26 January 2018

One chip instead of thousands of test tubes

A new system for manipulating liquid droplets will allow you to study thousands of reactions simultaneously

DailyTechInfo based on materials Phys.org : Using electric fields to manipulate droplets on a surface could enable high-volume, low-cost biology experiments

Researchers from the Massachusetts Institute of Technology have developed equipment that uses electric fields to move individual droplets of liquid solutions of chemicals and biological components. This, in turn, allows you to mix arbitrary combinations of reagents and study thousands of chemical reactions at the same time. This equipment is an alternative to microfluidic devices currently used in chemistry and biology, in which solutions move in microscopic channels through the use of micro pumps and valves, and are mixed in special cavities-reactors.

The main problem successfully solved by the researchers was the creation of a superhydrophobic coating of the working area, which covers a printed circuit board with rows of electrodes. The properties of this coating significantly reduce the friction forces, which allows the droplets to slide freely on the surface. In addition, the superhydrophobic coating prevents droplets from leaving traces behind them, which prevents contamination of some reagents with traces of others and maintains the purity of the experiments conducted.

The superhydrophobic properties of the new coating were obtained by creating a dense matrix of tiny microspheres on its surface. Now researchers are experimenting with surfaces covered with nanostructures of other shapes and sizes, some of which work better with certain types of biological fluids.

Since the surface has superhydrophobic properties, the droplets placed on it try to take a shape as close to spherical as possible. The electrical potential applied to the electrodes of the printed circuit board attracts droplets to the surface. And if you remove the potential from the electrode located under the droplet and apply it to the electrode located next to it, the droplet, sliding along the surface, will begin to move towards this electrode.

To control the movement of droplets, an electric potential in the range from 95 to 200 Volts is used. At the same time, high-voltage signals with a frequency of 1 kilohertz and low-voltage (3.3 Volts) signals with a frequency of 200 kilohertz are fed to the electrodes at certain intervals. A high-frequency low-voltage signal allows you to determine the current location of a liquid drop using the same principle used in touch displays. And a low-frequency high-voltage signal just causes liquid droplets to move.

If the droplet does not move at the set speed, the system automatically increases the voltage of the high-voltage low-frequency signal. In addition, based on the data on the position of the droplet, its speed of movement and the magnitude of the applied potential, the system can calculate the volume and mass of the liquid contained in it.

The signals supplied to the electrodes of the printed circuit board are controlled by a computer. This allows you to control thousands of droplets at the same time, which will move, mix and inside which certain chemical reactions will take place. All this is done completely automatically in accordance with the program embedded in the computer.

"The operator only needs to set a sequence of high–level operations of the type, reagent A must mix with reagent B in a certain proportion, and after a given time mix with a certain amount of reagent C," the researchers write. "The system will do everything else automatically in real time, including calculating the trajectories of the reagent droplets."

The introduction of the new technology, the researchers believe, will significantly reduce the cost of conducting complex chemical and biological research. Pharmaceutical companies, for example, will be able to experience the impact on one type of pathogenic microorganisms of several types or variants of medicines at once. Moreover, special robots will be able to conduct such studies, which will operate according to a single program, part of which will be a program for controlling the movement of droplets of the reagents under study.

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