Detecting cancer risk with a chip
By Nathan Seppa
Scientists adept at making microscopic machinery have devised a diagnostic
technique that may alert physicians to signs of prostate cancer more effectively
and inexpensively than current tests do.
Physicians screen men for prostate cancer risk by looking for elevated blood
concentrations of a protein called prostate specific antigen, or PSA. The most
commonly used test combines enzymes with antibodies to PSA. Physicians typically
send men with PSA readings greater than 10 nanograms per milliliter (ng/ml) of
blood to get further tests or a prostate biopsy, in which a surgeon removes a
small bit of the gland for analysis.
As an alternative to the strictly enzyme based PSA test, mechanical engineer Arun
Majumdar and his colleagues at the University of California, Berkeley measured PSA
in blood by using a chip mounted with a microcantilever that’s gold-plated on one
side. A cantilever is a beam supported on one end only, such as a diving board. In
this case, a glue holds antibodies that stick to PSA on the cantilever’s gold-plated side.
Over a period of hours, PSA accumulates on the microcantilever. As PSA molecules
attach to the antibodies, they cause the structure to bend. The steeper the
bending, the more PSA is present in the blood sample. The researchers measure the
amount of bending by bouncing a laser beam off the microcantilever and measuring
the deflection.
The researchers tried the new tool on previously tested blood samples with and
without PSA. The microcantilever proved able to detect PSA down to 0.2 ng/ml.
Other proteins added to the mix, including compounds typically found in human
blood, didn’t interfere with the measurements, the researchers report in the
September Nature Biotechnology.
The standard PSA test requires multiple steps, each with a different chemical
reagent, Majumdar says. Also, the test sometimes yields false positives or false
negatives. The former lead to anxiety in men being tested and costly retesting;
the latter can mean missed opportunities for the early detection of cancer.
The microcantilever approach “could be tremendously useful in bringing down
costs,” Majumdar says.
