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 Cu 2+ in domestic water with excellent sensitivity. The –OH and –NH 2 in polysaccharides and proteins of Padina australis had played a reduced and protected role for AuNPs and also been easy to complex Cu 2+ because of chelation. The complexed Cu 2+ 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 μM. The absorbance ratio (A 630 /A 520 ) showed an excellent linear relationship with Cu 2+ concentration (R 2 = 0.9926) with a range of 20–60 μM by UV–vis.