Looking for a specific protein in a drop of blood is like trying to find a notorious white whale on the seven seas — it takes some time. But a new device quickly filters the ocean of molecules in a blood sample, capturing proteins that may warn of an impending heart attack or out-of-whack insulin levels. Besides detecting potential emergencies, such devices could minimize the fraught days a patient spends waiting for lab results, providing them in mere minutes.
Experiments showed the setup detected various levels of troponin T, a cardiac-regulating protein that can signal an impending heart attack, in less than 10 minutes, researchers from Tel Aviv University report online August 2 in Nano Letters. In the future, people at home who are having chest pains might use the technology to find out quickly whether they need to get to an emergency room, says biomedical chemist Fernando Patolsky.
The sugar-cube–sized lab-on-a-chip consists of two small compartments connected by a thin channel. In the first compartment is a densely packed forest of silicon nanowires coated with antibodies, molecules that latch onto specific proteins. The researchers made these nanowires very rough and full of holes, greatly increasing the surface area for attaching the protein-grabbing antibodies.
“They are so rough and porous we can turn a 1-centimeter-square wafer into a 300-centimeter-square surface,” Patolsky says.
The second compartment also contains silicon nanowires, but these are laid flat and their ends are connected to tiny electrodes. After coating both sets of nanowires with antibodies for the specific protein that the researchers want to catch, a tiny drop of blood (between 50 and 250 microliters) is added to the first compartment.
The thick nanowire forest allows the small proteins in the blood that researchers are looking for to move through and be captured by the antibodies, while blocking out larger things, such as cells, that can clog up the works.
A few minutes after the sample is added, the forest is rinsed with water, and a solution that detaches the target proteins from the antibodies is added. Then this concentrated stream of proteins is sent through the channel to the second compartment. The proteins are snatched up again by the antibodies on the flat nanowires, which changes the amount of electrical current passing through the wires. The researchers read this change in current and can determine how much of the protein in question is present in the blood sample.
“It’s clever,” says biomedical engineer Tarek Fahmy of Yale University. “They are doing separation and concentration on the same chip.”
