Electrochemically‐controlled DNA Release under Physiological Conditions from a Monolayer‐modified Electrode

An indium tin oxide (ITO) electrode prepared on a flexible polymeric support was modified with an amino-silane and then functionalized with trigonelline and 4-carboxyphenylboronic acid covalently bound to the amino groups. The trigonelline species containing quarterized ammonium group produced positive charge on the electrode surface regardless of the pH value, while the phenylboronic acid species were neutral below pH8 and negatively charged above pH9 (note that their pK(a)=8.4). The total charge on the monolayer-modified electrode was positive at the neutral pH and negative at pH>9 (note that 4-carboxyphenylboronic acid was attached to the electrode surface in excess to trigonelline, thus allowing the negative charge to dominate on the electrode surface at basic pH). Single-stranded DNA molecules were loaded on the modified electrode at pH7.0 due to their electrostatic attraction to the positively charged surface. By applying electrolysis at -1.0V (vs. Ag/AgCl reference) electrochemical oxygen reduction resulted in the consumption of hydrogen ions and local pH increase in the vicinity of the electrode surface. The process resulted in the transition to the total negative charge due to the negative charges formed on the phenylboronic acid species. This resulted in the electrostatic repulsion and release of the loaded DNA. The developed approach allowed the electrochemically-triggered DNA release not only in the aqueous solutions, but also in human serum solution, thus giving promise for future biomedical applications.