Red emissive boron and nitrogen co-doped on-off-on carbon dots for detecting and imaging of mercury(II) and biothiols

Red emissive B,N co-doped carbon dots (BN-CDs) were hydrothermally synthesized from cresyl violet and boric acid. The BN-CDs exhibited excellent photostability, low cytotoxicity, excitation/emission maxima at 520/616 nm, and a relatively high quantum yield of 18%. The BN-CDs can binded to mercury(II), and this results in quenching of the red-colored fluorescence. However, on subsequent addition of the biothiol (such as cysteine, homocysteine or glutathione), fluorescence recovers. Therefore, the BN-CDs can be used as a multifunctional probe based on on-off-on fluorescence response for the detection of Hg(II) and biothiols. The following detection limits were accomplished: (a) Hg(II): 2.8 mu M; (b) glutathione: 1.7 mu M; (c) cysteine: 2.3 mu M; (d) homocysteine: 3.0 mu M. The BN-CDs also have been successfully applied for the imaging of Hg(II) and biothiols in HepG2 cells with excellent bio-compatibility.