Replacing a high-temperature processing technique with an infrared treatment allows the manufacture of tiny devices without damaging their polymer components.

Microfluidic Chip. Image: Stefan Schlautmann/ Flickr

Microfluidic devices allow microelectronic engineers to shrink laboratories to the size of a computer chip. By ferrying reagents through a series of microscopic channels and reservoirs carved into a flat plate, researchers can develop new chemical reactions or monitor the cellular effects of drugs on a much smaller scale, potentially saving time and money.

Some microfluidic devices have electrical components that act as heaters or sensors. But researchers have struggled to develop a rapid, low-cost method for creating the detailed metal patterns that make up these circuits.

Conventional techniques used to build these circuits tend to require high-temperature processing, which can damage the transparent polymers typically used to build microfluidic devices, such as polycarbonate or poly(methyl methacrylate). Despite this drawback, polymers are preferred over hardier alternatives because they “have very good optical properties, which most microfluidic devices require, and they are viable for plastic injection moulding, which enables high-volume production,” explains Zhaohong Huang of the A*STAR Singapore Institute of Manufacturing Technology.

Huang and his co-workers have developed an alternative process that avoids exposing the polymers to high temperatures. They first cover sheets of polymers with thin layers of chromium, copper and nickel, and add a coating of a light-sensitive material called a photoresist. Huang’s team then uses infrared heating elements to remove any residual solvents. The metal layer acts as a protective barrier, reflecting more than 95% of any infrared radiation that hits it. This means that the radiation warms the photoresist layer but not the polymer beneath.

The researchers then use standard photolithography processes to create the microfluidic device. They place a patterned mask over the sandwich and shine ultraviolet light to erode some areas of the photoresist. They then etch away the exposed areas of metal beneath using a wash of chemicals. This leaves a clean metal pattern, which has features as small as 10 micrometres in width.

“If the surface finish is gold, our method can cut costs by more than 90%,” says Huang. His team is now refining the process and creating patterns of different metals with catalytic properties, which could speed up chemical reactions inside microfluidic devices.



For further information contact:

Zhaohong Huang
Singapore Institute of Manufacturing Technology
Agency for Science, Technology and Research