S(O)MWCNT/modified Carbon Paste - A Non-enzymatic Amperometric Sensor for Direct Determination of 6-mercaptopurine in Biological Fluids

In this study, carbon paste electrode (CPE) modified with strongly oxidized MWCNT (S(O)MWCNT) was developed as an efficient, economical, electrochemical sensor for the detection of 6-mercaptopurine (6MP) with antineoplastic and immunosuppressive activities. However, this cytotoxic anticancer drug is associated with adverse side-effects; hence 6MP determination becomes crucial. Drop-cast-coating was an effective strategy in the fabrication of S(O)MWCNT/MCPE to increase surface area. Electrochemical measurements were performed using cyclic voltammetry (CV) and amperometry. Electrochemical Impedance Spectroscopy (EIS), Field Emission Scanning Electron Microscopy (FESEM) and Energy Dispersive X-ray (EDX) elucidated surface characteristics. With S(O)MWCNT's good conductive ability, we achieved rapid electron transfer that amplified 6MP anodic signal by 3.8 folds higher compared to bare CPE. Additionally, great consonance between CPE loaded with S(O)MWCNT yielded superior current response with decreased activation energy compared to S(O)MWCNT/modified glassy carbon electrode (S(O)MWCNT/MGCE). Under optimal conditions S(O)MWCNT/MCPE displayed a wide-single-linearity range from 1.0 to 100.0 mu M with an excellent detection limit of 0.24 mu M during amperometric quantification for the first time. It also exhibited good selectivity, after a series of common physiological interferents' assessment. As a part of proof-of-concept, the proposed sensor was investigated in 6MP fortified human fluids, and the satisfactory recoveries obtained authenticated S(O)MWCNT/MCPE's accuracy and reliability for practical applicability.