Covalent functionalization of carbon nanotubes with safranin O for electrocatalytic determination of nitric oxide

In this research, we have demonstrated that safranin O (SAF) can be coupled to acid-treated multiwalled carbon nanotubes (MWNTs) in the presence of 1-ethyl-3-(3-dimethylaminopropyl)- carbodiimide (EDC) and N-hydroxysuccinimide (NHS) and assembled as SAF-MWNT composites. These functionalized MWNTs can be used for modification of glassy carbon electrode and applied for electrocatalytic determination of nitric oxide. In a typical experiment, MWNTs were sonicated in ultrasonic bath for 2 h and refluxed in conc. nitric acid for 5 h. The black MWNTs suspension was filtered and then washed with doubly distilled water until neutral pH was reached. The treated MWNTs were dried at 80 °C and stored for further use. After that, SAF was covalently attached to the broken tips containing carboxylic acid groups of the MWNTs using water-soluble coupling agents EDC and NHS by forming amide linkages between the amine residue of SAF and carboxylic acid groups on the MWNTs. This was done by adding the carboxylated MWNTs (200 mg) into a freshly prepared 15 mL DMF solution of EDC (200 mg). After that, 500 mg of NHS was added to the solution. After 2 h, these MWNTs were filtered, washed and dried. After that, MWNTs was added to 200 mg SAF in KHP buffer solution. The reaction was allowed to complete at room temperature for 10 h and then the MWNTs were washed thoroughly with water and filtered. A glassy carbon electrode was modified with these functionalized MWNTs to cast 5 μL of a 1 mg/mL SAF-MWNT/nafion solution. The results of voltammetric studies indicate that the carbon nanotube and safranin o system can enhance electrocatalytic activity toward the reduction of nitric oxide. Under the optimized conditions, in 0.1 M KHP buffer solution pH 1, the reduction current increased linearly in the range of 0.08 ˗ 2.10 mM. The detection limit was 0.05 mM and RSD for 2 mM nitric oxide was 1.7 %.