Enzyme-coated gold nanoparticles make ultra-sensitive disease
30 May 2012
Enzyme-coated gold nanoparticles can detect disease biomarkers at
several orders of magnitude lower concentrations than current tests and will
make it possible to detect a range of diseases earlier.
There are already tests available for some diseases that look for such
biomarkers using biosensors. However, existing biosensors become
less sensitive and predictable at detecting biomarkers at very low concentrations, as occurs when a disease is in its early
Scientists from Imperial College London and the
University of Vigo demonstrated that the new biosensor test can find
a biomarker associated with prostate cancer, called Prostate
Specific Antigen (PSA). However, the team say that the biosensor can
be easily reconfigured to test for other diseases or viruses where
the related biomarker is known.
Professor Molly Stevens, senior author of the study from the
Departments of Materials and Bioengineering at Imperial College
London, said: "It is vital to detect diseases at an early stage if
we want people to have the best possible outcomes — diseases are
usually easier to treat at this stage, and early diagnosis can give
us the chance to halt a disease before symptoms worsen.
"However, for many diseases, using current technology to look for
early signs of disease can be like finding the proverbial needle in
a haystack. Our new test can actually find that needle. We only
looked at the biomarker for one disease in this study, but we're
confident that the test can be adapted to identify many other
diseases at an early stage."
The team demonstrated the effectiveness of their biosensor by
testing PSA biomarker samples in solutions containing a complex
mixture of blood derived serum proteins. Monitoring the levels of
PSA at ultralow concentrations can be crucial in the early diagnosis
of the reoccurrence of prostate cancer, but classic detection
approaches are not sensitive enough to carry out this analysis with
a high degree of accuracy. The new test could enable more reliable
diagnosis, but more research will need to be done to further explore
In their study, the team detected PSA at 0.000000000000000001
grams per millilitre, which is at the limits of current biosensor
performance. By comparison, an existing test called an Enzyme-Linked
Immunosorbent Assay (ELISA) test can detect PSA at 0.000000001 grams
per millilitre, which is nine orders of magnitude more concentrated.
The biosensors used in today's study consist of nanoscopic-sized
gold stars floating in a solution containing other blood derived
proteins. Attached to the surface of these gold stars are
antibodies, which latch onto PSA when they detect it in a sample.
A secondary antibody, which has an enzyme called glucose oxidase
attached to it, recognises the PSA and creates a distinctive silver
crystal coating on the gold stars, which is more apparent when the
PSA biomarkers are in low concentrations. This silver coating acts
like a signal that PSA is present, and it can be easily detected by
scientists using optical microscopes.
The next stage of the research will see the team carrying out
further clinical testing to assess the efficacy of the biosensor in
detecting a range of different biomarkers associated with conditions
such as HIV and other infections. They will also explore ways of
commercialising their product.
Laura Rodríguez-Lorenzo, Roberto de la Rica, Ramón A. Álvarez-Puebla,
Luis M. Liz-Marzán & Molly M. Stevens. Plasmonic nanosensors
with inverse sensitivity by means of enzyme-guided crystal growth.
Nature Materials, 2012. Published online: 27 May 2012. doi:10.1038/nmat3337