A bis-quinone-functionalized Au-electrode subjected to hydrophobic magnetic nanoparticles acts as a three-state "Write-Read-Erase" information storage system

A monolayer consisting of two quinone units Q_A and Q_B is assembled on a Au electrode and interacted with an aqueous electrolyte/toluene biphase system, where hydrophobic magnetic nanoparticles are dispersed in the toluene phase. The bis-quinone monolayer exposed to the aqueous electrolyte solution reveals two reversible 2e^-/2H⁺-waves at E₁° = -0.36 V and E₂° = -0.16 V (vs. SCE) for the Q_A and Q_B units in the cyclic voltammogram, respectively. The electrochemical features of the monolayer allow electrochemical encoding of information in the monolayer by applying three different potentials, -0.05 V, -0.3 V or -0.6 V, generating the Q_A-Q_B, Q_A-Q_BH₂ or Q_AH₂-Q_BH₂ states, respectively. The encoded states of the monolayer are read out by the magnetic attraction of the hydrophobic magnetic nanoparticles to the electrode surface, and by analyzing the electrochemical properties of the different monolayer states in the hydrophobic environment provided by the nanoparticles. The oxidized quinone units in the hydrophobic environment reveal a stepwise one-electron reduction process, while the hydroquinone units are electrochemically mute in the same potential range. The encoded information is erased, in the presence of the hydrophobic magnetic nanoparticles, by sweeping the potential to a positive value of 0.4 V that results in the oxidation of the Q_AH₂ and Q_BH₂ states. The magnetic removal of the hydrophobic nanoparticles from the electrode surface and the exposure of the modified surface to the aqueous electrolyte solution reset the Q_A and Q_B units for a further cycle of the information storage.