Improved LRET-based detection characters of Cu2+ using sandwich structured NaYF4@NaYF4:Er3+/Yb3+@NaYF4 nanoparticles as energy donor

Upconversion nanoparticles (UCNPs) are widely used as energy donors via a luminescence resonance energy transfer (LRET) technique in biosensing field. To enhance LRET efficiency and afford an improved sensitivity for Cu 2+ detection, sandwich structured NaYF 4 @NaYF 4 :Er 3+ /Yb 3+ @NaYF 4 UCNPs have been designed and prepared. For the core-internal shell-external shell structure, luminescence ions (Er 3+ ) are located in the internal shell near the nanoparticle surface, which is close enough to energy acceptors outside. To study the sensing properties, the UCNPs are used as energy donors and rhodamine B hydrazide (RBH) as energy acceptors to construct the nanoprobes. It is found that the sandwich structured nanoparticles gains more intense luminescence than the naked NaYF 4 :Er 3+ /Yb 3+ UCNPs, which is beneficial to the further improvement of signal sensitivity in biological detection. Moreover, the specificity for detecting Cu 2+ is also checked and found that the designed probe is much more sensitive to Cu 2+ than the other ions including K + , Na + , Li + , Ca 2+ , Ba 2+ , Mg 2+ , Zn 2+ and Sr 2+ . The experiment on the stability of UCNPs-RBH probe and RBH shows the 980   nm laser produces less photodamage to RBH than that of visible light. Therefore, the UCNPs can be used to construct potential probes for realizing effective detection of Cu 2+ .