Covalent attachment of cobalt (II) tetra-(3-carboxyphenoxy) phthalocyanine onto pre-grafted gold electrode for the determination of catecholamine neurotransmitters

Abstract

The fabrication of electroactive thin films onto gold electrode surfaces yields very interesting surfaces with excellent electrocatalytic activity. Cobalt (II) tetra-(3-carboxyphenoxy) phthalocyanine (CoTCPhOPc) was successfully synthesized and fully characterized using FT-IR spectroscopy, ultraviolet-visible (UV–Vis) spectroscopy, magnetic circular dichroism (MCD) spectroscopy, elemental analysis, and mass spectrometry. The CoTCPhOPc was immobilized onto phenylethylamino (PEA) pre-grafted gold electrode surface, Au-PEA, using amide coupling reaction to obtain Au-PEA-CoTCPhOPc. This yielded pH sensitive thin films due to the terminal carboxylic acid groups. The Au-PEA-CoTCPhOPc electrode was shown to possess pH-selective properties towards negatively charged [Fe(CN)6]−3/-4 and positively charged [Ru(NH3)6]2+/3+. Au-PEA-CoTCPhOPc electrode surface enabled the detection of catecholamines (dopamine, epinephrine, norepinephrine) and the screening off of ascorbic acid by means of pH functional groups. Excellent electrocatalytic oxidation with the limit of detection (LoD) determined using 3σ was found to be 1.32 (0.95), 3.08 and 2.11 (1.78) μM for electrooxidation and electroreduction (in brackets) of dopamine, epinephrine and norepinephrine; respectively. The limit of quantification (LoQ) was determined using 10σ and found to be 4.41 (3.17), 10.3 and 7.02 (5.93) μM electrooxidation and electroreduction (in brackets) for dopamine, epinephrine and norepinephrine; respectively. The Au-PEA-CoTCPhOPc thin monolayer film was shown to screen off ascorbic acid as no electrocatalytic oxidation was observed for up to 100 μM concentration.