TEMPO-Functionalized Carbon Nanotubes for Solid-Contact Ion-Selective Electrodes with Largely Improved Potential...

Area of Science:

• Electrochemistry
• Materials Science
• Sensor Technology

Background:

• Solid-contact ion-selective electrodes (SCISEs) offer advantages over liquid-contact electrodes but face challenges in reproducible electrode potential (E0) across fabrication batches.
• Achieving batch-to-batch E0 reproducibility is crucial for the 'calibration-free' application of SCISEs, a key step towards routine use as disposable or wearable sensors.
• Existing solid-contact materials like conducting polymers and carbon nanotubes show good potential stability but limited E0 reproducibility.

Purpose of the Study:

• To develop a novel solid-contact material for SCISEs with enhanced and reproducible electrode potential (E0).
• To improve the stability and reliability of SCISEs for demanding applications, including 'calibration-free' use.
• To enable accurate potentiometric sensing in undiluted biological samples like blood serum.

Main Methods:

• Covalent functionalization of multiwalled carbon nanotubes (MWCNTs) with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO), a stable redox molecule.
• Fabrication of potassium ion-selective electrodes (K+-SCISEs) using the novel TEMPO-MWCNT solid-contact material.
• Pre-polarization of the TEMPO-MWCNT suspension to adjust and stabilize the electrode potential (E0) prior to electrode fabrication.

Main Results:

• The developed TEMPO-MWCNT material exhibited excellent double-layer capacitance, adjustable redox properties, and covalent confinement of the redox couple.
• K+-SCISEs demonstrated superior analytical performance, potential stability, and resistance to O2, CO2, and light, without aqueous layer formation.
• Outstanding batch-to-batch E0 reproducibility was achieved using prepolarized TEMPO-MWCNT, overcoming hydration-related potential drifts.

Conclusions:

• Covalent functionalization of MWCNTs with TEMPO creates a robust solid-contact material for SCISEs with highly reproducible and stable electrode potentials.
• The novel SCISEs facilitate 'calibration-free' operation and enable accurate potassium measurements in undiluted blood serum without prior conditioning.
• This advancement addresses a major challenge for the routine use of SCISEs as disposable or wearable potentiometric sensors.