A Surface Fluorescent Sensing Membrane for Rapid Detection of Sodium

Abstract

A sensitive fluorescent sensing membrane has been developed for the rapid detection of sodium ions by immobilizing the membrane onto a glass slide surface. The membrane consists of a fluorophore, an ionophore, a plasticizer, and an anionic site of a lipophilic salt in a polyvinyl chloride (PVC) matrix. Based on the ion‐exchange response and photoinduced electron transfer mechanisms, the ionophore first captures target sodium ions from the solution into the membrane, and then the fluorophore emits a fluorescent signal based on the amount of sodium ions captured. To effectively transmit the signal and avoid the leaching of the fluorophore from the membrane, a newly synthesized fluorescent compound was used as a fluorophore in the fabrication of the membrane. Due to the special structure of the fluorophore, it remains trapped inside the membrane and thus gives a reliable fluorescent signal when sodium ions exist in the solution. Calix[4]arene tetraester acts as a sodium ion carrier, the crown size in its molecular structure is compatible with the sodium ionic size, making the membrane highly selective to sodium ions. Furthermore, the membrane demonstrates a rapid response to sodium ions—less than 1 min is required to reach a stable fluorescent signal. The sodium content in various real samples, such as mineral water, urine, and serum, were determined by the sensing membrane. The results highly correlate with the atomic absorption spectrometry method, confirming the validity of the fluorescent sensing membrane for sodium ion detection.

Keywords:

• Fluorescent sensing membrane
• Sodium detection
• Calix[4]arene tetraester
• Ion‐exchange response

Acknowledgment

The work described in this paper was fully supported by a grant from the Research Grants Council of the Hong Kong Special Administration Region, China (Project No. HKBU 2054/98P).