Poly ß-cyclodextrin/TPdye nanomicelle-based two-photon nanoprobe for caspase-3 activation imaging in live cells and tissues.

Two-photon excitation (TPE) with near-infrared (NIR) photons as the excitation source has important advantages over conventional one-photon excitation (OPE) in the field of biomedical imaging. ß-cyclodextrin polymer (ßCDP)-based two-photon absorption (TPA) fluorescent nanomicelle exhibits desirable two-photon-sensitized fluorescence properties, high photostability, high cell-permeability and excellent biocompatibility. By combination of the nanostructured two-photon dye (TPdye)/ßCDP nanomicelle with the TPE technique, herein we have designed a TPdye/ßCDP nanomicelle-based TPA fluorescent nanoconjugate for enzymatic activity assay in biological fluids, live cells and tissues. This sensing system is composed of a trans-4-[p-(N,N-diethylamino)styryl]-N-methylpyridinium iodide (DEASPI)/ßCDP nanomicelle as TPA fluorophore and carrier vehicle for delivery of a specific peptide sequence to live cell through fast endocytosis, and an adamantine (Ad)-GRRRDEVDK-BHQ2 (black hole quencher 2) peptide (denoted as Ad-DEVD-BHQ2) anchored on the DEASPI/ßCDP nanomicelle's surface to form TPA DEASPI/ßCDP@Ad-DEVD-BHQ2 nanoconjugate by the ßCD/Ad host-guest inclusion strategy. Successful in vitro and in vivo enzymatic activities assay of caspase-3 was demonstrated with this sensing strategy. Our results reveal that this DEASPI/ßCDP@Ad-DEVD-BHQ2 nanoconjugate not only is a robust, sensitive and selective sensor for quantitative assay of caspase-3 in the complex biological environment but also can be efficiently delivered into live cells as well as tissues and act as a "signal-on" fluorescent biosensor for specific, high-contrast imaging of enzymatic activities. This DEASPI/ßCDP@Ad-DEVD-BHQ2 nanoconjugate provides a new opportunity to screen enzyme inhibitors and evaluate the apoptosis-associated disease progression. Moreover, our design also provides a methodology model scheme for development of future TPdye/ßCDP nanomicelle-based two-photon fluorescent probes for in vitro or in vivo determination of biological or biologically relevant species.