Individual Modified Carbon Nanotube Collision for Electrocatalytic Oxidation of Hydrazine in Aqueous Solution

Collision at a single molecule level was achieved based on the nanoimpact of an individual pyrroloquinoline quinone (PQQ) modified multiwalled carbon nanotube (MWCNT) at the carbon fiber ultramicroelectrode (C UME). Electrocatalytic amplification of the current responses was observed when the PQQ-modified MWCNT collided with C UME in the presence of hydrazine (N₂H₄) in a Tris-HCl buffer solution, which was also supported by the conventional cyclic voltammetry and chronoamperometry techniques. The enhanced catalytic oxidation of N₂H₄ was due to the "addition-elimination" redox cycling mechanism of PQQ/PQQH₂, where the oxidation of N₂H₄ occurred together with the reduction of PQQ under an external bias, and the formed PQQH₂ intermediate would be reoxidized back to PQQ simultaneously. The average collision current, duration, and charge for PQQ-modified MWCNT at 1.0 V vs Ag/AgCl were 105 pA, 0.45 ms, and 49 fC, respectively. As a result, the turnover frequency of electrocatalytic oxidation of N₂H₄ by PQQ was calculated to be 54 s^-1. In this regard, the proposed individual carbon nanotube collision method can not only serve as a promising sensing technique to detect biochemical species, but more importantly provide a robust approach to determine the intrinsic catalytic activity as well.