L-cysteine and 3-mercaptopropionic acid capped cadmium selenide quantum dots based metal ion probes

Herein, a report on the synthesis of 3-mercaptopropionic acid (MPA) and L cysteine (Cyst) capped luminescent cadmium selenide (CdSe) quantum dots (QDs) was studied. The MPA-CdSe and Cyst-CdSe QDs were conducted with different physiologically important metal ions such as Cu2+, Fe2+, Zn2+, Co2+, Pb2+, Mg2+, Ni2+ and Ag+ ions in aqueous solution using fluorescence spectroscopic technique. It was found that the MPA-CdSe QDs, categorically sensitive to only Cu2+ ions only. However, other metal ions such as Zn2+, Co2+, Pb2+, Mg2+, Ni2+ and Ag+, did not exhibit measurable quenching. On the other hand, Cyst-CdSe QDs were very selective and sensitive to Zn2+ ions only, which showed fluorescence enhancement while for other ions no such behavior was noticed. Thus, MPA-CdSe and Cyst-CdSe QDs have successfully detected Cu2+ and Zn2+ ions in the linearity range from 4 to 160 µM, respectively. The effect of fluorescence response of QDs towards metals ions were described by Langmuir-type binding model or Stern-Volmer-type equation.