Tetracycline immobilization as hydroquinone derivative at dissolved oxygen reduction potential on multiwalled carbon nanotube

Upon continuous potential cycling of multiwalled carbon nanotube modified electrode (GCE/MWCNT) with Tetracycline antibiotic (Tet) at -0.5 to 0.4 V vs Ag/AgCl in pH 7 phosphate buffer solution, the Tet drug gets selectively immobilized as Tet-hydroquinone derivative (Tet-HQ) on the GCE/MWCNT (GCE/Tet-HQ@MWCNT) and showed a specific surface confined redox peak at E _1/2 =-0.24 ± 0.02 V vs Ag/AgCl. Control potential cycling experiment with o-cresol resulted to similar electrochemical characteristic too. But with p-cresol, no such surface confined redox peak was noticed. Dissolved oxygen reduction to hydrogen peroxide (as an intermediate species) at -0.45 V vs Ag/AgCl and its chemical oxidation of the surface bound Tet@MWCNT to Tet-HQ@MWCNT is proposed as a plausible mechanism. Separate ring-disk screen-printed carbon electrode assembly, where MWCNT and a H₂O ₂ detection catalyst (nano-MnO₂) modified on the ring and disk respectively, coupled with flow injection analysis showed specific current signals for oxygen reduction reaction at -0.45 V vs Ag/AgCl on the disk and subsequent H₂O₂ oxidation on ring at 0.8 V vs Ag/AgCl. The surface confined redox system showed highly selective electrocatalytic reduction signal to hydrogen peroxide at -0.22 V vs Ag/AgCl without any interference from the ascorbic acid, uric acid, cysteine and nitrite.