Labile copper(II) ions (Cu^(2+)) in serum are considered to be readily available for cellular uptake and to constitute the biologically active Cu^(2+) species in the blood. It might also be suitable to reflect copper dyshomeostasis during diseases such as Wilson’s disease (WD) or neurological disorders. So far, no direct quantification method has been described to determine this small Cu^(2+) subset. This study introduces a fluorometric high throughput assay using the novel Cu^(2+) …