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Posted: July 3, 2006
Multiple cancer biomarkers detected simultaneously
(Nanowerk News) Polymerase chain reaction (PCR) technology revolutionized diagnostic medicine and basic research through its ability to amplify and detect minute amounts of specific DNA sequences. Now, using oligonucleotide- and antibody-coated gold nanoparticles, researchers at the Nanomaterials for Cancer Diagnostics and Therapeutics Center for Cancer Nanotechnology Excellence (CCNE) at Northwestern University have developed an analogous technology for proteins that can simultaneously detect trace levels of multiple biomarkers associated with human cancer.
Reporting its work in the Journal of the American Chemical Society ("Multiplexed Detection of Protein Cancer Markers with Biobarcoded Nanoparticle Probes"), a team led by Chad Mirkin, Ph.D., principal investigator of the Northwestern CCNE, describes its development of nanoparticle-based biobarcodes that can detect three different protein tumor markers: prostate specific antigen (PSA); human chorionic gonadotrophin (HCG), a marker for testicular cancer; and α-fetoprotein (AFP), a liver cancer marker. Each protein is detected using a gold nanoparticle coated with an antibody that binds specifically to that protein. Each nanoparticle also contains an oligonucleotide “barcode” whose sequence is specific for each protein and a universal sequence common among all oligonucleotides. The assay also uses a set of three magnetic microparticles, each coated with an antibody that binds specifically to a different portion of the target protein.
To conduct the assay, the investigators “capture” the target proteins using the magnetic microparticle probes. They then add the set of antibody/barcode-labeled nanoparticles, creating sandwiches that have the target proteins in their center. The researchers isolate and wash the sandwiches with the help of a magnetic field. This last step has the effect of removing all of the unbound nanoparticles and microparticles from the test solution.
Next, the investigators add a chemical that causes the barcodes to wash off the nanoparticles and identify the barcodes using a chip-based optical method. Each barcode has a unique optical signature, making it relatively easy to distinguish among them and detect each of the three proteins uniquely. The assay is capable of selectively detecting each of the target proteins at concentrations as low as 170 femtomolar in diluted serum samples.