3D-networked carbon nanotube/diamond core-shell nanowires for enhanced electrochemical performance

Abstract

A boron-doped diamond/carbon nanotube (BDD–CNT) hybrid material with a core-shell three-dimensional random network structure was fabricated using the electrostatic self-assembly of nanodiamond. In general, CNTs are easily etched out as hydrocarbons or transformed to graphitic clusters at defect sites in hydrogen-rich environments (that is, the typical conditions employed for diamond deposition). However, attaching a dense layer of nanodiamond particles to the outer wall of the CNTs suppressed CNT etching and promoted BDD growth. To attach the dispersed nanodiamond particles on the CNT surface, we used an electrostatic self-assembly technique in which the surface charges on the CNTs and the nanodiamond were controlled using cationic and anionic polymers. Following BDD deposition, the electrochemical properties of the BDD–CNT structures were examined by cyclic voltammetry and electrochemical impedance spectroscopy. The results indicated that the BDD–CNTs exhibited enhanced electron transport efficiency, large effective surface areas and high sensitivity, with a remarkably low detection limit. Researchers in South Korea have coated carbon nanotubes with nanodiamonds to form a highly sensitive glucose biosensor. The team, led by Dae-Soon Lim at Korea University, deposited a layer of boron-doped diamond nanoparticles onto the outer walls of multiwalled carbon nanotubes. They then confirmed the structure of the resultant nanowires using an electron microscope and measured their electrochemical properties. Next, the team demonstrated that the nanowires exhibit a higher sensitivity to glucose — as well as a significantly lower detection limit — than other existing electrodes. The new nanowires could potentially be used for the noninvasive detection of glucose in human body fluids containing lower concentrations of glucose than blood, such as saliva, tears or sweat. They could help to estimate the size of bacteria populations in sea water, as many bacteria use glucose as an energy source. 3D-networked boron-doped diamond/carbon nanotube (BDD–CNT) core-shell nanowires were fabricated using the electrostatic self-assembly of nanodiamond. Although CNTs are easily etched out at their defect sites in hydrogen-rich environments, densely attached nanodiamond particles suppressed the etching of the CNTs and promoted BDD growth. After BDD deposition, 3D-networked BDD–CNT nanowires were successfully developed. In comparison to other electrodes, the BDD–CNT electrode exhibited better electrochemical performances, that is, low electron transfer resistance, large effective surface area and high sensitivity with significantly low detection range (8.7 mA mM−1 in the range 0.65–83.75 nM). The improvement in the performances of the BDD–CNT electrode could be attributed to the geometry and electron pathways offered by CNTs as well as to the synergistic material properties of BDD and CNT. The BDD–CNT electrode shows promise for application in the noninvasive measurement of glucose in living beings as well as for environmental monitoring in sea water.