Two-Photon Fluorescent Nanoprobe for Glutathione Sensing and Imaging in Living Cells and Zebrafish Using a Semiconducting Polymer Dots Hybrid with Dopamine and ß-Cyclodextrin.

Fabrication of hybrid semiconducting polymer dots (Pdots) endowed with special applications in biosensing and bioimaging in living systems has recently received considerable attention. In this study, novel two-photon fluorescent hybrid Pdots, DA-CD@Pdots, were first prepared by poly(styrene-co-maleic anhydride) (PSMA) being grafted with ß-cyclodextrin (ß-CD) and poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1',3}-thiadiazole)] (PFBT) through a nanoprecipitation method, followed by covalent attachment with dopamine (DA) by using an EDC-catalyzed carboxylamine coupling reaction. The DA molecules anchored on the surface of the Pdots were further oxidized to form their quinone-like structures (DQ) and act as good electron acceptors to magnifyingly quench the fluorescence of Pdots by intraparticle photoinduced electron transfer (PET) and the "molecular-wire effect". The finally achieved hybrid DQ-CD@Pdots display enhanced colloidal stability, higher resistibility to environmental effects, and lower biological toxicity. In the presence of glutathione (GSH), DQ molecules on the surface of Pdots are reduced into catechol molecules and result in the inhibition of PET and restoration of the fluorescence of the Pdots. On the basis of the above demonstrations, the hybrid DQ-CD@Pdots are used as fluorescent probes for "turn-on" detection of GSH in the range from 0.01 to 3.0 µM with the detection limit of 2.7 nM. The prepared DQ-CD@Pdots probe is also applied to the GSH detection and imaging in living systems including human cervical carcinoma HeLa cells and living zebrafish with satisfactory results.