Highly selective colorimetric detection of cysteine and homocysteine in water through a direct displacement approach

The complex CuQ2 (HQ = 8-hydroxy-7-(4-tolyldiazenyl)quinoline-5-sulfonic acid) has been synthesized and used as a colorimetric probe for the specific detection of cysteine and homocysteine in water through a displacement reaction. The detection can be performed either by the spectroscopy from the increased UV–vis absorbance at 498 nm or by the change of color from yellow to red upon addition of cysteine or homocysteine to the solution of the complex. The experimental results show no interference by other amino acids to the detection of cysteine and homocysteine.