A metal-free voltammetric sensor for sensitive determination of Rhodamine B using carboxyl-functionalized carbon nanomaterials

Rhodamine B (RhB) is a synthetic xanthine dye that is harmful to environment and human health. Therefore, the development of low cost and efficient analytical techniques for RhB monitoring is very critical for environmental protection and food safety. Herein, a novel metal-free voltammetric sensor was constructed for sensitive detection of RhB using carboxyl-functionalized carbon nanomaterials. To understand the role of carboxyl functionalization in RhB electrooxidation, the electrochemical properties and voltammetric responses of carboxyl-functionalized multi-walled carbon nanotube (f-MWCNT), carboxyl-functionalized reduced graphene oxide (f-RGO), multi-walled carbon nanotube (MWCNT) and reduced graphene oxide (RGO) were compared. Amongst, the f-MWCNT/GCE exhibited the lowest charge transferred resistance and the largest electroactive surface area. The f-MWCNT/GCE showed extraordinary electrocatalytic activity for RhB oxidation, which is primarily attributed to the unique 3D structure and the carboxyl functionalization. The anodic peak current of RhB is linearly correlated to RhB concentration from 0.05 to 100 μM with a low limit of detection (LOD, 2.6 nM). In addition, the f-MWCNT/GCE achieved the selective identification and detection of RhB in presence of common metal ions and other red dyes, and retained a robust and stable voltammetric responses for at least a week. The f-MWCNT/GCE was successfully applied to detect RhB concentration in tomato sauce samples with good recovery.