Harvard researchers combine optics and microfluidics to improve lab-on-a-chip devices

Cambridge, MA--Harvard University researchers have successfully combined a silicone rubber stick-on sheet containing dozens of miniature, powerful lenses with lab-on-a-chip devices—a marriage of high-performance micro-optics and microfluidics that could bring researchers one step closer to putting the capacity of a large laboratory into a micro-sized package.

Microfluidics, the ability to manipulate tiny volumes of liquid, is at the heart of many lab-on-a-chip devices. Such platforms can automatically mix and filter chemicals, making them ideal for disease detection and environmental sensing. The performance of these devices, however, is typically inferior to larger scale laboratory equipment. While lab-on-a-chip systems can deliver and manipulate millions of liquid drops, there is not an equally scalable and efficient way to detect the activity, such as biological reactions, within the drops.

The Harvard team’s zone-plate array optical detection system, described in an article appearing in the journal Lab on a Chip, may offer a solution. The array, which integrates directly into a massively parallel microfluidic device, can analyze nearly 200,000 droplets per second; is scalable and reusable; and can be readily customized.

“In essence, we’ve integrated some high performance optics onto a chip that contains microfluidics as well. This allows us to be able to parallelize the optics in the same way that a microfluidic device parallelizes sample manipulation and delivery,” says Ken Crozier, an associate professor of electrical engineering at Harvard’s School of Engineering and Applied Sciences (SEAS), who directed the research.

Unlike a typical optical detection system that uses a microscope objective lens to scan a single laser spot over a microfluidic channel, the team’s zone-plate array is designed to detect light from multiple channels simultaneously. In their demonstration, a 62 element zone-plate array measured a fluorescence signal from drops traveling down 62 channels of a highly parallel microfluidic device. The device works by creating a focused excitation spot inside each channel in the array and then collects the resulting fluorescence emission from water drops traveling through the channels, literally taking stop-motion pictures of the drops as they pass.

The system can detect nearly 200,000 drops per second, or about four times the existing state-of-the-art detection systems. Further, the lens array is scalable, without any loss in efficiency, and can be peeled on-and-off like a reusable sticker. Ultimately, the integrated design offers the sensitivity of a larger confocal microscope and the ability to measure over a larger area, all in a much smaller, cheaper package.

The researchers, who have filed a patent on their invention, are optimistic that with further research and development, the device could enhance a range of microfluidic and microfluidic-based lab-on-chip devices and speed the advance of using them for applications such as in-the-field biological assays.

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