Single-Molecule Assay Detects Cancer

A Massachusetts company has developed an assay that is 1,700 times more sensitive for detecting a cancer biomarker than existing tests (Nat. Biotechnol., DOI: 10.1038/nbt.1641). The technology, which Cambridge-based Quanterix calls SiMoA (single-molecule array), uses femtoliter-sized chambers to individually isolate antibody-coated microbeads that trap single biomarker molecules. Labeling the biomarker with an enzyme permits its detection by fluo­res­cence microscopy. Quanterix researchers led by David C. Duffy in collaboration with Tufts University’s David R. Walt have shown SiMoA’s effectiveness in detecting prostate-specific antigen (PSA) in blood samples. PSA is produced by the prostate in exponentially higher levels when cancer is present in the gland. Current assays measure PSA concentrations down to 10^–12 M, but the Quanterix assay allows PSA detection in blood at concentrations of 10^–15 M, the researchers note. Duffy says a simple blood test using SiMoA could detect any residual cancer or cancer recurrence after surgery. The technology is due to launch in 2011 with clinical studies to follow, he adds. The researchers hope the ability to detect single protein molecules will accelerate the discovery of additional concentration-sensitive diagnostic biomarkers that lend themselves to monitoring diseases.