Green and ligand-free gold nanoparticles in Padina australis extract for colorimetric detection of Cu2+in water

The green and ligand-free gold nanoparticles (P-AuNPs) from Padina australis extract were easily and quickly prepared. A colorimetric probe based on P-AuNPs was designed for easy and visual detection of Cu2+ in domestic water with excellent sensitivity. The -OH and -NH2 in polysaccharides and proteins of Padina australis had played a reduced and protected role for AuNPs and also been easy to complex Cu2+ because of chelation. The complexed Cu2+ dragged P-AuNPs closely to aggregation, causing the red sol to turn blue. Also, the UV-vis spectrum was red-shifted, and a new peak developed. The limits of UV-vis detection are as low as 0.43 & mu;M. The absorbance ratio (A630/A520) showed an excellent linear relationship with Cu2+ concentration (R2 = 0.9926) with a range of 20-60 & mu;M by UV-vis.