In the paper, a novel fluorescent sensor L based on phenolphthalein derivative bis-Schiff base was synthesized and characterized. Chemosensor L was found to be an excellent specific receptor for Al3+ via significant fluorescent enhancement resulting from the inhibition of an internal charge transfer (ICT) process and an efficient chelation-enhanced fluorescence (CHEF) effect. A good linear relationship was obtained in the Al3+ concentration from 0 to 50 μM with the detection limit reaching below 15 nM. Moreover, the addition of 2 equiv. of Cu2+ can almost completely quench the emission intensity of L due to a ligand–metal charge transfer (LMCT) process. The resulting L–Cu(II) complex showed a satisfactory sensing ability toward cysteine (Cys) through naked-eye and recovered fluorescence intensity with the detection limit of 0.36 nM. The fluorescence recovering process was caused by the stronger coordination ability of Cys with Cu2+ than with L and therefore free L was released from the L–Cu(II) complex. Furthermore, the sensor was used to detect Cys in practical samples with a high accuracy.

•This sensor NDPA-Fe3O4@SiO2-Cu(II) is capable to detect GSSG with high sensitivity and good selectivity.•The limit of detection for GSSG was 50 pM.•The sensor shows a good linear relationship from 5 nM to 60 μM.•We determined the concentration of GSSG in HEK 293 cell lysate to be 1.15 μM by using of added internal standards.•The presence of magnetic Fe3O4 nanoparticles (NPs) in NDPA-Fe3O4@SiO2 NPs facilitate the magnetic separation of the NDPA-Fe3O4@SiO2 from the solution.A sensitive and selective sensor for oxidized glutathione (GSSG) detection based on the recovered fluorescence of naphthalimide-DPA (NDPA)-Fe3O4@SiO2-Cu(II) system is reported. NDPA-Fe3O4@SiO2 was characterized by X-ray power diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR) and fluorophotometry. The fluorescence of NDPA-Fe3O4@SiO2 could be quenched by Cu2+ due to the coordination of Cu2+ with the tridentate receptor DPA. This coordination process reduced the electron-donating ability of the nitrogen atom in the DPA moiety, thus suppressing the internal charge transfer (ICT) process in NDPA-Fe3O4@SiO2. In the presence of GSSG, the fluorescence of NDPA-Fe3O4@SiO2-Cu(II) was recovered because of strong coordination of Cu2+ with GSSG, which promoted the decomplexation between NDPA-Fe3O4@SiO2 and Cu2+, and enhanced the ICT process. The NDPA-Fe3O4@SiO2-Cu(II) nanomaterial exhibited high sensitivity towards GSSG, and a good linear relationship was obtained from 5 nM to 60 μM. The limit of detection, based on a signal-to-noise ratio of 3, was 50 pM. In addition, the presence of magnetic Fe3O4 nanoparticles (NPs) in NDPA-Fe3O4@SiO2 NPs would also facilitate the magnetic separation of NDPA-Fe3O4@SiO2 from the solution. Through the use of added internal standards, we successfully determined the concentration of GSSG in HEK 293 cell lysate to be 1.15 μM by the prepared chemsensor NDPA-Fe3O4@SiO2-Cu(II). The proposed method is anticipated to fabricate other sensitive fluorescence sensors based on organic–inorganic hybrid magnetic nanoparticles.

A novel prepared mercuric ion PVC membrane sensor based on a Rhodamine B derivative (RND) as a selective sensing material was described. The sensor exhibited a specific fluorescent off-on response to Hg2+, and showed a linear response over the Hg2+ concentration range from 1.0 × 10−9 to 2.0 × 10−3 M with a very low detection limit of 8.1 × 10−10 M in bulk method. The sensor has also been incorporated into a flow-cell for determination of Hg2+ in flowing streams with improved sensitivity and detection limit. The sensor shows excellent selectivity toward Hg2+ with respect to common coexisting cations. The proposed fluorescence optode was successfully applied to detect Hg2+ in environmental water samples and fish.Highlights► A reversible RND-based mercuric ions PVC membrane sensor was described. ► The unique dual chromo- and fluorescence enhancement was observed. ► The optode has a wide dynamic range, high reproducibility, good selectivity. ► The LODs are 8.1 × 10−10 M and 8.3 × 10−11 M in bulk and flow-cell methods. ► It is useful for routine analysis and the analysis in situ without prior treatment.

A novel rhodamine-based fluorescent chemosensor (RND) was synthesized that contains two independent fluorophores and acts as a very sensitive, selective and reversible off–on probe for Hg(II). Importantly, this newly developed sensing system exhibited different fluorescent responses toward Hg(II) and Mg(II) at 589 nm and 523 nm, respectively. RND also displayed detectable color change upon treatment with Hg(II). Results from confocal laser scanning microscopy experiments demonstrated that this chemosensor is cell permeable and can be used as a fluorescent probe for monitoring Hg(II) or Mg(II) in living cells. This probe can also indirectly detect glutathione (GSH) and cysteine (Cys) with good linear relationships.