Distributed pH sensing based on hydrogel coated single mode fibers and optical frequency domain reflectometry

Area of Science:

• Sensing Technology
• Materials Science
• Biomedical Engineering

Background:

• Accurate, real-time pH monitoring is crucial for various environmental and biological applications.
• Existing pH sensors often lack spatial resolution or are unsuitable for large-scale deployment.
• Optical sensing offers a promising alternative for distributed and remote measurements.

Purpose of the Study:

• To develop and demonstrate a distributed pH sensor utilizing optical frequency domain reflectometry (OFDR).
• To investigate the use of a polyethylene glycol diacrylate (PEGDA)-based hydrogel for pH-sensitive strain transduction.
• To optimize hydrogel properties for enhanced sensor performance.

Main Methods:

• Coating a single-mode fiber with a PEGDA-based pH-sensitive hydrogel.
• Utilizing OFDR to measure axial strain induced by hydrogel volume changes.
• Analyzing wavelength shifts in Rayleigh backscattering spectra for distributed pH measurement.
• Optimizing hydrogel molecular weight for sensitivity, response time, and stability.

Main Results:

• The sensor successfully measured pH values in the range of 2 to 6.
• Achieved a high sampling resolution of 1.7 mm.
• Demonstrated a sensitivity of -199 pm/pH.
• Reported a response time of 14 minutes with a 2 mm hydrogel coating diameter.

Conclusions:

• The developed OFDR-based distributed pH sensor offers high spatial resolution and sensitivity.
• The PEGDA hydrogel effectively converts pH changes into measurable optical signals.
• This technology holds potential for detecting and locating chemical or biological substances in extensive environments.