Substrate-Controlled\nBidirectional Pumping by a Bienzymatic\nMicropump

The development of autonomous, miniaturized\npumps remains\na problem\nof much interest, particularly with a view on microfluidics-based\ndevices with increased portability and simplicity of use by nonspecialists.\nSpatially localized patches of enzyme imprinted on walls have been\nshown to induce a hydrodynamic flow when supplied with the corresponding\nenzyme substrate. Thus, such enzymatic micropumps are seen as a possible\nway of providing the means for nonmechanical, structurally simple,\nautonomous pumping. Hereby, we extend the current knowledge of enzymatic\nmicropumps in two ways. First, we introduce β-glucosidase as\nan enzyme that facilitates building micropumps with robust inward\nflows in the presence of cellobiose (e.g., 2.51 ± 0.56 μm\ns<sup>–1</sup> in the presence of 80 mM cellobiose). Second,\nwe embed β-glucosidase and urease within the same patch and\nthus obtain a bienzymatic micropump. The latter exhibits the so far\nmissing capability of bidirectional pumping as it produces inward\nflows in the presence of cellobiose (e.g., 0.95 ± 0.37 μm\ns<sup>–1</sup> in the presence of 20 mM cellobiose) and outward\nflows in the presence of urea (e.g., 1.46 ± 0.47 μm s<sup>–1</sup> in the presence of 20 mM urea). This bienzymatic\nmicropump is a significant step for the development of biocompatible\nmicropumps with versatile, controlled, and on-demand hydrodynamic\npumping capabilities.