Study on Highly Sensitive Ru(bpy)32+ Electrochemiluminescence Sensor based on Nanofibers

Abstract

Electrospun nanofiber-modified ITO electrodes were investigated to develop a highly sensitive solid-state Ru(bpy)32+ electrochemiluminescence (ECL) sensors. As the first try, the ECL-sensing electrodes had been fabricated by means of the sequential formation of cation-exchangeable polyacrylicacid (PAA) and hydrophobic polyacrylonitrile (PAN) nanofiber layers on a patterned ITO substrate. The luminescent Ru(bpy)32+ centers were immobilized on the PAA nanofibers via electrostatic interactions in a post-wet process. The fibrous microstructures with a uniform diameter and smooth surface were confirmed by SEM, thus providing high porosity and a large surface area. The average diameters were 154 nm for PAN and 214 nm for PAA. Furthermore, the atomic compositions and the existence of chemical functional groups were probed by XPS, and FT-IR analyses. The cyclic voltammograms (CVs) and light emission profiles of the nanofiber-based PAN/PAA-Ru(bpy)3/ITO electrodes were investigated to characterize electrochemical and ECL properties. From these measurements, the new solid-state ECL-sensing electrodes were found to follow the surface-controlled quasi-reversible electrode process similar to the ECL mechanism of liquid-phase Ru(bpy)32+ ECL systems. Next, PAN-TiO2-Ru(bpy)3Cl2 nanofiber-modified ITO electrodes were also fabricated for achieving a sensitive solid-state ECL sensor together with the PAN-TiO2-Ru(bpy)3Cl2 film-modified ones. The composite nanofibers with an average diameter of 180 nm were successfully prepared by the electrospinning method. Their microstructure and atomic compositions were probed by using SEM, EDX, XPS, and FT-IR. These results exhibited that the titanium oxides were synthesized via sol-gel reactions and the Ru(bpy)32+ molecules were strongly immobilized in the PAN- TiO2 nanofiber matrix. The quasi-reversible redox reactions between Ru(bpy)32+ and Ru(bpy)33+ were confirmed by CVs measurements. Compared to the PAN-TiO2-Ru(bpy)3Cl2 film-modified electrode, the nanofiber-modified electrode exhibited a dramatically-enhanced ECL emission intensity larger than 50 times for tri-n-propylamine (TPA) co-reactant and a higher diffusion coefficient. This improvement in sensitivity was interpreted by the microstructural differences of the nanofiber and film-modified electrodes. Furthermore, ECL responses of the nanofiber-based ECL sensor had a good linear relationship with respect to the TPA concentration in the range of 0.1 ? 10 mM.