Our laboratory has developed several methods, on the nano-and micro-scale,for analysing ions, biomolecules and mammalian cells.We report a method for the detection of Cu2+ ions by azide-and alkyne-functionalized gold nanoparticles in aqueous solutions using click chemistry.This method allows the naked eye, without the aid of any advanced instrument, to assay for the presence of Cu2+ ions, with high selectivity and sensivity.This type of analysis may eventually be useful for lab-on-a-chip and related applications.