Carbon nanospikes have better electrochemical properties than carbon nanotubes due to greater surface roughness and defect sites

Abstract

Carbon nanomaterials are used to improve electrodes for neurotransmitter detection, but what properties are important for maximizing those effects? In this work, we compare a newer form of graphene, carbon nanospikes (CNSs), with carbon nanotubes (CNTs) grown on wires and carbon fibers (CFs). CNS electrodes have a short, dense, defect-filled surface that produces remarkable electrochemical properties, much better than CNTs or CFs. The CNS surface roughness is 5.5 times greater than glassy carbon, while CNTs enhance roughness only 1.8-fold. D/G ratios are higher for CNS electrodes than CNT electrodes, an indication of more defect sites. For cyclic voltammetry of dopamine and ferricyanide, CNSs have both higher currents and smaller ΔE_p values than CNTs and CFs. CNS electrodes also have a very low resistance to charge transfer. With fast-scan cyclic voltammetry (FSCV), CNS electrodes have enhanced current density for dopamine and cationic neurotransmitters due to increased adsorption to edge plane sites. This study establishes that not all carbon nanomaterials are equally advantageous for dopamine electrochemistry, but that short, dense nanomaterials that add defect sites provide improved current and electron transfer. CNSs are simple to mass fabricate on a variety of substrates and thus could be a favorable material for neurotransmitter sensing.

Figure 1.

SEM images of a-b) CNS, c-d) CNT and e-f) CF microelectrodes. a), c) and e) Zoomed out CNS, CNT and CF cylindrical microelectrodes to see the coating efficiency; b), d) and f), Higher zoom images to understand the morphology of the CNS, CNT and CF electrode surface.

Figure 2.

The background charging current CV for CNS, CNT and CF microelectrodes. Electrodes were scanned from −0.2 to 1.0 V at 100 mV/s scan rate in 0.1 M PBS pH 7.4 buffer.

Figure 3.

a) Chronoamperometry current response with time, b) linear fitting of current vs. $\frac{1}{\mathrm{l}\mathrm{n}\mathrm{\tau }}$.

Figure 4.

Raman spectra of CNSs, CNTs and CF. The peak at 1360 cm⁻¹ is the D peak and at 1580 cm⁻¹ is the G peak.

Figure 5.

Electrochemical characterization of CNS, CNT and CF electrodes. Currents are normalized by geometric area. a) CV of 10 mM Ru(NH₃)₆^3+/2+; b) CV of 10 mM Fe(CN)₆^3-/4-; c) CV of 20 μM dopamine; and d) EIS Nyquist plot obtained in 10 mM Fe(CN)₆^3-/4-.

Figure 6.

Fast-scan cyclic voltammetry background current (Left column) and background subtracted detection of 1 μM dopamine (Right column) for a) CNS microelectrodes; b) CNT microelectrodes; c) CF microelectrode. d) Scan rate study for all electrodes (n = 3).

Figure 7.

Detection of other neurochemicals at CNS, CNT and CF microelectrodes. FSCV responses (Left column) and scan rate study (Right column, n = 3) of a) 1 μM epinephrine, b) 1 μM norepinephrine, c) 1 μM serotonin, d) 200 μM ascorbic acid in PBS buffer. For slopes of lines in log i vs log v plots, see Table S2.