laccase activity assay using surface plasmon resonance band of gold nanoparticles formed by dopamine

A simple, fast, and sensitive colorimetric technique for determination of laccase activity using dopamine (da) induced growth of colloidal gold nanoparticles is proposed. it was found that the reduction of aucl4 − to colloidal gold nanoparticles (aunps) by dopamine (da) in the presence of citrate ion as stabilizing agent produced a very intense surface plasmon resonance peak of aunps at 530 nm. as the activity of laccase (at fixed concentration of da) increases, the oxidation of da to dopamine-o-quinone (doq) is enhanced. the latter product could not act as the reducing agent for the reduction of aucl4 − to aunps. so, as the activity of laccase increases, the absorbance characteristic to the plasmon of the aunps at 530 nm is diminished. this reductive mechanism of the plasmon absorbance of the aunps allows the quantitative colorimetric assay for laccase activity. the linear range of the method is 0.1–10 u ml−1 laccase. the developed method has been applied to assay laccase activity in 12 samples per hour.