Functionalized multiwall carbon nanotubes combined with bis(2,2′-bipyridine)-5-amino-1,10-phenanthroline ruthenium(II) as an electrochemiluminescence sensor

An effective electrochemiluminescence (ECL) sensor was developed by combining bis(2,2′-bipyridine)-5-amino-1,10-phenanthroline ruthenium(II) [Ru(bpy)2(5-NH2-1,10-phen)2+] with functionalized carbon nanotubes (FCNTs) coated on a glassy carbon electrode. Treatment with a nitric acid and sulfuric acid mixture (1:3, v/v) led to multiwall carbon nanotubes terminated with carboxylic acid groups. These were characterized using Fourier transform infrared absorption spectroscopy (FTIR) measurement and a transmission electron microscope (TEM). N-hydroxy-succinimide and 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride were applied to activate the carboxyl groups and, according to the observation from FTIR and energy-dispersed spectroscopy (EDS) measurements, they catalyzed the formation of an amide bond between the FCNTs and Ru(bpy)2(5-NH2-1,10-phen)2+, resulting in a covalent bond. The FCNTs could provide a good immobilization matrix on the electrode by means of a hydrophobic interaction. In addition, because the FCNTs on the electrode surface were open structures with a large surface area and excellent conductivity, the modified electrode exhibited good electrochemical activity and ECL response. The ECL detection limit (S/N) for tripropylamine using this modified electrode was 8.8 × 10−7 mol L−1 with a linear range from 1.0 × 10−6 to 2.0 × 10−3 mol L−1 (R2 = 0.9969). The ECL sensor presented good characteristics in terms of stability and reproducibility.