Copper Ions Interfere with the Reduction of the Water-Soluble Tetrazolium Salt-8

Metabolic activity as a measure of cell viability is frequently determined using the water-soluble tetrazolium salt 2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium monosodium salt (WST-8), commercially available as CCK-8 reagent. In this study, CCK-8 was investigated with respect to its suitability for investigating nano- and microscale copper oxide (CuO NP and CuO MP) as well as water-soluble copper chloride (CuCl2). The results were compared to cell number and colony forming ability. Our data demonstrate that the CCK-8 assay overestimates the loss of metabolic activity by CuCl2 and CuO NP, because of interference by copper ions with the reduction of the dye.