In an office park in Woburn, MA, a volunteer presents his fingertip for a quick finger stick. A phlebotomist wicks up the small drop of blood with a specially made square of plastic, then snaps the plastic into a credit-card sized microfluidics cartridge and feeds it into a special reader. Fifteen minutes later, the device spits out the volunteer's prostate specific antigen (PSA) level, a protein used to monitor the return of prostate cancer after treatment.

The rapid results are possible because of a novel microfluidics technology developed by startup Claros Diagnostics, which hopes to make quick PSA monitoring in the doctor's office a reality. If approved by the U.S. Food and Drug Administration, the device will be one of the first examples of long-awaited microfluidics-based diagnostics tests that can be performed in the hospital or doctor's office. While microfluidics--which allows for the manipulation of fluids on a chip at microscopic scales--has been around for a decade, the complexity and expense has kept it largely limited to research applications.

Claros's technology, which consists of a small blood-collector device, a disposable cartridge, and a toaster-sized reader, could, in theory at least, be adapted to detect any number of different proteins. But the company has initially chosen to focus on PSA, which is routinely monitored. With current testing, blood samples are typically sent to a centralized lab for PSA analysis. Results are returned in a day or two. Claros's test, now in clinical trials, would allow PSA readings to be determined during the patient's visit. While there is debate over how useful PSA testing is in diagnosing cancer, it is a well-accepted tool for monitoring those who have it. Within a month after prostate surgery, a man's PSA levels drops--a subsequent increase suggests that PSA producing cancer cells have returned.

"Having a quick PSA test that is accurate would certainly be helpful to most urologists--simple and inexpensive being the two key words," says Jerome Richie, chief of urology at Brigham and Women's hospital in Boston. But he says that such a test must be able to accurately analyze the low levels of PSA that are present after prostate surgery.

Key to Claros's device is its ability to perform the test on a small drop of blood. The surface of the cartridge is covered in narrow channels, which serve as both storage for the chemicals needed for the assay and as tiny test tubes in which to carry out the reaction. Each reagent is lined up sequentially in one long channel and separated by small air bubbles. Once the cartridge is inserted into the reader, a vacuum pulls the blood through one channel and delivers the appropriate sequence of reagents. This approach avoids the pumps used to move chemicals in other microfluidics chips, enabling a simple and robust design with no moving parts. The reader itself is simple, using an LED and photodiode to detect the buildup of silver--the output of the reaction--on the cartridge. The more silver, the less light passes through the chip and the higher the PSA level.