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A facile and effective approach of fabricating oxidized multiwalled carbon nanotube/glassy carbon electrode (OMWCNT/GCE) is herein reported. The OMWCNT/GCE was prepared by electrochemical oxidation method in basic media (0.5 mol L(-1) NaOH solution) and used as a sensor for simultaneous determination of dopamine (DA) and doxorubicin (DOX). Scanning electron microscopy, energy dispersive X-ray spectroscopy and cyclic voltammetry were used for characterization and performance study of the OMWCNT/GCE. The modified electrode exhibited good electrocatalytic properties toward the oxidation of DA and DOX. Peaks potential difference of 240 mV between DA and DOX was large enough to determine DA and DOX individually and simultaneously. Square wave voltammetry (SWV) was used for the simultaneous determination of DA and DOX in their binary mixture. Under the optimum conditions, the linear concentration dependences of SW peak current responses were observed for DA and DOX in the concentration ranges of 0.03-55 μmol L(-1) and 0.04-90 μmol L(-1), respectively. The detection limits (S/N = 3) were 8.5 × 10(-3) μmol L(-1), and 9.4 × 10(-3) μmol L(-1) for DA and DOX, respectively. The analytical utility of OMWCNT/GCE was also successfully demonstrated for the simultaneous determination of DA and DOX in human blood serum and urine samples. Graphical Abstract Fabrication of new oxidized multiwalled carbon nanotube/glassy carbon electrode for simultaneous determination of dopamine and doxorubicin.

Vinblastine (VLB) is prescribed for a wide variety of cancers. Therefore, development of sensitive methods for early diagnosis is urgently required. In this work, a highly sensitive and label-free impedimetric biosensor was fabricated for the electrochemical detection of VLB. First, the gold nanoparticles (AuNPs) were electrodeposited on the surface of a glassy carbon electrode (GCE). 3-Mercaptopropionic acid (MPA) was self-assembled over the AuNPs. Then, tubulin (TUB), as a receptor, was covalently immobilized at the AuNPs/GCE surface via carbodiimide coupling reaction using N-(3 dimethylaminopropyl)-N'-ethyl carbodiimide (EDC) and N-hydroxy succinimide (NHS). The step-by-step modification process was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in the presence of a redox probe [Fe(CN)]. The VLB concentration was measured through the increase of impedance values in the corresponding specific binding of VLB and TUB. The increased electron-transfer resistance (R ) values were proportional to the value of VLB concentrations in the range of 0.4 to 65.0 nmol L with a detection limit of 8.4 × 10 nmol L (SN = 3). The practical analytical performance of the proposed method was demonstrated by determination of VLB in plant extracts and human serum samples with satisfactory recoveries.