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.

Autonomous macroscopic signal deciphering the geometric self-sorting of pillar[n]arenes.

In this communication, we have deciphered the geometric self-sorting of pillar[n]arenes by analyzing the fluid flow pattern obtained during the self-assembly of complementary pillar[n]arenes on the surface. The concept was further extended to demonstrate flow manipulation inside a microchannel where multiple sites were available for self-sorting, and the resultant flow velocity was tuned by the feeding ratio of the complementary pairs.

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.

Anisotropic Compartmentalization of the Liquid-Liquid Interface using Dynamic Imine Chemistry.

The liquid-liquid interface offers a fascinating avenue for generating hierarchical compartments. Herein, the dynamic imine chemistry is employed at the oil-water interface to investigate the effect of dynamic covalent bonds for modulating the droplet shape. The imine bond formation between oil-soluble aromatic aldehydes and water-soluble polyethyleneimine greatly stabilized the oil-water interface by substantially lowering the interfacial tension. The successful jamming of imine-mediated assemblies was observed when a compressive force was applied to the droplet. Thus, the anisotropic compartmentalization of the liquid-liquid interface was created, and it was later altered by changing the pH of the surrounding environment. Finally, a proof-of-concept demonstration of a pH-triggered cargo release across the interfacial membrane confirmed the feasibility of stimuli-responsive behavior of dynamic imine assemblies.

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.

Modulation of liquid structure and controlling molecular diffusion using supramolecular constructs.

The non-equilibrium liquid structure was achieved by interfacial jamming of pillar[5]arene carboxylic acid (P[5]AA) mediated by hydrogen bonding interactions. The assembly was reversibly modulated via jamming to unjamming transition thus dynamically shaping the liquid droplets. Interestingly, these supramolecular constructs showed pH-switchable gated diffusion of encapsulants, hence showcasing a next generation smart release system.

Valveless flow reversal by a pH responsive supramolecular micropump.

A valveless micropump was designed via dynamic supramolecular interaction between beta-cyclodextrin (ß-CD) and benzimidazole (BzI). It shows flow reversal in response to the pH change. An L-shaped microchannel was used to demonstrate the flow reversibility over long distances.

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

In view to develop an autonomous lab-on-a-chip device for detection of toxins without using any spectroscopic or electrochemical equipment, self-powered enzyme micropumps were fabricated via layer-by-layer assembly of enzymes and polyelectrolytes. The thin film-based enzyme micropumps turned on fluid flow in the presence of respective substrates in a concentration-dependent manner, and the rate of the enzymatic reaction was the key for maneuvering the fluid flow. Furthermore, the newly engineered enzyme-based micropumps were able to detect toxic metals and organophosphorus pesticides by modulating the fluid flow speed as the rate of the enzymatic reaction was altered by the presence of inhibitors. Thus, by regulating fluid flow in a micropump, low concentrations of analytes (e.g., target biomarkers and inhibitors) in biological fluids can be quantitatively identified for testing in a resource-constrained environment.

Pillar[5]arene microcapsules turn on fluid flow in the presence of paraquat.

We report the fabrication of pillar[5]arene (P[5]A) stabilized MCs via the self-assembly and crosslinking of P[5]A nanoaggregates at the liquid-liquid interface. These MC microengines turn on fluid flow in the presence of paraquat (PQ) due to "host-guest" molecular recognition. The microengines could be useful in designing non-mechanical micropumps, powerless microfluidics, and diagnostic devices.