Dual-Lifetime Referencing (t-DLR) Optical Fiber Fluorescent pH Sensor for Microenvironments

Area of Science:

• Marine Biology
• Oceanography
• Sensor Technology

Background:

• The diffusion boundary layer (DBL) microenvironment around aquatic organisms exhibits unique pH dynamics.
• DBL pH differs from bulk seawater, potentially mitigating ocean acidification effects for calcifying species.

Purpose of the Study:

• To develop a low-cost optical fiber fluorescent pH sensor for measuring pH in the DBL.
• To assess the sensor's performance and suitability for real-time monitoring of metabolic-induced pH changes.

Main Methods:

• A time-domain dual-lifetime referencing (t-DLR) system was coupled with a dual-layer sol-gel coated optical fiber pH sensor.
• The sensor employed pH-sensitive iminocoumarin and pH-insensitive Ru(dpp)3-PAN, with measurements validated against GOA-ON guidelines.
• Real-time pH measurements were conducted in the DBL of Ulva sp. seaweed.

Main Results:

• The developed sensor demonstrated a dynamic pH range of 7.41-9.42, response time of 29-100 s, and minimal salinity dependency.
• Sensor precision was ~0.02 pH units, meeting GOA-ON 'weather' guidelines.
• Successful real-time pH monitoring in the seaweed DBL confirmed its practicability.

Conclusions:

• The developed t-DLR optical fiber pH sensor is a practical tool for DBL microenvironment studies.
• This technology can provide crucial insights into organismal responses to changing ocean conditions.
• The sensor facilitates understanding of light-controlled metabolic activities influencing aquatic pH.