A new “on–off” fluorescent probe 4′,5′-bis((bis(thiophen-2-ylmethyl)amino)methyl)-2′,7′-dichloro-3′,6′-dihydroxy-3H-spiro[isobenzofuran-1,9′-xanthen]-3-one (probe F) for the selective detection of copper ions was synthesized and characterized. The favorable features of the proposed probe included good selectivity, high sensitivity, excellent water solubility, low toxicity, and simple operation. In addition, the probe has good reusability and a wide range of applications. The linear range for copper ions was 0.005–100 μM with a limit of detection of 5 nM. Moreover, the experiments also showed that the probe was a reliable and specific probe for copper ion imaging in living cells.

Synthesis of graphene oxide quantum dots (GO-dots) often requires strong concentrated acid, and takes a long time. Herein, we used black carbon as a precursor and H2O2 as a facile oxidant and developed a simple and facile one-pot hydrothermal method for synthesis of GO-dots without the need to use strong concentrated acid and the entire synthetic process only took 90 min. Furthermore, any other post-processing steps are avoided.

A novel coumarin-based nonsulfur probe, 7-(propargylamino)-4-methyl-2H-chromene-2-one (CNP), for selective detection of Hg2+ was synthesized by one-step substitution reaction. In the probe, alkyne was exploited as the specific recognition unit, which would be transformed into ketone in the presence of mercuric ion with a catalytic amount. The intramolecular charge-transfer (ICT) process was modulated and thus the fluorescence of CNP was quenched. The detection limit of mercury (II) was in the nanomolar range and the probe can be used to accurately quantify the ion spiked in river water specimens. Moreover, agar gels based on CNP were fabricated, which could be acted as a solid optical sensor to detect Hg2+ conveniently and efficiently.

•A sensitive and selective fluorescent probe for sensing H2S was developed.•The sensing mechanism of the synthesized probe was based on ESIPT.•Upon treatment with H2S, fluorescence of the probe shows a large Stokes shift.•The probe can be used for fluorescence imaging of H2S in living cells.A novel probe based on the fluorescence off–on strategy was prepared to optically detect hydrogen sulfide (H2S) via an excited state intramolecular proton transfer (ESIPT) mechanism. The probe shows high sensitivity and excellent selectivity to H2S. It also displays a large Stokes shift (∼140 nm) and a remarkable quantum yield enhancement (Ф = 0.412) after interaction with H2S. Moreover, the cellular imaging experiment demonstrated that it has potential utility for H2S sensing in biological sciences.

Two novel ESIPT-based fluorescent probes, N-(2-(1-(p-tolyl)-1H-phenenanthro[9,10-d]imidazol-2-yl)phenyl) picolinamide (Pi-A) and 2-(1-(p-tolyl)-1H-phenanthro[9,10-d]imidazol-2-yl)phenylpicolinate (Pi-E), were designed and synthesized. The favorable features of the proposed probes included excellent water solubility, wide pH range, high selectivity and sensitivity to Cu2+. Interestingly, the difference in the linker of the probe molecules led to a radical change in the fluorescent response of the probes to Cu2+. Pi-A showed fluorescence turn-off towards Cu2+ with a detection limit of 1.6 × 10−9 M and Pi-E showed fluorescence turn-on towards Cu2+ with a detection limit of 1.8 × 10−8 M in the same condition. The Cu2+ recognition mechanisms of the probes were investigated by Job's plot analyses, NMR and ESI-MS spectroscopy experiments. Moreover, our experiments also showed that the probes are of excellent cell permeability and are capable of imaging Cu2+ within living cells.

•A new ferrocene benzyne derivative modified magnetic composite was firstly synthesized.•A double signal amplification platform was fabricated by a ferrocene nanocomposite.•Fe3O4@Au–S–Fc/GS-chitosan/GCE exhibits amplification effect to AA, DA, UA and AC.•Simultaneous and ultrasensitive detection of AA, DA, UA and AC were realized.A double signal amplification platform for ultrasensitive and simultaneous detection of ascorbic acid (AA), dopamine (DA), uric acid (UA) and acetaminophen (AC) was fabricated by a nanocomposite of ferrocene thiolate stabilized Fe3O4@Au nanoparticles with graphene sheet. The platform was constructed by coating a newly synthesized phenylethynyl ferrocene thiolate (Fc-SAc) modified Fe3O4@Au NPs coupling with graphene sheet/chitosan (GS-chitosan) on a glassy carbon electrode (GCE) surface. The Fe3O4@Au–S–Fc/GS-chitosan modified GCE exhibits a synergistic catalytic and amplification effect toward AA, DA, UA and AC oxidation. The oxidation peak currents of the four compounds on the electrode were linearly dependent on AA, DA, UA and AC concentrations in the ranges of 4–400 μM, 0.5–50 μM, 1–300 μM and 0.3–250 μM in the individual detection of each component, respectively. By simultaneously changing the concentrations of AA, DA, UA and AC, their electrochemical oxidation peaks appeared at −0.03, 0.15, 0.24 and 0.35 V, and good linear current responses were obtained in the concentration ranges of 6–350, 0.5–50, 1–90 and 0.4–32 μM with the detection limits of 1, 0.1, 0.2 and 0.05 μM (S/N=3), respectively.

A novel label-free and sensitive fluorescent aptasensor for the detection of potassium ion (K+) was developed based on the horseradish peroxidase–mimicking DNAzyme (HRP–DNAzyme). In this work, we selected a K+-stabilized single stranded DNA (ssDNA) with G-rich sequence as the recognition element. In the presence of K+, the G-rich DNA folded into the G-quadruplex structure, and then hemin can bind to the G-quadruplex structure as a co-factor and form HRP–DNAzyme. 3-(p-Hydroxyphenyl)-propanoic acid (HPPA) can be oxidized by H2O2 into a fluorescent product in the presence of DNAzyme. The fluorescence intensity of the HPPA oxidative product increased with the K+ concentration. Under the optimal conditions, the fluorescence intensity was linearly related to the logarithm of K+ concentration in the range of 2.5 μM to 5 mM. Other metal ions, such as Na+, Li+, NH4+, Mg2+ and Ca2+ caused no notable interference on the detection of K+.Highlights► A novel label-free potassium ions (K+) fluorescent aptasensor was developed. ► A single stranded G-rich DNA (ssDNA) was used as the recognition element for K+. ► The employed DNA specifically interacts with K+ and hemin to form a DNAzyme. ► H2O2-mediated oxidation of 3-(p-Hydroxyphenyl)-propanoic is accelerated by the DNAzyme. ► The proposed aptasensor is of high selectivity and sensitivity for K+ detection.

A novel symmetric conjugated oligo(phenylene-ethynylene) (OPE) linear molecule (1,4-bis(4-aminophenylethynyl)benzene); BAB) was synthesized by Sonogashira cross-coupling reactions. The structure and purity of the compound were confirmed by 1H NMR, 13C NMR and infrared (IR) and mass spectrometry (MS). The electrochemical oxidation process and mechanism of BAB were investigated via in situ Fourier transform infrared (FTIR) spectroelectrochemistry and electrochemical quartz crystal microbalance (EQCM). The electrochemical oxidation mechanism of BAB was proposed. The studies revealed that the BAB concentration and oxidation potential had a significant influence on the growth of the polymer film. A densely packed polymer film, which exhibited nonelectroactivity, was formed when a high monomer concentration and a high oxidation potential were used. When the electropolymerization of BAB was conducted at a lower concentration, a new pair of redox peaks appeared, and the resultant thin film had better electroactivity. The in situ FTIR studies confirmed that BAB could be electro-oxidized into radical cations and then electropolymerized via para (N-N) and/or ortho (N-C) coupling reactions to form polymers with a larger conjugated π-electron system. The surface morphology of the poly-BAB was also investigated with atomic force microscopy (AFM) and scanning electron microscopy (SEM).

Macroporous poly(methyl methacrylate-co-divinylbenzene) (PMMA), interpenetrating polymer adsorbent based on poly(styrene-co-divinylbenzene) (PS) and poly(methyl methacrylate-co-divinylbenzene) (PMMA/PS), and macroporous cross-linked poly(N-p-vinylbenzyl acetylamide) (PVBA) were prepared for the adsorption of phenol from cyclohexane. The sorption isotherms of phenol on the three polymeric adsorbents were measured and fitted to Langmuir and Freundlich isotherms. It is shown that the Langmuir isotherm, which is based on a homogeneous surface model, is unsuitable to describe the sorption of phenol on the adsorbents from nonaqueous solution and the Freundlich equation fits the tested three adsorption systems well. The isosteric enthalpy was quantitatively correlated with the fractional loading for the sorption of phenol onto the three polymeric adsorbents. The surface energetic heterogeneity patterns of the adsorbents were described with functions of isosteric enthalpy. The results showed that the tested three polymeric adsorbents exhibited different surface energetic heterogeneity patterns. The initial isosteric enthalpy of phenol sorption on polymeric adsorbent has to do with the surface chemical composition and is free from the pore structure of the polymeric adsorbent matrix. Forming hydrogen bonds between phenol molecules and adsorbent is the main driving force of phenol sorption onto PVBA and PMMA adsorbent from nonaqueous solution. When phenol is adsorbed on PMMA/PS, π–π interaction resulting from the stacking of the benzene rings of the adsorbed phenol molecules and the pendant benzene ring of adsorbent is involved.

•A benzothiazole-based probe for multiple metal ions has been firstly developed.•The differential sensing mechanisms of Hg2+ and Cu2+ relied on different reaction.•The probe could be used to monitor Hg2+ and Cu2+in vitro and in vivo with distinct fluorescence changes.A new benzothiazole-based fluorescent probe 2-(benzo[d]thiazol-2-yl)-4-(1,3- dithian-2-yl)phenol (BT) with two different reaction sites, a thioacetal group (site 1 for Hg2+), and O and N atoms of the benzothiazole dye (site 2 for Cu2+), was designed and synthesized. The probe BT showed ratiometric fluorescent response to Hg2+ and fluorescence quenching behavior to Cu2+, which induces naked-eye fluorescent color changes from green to blue and colorless, respectively. Moreover, it displayed highly sensitivity and selectivity toward Hg2+ and Cu2+ without interference from other metal ions. The sensing mechanisms were also confirmed by 1H NMR titration, mass spectrum and Job's plot analyses. Finally, probe BT was successfully used for fluorescent imaging of Hg2+ and Cu2+ in living cells, demonstrating its potential applications in biological science.