A ratiometric fluorescence strategy based on inner filter effect for Cu2+-mediated detection of acetylcholinesterase.

A novel ratiometric fluorescence strategy for detection of acetylcholestinerase (AChE) is proposed based on carbon nitride quantum dots (g-CNQD) and the complex (PA) formed between phenylboronic acid (PBA) and alizarin red S (ARS). PA showed fluorescence at 598 nm and quenched the fluorescence of g-CNQD at 438 nm. Through UV-visible absorption, fluorescence, and fluorescence lifetime measurements, the quenching effect was demonstrated as inner filter effect (IFE). When Cu2+ was added, the coordination of ARS and Cu2+ decreased the fluorescence of PA at 598 nm and recovered that of g-CNQD at 438 nm. In the presence of AChE it catalyzed the hydrolysis of acetylthiocholine (ATCh) to produce thiocholine (TCh) which competed with ARS for binding to Cu2+; thus, the fluorescence at 598 nm increased and that at 438 nm decreased again. Under the mediation of Cu2+, the fluorescence ratio F598/F438 of PA-CNQD probe had good linear relationship with AChE concentration in the range 0.5-15 mU/mL with a detection limit of 0.36 mU/mL. The method was successfully applied to the determination of AChE in human serum and the screening of inhibitors.

Matrix metalloproteinase-2-targeted superparamagnetic Fe3O4-PEG-G5-MMP2@Ce6 nanoprobes for dual-mode imaging and photodynamic therapy.

This work explored the application of matrix metalloproteinase 2-targeted superparamagnetic nanoprobes for magnetic resonance imaging (MRI), near infrared (NIR) fluorescence imaging and photodynamic therapy of tumors. PEG, PAMAM (G5) and matrix metalloproteinase 2 (MMP2) were attached to the surface of carboxylated Fe3O4 nanoparticles (NPs) using a chemical coupling method and then finally loaded with the photosensitizer chlorin e6 (Ce6). In vitro and in vivo experiments demonstrated that the Fe3O4-PEG-G5-MMP2@Ce6 nanoprobes exhibited excellent stability, precise tumor targeting and biocompatibility. Furthermore, the fluorescence properties of Fe3O4-PEG-G5-MMP2@Ce6 nanoprobes were analogous to Ce6 and could be employed for fluorescence imaging. Meanwhile, the Fe3O4-PEG-G5-MMP2@Ce6 nanoprobes have also been shown to be effective as contrast agents for T2-weighted MRI. The target molecule MMP2 enhanced the tumor targeting ability of Fe3O4-PEG-G5-MMP2@Ce6 nanoprobes. Additionally, the Fe3O4-PEG-G5-MMP2@Ce6 nanoprobes significantly inhibited tumor growth compared with PBS and free Ce6. This work will inspire greater enthusiasm for the construction of multifunctional magnetic nanoplatforms for biomedical applications.