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A FRET ratiometric fluorescent sensor was developed for detecting H(2)S in aqueous media and serum, as well as inside live cells. For this sensor, carbon dots serve as the energy donor and also the anchoring site for the probe. This sensor is highly selective and sensitive with a detection limit of 10 nM which is the lowest among fluorescent H(2)S sensors.

Hydrogen peroxide (H2 O2 ) is a prominent member of the reactive oxygen species family and plays crucial roles in living organisms, thus detecting H2 O2 and elucidating its biological functions has become an important area of biological and biomedical research. Herein, a multifunctional fluorescent nanoprobe is demonstrated for detecting mitochondrial H2 O2 . The nanoprobe is prepared by covalently linking a mitochondria-targeting ligand (triphenylphosphonium, TPP) and a H2 O2 recognition element (PFl) onto carbon dots (CDs). For this nanoprobe, the CD serves as the carrier and the FRET donor. In the presence of H2 O2 , the PFl moieties on a CD undergo structural and spectral conversion, affording the nanoplatform a FRET-based ratiometric probe for H2 O2 . The nanoprobe displays excellent water dispersibility, high sensitivity and selectivity, satisfactory cell permeability, and very low cytotoxicity. Following the living cell uptake, this nanoprobe can specifically target and stain the mitochondria; and it can detect the exogenous H2 O2 in L929 cells, as well as the endogenously produced mitochondrial H2 O2 in Raw 264.7 cells upon stimulation by PMA. This study shows that CDs can serve as promising nano-carriers for fabricating practical multifunctional fluorescent nanosensors.

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An activatable nanoprobe for imaging breast cancer metastases through near infrared‐I (NIR‐I)/NIR‐II fluorescence imaging and multispectral optoacoustic tomography (MSOT) imaging was designed. With a dihydroxanthene moiety serving as the electron donor, quinolinium as the electron acceptor and nitrobenzyloxydiphenylamino as the recognition element, the probe can specifically respond to nitroreductase and transform into an activated D‐π‐A structure with a NIR emission band extending beyond 900 nm. The activated nanoprobe exhibits NIR emission enhanced by aggregation‐induced emission (AIE) and produces strong optoacoustic signal. The nanoprobe was used to detect and image metastases from the orthotopic breast tumors to lymph nodes and then to lung in two breast cancer mouse models. Moreover, the nanoprobe can monitor the treatment efficacy during chemotherapeutic course through fluorescence and MSOT imaging.

Amphiphilic core–shell nanoparticles containing spiropyran moieties have been prepared in aqueous media. The nanoparticles consist of hydrophilic and biocompatible poly(ethyleneimine) (PEI) chain segments, which serve as the shell, and a hydrophobic copolymer of methyl methacrylate (MMA), a spiropyran‐linked methacrylate, and a cross‐linker, which forms the core of the nanoparticles. A hydrophobic fluorescent dye based on the nitrobenzoxadiazolyl (NBD) group was introduced into the nanoparticles to form NBD–nanoparticle complexes in water. The nanoparticles not only greatly enhance the fluorescence emission of the hydrophobic dye NBD in aqueous media, probably by accommodating the dye molecules in the interface between the hydrophilic shells and the hydrophobic cores, but also modulate the fluorescence of the dye through intraparticle energy transfer. This biocompatible and photoresponsive nanoparticle complex may find applications in biological areas such as biological diagnosis, imaging, and detection. In addition, this nanoparticle approach will open up possibilities for the fluorescence modulation of other hydrophobic fluorophores in aqueous media.