Solutal and thermal buoyancy effects in self-powered phosphatase micropumps

Abstract

Immobilized enzymes generate net fluid flow when exposed to specific reagents in solution. Thus, they function as self-powered platforms that combine sensing and on-demand fluid pumping. To uncover the mechanism of pumping, we examine the effects of solutal and thermal buoyancy on the behavior of phosphatase-based micropumps, using a series of reactants with known thermodynamic and kinetic parameters. By combining modeling and experiments, we perform the first quantitative comparison of thermal and solutal effects in an enzyme micropump system. Despite the significant exothermicity of the catalyzed reactions, we find that thermal effects play a minimal role in the observed fluid flow. Instead, fluid transport in phosphatase micropumps is governed by the density difference between the reactants and the products of the reaction. This surprising conclusion suggests new design principles for catalytic pumps.

Enzymatically Powered Surface‐Associated Self‐Motile Protocells

“…In a recent study, Balazs and Sen and co-workers measured the solvent flow that emanated from immobilized enzymes, examining a panel of different substrates that could be catalyzed by the same enzyme, each of which had widely different heat generation. [31] The flow most closely correlated not with the exothermicity of the reaction, but rather the difference in osmolarity between reactants and products. It is also possible that the conformational change of the enzymes during turnover leads to an impulsive force.…”

“…Two other possibilities are that the enzymatic reaction generates a local pressure wave, emanating from the local difference in osmolarity between reactants and solutes, or that the enzymes undergo conformational changes that generate forces. In a recent study, Balazs and Sen and co‐workers measured the solvent flow that emanated from immobilized enzymes, examining a panel of different substrates that could be catalyzed by the same enzyme, each of which had widely different heat generation . The flow most closely correlated not with the exothermicity of the reaction, but rather the difference in osmolarity between reactants and products.…”

“…For self‐phoresis, an asymmetric distribution of reaction products in vicinity of the enzyme creates corresponding shear or osmotic flows. Sen and Balazs and co‐workers have presented a theoretical model for micropumps driven by surface bound enzymes . When substrate‐loaded microparticles release substrate near an enzyme patch, the subsequent enzymatic reaction leads to spatial variation in the fluid density that causes convectional flow, which in turn induces a directional motion of substrate‐loaded microparticles.…”

“…Sen and Balazs and co-workers have presented a theoretical model for micropumps driven by surface bound enzymes. [28][29][30][31] When substrate-loaded microparticles release substrate near an enzyme patch, the subsequent enzymatic reaction leads to spatial variation in the fluid density that causes convectional flow, which in turn induces a directional motion of substrate-loaded microparticles. In enzyme fluctuation, the continuous deformation of enzymes during substrate turnover leads to a propulsive force.…”

Dynamic Coupling at Low Reynolds Number

“…[22][23][24][25][26][27][28][29][30][31] These systems offer unprecedented opportunities to understand local energy transduction in colloidal systems and explore possibilities to harness non-equilibrium phenomena for useful applications.I nr ecent years,r esearch in this direction has resulted in many interesting designs and propulsion strategies for artificial micro-and nanomachines-with demonstrations on their futuristic applications as sensors, [32][33][34][35] assemblers, [36][37][38][39] and fluid pumps. [40][41][42][43] Thet ransport properties of active systems have,i ns everal reports,b een shown to be distinctly different from those at equilibrium. [44][45][46][47] This allows them to exhibit many anomalous features,including enhanced fluid mixing, [12,[48][49][50] work extraction from fluctuations, [51,52] unusual rheology, [53][54][55][56][57][58] and complex interparticle interactions.…”