Chemical sensor based on a long-period fibre grating modified by a functionalized polydimethylsiloxane coating

Area of Science:

• Chemical sensing
• Materials science
• Optical physics

Background:

• Long-period gratings (LPGs) are sensitive to changes in their surrounding refractive index.
• Developing selective and sensitive chemical sensors for environmental monitoring remains a significant challenge.

Purpose of the Study:

• To design and characterize a chemical sensor based on a coated LPG for environmental pollutant detection.
• To enhance the sensitivity and selectivity of the LPG sensor through tailored polymer coatings.
• To demonstrate the sensor's capability for chemical differentiation and low-level detection.

Main Methods:

• Fabrication of a long-period grating coated with a designer polydimethylsiloxane (PDMS) polymer.
• Incorporation of diphenylsiloxane and a titanium cross-linker into the PDMS coating to optimize refractive index and sensitivity.
• Utilizing ring-down detection to interrogate the LPG, amplifying optical loss and ensuring stability.
• Exposure of the sensor to analytes (cyclohexane and xylene) to monitor changes in the attenuation spectrum.

Main Results:

• The coated LPG sensor exhibited changes in its attenuation spectrum upon analyte microextraction into the polymer matrix.
• Chemical differentiation between cyclohexane and xylene was successfully achieved.
• A detection limit of 300 parts per million (ppm) for xylene vapor was realized.

Conclusions:

• The developed coated LPG sensor demonstrates potential for sensitive and selective detection of volatile organic compounds.
• The use of designer PDMS coatings and ring-down detection offers a robust platform for chemical sensing applications.
• Further optimization could lead to enhanced detection limits and broader applicability in environmental monitoring.