The scientists have attached special organic molecules ta the surfaces of gold nanoparticles .These molecules act like ligants for arsenic ,meaning that they form a
complex with it.Each arsenic ion can bind to three ligands, which allows it to link together
up to three gold particles . The higher the arsenic concentration in the sample, the more
strongly the gold particles clump together and the number of bigger aggregates increases.
The color of gold nanoparticles in a liquid depends on their size. Whereas the arsenic-free gold
nanoparticles appear red , arsenic-induced aggregation causes the color to change to blue