May 2006

Printing Press for Biosensors

Making microparticles in a single step.

By Katherine Bourzac

Biologists have long sought a cheap way to simultaneously detect different types of biological molecules in a sample, such as the several malarial proteins that might be present in a patient's blood. One approach uses polymer tags with bar code-like lines that glow different colors when receptors on the tags bind to specific molecules. But making such tags on a large scale has been prohibitively expensive, as each extra bar line adds another step to the manufacturing process.

Now a group of MIT researchers has created a microfluidic printing press that can produce tiny particles in a single step. In addition to biotags, the method can turn out all kinds of shapes -- from keys to cylinders to swirls -- that could be used to make everything from microelectromechanical machines to optical devices, fabrics, and even the miniature stirring bars and valves used in microfluidics. "This is a beautiful piece of work for continuous synthesis of particles, with great flexibility in the shapes that can be produced," says Howard Stone, a professor of engineering at Harvard University.

The process, developed by an MIT group led by chemical engineer Patrick Doyle, begins with one or several closely spaced, parallel, 100--micrometer--scale streams of liquid. The liquids contain the polymers' precursors, some of which may be bound to proteins that can serve as receptors on a biotag. A flash of ultraviolet light projected through a stencil causes the polymers to solidify in specific shapes. The resulting particles can have several "stripes" -- each created from a separate stream of fluid.