A comparative study of carboxylic acid and benzimidazole phthalocyanines and their surface modification for dopamine sensing

Novel iron tetrabenzimidazole phthalocyanine (FeTBImPc) was synthesized from iron tetracarboxylicacid phthalocyanine (FeTCAPc) in pure state with good yield. The synthesized complexes were characterized with analytical and spectroscopic methods such as elemental analysis, UV-Visible, IR spectroscopy, mass, PXRD, TGA and cyclic voltammetry. The peripheral benzimidazole substituted phthalocyanine showed red shift in the absorption spectrum due to the change in the electron density because of the electron accepting functional group and extended conjugation. The synthesized phthalocyanine complexes are found to be electrochemically active and were immobilized on the glassy carbon electrode by drop-casting method or electropolymerization. The modified electrodes were characterized by cyclic voltammetry and impedance spectroscopy and used for the detection of biologically important molecule, dopamine. The hybrid composite electrode, GCE/CNP-FeTCAPc, exhibited good electrocatalytic ability towards the oxidation of dopamine and displayed a good linear dependence in the concentration range of 100-1000 nM with LOD of 22 nM. The GCE/CNP-polyFeTBImPc exhibited linear relationship in the concentration range 100-1000 nM with LOD 20 nM and sensitivity of 67.2039 mA nM(-1) cm(-2). The fabricated amperometric sensors GCE/CNP-FeTCAPc and GCE/CNP-polyFeTBImPc displayed linear response in the concentration range 50-500 nM with LOD values 16 and 14 nM, respectively for the detection of dopamine. The fabricated GCE/CNP-po/yFeTBImPc sensor exhibited high stability and selectivity for the detection of dopamine compared to other electrodes and the practicality of the developed method has been investigated by the analysis of real sample.