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Polymeric nanoparticles (NPs) with two-photon (TP) activity were prepared by grafting a naphthalimide fluorophore onto poly(acrylic acid) to yield an amphiphilic polymer, which self-assembled in water. The NPs were characterized using various analytical techniques such as transmission electron microscopy, dynamic light scattering and spectroscopic measurements. The in vitro and in vivo biocompatibilities of the NPs were assessed by a cytotoxicity assay using HeLa cells and a feeding assay using Caenorhabditis elegans ( C. elegans ) as a small animal model, respectively. Finally, TP fluorescence imaging (FI) of living cells and C. elegans labelled with the NPs were observed by TP confocal microscopy. The experimental outcomes demonstrated that the NPs had sufficient water-dispersity and biocompatibility, had TP fluorescence activity, were resistant to pH variation and illumination, and were physically stable. TP FI revealed that the NPs could enter living cells and were primarily located in the cytoplasm. In addition, the NPs were ingested by C. elegans during the feeding process and were recognized and taken up by the active transport system of the intestinal cells. These findings indicated the feasibility of using the developed NPs as a nanolabel for TP FI. Moreover, with numerous modifiable carboxyl groups on its surface, the NPs could act as a platform to build multifunctional probes for potential applications in biosensing and assay labeling. [ABSTRACT FROM AUTHOR]

In this work, a hydrophilic naphthalimide-based fluorescence chemosensor (sensor 1) was synthesized for Cu2+ recognition, in which 2-(2-aminoethoxy)ethanol was introduced to improve the hydrophily and Schiff base acted as the multidentate ligand for Cu2+. The effect factors, sensing mechanism and regenerability of sensor 1 for Cu2+ sensing were systematically investigated. It was found that sensor 1 displayed a long emission wavelength of 532 nm upon excited in visible light region (436 nm), and the good water solubility made it utilized in aqueous media. It could selectively react with Cu2+ over other common metal ions to form a 2:1 complex within 1 min and result in significant fluorescence quench. The fluorescence change was linear to 0.5–10.0 μmol L−1 of Cu2+ with a low detection limit of 3.74 × 10−8 mol L−1. Sensor 1 has been successfully utilized for analyzing Cu2+ in water samples as well as imaging cellular Cu2+. Moreover, in view of fluorescence "on-off-on" switches of sensor 1 induced by Cu2+ and EDTA, an IMPLICATION logic gate was constructed based on fluorescence mode with Cu2+ and EDTA as inputs. Unlabelled Image • A hydrophilic Schiff base-linked naphthalimide as a new Cu2+ fluorescence sensor • Fluorescence "turn-off" change at 532 nm due to the complex of the sensor and Cu2+ • Rapid and selective Cu2+ sensing in aqueous solution with large Stokes shift • Applications in real samples analysis, living cells imaging and molecular logic gate. [ABSTRACT FROM AUTHOR]

A maleimide coupling naphthalimide was reported as new two-photon fluorescent (TPF) probe for cysteine (Cys). The probe was weakly fluorescent itself due to the donor-excited photoinduced electron transfer (d-PET). After reaction with Cys, d-PET process was blocked and fluorescence enhancement of the probe was observed at 470 nm. The d-PET principle was rationalized by theoretical calculations with density functional theory and time-dependent density functional theory. Thiol-maleimide addition between the probe and Cys was confirmed by 1 H NMR and mass spectrum measurements. TPF analysis demonstrated a 24.7-fold emission increase of the probe induced by Cys upon excitation at 760 nm. The two-photon action cross-section of probe-Cys adduct at 760 nm reached 42 GM compared to 1.7 GM for free probe. The probe showed high sensitivity and selectivity to Cys over other potential interferences; especially it had the capability to discriminate Cys from glutathione and homocysteine. Through TPF imaging, the probe was successfully applied in the detection of Cys in living cells. [ABSTRACT FROM AUTHOR]