Maneuvering Fluid Motion and Flow-Induced Detection of Toxins by Enzyme Multilayer Films

Substrate-Controlled Bidirectional Pumping by a Bienzymatic Micropump

The development of autonomous, miniaturized pumps remains a problem of much interest, particularly with a view on microfluidics-based devices with increased portability and simplicity of use by nonspecialists. Spatially localized patches of enzyme imprinted on walls have been shown to induce a hydrodynamic flow when supplied with the corresponding enzyme substrate. Thus, such enzymatic micropumps are seen as a possible way of providing the means for nonmechanical, structurally simple, autonomous pumping. Hereby, we extend the current knowledge of enzymatic micropumps in two ways. First, we introduce β-glucosidase as an enzyme that facilitates building micropumps with robust inward flows in the presence of cellobiose (e.g., 2.51 ± 0.56 μm s-1 in the presence of 80 mM cellobiose). Second, we embed β-glucosidase and urease within the same patch and thus obtain a bienzymatic micropump. The latter exhibits the so far missing capability of bidirectional pumping as it produces inward flows in the presence of cellobiose (e.g., 0.95 ± 0.37 μm s-1 in the presence of 20 mM cellobiose) and outward flows in the presence of urea (e.g., 1.46 ± 0.47 μm s-1 in the presence of 20 mM urea). This bienzymatic micropump is a significant step for the development of biocompatible micropumps with versatile, controlled, and on-demand hydrodynamic pumping capabilities.

Programming Fluid Motion Using Multi-Enzyme Micropump Systems

In the presence of appropriate substrates, surface-anchored enzymes can act as pumps and propel fluid through microchambers. Understanding the dynamic interplay between catalytic reactions and fluid flow is vital to enhancing the accuracy and utility of flow technology. Through a combination of experimental observations and numerical modeling, we show that coupled enzyme pumps can exhibit flow enhancement, flow suppression, and changes in the directionality (reversal) of the fluid motion. The pumps' ability to regulate the flow path is due to the reaction selectivity of the enzymes; the resultant fluid motion is only triggered by the presence of certain reactants. Hence, the reactants and the sequence in which they are present in the solution and the layout of the enzyme-attached patches form an "instruction set" that guides the flowing solution to specific sites in the system. Such systems can operate as sensors that indicate concentrations of reactants through measurement of the trajectory along which the flow demonstrates a maximal speed. The performed simulations suggest that the solutal buoyancy mechanism causes fluid motion and is responsible for all of the observed effects. More broadly, our studies provide a new route for forming self-organizing flow systems that can yield fundamental insight into nonequilibrium, dynamical systems.

Supramolecular Modulation of Fluid Flow in a Self-Powered Enzyme Micropump

Regulating macroscopic fluid flow by catalytic harnessing of chemical energy could potentially provide a solution for powerless microfluidic devices. Earlier reports have shown that surface-anchored enzymes can actuate the surrounding fluid in the presence of the respective substrate in a concentration-dependent manner. It is also crucial to have control over the flow speed of a self-powered enzyme micropump in various applications where controlled dosing and mixing are required. However, modulating the flow speed independent of the fuel concentration remains a significant challenge. In a quest to regulate the fluid flow in such a system, a supramolecular approach has been adopted, where reversible regulation of enzyme activity was achieved by a two-faced synthetic receptor bearing sulfonamide and adamantane groups. The bovine carbonic anhydrase (BCA) enzyme containing a single binding site favorable to the sulfonamide group was used as a model enzyme, and the enzyme activity was inhibited in the presence of the two-faced inhibitor. The same effect was reflected when the immobilized enzyme was used as an engine to actuate the fluid flow. The flow velocity was reduced up to 53% in the presence of 100 μM inhibitor. Later, upon addition of a supramolecular "host" CB[7], the inhibitor was sequestered from the enzyme due to the higher binding affinity of CB[7] with the adamantane functionality of the inhibitor. As a result, the flow velocity was restored to ∼72%, thus providing successful supramolecular control over a self-powered enzyme micropump.

Discrimination of enantiomers and constitutional isomers by self-generated macroscopic fluid flow

The amplification of weak molecular signals to visible output could provide a gateway to the macroscopic world. In this context, supramolecular interfaces were designed by depositing macrocyclic "host" molecules in a multilayer film that can be utilized to discriminate isomers by their fluid flow response upon "host-guest" molecular recognition.

A visible-light activated ROS generator multilayer film for antibacterial coatings

The current scenario of antibiotic-resistant bacteria and pandemics caused by viruses makes research in the area of antibacterial and antiviral materials and surfaces more urgent than ever. In this regard, salicylideneimine based tetracoordinate boron-containing organic compounds are emerging as a new class of photosensitizers for singlet oxygen generation. However, the inherent inability of small organic molecules to be processed limits their potential use in functional coatings. Here we show the synthesis of a novel polymer functionalized with diiodosalicylideneimine-boron difluoride (PEI-BF2) and its utility for surface coating inside glass vials via layer-by-layer (LbL) assembly. The multilayer thin films are characterized using AFM and UV-Vis spectroscopy and the resultant coatings display excellent stability. The multilayer coating could be activated using visible light, and owing to the photocatalytic activity of the incorporated PEI-BF2, the surface coating is able to generate singlet oxygen efficiently upon light irradiation. Further, the multilayer coated surfaces exhibit remarkable antimicrobial activity towards both Gram-positive and Gram-negative bacteria under a variety of conditions. Thus, owing to the simple synthesis and the convenient methodology adopted for the preparation of multilayer coatings, the material reported here could pave the way for the development of sunlight activated large area self-sterile surfaces.

Polymer multilayer films regulate macroscopic fluid flow and power microfluidic devices via supramolecular interactions

Self-powered supramolecular micropumps could potentially provide a solution for powerless microfluidic devices where the fluid flow can be manipulated via modulating non-covalent interactions. An attempt has been made to fabricate thin-film-based micropumps by depositing a β-cyclodextrin ('host') functionalized polymer on a glass slide via layer-by-layer assembly. These supramolecular micropumps turned on the fluid flow upon addition of 'guest' molecules to the multilayer films. The flow velocity was tuned using the concentration of the guest molecules as well as the number of host layers inside the multilayer films. Numerical modelling reveals that the solutal buoyancy, which originates from host-guest complexation, is primarily responsible for the fluid flow. In view of its potential application in self-powered devices, the thin-film-based micropump was integrated into a microfluidic device to show molecular and colloidal transport over long distances.

Inhibitory effect of nucleotides on acetylcholine esterase activity and its microflow-based actuation in blood plasma

The inhibitory effect of nucleotides on the catalytic activity of acetylcholine esterase (AChE) was rationalized and similar inhibition trend was observed when analyzing the macroscopic fluid flow generated by surface...

Fluid actuation and buoyancy driven oscillation by enzyme-immobilized microfluidic microcapsules

Mimicking microorganism's locomotion and actuation under fluid is difficult to realize. To better comprehend the motility in non-living matter, self-propelled synthetic systems are being developed as a fast-growing area of research. Inspired by the self-powered enzyme micropumps where the enzyme catalysis was harnessed to create motion, herein, enzyme-immobilized microfluidic microcapsules (MCs) were used as a microscale engine to maneuver the fluid flow. The fluid actuation was tuned by various parameters such as substrate concentration, reaction rate, diameter of MCs and the population of the MCs inside the flow chamber. The same MCs, when suspended in a solution, showed buoyancy driven motility by creating oxygen bubbles via an enzymatic reaction and the velocity of the MCs was directly dependent on the number of nucleated oxygen bubbles generated on the MC surface.