Further functionalization with PEI resulted in a lower immobilization yield, but a higher specific activity (Table , compare HeWT_PP3 and TsRTA_PP3 with HeWT_PP2 and TsRTA_PP2 respectively). The enhanced specific activity recovery displayed by TA_PDA_GDE_PEI can be tentatively attributed to a more favorable (hydrated) chemical microenvironment conferred by the PEI layer to the immobilized TAs .