Stimuli responsive hollow layer-by-layer microcapsules for enzymatic cascade reactions

Stimuli-responsive hollow polymer capsules were prepared through layer-by-layer self-assembly (LbL) technique for use as microreactors. pH-sensitive Tannic Acid (TA), temperature-sensitive poly(2-isopropyl-2-oxazoline) (PiPOX), and the cascade reaction enzymes glucose oxidase (GOx) and horseradish peroxidase (HRP) were used as LbL building blocks. Multilayers were deposited on silica microparticles to form two different stacks. The first stack contained GOx immobilized between PiPOX and TA layers, while the second stack had HRP included between the polymer layers. To obtain a compartmentalized structure, these stacks were separated using a TA/ poly-L-lysine (PLL) pair. The effect of stimuli-induced conformational rearrangement within the capsule wall on the enzymatic cascade reactions was examined at varying pH and temperature conditions. Enzymatic cascade activity was greater under slightly acidic conditions than that at pH 7.4. Activity increased at temperature values (e.g. 37 degrees C) close to the critical temperature of PiPOX, especially when the number of PiPOX layers between the enzyme layers was increased. HeLa cells incubated with LbL capsules showed dose-dependent viability and the capsules exhibited a marked interaction with the cell membrane. Overall, this study generated fundamental knowledge on the structure-property relationship in stimuli-responsive polymer/enzyme hybrid LbL capsules for enzymatic cascade reactions.