Electrochemical sensing performance of nanodiamond-derived carbon nano-onions: Comparison with multiwalled carbon nanotubes, graphite nanoflakes, and glassy carbon

Carbon nano-onions (CNOs) are emerging carbon nanomaterials with unique microstructure and electronic properties. CNOs are 0-D carbon analogs of 1-D carbon nanotubes (CNTs) and 2-D graphenes. CNOs are composed of sp²-bonded, concentric nanographene shells surrounding a hollow core. Microstructure, electrochemical properties, and biosensing performances of nanodiamond-derived CNOs (N-CNOs) were studied in comparison with other popular carbon electrodes: multiwalled carbon nanotubes (MWCNTs), graphite nanoflakes (GNFs), and glassy carbon (GC). First, morphology and microstructure of N-CNOs were characterized by scanning and transmission electron microscopies (SEM, TEM), X-ray diffraction (XRD), and Raman spectroscopy. Chemical composition and chemical functional groups were probed by X-ray photoelectron spectroscopy (XPS). Raman spectra of N-CNOs showed a large value of I_D/I_G, indicating that N-CNOs include defects, i.e., exposed edge planes. Second, electrocatalytic activity of N-CNOs toward oxygen reduction reaction was tested in comparison with MWCNTs, GNFs, and GC. Last, biosensing performances of N-CNOs were studied. Cyclic voltammetric and differential pulse voltammetric measurements were carried out for the detection of redox-active biomolecules such as dopamine, epinephrine, and norepinephrine. The results showed remarkable electrochemical activities of N-CNOs with high sensitivity, high selectivity, and stable electrode responses for the detection of biologically important molecules.