Development of luminescence probes with polarized and narrow emissions simultaneously is helpful for removing multiply scattered light and enables multiplexing detection, but it remains challenging to use conventional organic dyes, fluorescence proteins, and quantum dots. Here, we demonstrated smart one-dimensional microlaser probes (MLPs) by coating a thin layer of silica shell on the surface of organic nanowires (ONWs) of 1,4-dimethoxy-2,5-di[4′-(methylthio)styryl]benzene (TDSB), namely, ONW@SiO2 core–shell structures. Different from the Fabry–Pérot (FP) cavity formed between two end-faces of semiconductor nanowires, whispering gallery mode (WGM) microresonators are built within the rectangular cross section of ONW@SiO2 MLPs. This enables a lasing threshold as low as 1.54 μJ/cm2, above which lasing emissions are obtained with a full width at half-maximum (fwhm) < 5 nm and a degree of polarization (DOP) > 83%. Meanwhile, small dimensions of ONW@SiO2 MLPs with a side-length of ca. 500 nm and a length of 3–8 μm help to reduce their perturbations in living cells. With the help of mesoporous silica shells, which provide both high biocompatibility and good photostability, ONW@SiO2 MLPs can be easily introduced into the cell cytoplasm through natural endocytosis. Using their narrow and highly polarized lasing emissions in vitro, we demonstrate that it is possible to tag individual cells using ONW@SiO2 MLPs with high stability.Keywords: biological imaging; core−shell structure; intracellular microlaser; organic nanowire; polarization probes;

•We synthesized and investigated the photophysical properties of a new donor–π–acceptor molecule BNSN.•BNSN exhibits a red-shifted emission and an unconventional dramatic increase of emission efficiency in polar solvent.•The fluorescence intensity and two-photon absorption cross-section all enhanced when the molecules aggregated.•The nanoparticles of BNSN exhibited aggregation-enhanced two-photon fluorescence in aqueous media.•Cell imaging capability in living cancer cells was examined with low toxicity and high photostability.Two-photon excited fluorescence bio-probes have obtained a great deal of interests in biological imaging and sensing applications. We synthesized a new donor–π–acceptor molecular (BNSN) with strong intramolecular charge-transfer (ICT). Interestingly, different from conventional ICT compounds, BNSN molecules present an unusual ICT phenomenon, leading to a red-shifted emission and an increased fluorescence quantum yield (Φ) with increasing the polarity of solvents. Moreover, the fluorescence intensity and two-photon absorption cross-section all enhanced when the molecules aggregated. The nanoparticles of BNSN exhibit strong two-photon excited fluorescence in aqueous media, exhibiting the property of aggregation-enhanced two-photon fluorescence (AE-TPF). Our results demonstrate that the BNSN molecules with AE-TPF effect provide a new molecular type to construct efficient two-photon excited fluorescence nano-probes for bio-imaging.