To detect DNA, chemists coat gold nanoparticles with multiple strands of DNA that are complementary to the target DNA sequence. Once these nanoparticles bind to the target DNA, they are captured on a microarray that has also been decorated with complementary strands of DNA. As light passes through the array, it’s scattered by the particles, creating a pattern that can be captured with a digital camera sensor. By varying the location and density of the DNA on the array, researchers can determine the concentration of the DNA in a sample, as well as look for multiple genetic markers with one test.
Detecting proteins requires an additional step, since the DNA strands will not attach specifically to proteins. In place of DNA, Nanosphere scientists use antibodies to capture a target protein. They attach these antibodies to magnetic beads, which pull the protein out of a blood sample using a magnetic field. They also attach antibodies to gold nanoparticles, causing these particles to stick to the protein. As with the DNA detection method, these gold particles bear strands of DNA, but here these strands act, not as links to the target protein, but as labels – hundreds of them for each protein. This DNA can then readily be detected by the same microarray detection method.
Mirkin says that the Nanosphere technology is orders of magnitude more sensitive than other detection techniques, as well as fast and accurate. What’s more, the technology detects DNA or proteins directly, does not require expensive and time-consuming preparation of blood samples, and can test for multiple targets at once. “It will completely change the way the world looks at diagnostics, he says. “I’m very confident that we’re going to see a lot of new diagnostic tools come out of this.”