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CUE 2004

CHEMICAL AND BIOLOGICAL ENGINEERING
Detecting Toxins on a Micro-Scale with Microfluidic Devices

Graduate student Bobby Sebra uses a novel technique for micro-shaping plastic materials to create microfluidic devices that can be used for biological analyses.

The industrial development we see today would have looked very different if it weren"t for plastics. Their low cost and excellent mechanical properties, combined with an almost limitless number of material properties, make plastics useful in everything from packaging to construction materials. Most researchers realize these advantages also would translate very well to the latest trend in engineering: miniaturization.

Given that plastics are vastly superior to other potential materials, it is surprising that most microfluidic devices sold today are made using glass and silicon substrates. These structures are designed to manipulate minute amounts of liquids by enclosing them in tiny vessels and channels, where dimensions are smaller than the human hair. Microfluidic devices, which are particularly important in biological analyses where manipulation and analysis of small samples is critical, make it possible to reduce reaction times and use of expensive reagents while retaining or surpassing accuracy, detection limits, and reaction speed compared to their macroscopic counterparts.

The reasons for the low use of plastics in manufacturing these devices stem from the difficulties in using traditional techniques for shaping plastics into highly complex microstructures. To address these issues, a research group composed of CU-Boulder Professors Kristi Anseth, Christopher Bowman, and Robert Davis in the Department of Chemical and Biological Engineering has invented a novel technique for micro-shaping plastic materials.

The technique makes use of traditional photolithography—defining a pattern with a photomask, exposing transparent regions in the mask with ultraviolet light to polymerize a liquid plastic precursor, and rinsing off the excess liquid to obtain a durable plastic microstructure. While the basic approach has been used for decades, the CU team allows the liquid to contact the photomask, leading to dramatic improvements over standard photolithographic methods such as spin coating. With this new method, the solid layer takes on the flat shape of the mask, and layer thickness is easily dialed in when the sample is in its liquid state through a moveable bottom plate. In this way, tailored properties for each component in a plastic microfluidic device can be achieved.

Using this technique, microfluidic devices can be fabricated for a wide variety of applications, including detection of biological and chemical hazards, point-of-care medical diagnostics, and other common biological and chemical analyses. One particularly critical application the CU group is working on is the detection of certain biological species caused by the onset of a disease. Through the use of a wide variety of surface-attached biomolecules that can be spatially patterned on these devices, a number of different disease-specific toxins can be captured in miniature detection wells and indicated by a color change on the device in as little as 10 minutes.

When compared with more traditional methods for disease and toxin detection, which can take hours or even days of laboratory analysis, it is clear that microfluidic devices could have a profound impact. Soon, we could be purchasing micro-devices for detecting bacteria, disease or other toxins in our water, food, or bodies.

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