sensors are under rapid development because of their important applications in environmental monitoring and clinical analysis
The side surface of the sensor is deposited with poly(allylamine hydrochloride) and poly(acrylic acid) nanocoating by electrostatic self-assembly technique
The TCFMI sensor proposed in this paper has advantages of low-cost, robustness, reversibility, high sensitivity to external refractive index (RI), and low temperature sensitivity, and is very suitable for use as remote single-point monitoring biosensors or disposable low-cost fiber-optic bioprobes
Summary
Optical biochemical sensors are under rapid development because of their important applications in environmental monitoring and clinical analysis. One type of fiber-optic pH sensor is based on pH indicator immobilized in the matrix materials. The other type of fiber-optic pH sensor is based on the morphology of nanostructured film, usually known as swelling. Corres et al presented a long-period grating (LPG) pH sensor, in which nanocoating was deposited on the side-surface of the LPG as the reacting functional film and the shift of the resonant wavelength of the LPG is utilized for the determination of pH-induced RI changes. The present sensor has a slightly higher sensitivity to external RI, and much lower sensitivity to temperature It has the advantages of the robustness (because of the avoidance of grating degradation issue) and the lower fabrication cost
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