Bio-CDs Could Transform Blood Testing

Since the concentration of certain proteins in the bloodstream can indicate the onset of many diseases, a cheap, quick method of detecting these molecules would be a big breakthrough. Currently, when blood samples are sent to a laboratory for analysis, only a few of the thousands of blood proteins are screened, and the process is costly and time consuming.

"This technology could revolutionize medical testing,” said David D. Nolte, leader of the research team and a professor of physics in the School of Science at Purdue. "We have patented the concept of a ‘bio-optical CD,' which could be a sensitive and high-speed analog sensor of biomolecules. Technology based on this concept could provide hospitals with a fast, easy way to monitor patient health.”

Ordinarily, CDs store digital information as billions of tiny "pits” in their surface. Representing ones or zeroes, depending on their size, the pits are etched in concentric tracks circling the midpoint from the inner to the outer edge of a CD. "It is these pits which we transform into miniature test tubes,” said Prof. Nolte. "Each pit can hold a trace quantity of a chemical that reacts to a certain protein found in the blood.”

Blood contains more than 10,000 proteins that doctors would like to monitor, and up to 10,000 tracks on a CD could be paired up with a different protein. "Once the surface of a Bio-CD has been exposed to a blood serum sample, which would not need to be larger than a single drop, you could read the disk with laser technology similar to what is found in conventional CD players,” explained Prof. Nolte. "However, instead of seeing digital data, the laser reader would see how concentrated a given protein had become on each track.”

Each pit is only a few micrometers in diameter but is still large enough to hold many thousands of individual detector molecules, each of which could pair up with and bond to a single protein molecule. The pits' capacity would make the Bio-CDs an analog, rather than merely digital, screening tool. "Because many detector molecules can theoretically be deposited on the surface of each pit, the CDs should measure concentrations with high sensitivity,” noted Prof. Nolte. "If the concentration of a given protein is high, many detector molecules will snag a partner from a sample; if it's low, only a few will pair up.”

In recent experiments, the team has demonstrated a sensitivity of 10 nanograms per millileter, with a selectivity greater than 10,000. These numbers are high enough to warrant the making of a working prototype Bio-CD that can seek biologically relevant molecules.

"CDs and CD drives are very cheap to manufacture, and the changes that would need to be made to transform them into bio-assays are not unreasonable,” added Prof. Nolte.
The changes would include exposing the pitted surface of the CD, ordinarily protected by an acrylic coating, and depositing the plethora of detector molecules onto the CD track by track.

"While in principle they can be developed, significant work will need to be done to refine these techniques sufficiently,” noted Prof. Nolte. "It will be at least 10 years before doctors have Bio-CDs at their disposal, and that assumes everything goes smoothly in the interim.”

Bio-CDs would use a modified version of the technology used in standard CD players, but instead of containing digital data, their surfaces would hold molecules that could detect levels of proteins in blood samples.