An electrochemical bifunctional sensor for the detection of nitrite and hydrogen peroxide based on layer-by-layer multilayer films of cationic phthalocyanine cobalt(II) and carbon nanotubes

As vital biological mediators, the accurate detection of nitrite (NO2-) and hydrogen peroxide (H2O2) is desirable for clinical monitoring and diagnosis. Herein, cationic 2,9,16,23-tetra[4-(N-methyl) pyridinyloxy]-phthalocyanine cobalt(II) ([TMPyPcCo](4+)) and acid-treated multiwalled carbon nanotubes (aCNTs) were alternately self-assembled on the glassy carbon electrode (GCE) by means of the electrostatic interaction, leading to a 3D loose and interconnected assembly of [TMPyPcCo/aCNTs](n) multilayer films. In the [TMPyPcCo/aCNTs](n) films, [TMPyPcCo](4+) is anchored onto the surface of aCNTs without any inert polymer binders, which is beneficial to expose more active sites for electrocatalysis. The effective combination of [TMPyPcCo](4+) and aCNTs brings many advantages in electrochemical detection, involving the fast oriented transmission of charges, permeable channels for ion adsorption and transport, and more sensing sites, thus the [TMPyPcCo/aCNTs](n) films display excellent electrochemical sensitivity towards both NO2- and H2O2. The responses of NO2- and H2O2 vary linearly with respect to the concentration from 5 mM to 30 mM and 10 mM to 9 mM. Furthermore, the superior cycling stability, reproducibility, and selectivity make [TMPyPcCo/aCNTs](n) films suitable for the real samples.