Optical pH Sensor Based on a Long-Period Fiber Grating Coated with a Polymeric Layer-by-Layer Electrostatic...

Area of Science:

• Photonics and Sensing Technologies
• Materials Science and Engineering
• Analytical Chemistry

Background:

• Optical fiber sensors offer advantages for remote and real-time monitoring.
• Developing robust and sensitive pH sensors is crucial for various applications.
• Layer-by-layer (LbL) self-assembly provides a versatile method for creating functional coatings.

Purpose of the Study:

• To develop and characterize an optical fiber pH sensor based on a long-period fiber grating (LPFG).
• To utilize pH-sensitive polymers, polyethylenimine (PEI) and polyacrylic acid (PAA), for sensing applications.
• To investigate the performance of an LPFG coated with PEI/PAA bilayers for pH detection.

Main Methods:

• Fabrication of an LPFG coated with alternating layers of PEI and PAA using LbL electrostatic self-assembly.
• Characterization of the sensor's response to varying pH solutions by monitoring resonance band shifts.
• Utilizing simulation and Fabry-Perot (FP) cavity experiments to estimate coating properties.

Main Results:

• The LPFG-based sensor achieved a pH sensitivity of (6.3 ± 0.2) nm/pH within the 5.92-9.23 pH range.
• The sensor demonstrated excellent reversibility and repeatability over multiple pH cycles.
• The polymer coating exhibited pH-dependent swelling/deswelling, with thickness varying from 200 nm (low pH) to 310 nm (high pH).

Conclusions:

• The developed optical fiber pH sensor using LbL-coated LPFG is effective for pH monitoring.
• The sensor exhibits high sensitivity, reproducibility, and reversibility, making it suitable for practical applications.
• The study highlights the potential of LbL self-assembly for creating advanced fiber optic sensing platforms.