A new and simple fluorescent sensorbased on unmodified BINOL was developed. The fluorescence of BINOL could be turned off with high selectivity toward Cu(II) among 27 metal ions. Meanwhile, it was found that BINOL was oxidized to dibenzo[a,kl]xanthen-1-ol (A) by Cu(NO3)2. A new peak appeared at ∼482 nm upon addition of thiol-containing cysteine (Cys), homocysteine (Hcy), and glutathione (GSH). Thus