Lanthanide/Cu 2- x Se Nanoparticles for Bacteria-Activated NIR-II Fluorescence Imaging of Infection.

A material system enabling specific NIR-II fluorescence imaging of Gram-positive bacteria is described. The material system is based on the electrostatic binding of Cu 2- x Se and vancomycin-modified NaGdF 4 :Nd,Yb@NaGdF 4 downconversion nanoparticles (DCNPs), the fluorescence of which is weak owing to the spectral overlap of Cu 2- x Se absorption with the DCNP NIR emission. The presence of Gram-positive bacteria precisely disconnects the bond between vancomycin-modified DCNPs and Cu 2- x Se, thus enabling a strong fluorescent signal. In vivo studies show that the material system can be specifically activated at the site of Gram-positive bacterial infection but is essentially nonfluorescent in the area of Gram-negative bacterial infection.