Cambridge (MA) startup Quanterix is developing a protein-detection technology that can count single molecules in blood samples.

The technology uses “microwells” etched into an optical fiber and coated with protein-capturing antibodies. Each well is 2.5 micrometers wide and sits at the tip of an individual thread of the fiber. If the antibodies capture a protein from a blood sample, a chemical reaction will be triggered and fluoresce when light is sent up the fiber. The concentration of a protein in a blood sample is indicated by the number of microwells that light up.

With current clinical technologies, hospital labs can detect only the most abundant proteins–only a quarter of all those known to be present in the blood. In tests, the optical-fiber method was able to detect a human cancer biomarker in cow’s blood at concentrations 250 times lower than that possible using clinical techniques.

It could potentially detect the trace amounts of characteristic proteins that tiny tumors release into the blood. Trace proteins could also reveal early signs of heart disease, Alzheimer’s, and other ailments, and enable noninvasive fetal diagnostics.