Versatile polymeric membrane ion-selective electrodes based on cellulose triacetate

Nowadays, polymeric membrane ion-selective electrodes (ISEs) based on poly(vinyl chloride) (PVC) matrices are widely used in clinical diagnosis and environmental monitoring. However, the chemical inertness of PVC may limit sensor applications in some scenarios, such as surface modification and construction of potentiometric biosensors through surface grafting of receptors. In this work, cellulose triacetate (CTA) is employed as a membrane matrix to prepare polymeric membrane ISEs. The versatile properties of the proposed CTA-based potentiometric sensors in terms of biocompatibility, biodegradability and easy chemical modification are illustrated. As a proof-of-concept experiment, polymeric membrane Ca²⁺-ISEs using CTA as the membrane matrix have been fabricated. The electrode has a linear range of 1.0 × 10^-5 to 1.0 × 10^-2 M with a Nernstian slope of 29.19 ± 0.97 mV dec^-1. A surface hydrophilic CTA-based Ca²⁺-ISE membrane can be simply obtained by alkaline hydrolysis of the electrode. The hydrolyzed surface of the obtained membrane can further be activated with carbonyldiimidazole (CDI) for the direct immobilization of the functionalized agent, polysaccharide chitosan, on the surface of the membranes. In addition, an enzyme, butyrylcholinesterase, can also be immobilized onto the ISE surface through a similar CDI reaction, which provides great potential for fabrication of new potentiometric biosensors. It will be shown that CTA can be used as a powerful membrane matrix alternative to the classical PVC matrix for fabrication of polymeric membrane optical and electrochemical sensors in clinical applications.