RuNH2@AuNPs as two-photon luminescent probes for thiols in living cells and tissues

Two-photon luminescent sensors have emerged as promising molecular tools for imaging biomolecules in living systems. Here, we present hybrid gold nanocomposites RuNH2@AuNPs as luminescence off-on probes in response to thiols, which can replace the Ru(II) complexes on the surfaces of the AuNPs to release the luminophore RuNH2. The liberated Ru(II) complexes exhibit strong two-photon luminescence and a large two-photon absorption cross section by using the two-photon excitation wavelength at 800 nm. Furthermore, the probe responses toward thiols with high selectivity and insensitivity to pH over the biologically relevant pH range. This two-photon probe can visualize biological thiols levels in live cells as well as in living mouse tissues at depths of 80-170 μm by two-photon microscopy.