Benzene layers-aligned electrochemical transformation of SWCNTs to redox-active macro-walled CNTs: Enabling oxygen interference-free monitoring of ROS release from HeLa cancer cells

Abstract

The search for novel carbon allotropes with unique electrochemical properties remains a key area of research in materials science. Here, we introduce a novel carbon nanotube material, termed macro-walled CNTs, synthesized through an in-situ benzene (BZ) electrochemical reaction on a glassy carbon electrode modified with single-walled carbon nanotubes (GCE/SWCNT) in a pH 2 KCl-HCl electrolyte solution. The modified electrode, denoted as GCE/SWCNT@BZ-Redox (where BZ-Redox represents redox-active benzene species), exhibited a well-defined redox peak at E°’ = 150 ± 10 mV vs. Ag/AgCl, along with a surface excess value of 5.1 nmol cm-2. Physicochemical characterization of SWCNT@BZ-Redox, conducted through techniques such as TEM, FTIR, Raman spectroscopy, and various electrochemical methods including scanning electrochemical microscopy (SECM) imaging, revealed a significant modification involving highly redox-active benzene multilayers with a diameter of approximately ~200 nm, which is about 10 times larger than that of pristine SWCNTs (~10-15 nm). Of particular interest is the stability of the redox peak under physiological pH conditions, as well as its ability to mediate hydrogen peroxide reduction reactions at a potential of -0.25 V vs. Ag/AgCl, akin to the reaction catalyzed by horseradish peroxidase enzymatic systems. For practical application, continuous monitoring of reactive oxygen species (ROS), specifically H2O2 release kinetics from stressed HeLa cancer cells under simulated conditions, without any dissolved oxygen interference, was demonstrated using a home-made bath-injection analysis system coupled with a screen-printed electrode modified with SWCNT@BZ-Redox as detector.