Development of fluorescent pH sensors based on a sol-gel matrix for acidic and neutral pH ranges in a microtiter plate

Abstract

In this study, two typical pH-sensitive dyes, fluorescein amine (FA) and 8‑hydroxypyrene‑1,3,6‑trisulfonic acid trisodium salt (HPTS), were doped with two types of silica particles. The dye-doped silica particles were entrapped in a mixture of 3‑glycidoxypropyltrimethoxysilane (GPTMS) and 3-aminopropyltrimethoxysilane (APTMS) sol-gel matrix (GA) and a polyurethane hydrogel (PU) to prepare stable pH-sensitive membranes in a microtiter plate. Four pH-sensing membranes prepared at the bottom of wells in 24-well microtiter plates showed high sensitivity, fast recoverability, and good photostability. Supporting materials with fast ion transport properties were used to produce a pH-sensing membrane with rapid response time. The membranes entrapped with FA-doped silica particles had a dynamic detection range from pH 2 to pH 6, while the membranes entrapped with HPTS-doped silica particles had a dynamic detection range from pH 5 to pH 8. Dye-leaching from the pH-sensing membranes did not occur due to tight binding of functional groups in the dyes (FA and HPTS) to the sol-gel GA matrix, the doping of dyes in the silica particles, and the addition of an anti-fading agent (DABCO). Four pH-sensing membranes were used to measure the pH of wastewater. The measured results were consistent with standard pH values.