Overcoming Evaporation For Miniaturization

By using non-volatile ionic solvents, scientists have circumvented one of the major obstacles to lab-on-a-chip miniaturization.

AsianScientist (May 8, 2014) – Researchers have invented a new type of lab-on-a-chip device that could have a diverse range of applications, including the detection of toxic gases, fabrication of integrated circuits and screening of biological molecules.

The novel technique, developed by a team at the University of New South Wales (UNSW), involves printing a pattern of minuscule droplets of a special solvent onto a gold-coated or glass surface. The research has been published in the journal Nature Communications.

“We use a class of ‘green’ solvents called ionic liquids, which are salts that are liquid at room temperature. They are non-volatile, so this overcomes one of the main problems in making useful miniaturized devices – rapid evaporation of the solvents on the chip,” says Dr. Zhao Chuan, senior author of the study.

“The versatility of our chips means they could have a wide range of prospective functions, such as for use in fast and accurate hand-held sensors for environmental monitoring, medical diagnosis and process control in manufacturing.”

Lab-on-a-chip devices, where chemical reactions are carried out on a miniature scale, are under intensive development because they offer the promise of faster reaction times, reduced use of materials and high yields of product.

Evaporation of solvents on the chip, however, is a big problem because this can affect the concentration of substances and disrupt the reactions. Attempted solutions include containing the solvents within tiny channels or “walls”, and having reservoirs to store extra solvent on the chip.

The “wall-less” design developed by the UNSW team – using non-volatile ionic liquids as solvents to fabricate a microarray of droplets chemically anchored to the chip – has several significant advantages.

“Ionic liquids are designer solvents and have wide application. We can now carry out many reactions or analytical procedures in ionic liquids at the micro-scale on a chip with enhanced yields and efficiency,” says Zhao.

“These microarray chips can be easily produced in high numbers and are very stable. They can survive being turned upside down and heated to 50 degrees and some can even survive being immersed in another liquid. These properties will be important for commercial applications, including storage and transportation of microchips.”

The droplets of ionic liquid are about 50 micrometers across (about half the width of a human hair) and ten micrometers high.

The UNSW researchers demonstrated several potential uses of the microarrays. They showed the tiny droplets can act as rapid, sensitive monitors of the presence of a gas, due to their small volume. They also demonstrated that metal salts dissolved in the droplets could be electrically deposited as microstructures, a technique which could be of use in fabrication of integrated circuits.

Some biological molecules added to the droplets also remained stable and active, opening up the possibility of using the microarrays for diagnostic purposes.

The article can be found at: Gunawwan et al. (2014) Robust and Versatile Ionic Liquid Microarrays Achieved by Microcontact Printing.

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Source: University of New South Wales.

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