Cooperative and FRET‐Assisted Brightness Enhancement in Oligo(phenylene ethynylene): Quantum Dot Organic–Inorganic Nanohybrids

Herein, we combine the ideas of concerted emission from fluorophore ensembles and its further amplification through FRET in an organic–inorganic hybrid approach. Spherical and highly fluorescent organic nanoparticles (FONPs, Φ_f=0.38), prepared by the self‐assembly of oligo(phenylene ethynylene) (OPE) molecules, were selected as a potential donor material. This organic core was then decorated with a shell of fluorescent CdSe/ZnS core–shell quantum dots (QDs; <d>?5.5 nm, Φ_f=0.27) with the aid of a bifunctional ligand, mercaptopropionic acid. Its high extinction coefficient (?≈4.1×10⁵ m ^?1 cm^?1) and good spectral match with the emission of the FONPs (J(λ)≈4.08×10¹⁶ m ^?1 cm^?1 nm⁴) made them a better acceptor candidate to constitute an efficient FRET pair (Φ_FRET=0.8). As a result, the QD fluorescence intensity was enhanced by more than twofold. The fundamental calculations carried out indicated an improvement in all the FRET parameters as the number of QDs around the FONPs was increased. This, together with the localization of multiple QDs in a nanometric dimension (volume≈1.8×10⁶ nm³), gave highly bright reddish luminescent hybrid particles as visualized under a fluorescence microscope.     

Cytochrome c‐Capped Fluorescent Gold Nanoclusters: Imaging of Live Cells and Delivery of Cytochrome c

Cytochrome c‐capped fluorescent gold nanoclusters (Au‐NCs) are used for imaging of live lung and breast cells. Delivery of cytochrome c inside the cells is confirmed by covalently attaching a fluorophore (Alexa Fluor 594) to cytochrome c‐capped Au‐NCs and observing fluorescence from Alexa 594 inside the cell. Mass spectrometry studies suggest that in bulk water, addition of glutathione (GSH) to cytochrome c‐capped Au‐NCs results in the formation of glutathione‐capped Au‐NCs and free apo‐cytochrome c. Thus glutathione displaces cytochrome c as a capping agent. Using confocal microscopy, the emission spectra and decay of Au‐NCs are measured in live cells. From the position of the emission maximum it is shown that the Au‐NCs exist as Au₈ in bulk water and as Au₁₃ inside the cells. Fluorescence resonance energy transfer from cytochrome c–Au‐NC (donor) to Mitotracker Orange (acceptor) indicates that the Au‐NCs localise in the mitochondria of live cells.     

Multilayer Microcapsules for FRET Analysis and Two‐Photon‐Activated Photodynamic Therapy

Microcapsules obtained by layer‐by‐layer assembly provide a good platform for biological analysis owing to their component diversity, multiple binding sites, and controllable wall thickness. Herein, different assembly species were obtained from two‐photon dyes and traditional photosensitizers, and further assembled into microcapsules. Fluorescence resonance energy transfer (FRET) was shown to occur between the two‐photon dyes and photosensitizers. Confocal laser scanning microscopy (CLSM) with one‐ and two‐photon lasers, fluorescence lifetime imaging microscopy (FLIM), and time‐resolved fluorescence spectroscopy were used to analyze the FRET effects in the microcapsules. The FRET efficiency could easily be controlled through changing the assembly sequence. Furthermore, the capsules are phototoxic upon one‐ or two‐photon excitation. These materials are thus expected to be applicable in two‐photon‐activated photodynamic therapy for deep‐tissue treatment.     

Broadband Light‐Harvesting Molecular Triads with High FRET Efficiency Based on the Coumarin–Rhodamine–BODIPY Platform

Broadband capturing and FRET‐based light‐harvesting molecular triads, CRBs, based on the coumarin–rhodamine–BODIPY platform were rationally designed and synthesized. The absorption band of CRBs starts from blue–green to yellow–orange regions (330–610 nm), covering the strong radiation scope of sunlight. The peripheral coumarin and BODIPY chromophore energy could transfer to the central acceptor rhodamine by a one‐step direct way. The energy of the coumarin moiety could also transfer to the BODIPY unit, subsequently transferring to the rhodamine core by two‐step sequential ways. Both the efficiencies of the coumarin moiety and the BODIPY unit to the rhodamine core in CRBs, determined by two different ways, are very high.