A dual-mode luminescent probe composed of co-assembled down-conversion CdTe and up-conversion NaYF4:Yb, Tm(Er) nanoparticles

Multiplex luminescent probes with good water-dispersibility are basic materials in current biological research as labels and sensors. In this work, we demonstrate a facile approach to fabricate water-dispersible dual-mode luminescent probes by co-assembling down-conversion CdTe nanoparticles (NPs) and up-conversion NaYF4:Yb, Tm(Er) NPs. 3-Mercaptopropionic acid (MPA)-capped CdTe NPs are water soluble, while oleic acid (OA)-capped NaYF4: Yb, Tm(Er) NPs are dispersed in chloroform. There also exists an excess of Cd-MPA complex in the CdTe aqueous solution. After mixing CdTe and NaYF4:Yb, Tm(Er), the MPA on CdTe NPs and Cd-MPA complexes is capable of partially replacing the OA on NaYF4:Yb, Tm(Er) NPs, thus transferring NaYF4:Yb, Tm(Er) NPs to water and forming CdTeNaYF4:Yb, Tm(Er) hybrid NPs. The hybrid NPs combine the down-conversion emission of CdTe and the up-conversion emission of NaYF4:Yb, Tm(Er), which can be excited both by 400 and 980 nm irradiation and exhibit dual-mode emission. Both Forster resonance energy transfer from NaYF4:Yb, Tm(Er) to CdTe and photon re-absorption are observed as the hybrid NPs are excited by 980 nm irradiation.