Question

Briefly explain how a medical diagnostic test kit based on gold nanoparticles works. Pitch your answer at the level of a scientifically-literate audience that are not physicists. (A diagram could be useful)

Answer 1

Nanoparticle kit could diagnose disease early:

Colour change shows the presence of minuscule amounts of key enzymes.

Enzymes snip apart the links between nanoparticles, prompting a colour change.

A detection kit that uses nanoparticles to seek out tiny amounts of disease-related enzymes could offer sensitive and fast diagnoses of cancer, HIV and other diseases.

The diagnostic test has been developed and refined by Molly Stevens, a biomedical materials scientist at Imperial College London, and her colleagues.

The tests useugold particles, 10 nanometres wide, stuck short peptide chains to their surface. These peptides help link the gold nanoparticles together because they are attached at the other end to aromatic chemical groups called Fmoc that stack on top of one another and stick together.

When the nanoparticles are linked together in this way, they form a blue solution. But when the solution is exposed to the specific enzyme related to specific disease, it turns red.(ex nACT-PSA of prostate cancer).

This colour change happens because the nanoparticles disperse after the enzyme — a protease — munches its way through the peptides in the linking groups. This frees the nanoparticles from the peptide links and means they speedily scatter. "Once cleaved the peptide, at the end of the peptide ,it will be left with a positive charge and these positive charges make the particles repel each other.

Detecting recurrence

The colour changes within minutes, and can happen with just zeptograms (10-21 grams) of enzyme per millilitre — although these concentrations take longer to bring about the colour change. The test is more sensitive than anything previously reported, and can almost detect a single enzyme molecule.