Ratiometric upconversion luminescence nanoprobes for quick sensing of Hg2+ and cells imaging

Rare earth upconversion nanomaterials have the advantages of near-infrared region excitation, almost zero interference background, large anti-Stokes shifts without broad emission peaks, which can overcome parts of the defects of organic fluorescent probes. In this work, core-shell rare earth upconversion nanoparticles NaYF4:Yb,Tm:20 %Yb,0.35 %[email protected]4 (UCNPs) were synthesized, and then water-soluble nanoparticles DMSA-UCNPs and PAA-UCNPs were subsequently fabricated. Meanwhile a naphthalimide-based colormetric Hg2+-probe was synthesized, and assembled with DMSA-UCNPs and PAA-UCNPs to give composite nanoprobes A-DMSA-UCNPs and A-PAA-UCNPs toward mercury ions. Both nanoprobes use the upconversion luminescence ratio at 451 nm and 361 nm (UCL451/UCL361) as the detection signal, and can quickly respond to Hg2+ ions within 1–2 min. The detection limits of A-DMSA-UCNPs and A-PAA-UCNPs were calculated to be 2.47 μmol/L and 8.15 μmol/L respectively. A-DMSA-UCNPs and A-PAA-UCNPs both could be employed as ratiometric nanoprobes for Hg2+ imaging in living cell and lysosomal localization.