Multi-walled carbon nanotubes co-doped with sulfur and nitrogen as sensors for the simultaneous electrochemical determination of biomolecules

Multi-walled carbon nanotubes co-doped with sulfur and nitrogen (S-N-MWCNTs) were produced onto silicon/silicon oxide by means of chemical vapor deposition (CVD) upon decomposition of dimethyl sulfoxide (DMSO) and acetonitrile (ACN) in the presence of ferrocene (FeCp2). The synthesized S-N-MWCNTs were characterized by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) combined with energy dispersive X-ray spectroscopy (EDX), Raman spectroscopy, and electrochemical impedance spectroscopy (EIS). The electrochemical response of S-N-MWCNTs towards oxidation of ascorbic acid (AA), dopamine (DA), uric acid (UA), and glucose (GL) was investigated in phosphate buffer solution (PBS) (pH 7.4) by means of cyclic voltammetry (CV). Strong dependence of electrochemical quality of S-N-MWCNTs on the concentration of decomposed DMSO precursor was observed. Namely, upon increasing the percentage of decayed DMSO from 1.0 up to 2.0% wt., the electrocatalytic activity of S-N-MWCNTs tends to improve. The separations of oxidation waves between AA-DA, DA-UA, and AA-UA reached their maximum values on S-N-MWCNTs-3, fabricated upon decomposition of 2.0% wt. DMSO precursor, permitting their individual and simultaneous electrochemical determination. Strong interference of GL in the analysis of DA was observed, and consequently, simultaneous analysis of AA, DA, and UA can be only carried out in the absence of GL. A great influence of concentration of decomposed DMSO precursor on the sensitivity of S-N-MWCNTs was also observed. Specifically, upon increasing the percentage of decayed DMSO from 1.0 up to 2.0% wt., the sensitivity and detection capability of S-N-MWCNTs towards AA, DA, UA, and GL analytes tend to enhance.