Catalytic Conveyer Belt

A new method for controlled delivery of particles via fluid flow

Particles transported along a channel by chemically-driven fluid flow. The flow is generated by reagent entering at one end of the channel (A) and reacting at the enzyme covered surface. The cargo is deposited at position B, which can be controlled by varying the reaction rate. Image: Balazs Laboratory, University of Pittsburgh

Researchers have developed a new method of transporting particles that utilizes chemical reactions to drive fluid flow within microfluidic devices. The research, which capitalizes on previous studies in self-powered chemo-mechanical movement, is a collaboration between scientists at Penn State’s Department of Chemistry and the University of Pittsburgh’s Swanson School of Engineering. A paper describing the research appeared Feb. 17 in the journal Nature Communications.

The combined theoretical and experimental findings of the research could enable controllable transport of particles and cells, allowing highly sensitive chemical assays to be performed more rapidly and efficiently.

“Utilizing catalytic reactions to drive fluids to controllably transport particulates in solution is a relatively new field,” said Ayusman Sen, distinguished professor of chemistry at Penn State and an author of the paper, “even though it’s what our bodies do at any given moment using food as the power source. Replicating it within a synthetic system however is very difficult. In our lab, we were able to design a ‘machine’ without the need for moving parts, that could be used many times over simply by adding fuel to the chamber, while allowing the particle to remain a passive participant along for the ride.”

“One of the critical challenges in transporting microparticles within devices is delivering the particle to a specific location,” said Anna C. Balazs, distinguished professor of chemical and petroleum engineering at Pitt and the leader of computational modeling for the research team. “Much like a conveyer belt in a factory, you want to move the particle within a closed system without any modification to its surface or damage to its structure.”

In addition to successfully delivering the particles, the other challenges the researchers faced were maintaining unidirectional flow from point A to point B within a closed chamber, and ensuring that a critical concentration of these particles could be delivered to sensors, which only operate above a critical threshold. The solution was to generate a gradient of a chemical reagent between the inlet, point A, and a patch of enzymes on the surface where the reagent is decomposed. A fluid flow, driven by the fluid density variation associated with the reagent concentration, represents the “belt” that conveys the cargo in the solution to the destination, point B.

“Previously, to generate spontaneous propulsion of microparticles, one needed to chemically modify the surface of these particles, thus altering their inherent properties,” said Balazs. “Moreover, modifying the particle’s surface does not necessarily allow you to direct its motion within the chamber. We were able to predicate through our computational models and demonstrate in the experiments performed at Penn State that the flow generated by the catalytic chemical reaction in the chamber could effectively transport particles to a particular sensor, and could permit control over the speed and direction of the particle transport, without having to use an external pump or any modification of the cargo.”

“Additionally, one advantage of the transport system described in the paper is its versatility,” said Alicia Altemose, a graduate student at Penn State and coauthor of the paper. “Either inorganic catalysts or enzymes, which are biocompatible, can be used to drive the fluid flow in the system.”

In addition to Sen, Balazs, and Altemose the research team includes Evan Pugh Professor of Chemistry, Physics, and Biochemistry and Molecular Biology Thomas E. Mallouk and graduate students Sambeeta Das, Isamar Ortiz-Rivera and Lyanne Valdez at Penn State; and postdoctoral associates Oleg E. Shklyaev and Henry Shum at University of Pittsburgh. The research is funded by the Charles E. Kaufman Foundation, the Defense Threat Reduction Agency and the U.S. National Science Foundation.