A unique red-emitting two-photon fluorescent probe with tumor-specificity for imaging in living cells and tissues.

Tumor-specific imaging can provide an attractive approach for the early detection and prognosis of cancer, as well as the precise image-guided tumor-removal surgery. Herein, we describe a unique red-emitting two-photon fluorescent probe (N-BN) for tumor-specific imaging. N-BN utilized Nile Red as the red-emitting two-photon fluorophore and employed biotin as the tumor-specific ligand. In the presence of a variety of biomolecules or in different pH buffers, the fluorescence intensity of N-BN at 655nm showed no noticeable change. N-BN exhibited the remarkable two-photon absorption cross sections of 15.4g under excitation at 800nm. Under the guidance of biotin, N-BN can be applied for the imaging of biotin-receptor positive cancer cells over biotin-negative cells under red-emitting one- and two-photon manners. Assisted by high-definition three-dimensional imaging, the living tumor tissues loaded with N-BN could display strong red two-photon fluorescence with a penetration depth of about 90µm. Moreover, the in vivo and ex vivo imaging studies intuitively revealed that N-BN could track the tumor with highly tumor-specific property by a near-infrared manner.