Magnetoswitchable Controlled Hydrophilicity/Hydrophobicity of Electrode Surfaces Using Alkyl-Chain-Functionalized Magnetic Particles: Application for Switchable Electrochemistry

Magnetic nanoparticles consisting of undecanoate-capped magnetite (average diameter ~4.5nm;saturated magnetization, M_s, 38.5 emu g^-1) are used to control and switch the hydrophobic or hydrophilic properties of the electrode surface. A two-phase system consisting of an aqueous buffer solution and a toluene phase that includes the suspended capped magnetic nanoparticles is used to control the interfacial properties of the electrode surface. The magnetic attraction of the functionalized particles to the electrode by means of an external magnet yields a hydrophobic interface that acts as an insulating layer, prohibiting interfacial electron transfer. The retraction of the magnetic particles from the electrode to the upper toluene phase by means of the external magnet generates a hydrophilic electrode that reveals effective interfacial electron transfer. The electron-transfer resistance and double-layer capacitance of the electrode surface upon the attraction and retraction of the functionalized magnetic particles to and from the electrode, respectively, by means of the external magnet were probed by Faradaic impedance spectroscopy (R_et = 170 Ohm and C_dl = 40 uF sm^-2 in the hydrophilic state of the electrode and R_et = 22 kOhm and C_dl = 0.5 uF sm^-2 in the hydrophobic state of the interface). The magnetoswitchable control of the interface enables magnetic switching of the bioelectrocatalytic oxidation of glucose in the presence of glucose oxidase and ferrocene dicarboxylic acid to "ON" and "OFF" states.