Electrochemical Sensing of Dopamine Using Onion-like Carbons and Their Carbon Nanofiber Composites

This work describes the electrochemical detection of dopamine in samples (pure raw materials as well as pharmaceutical formulation) using onion-like carbon (OLC) and its carbon nanofiber composites (OLC-CNF). The OLC-CNF and precursor materials (polyacrylonitrile (PAN) fiber and OLC-PAN) were synthesized using electrospinning process. The morphologies of the samples were obtained using scanning electron microscopy (SEM) while surface area and porosity were determined using the Brunauer–Emmett–Teller (BET) analysis. OLC gave the best surface area (279 m 2 g −1 ) and highest pore volume (1.2 cm 3 g −1 ). To determine electrochemical sensing properties, the materials were drop-cast on the glassy carbn electrode (GCE). The electron transfer properties decrease as follows: OLC > OLC-PAN > OLC-CNF > PAN, suggesting that OLC is the most conductive materials. The modified GCE were used as sensors for the dopamine using electrochemical techniques such as cyclic voltammetry (CV), square wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS). OLC and OLC-CNF gave comparable electrocatalytic activities in terms of sensitivity and limit of detection (OLC 1.23 μM and sensitivity of 0.74 μA/μM, and OLC-CNF 1.42 μM, 0.31 μA/μM). The high performance of OLC is attributed to its advantageous nanoparticulate nature and high conductivity. Both sensors (OLC and OLC-CNF) could be reliably used in the assay of dopamine raw material and its pharmaceutical formulation, dopamine HCl injection (Rotexmedica®). One of the key fndings here is that the incorporation of the CNF into the OLC does not significantly impact on its inherent tensile strain that defines its electrochemical performance. Graphical Abstract Onion-like carbon (OLC) and its carbon nanofiber (CNF) composites gave comparable electrocatalysis toward sensitive and selective detection of dopamine.