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Detecting the Undetectable

Detecting the Undetectable

photo: bars of gold

The researchers at Northwestern University found measureable PSA levels in each post-operative patient in its study, thanks to the power of the nanoparticle-based bio-barcode assay developed at Northwestern. The technology is 300 times more sensitive than commercially available PSA tests. After the removal of the prostate gland, patients typically have PSA levels that are undetectable when measured using conventional diagnostic tools.

This ability to easily and quickly detect very low levels of PSA may enable doctors to diagnose men with prostate cancer recurrence years earlier than is currently possible.

PSA is a protein produced by the cells of the prostate gland and found in the bloodstream. This pilot study looked at serum samples from 18 post-prostatectomy patients collected over the course of a number of years.

The researchers were able to reliably and accurately quantify PSA values at less than 0.1 nanograms per milliliter, the clinical limit of detection for commercial assays.

The ultra-sensitive technology is based on gold nanoparticle probes, decorated with DNA and antibodies that can recognize and bind to PSA when present at extremely low levels in a blood sample. A magnetic microparticle, outfitted with a second antibody for PSA, also is used in the assay. When in solution, the antibody-functionalized particles "recognize" and bind to PSA, sandwiching the protein between the two particles.

The key is that attached to each tiny gold nanoparticle are hundreds of identical strands of DNA. Chad A. Mirkin, professor of Chemistry in the Weinberg College of Arts and Sciences, calls this "bar-code DNA" because they have designed it as a label specific to the PSA target. After the "particle-protein-particle" sandwich is removed magnetically from solution, the DNA is removed from the sandwich and read using a Verigene® ID system, a nanotechnology platform designed to detect and quantify DNA.

The amount of PSA present is calculated based on the amount of bar-code DNA. For each molecule of captured PSA, hundreds of DNA strands are released, which is one of the ways the PSA signal is amplified.

MEDICA.de; Source: Northwestern University

 
 
 

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