A microchip that can detect tiny amounts of a protein associated with prostate and breast cancer could provide an early-warning detection system for the diseases.

Chang Liu, at the University of Illinois at Urbana-Champaign, US, led the team that produced the chip. 'Detecting protein biomarkers with high sensitivity and selectivity is critical for rapid disease diagnosis,' said Liu. Our microchip can detect the cancer indicator prostate specific antigen (PSA) at concentrations as low as 300 copies per microlitre of sample, 'a task akin to fishing out a needle out of a haystack.'

The detection process revolves around two types of particle: gold nanoparticles with hundreds of copies of a DNA 'barcode' attached, and magnetic beads. Both the nanoparticles and beads are attached to antibodies that can bind to PSA. 

Bio-barcodes for cancer detection

When these particles meet PSA, they form a DNA-PSA-magnet complex resembling a sandwich. The complexes can be extracted from the sample using a magnet and, by measuring the total number of DNA barcodes, the sample's PSA level can be calculated. Because there are several hundred copies of DNA barcode for each copy of PSA, detecting tiny amounts of the antigen becomes much easier, said Liu.

The team's aim was to fit all the stages of this complex process onto a single microchip that could be used at the point of care, removing the need to send samples away for analysis, explained Liu. The group is currently working on microchips to detect proteins used to diagnose testicular cancer and Alzheimer's disease.

Larry Kricka, professor of pathology and laboratory medicine at the University of Pennsylvania, US, agrees that the microchip is 'an important step forward.' However, he highlights the need for a detailed study into how complex biological specimens, such as human serum, will affect the microchip. Unforeseen interactions between sample and chip 'have been the downfall of many new assay methods and formats,' warned Kricka.

Clare Boothby