Fiber optic pH sensor with self-assembled polymer multilayer nanocoatings.

Area of Science:

• Materials Science
• Optical Sensors
• Analytical Chemistry

Background:

• Fiber-optic sensors offer advantages in harsh environments.
• Developing precise and sensitive pH monitoring tools is crucial for various applications.
• Tilted Fiber Bragg Gratings (TFBGs) provide a versatile platform for sensing applications.

Purpose of the Study:

• To develop and characterize a novel fiber-optic pH sensor.
• To utilize electrostatic self-assembly for creating a pH-sensitive multilayer film on a TFBG.
• To evaluate the sensor's sensitivity, accuracy, and dynamic response.

Main Methods:

• Fabrication of a TFBG-based sensor.
• Deposition of poly(diallyldimethylammonium chloride) (PDDA) and poly(acrylic acid) (PAA) multilayer films using layer-by-layer (LbL) electrostatic self-assembly.
• Characterization of the sensing film's properties (thickness, morphology).
• Analysis of spectral shifts and transmission changes in response to varying pH levels using FFT analysis.

Main Results:

• The PDDA/PAA film's refractive index changes with pH due to swelling.
• The TFBG sensor exhibited a near-linear pH sensitivity of 117 a.u./pH unit.
• The sensor achieved an accuracy of ±1 a.u. within the pH range of 4.66 to 6.02.
• Dynamic response measurements showed a 10 s rise time and 18 s fall time for a six-bilayer sensor.

Conclusions:

• The developed fiber-optic pH sensor based on TFBG and LbL-assembled PDDA/PAA films is effective for pH monitoring.
• The sensor demonstrates excellent sensitivity and accuracy in a specific pH range.
• The LbL technique provides a robust method for fabricating functional sensing layers for optical sensors.