Interaction between LDL-mimetic liposomes and acid-treated carbon nanotube electrode during Cu²⁺-mediated oxidation

Oxidation of low-density lipoproteins (LDL) causes atherosclerosis. Detection of oxidation of LDL-mimetic liposomes using an electrode might serve as a convenient tool in the search of antioxidants for the prevention of atherosclerosis. This report proposes a reaction mechanism between LDL-mimetic liposomes and an acid-treated carbon nanotube (CNT) electrode. Oxidation of the liposomes, mediated by Cu²⁺, was monitored by the change in electrode potential, and the fluorescence intensity generated by diphenyl-1-pyrenylphosphine (DPPP) as control. The electrode potential and fluorescence intensity increased concomitantly during oxidation, followed by a gradual decrease. Although the electrical potential peaked faster than the fluorescence intensity, addition of CNT to the DPPP reaction accelerated the latter, suggesting the role of CNT as an accelerator of liposome oxidation. Atomic force microscopy showed increased binding of liposomes to CNT along with liposomal deformation. Further, binding of Cu²⁺ to the liposome-bound CNT surface was observed by quartz crystal microbalance. In conclusion, the interaction of liposomes with Cu²⁺ and CNT surface explains the rapid response of the electrode in liposome oxidation.