Microcontact Printing Update for Microfluidic Assays

Microfluidic bioassay devices can indicate the likelihood of a disease based on a comparison of biomarker concentrations in a sample relative to the normal level. To detect this concentration, the patient’s sample is passed across a surface containing immobilized bioreceptors, or “biomarker-capturing” molecules that have been attached to this surface. A researcher can then record biomarker abundance, determine whether the level is normal and reach a diagnosis.

Since the efficiency of these devices relies on how intact and functional the attached bioreceptors are, immobilizing without damaging the bioreceptors has proved daunting. Over the last two decades, microcontact printing, which uses a rubber stamp to immobilize the bioreceptors, has been established as a robust method to create a variety of assays with multiple applications. Yet this method also has its flaws, particularly at the nano scale required to assay proteins and DNA.

A new sequence of printing steps that have rectified these diagnostic issues was developed by researchers 

One stamp allows for multiple tests and diagnoses on a single surface. Image credit: Okinawa Institute of Science and Technology Graduate Universityfrom Okinawa Institute of Science and Technology Graduate University.

The microprinting stamp is made of polydimethylsiloxane, which is a flexible solid similar to the rubber used in everyday stamps. The ink is a solution composed of silicon- and oxide-containing molecules called APTES, and the surface is glass. After coating the stamp with the ink, the stamp is pressed onto the glass, and then removed after a short incubation. The result is a patterned layer of APTES on the glass—a checkerboard of regions with or without APTES

Next, a microfluidic device containing one or more microchannels configured to guide fluid through specified pathways is sealed over the patterned glass. Bioreceptors are then chemically linked to the APTES regions within the microfluidic channels.

To perform an assay, a fluid sample from a patient is delivered through the microfluidic device attached to the glass. If the pertinent disease biomarker is present, the molecule will “stick” to the areas containing the bioreceptors. One stamp allows for multiple tests and diagnoses on a single surface.

The researchers demonstrated the efficacy of the final device by running an assay to capture the biomarkers interleukin 6 and human c-reactive protein, two substances that are often elevated in the body during inflammation.