An upconversion fluorescence based turn-on probe for detecting lead(II) ions

A new fluorescent probe for detecting lead ions (Pb2+) is reported in this work. Positively charged UCPs capped with ethylene imine polymer (PEI) and negatively charged AuNPs capped with 11-mercaptoundecanoic acid (MUA) were used as fluorescent donors and acceptors, respectively. The fluorescence quenching process was initiated by the electrostatic interaction between PEI–UCPs and MUA–AuNPs. Upon the addition of Pb2+, functionalized AuNPs were aggregated by an ion-templated chelation process, causing the departure of AuNPs from UCPs. As a result, the fluorescence of the donor was restored and the recovery was found to be proportional within the range of 0.5–10 μM to the concentration of Pb2+. The detection limit was found to be 20 nM. This method was easy to operate with satisfactory selectivity and remarkable sensitivity which would be meaningful in Pb2+-related detection.