Non-responsive emission enhancement is the disadvantage of upconversion nanomaterials (UCNM) when compared with conventional organic based agents for molecular imaging. We herein show a new strategy by conjugating NaGdF4:Yb3+,Er3+@NaGdF4 (UCNP) with peptides to achieve responsive UC emission enhancement upon binding to a targeted protein - EBNA1. EBNA1 is a well-known viral latent protein for the EBV-associated cancer. Peptide-coating of the functionalized core-shell nanoparticle diminishes upconverted emission intensity drastically. However, the peptide-coated UCNP shows selective and responsive UC emission enhancement via aggregation with the targeted protein. This phenomenon paves a new way for UCNM in molecular imaging.

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A cell-permeable ytterbium complex shows reversible binding with Hg in aqueous solution and in vitroby off-on visible and NIR emission. The fast response and 150 nM sensitivity of Hg detection is based upon FRET and the lanthanide antenna effect. The reversible Hg detection can be performed in vitro, and the binding mechanism is suggested by NMR employing the motif structure in a La complex and by DFT calculations.

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