Insights into the surface and redox properties of single-walled carbon nanotube—cobalt(II) tetra-aminophthalocyanine self-assembled on gold electrode

This paper describes for the first time the electrochemical properties of redox-active selfassembled films of single-walled carbon nanotubes (SWCNTs) coordinated to cobalt(II)tetra-aminophthalocyanine (CoTAPc) by sequential self-assembly onto a preformed aminoethanethiol (AET) self-assembled monolayer (SAM) on a gold electrode. Both redox-active SAMs (Au-AET-SWCNT and Au-AET-SWCNT-CoTAPc) exhibited reversible electrochemistry in aqueous (phosphate buffer) solution. X-ray photoelectron spectroscopy (XPS) confirmed the appearance on the gold surface of the various elements found on the SAMs. Atomic force microscopy (AFM) images prove, corroborating the estimated electrochemical surface concentrations, that these SAMs lie normal to the gold surface. Electrochemical impedance spectroscopy (EIS) analyses in the presence of [Fe(CN)6] 3−/4− as a redox probe revealed that the Au-AET-SWCNTCoTAPc showed much lower ( 10 times) electron-transfer resistance (Ret) and much higher ( 10 times) apparent electron-transfer rate constant (kapp) compared to the AuAET-SWCNT SAM. Interestingly, a preliminary electrocatalytic investigation showed that both SAMs exhibit comparable electrocatalytic responses towards the detection of