Reversible turn-on fluorescent Cu(II) sensors: rather dream than reality?

Reversible turn-on fluorescent sensors of Cu(II) are of high interest for biological studies. We re-investigate a reported sensor, showing that turn-on occurs via irreversible Cu(II)-induced sensor oxidation only in the presence of acetonitrile. This prevents its application in biological studies and highlights the challenge of establishing a reversible Cu(II) turn-on sensor. [ABSTRACT FROM AUTHOR]