Detecting cancer risk with a chip

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.

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