Electrochemically Produced pH Change Triggering Doxorubicin Release from Cystamine Cross-Linked Microgels Covalently Immobilized on the Gold Interface

Herein, the usage of polyacrylic acid (AA) based and N,N′-bis(acryloyl)cystamine (BAC) cross-linked microgel (AA-BAC) as a doxorubicin (DOX) carrier and stimuli-responsive material for the controllable drug release is described. The carboxylic groups of AA provide a pH-responsive and DOX-holding ability of the polymer matrix, while sulfur groups of BAC provide a covalent immobilization of the AA-BAC microgel onto the gold electrode surface. The microgel is responsive to electrochemically generated pH decrease due to ascorbate oxidation. As a result of the local pH drop on the electrode interface electrostatic attraction between the carrier and the positively charged DOX diminishes, which together with the shrinkage of the matrix results in the controlled release of DOX from the microgel. The electrodes modified by microgel based on N,N′-methylene-bis-acrylamide (BIS) as a crosslinker are used as a control. However, AA-BIS microgel does not contain sulfur groups and it can only be not explicitly adsorbed on the gold electrode while the efficacy of this modification is significantly worse compared to covalent immobilization of AA-BAC via sulfur groups of BAC. Thus, electrode surface area covered by adsorbed (AA-BIS)-DOX microgel is approximately estimated as 34% compared to 90% for covalently immobilized (AA-BAC)-DOX microgel.