Journal Article

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

McGraw, Christina M., Chen, Wan-Har, Dillingham, Peter W., Armstrong, Evelyn, Ennis, Courtney, Moratti, Stephen C.

2023

Overview

The pH behavior in the μm to cm thick diffusion boundary layer (DBL) surrounding many aquatic species is dependent on light-controlled metabolic activities. This DBL microenvironment exhibits different pH behavior to bulk seawater, which can reduce the exposure of calcifying species to ocean acidification conditions. A low-cost time-domain dual-lifetime referencing (t-DLR) interrogation system and an optical fiber fluorescent pH sensor were developed for pH measurements in the DBL interface. The pH sensor utilized dual-layer sol-gel coatings of pH-sensitive iminocoumarin and pH-insensitive Ru(dpp)3-PAN. The sensor has a dynamic range of 7.41 (±0.20) to 9.42 ± 0.23 pH units (95% CI, T = 20 °C, S = 35), a response time (t90) of 29 to 100 s, and minimal salinity dependency. The pH sensor has a precision of approximately 0.02 pHT units, which meets the Global Ocean Acidification Observing Network (GOA-ON) “weather” measurement quality guideline. The suitability of the t-DLR optical fiber pH sensor was demonstrated through real-time measurements in the DBL of green seaweed Ulva sp. This research highlights the practicability of optical fiber pH sensors by demonstrating real-time pH measurements of metabolic-induced pH changes.

• Publisher: MDPI AG
• Subject: Chemicals / Computer software industry / dual-layer sensing film / Electromagnetism / Equipment and supplies / Fiber optics / Hydrogen-ion concentration / inverse calibration / marine microenvironments / Measurement techniques / Metabolism / Nanoparticles / Ocean acidification / optical fiber fluorescent pH sensor / Resveratrol / Seawater / Sensors / Spectrum analysis / time-domain dual-lifetime referencing