Simple immobilization of pyrroloquinoline quinone on few-walled carbon nanotubes

Abstract

Pyrroloquinoline quinone (PQQ) was immobilized on glassy-carbon electrodes (GCE) modified with single-walled carbon nanotubes (SWCNT), few-walled carbon nanotubes (FWCNT) and carbon black (Vulcan XC72R). Modified electrodes were prepared by drop-casting. Immobilization was achieved with an extremely simple dipping procedure and without any further modification to the electrodes. Electrochemical performance of the electrodes was studied by cyclic voltammetry and spectroelectrochemistry. FWCNT adsorbed 30 times more PQQ than the other carbon materials. Compared to more complicated immobilization methods, PQQ/FWCNT/GCE showed well-defined electrochemistry in a considerably wide pH area from 2 to 12. The dipping process is affected by pH and electrostatic forces. At dipping pH 9.5, where both FWCNTs and -2 -PQQ have strong negative charge, the adsorption was halved compared to dipping pH 2, where the charges are smaller.

A prototype device of microliter volume voltammetric pH sensor based on carbazole–quinone redox-probe tethered MWCNT modified three-in-one screen-printed electrode

“… Quinoline GCE/MWCNT@QLO − 450 ± 5 64 Hyd 40 4. Pyrroloquinoline quinone GCE/fWCNT +210 – Hyd 41 5. Hematin GCE/GMC/Hemt@Chit − 390 − 32 DO, H 2 O 2 42 6.…”

Electrochemistry of Pyrroloquinoline Quinone (PQQ) on Multi-Walled Carbon Nanotube-Modified Glassy Carbon Electrodes in Biological Buffers

“…7 Improper orientation of PQQ could affect its reversible oxidation process. Kanninen et al 8 reported the physical adsorption of PQQ to single-walled and few-walled carbon nanotube (FWCNT)-modified glassy carbon electrodes. Multi-walled carbon nanotubes (MWCNTs) are commerically available in different lengths and with different functionalities, which makes them useful for electrode surface modification for improved electrochemical response and for biomolecule immobilization.…”

“…6,7 These studies can be challenging due to the pH dependence of the redox potentials. 6,8,9 Using a cystamine-monolayer Au-modified electrode, Katz et al6 studied the electrochemistry of PQQ in solution using CV and reported the change in potential with pH to be about 60 mV pH −1 at pH < 6.2; 30 mV pH −1 at 6.2 < pH < 8.6; and about 60 mV pH −1 at pH > 8.6. In another study using PQQ immobilized on few-walled carbon nanotube (FWCNT)-modified glassy carbon electrodes, the change in PQQ's redox potential was estimated to be approximately 67 mV pH −1 , with the highest reversible reduction-oxidation observed at ∼pH 2.…”

“…6,7 These studies can be challenging due to the pH dependence of the redox potentials. 6,8,9 Using a cystamine-monolayer Au-modified electrode, Katz et al…”

“…6,7 These studies can be challenging due to the pH dependence of the redox potentials. 6,8,9 Using a cystamine-monolayer Au-modified electrode, Katz et al 6 studied the electrochemistry of PQQ in solution using CV and reported the change in potential with pH to be about 60 mV pH −1 at pH < 6.2; 30 mV pH −1 at 6.2 < pH < 8.6; and about 60 mV pH −1 at pH > 8. 6.…”