A novel dihydro phenylquinazolinone-based two-in-one colourimetric chemosensor for nickel(ii), copper(ii) and its copper complex for the fluorescent colourimetric nanomolar detection of the cyanide anion

Currently, considerable efforts have been devoted to the detection and quantification of hazardous multi-analytes using a single probe. Herein, we have developed a simple, environment-friendly colourimetric sensor for the sensitive, selective and rapid detection of Ni²⁺ and Cu²⁺ ions using a simple organic Schiff base ligand L in methanol–Tris–HCl buffer (1 : 1 v/v, 10 mM, pH = 7.2). The probe L exhibited a binding-induced colour change from colourless to yellow and fluorescence quenching in the presence of both Ni²⁺ and Cu²⁺ ions. The interactions between L and the respective metal ions were studied by Job''s plot, electrospray ionisation-mass spectrometry (ESI-MS), Fourier-transform infrared spectroscopy (FT-IR), density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations. The limit of detection (LOD) of L towards Ni²⁺ and Cu²⁺ was calculated to be 7.4 × 10⁻⁷ M and 4.9 × 10⁻⁷ M, respectively. Furthermore, the L–Cu²⁺ complex could be used as a new cascade fluorescent-colourimetric sensor to detect CN⁻ ions with a very low level of detection (40 nM). Additionally, L could operate in a wide pH range, and thus was successfully applied for the detection and quantification of Ni²⁺ and Cu²⁺ in environmental samples, and for building OR- and IMPLICATION-type logic gates.

A novel colorimetric chemosensor L has been developed for the detection of Ni²⁺ and Cu²⁺ ions. The obtained L–Cu²⁺ complex can be used as a new cascade fluorescent-colorimetric sensor for the nanomolar detection of CN⁻ ions. This chemosensor has practical application.     

A dipodal molecular probe for naked eye detection of trivalent cations (Al3+, Fe3+and Cr3+) in aqueous medium and its applications in real sample analysis and molecular logic gates

A simple and low cost multifunctional colorimetric receptor L has been designed, synthesized and characterized by ¹H-NMR, IR spectroscopy, ESI-MS spectrometry and elemental analysis. The chemosensor L can selectively detect three biologically and environmentally important trivalent metal ions (Al³⁺, Fe³⁺and Cr³⁺) both visually and spectrophotometrically in CH₃CN–H₂O (1 : 1, v/v) solution in the presence of other biologically relevant metal ions. The Job''s plot analyses indicate the 2 : 2 binding stereochemistry for Al³⁺, Fe³⁺ and Cr³⁺ ions with L, which was further confirmed by ¹H-NMR and ESI-MS studies. The binding constant values were found to be 2.9 × 10⁴ M⁻¹ for Al³⁺, 1.079 × 10⁵ M⁻¹ for Fe³⁺ and 1.366 × 10⁵ M⁻¹ for Cr³⁺ respectively. The detections limits of the sensor for Al³⁺ (2.8 × 10⁻⁷ M), Fe³⁺ (1.9 × 10⁻⁷ M) and Cr³⁺ (2.5 × 10⁻⁷ M) are far below than the limit set by the World Health Organization (WHO) for drinking water. Moreover, colorimetric test kits for rapid detection of Al³⁺, Fe³⁺, and Cr³⁺ could be successively applied for all practical purposes, indicating its potential use in environmental samples. It has also been used in building molecular logic gates.

A dipodal reversible colorimetric trivalent metal ion chemosensor (L) has been designed and synthesized. The chemosensor L successfully detects Al³⁺, Fe³⁺ and Cr³⁺ based on binding site-signaling approach and it has practical application.     

A bifunctional sensor based on diarylethene for the colorimetric recognition of Cu2+ and fluorescence detection of Cd2+

A novel bifunctional sensor based on diarylethene with a benzyl carbazate unit was synthesized successfully. It not only served as a colorimetric sensor for the recognition of Cu²⁺ by showing changes in absorption spectra and solution color, but also acted as a fluorescent sensor for the detection of Cd²⁺ through obvious emission intensity enhancement and fluorescence color change. The sensor exhibited excellent selectivity and sensitivity towards Cu²⁺ and Cd²⁺, and the limits of detection for Cu²⁺ and Cd²⁺ were 8.36 × 10⁻⁸ mol L⁻¹ and 1.71 × 10⁻⁷ mol L⁻¹, respectively, which were much lower than those reported by the WHO and EPA in drinking water. Furthermore, its application in practical samples demonstrated that the sensor can be effectively applied for the detection of Cu²⁺ and Cd²⁺ in practical water samples.

A bifunctional sensor for colorimetric recognition of Cu²⁺ and fluorescent detection of Cd²⁺ was synthesized. It not only showed high selectivity and sensitivity to Cu²⁺ and Cd²⁺, but also could be used in practical water samples with high accuracy.     

Naphthalimide based smart sensor for CN−/Fe3+ and H2S. Synthesis and application in RAW264.7 cells and zebrafish imaging

Achieving selective detection of target analytes in aqueous media continues to be an arduous proposition. Herein, we report the conceptualization and synthesis of a novel tailor-fit molecular probe R based on 1,8-naphthalimide which acts as a trifunctional molecular sensor for CN⁻, Fe³⁺ and H₂S. R shows colorimetric and fluorometric “on–off” relay recognition for CN⁻ (red colour and orange emission) and Fe³⁺ (no colour and no emission) in 5% H₂O + DMSO medium which is experimentally ascertained to be a tandem deprotonation–protonation process and is supported by ¹H-NMR titration. Among all RSS (Reactive Sulphur Species), R shows selectivity for H₂S through red colouration. Other coexistent anions, cations and RSS cause no discernible perturbation to the detection process. The detection of H₂S is attributed to a chemodosimetric reduction of the nitro to amino group as evidenced by a potentiometric titration assay. The experimental observations are well supported by DFT theoretical calculation. The K_a for CN⁻/Fe³⁺ are 1.4 × 10⁴ M⁻¹, 6.07 × 10⁴ M⁻¹ respectively and photochemical yield of R + CN⁻ is 0.86. Limit of detections for CN⁻, Fe³⁺ and H₂S are 17.5 nM, 8.69 μM and 8.1 μM respectively. Receptor R is effective for real time applications, bio-compatible and has been successfully employed for confocal fluorescence imaging of RAW264.7 cell and zebrafish.

Probe R designed as tailor-fit triple action smart chemosensor for the sequential detection of CN⁻ and Fe³⁺via colorimetric and fluorometric ‘on–off’ method and H₂S through colorimetric method in semi-aqueous conditions.     

Dual-response detection of Ni2+ and Cu2+ ions by a pyrazolopyrimidine-based fluorescent sensor and the application of this sensor in bioimaging

Herein, a dual-response fluorescent sensor, L, based on pyrazolopyrimidine was designed and developed for the simultaneous detection of Ni²⁺ and Cu²⁺ ions in the presence of other metal ions; the structural characterization of L was carried out by FTIR spectroscopy, NMR spectroscopy, HRMS and X-ray diffraction analysis. The sensor L effectively displayed fluorescence quenching towards the Ni²⁺ and Cu²⁺ ions with high sensitivity without interference from other metal ions. The results reveal that L binds to Ni²⁺ and Cu²⁺ in a 2 : 1 pattern, which matches well with the result of the Job''s plot. The association constants of L with Ni²⁺ and Cu²⁺ were 3.2 × 10⁴ M⁻¹ and 7.57 × 10⁴ M⁻¹, respectively. The detection limits (DLs) are down to 8.9 nM for Ni²⁺ and 8.7 nM for Cu²⁺. The fluorescence imaging of L in T-24 cells was investigated because of the low cytotoxicity of L, indicating that L could be used to detect Ni²⁺ and Cu²⁺ in living cells.

A pyrazolopyrimidine-based fluorescent sensor L was developed and applied for detection of Cu²⁺ and Ni²⁺ in ethanol solution by photoluminescence quenching. It shows low cytotoxicity and good imaging characteristics for Cu²⁺ and Ni²⁺ in living cells.     

A solvent-dependent chemosensor for fluorimetric detection of Hg2+ and colorimetric detection of Cu2+ based on a new diarylethene with a rhodamine B unit

A novel solvent-dependent chemosensor 1o based on a diarylethene containing a rhodamine B unit has been designed. It could be used as a dual-functional chemosensor for selective detection of Hg²⁺ and Cu²⁺ by monitoring the changes in the fluorescence and UV-vis spectral in different solvents. A striking fluorescence enhancement at 617 nm was observed in DMSO upon the addition of Hg²⁺. However, 1o showed a remarkable absorption band appeared with maximum absorption at 555 nm after the addition of Cu²⁺ in THF. The results of ESI-MS spectra and Job''s plot confirmed a 1 : 1 binding stoichiometry between 1o and the two ions. The limits of detection of Hg²⁺ and Cu²⁺ were determined to be 0.14 μM and 0.51 μM, respectively. A 1 : 2 demultiplexer circuit was constructed by using UV light as data input, Cu²⁺ as the address input, and the absorbance at 555 nm and the absorbance ratio of (A₆₀₃/A₂₇₄) as the dual data outputs.

A novel solvent-dependent chemosensor based on a diarylethene derivative for fluorescent “turn-on” recognition of Hg²⁺ and colorimetric detection of Cu²⁺ was synthesized, its multi-controllable photoswitchable behaviors with light and chemical stimuli were investigated.     

A highly sensitive and selective chemosensor for Pb2+ based on quinoline–coumarin

In this study, a highly sensitive and selective fluorescent chemosensor, ethyl(E)-2-((2-((2-(7-(diethylamino)-2-oxo-2H-chromene-3-carbonyl)hydrazono)methyl)quinolin-8-yl)oxy)acetate (1), was synthesized and characterized by ¹H NMR, ¹³C NMR and ESI-MS. Sensor 1 showed an “on–off” fluorescence response to Pb²⁺ with a 1 : 1 binding stoichiometry in CH₃CN/HEPES buffer medium (9 : 1 v/v). The detection limit of sensor 1 to Pb²⁺ was determined to be 0.5 μM, and the stable pH range for Pb²⁺ detection was from 4 to 8.

A highly sensitive and selective fluorescent chemosensor 1 was synthesized and used for naked eye detection of Pb²⁺.     

A chemosensor with a paddle structure based on a BODIPY chromophore for sequential recognition of Cu2+ and HSO3−

In this study, a highly selective chemosensor ML based on a BODIPY fluorescent chromophore was synthesized for sequential recognition of Cu²⁺ and HSO₃⁻ in a CH₃OH/H₂O (99 : 1 v/v) system, which contained three recognition sites and its structure characterized by ¹H NMR, ¹³C NMR and ESI-HR-MS. The sensor ML showed an obvious “on–off” fluorescence quenching response toward Cu²⁺ and the ML-Cu²⁺ complex showed an “off–on” fluorescence enhancement response toward HSO₃⁻. The detection limit of the sensor ML was 0.36 μM to Cu²⁺ and 1.4 μM to HSO₃⁻. In addition, the sensor ML showed a 1 : 3 binding stoichiometry to Cu²⁺ and the recovery rate of ML-Cu²⁺ complex identifying HSO₃⁻ could be over 70%. Sensor ML showed remarkable detection ability in a pH range of 4–8.

A highly selective chemosensor based on a BODIPY chromophore for sequential recognition of Cu²⁺ and HSO₃⁻.     

A simple hydrazone as a multianalyte (Cu2+, Al3+, Zn2+) sensor at different pH values and the resultant Al3+ complex as a sensor for F−

A new colorimetric and fluorescence molecular chemosensor based on triazole hydrazone can be used as a multi-probe for selective detection of Al³⁺, Zn²⁺, and Cu²⁺ by monitoring changes in the absorption and fluorescence spectral patterns. Results show that Al³⁺ and Zn²⁺ ions can induce remarkable fluorescence enhancement at pH 6.0 and pH 10.0, respectively, while the addition of Cu²⁺ ions leads to a significant UV-visible absorption enhancement in the visible range at pH 6.0. In addition, the resultant Al³⁺ complex could act as an ‘on–off’ fluorescence sensor for F⁻. The fluorescence sensor was also used to monitor intracellular Al³⁺, Zn²⁺, and F⁻ in Hela cells.

A fluorescent probe for Al³⁺ and Zn²⁺ was synthesised, and the resultant Al³⁺-complex was used for the detection of F⁻.     

A curcumin-based AIEE-active fluorescent probe for Cu2+ detection in aqueous solution

Curcuminoids have been extensively investigated as metal ion probes, but the intrinsic aggregation-caused-quenching (ACQ) characteristic of curcumin would hinder their applications in aqueous solution. Fortunately, tetraphenylethylene (TPE) could endow the compounds with aggregation-induced emission (AIE)/aggregation-induced enhanced emission (AIEE) characteristics to eliminate the ACQ effect. According to this strategy, a series of TPE-modified curcumin derivatives L1–4 were prepared and studied for their AIEE properties. Among the four TPE-curcumin analogues, only L1 particles have been successfully used as an on-off fluorescence probe for detecting Cu²⁺ in aqueous solution. The fluorescence titration experiment determined its detection limit of 1.49 × 10⁻⁷ mol L⁻¹, and the binding ratio between L1 and Cu²⁺ was estimated as 2 : 1, which was in agreement with the results of high resolution mass spectrum and Job''s plot. In addition, the binding constant was evaluated as 6.77 × 10² M⁻¹ using a Benesi–Hildebrand plot. Finally, the obtained L1-based indicator paper showed significant fluorescence response to Cu²⁺ aqueous solution. This TPE-modified strategy improves the detection capability of curcumin probe in aqueous solution and provides a feasible way to obtain other probes with ACQ characteristics.

A curcumin-based AIEE-active L1 was synthesized and used to prepare an on-off fluorescent probe for Cu²⁺ detection in aqueous solution.     

Novel single excitation dual-emission carbon dots for colorimetric and ratiometric fluorescent dual mode detection of Cu2+ and Al3+ ions

In this study, dual-emission carbon dots (D-CDs) are synthesized via a simple one-step solvothermal treatment of red tea. The obtained D-CDs are characterized by XPS, IR, TEM, XRD, fluorescence and UV-vis spectroscopy techniques. It is found that D-CDs present a strong red fluorescence emission peak at 671 nm and weak blue fluorescence emission peak at 478 nm under the excitation wavelength of 410 nm. The unique dual-emission properties of D-CDs provide great opportunities in ratiometric fluorescence sensing applications. The results show that Cu²⁺ ions can quench the fluorescence of the red emission band of D-CDs effectively, resulting in the disappearance of red fluorescence ultimately. Upon the addition of Al³⁺ ions, the fluorescence of blue emission band at 478 nm grows apparently, and the fluorescence color transforms gradually from red to orange, then to yellow-green. Based on these findings, a novel ratiometric fluorescence and colorimetric dual mode nanosensor is developed for simultaneous detection of Cu²⁺ and Al³⁺ ions. Regarding Cu²⁺ ions, the fluorescent detection linear range is 0.1–50 μM with detection limit of 0.1 μM, and the colorimetric detection limit is estimated as 25 μM. With regard to Al³⁺ ions, the fluorescent detection linear range is 0–20 μM and 25–100 μM with detection limit of 0.5 μM, and the colorimetric detection limit is 20 μM. Furthermore, the fluorescence response mechanisms of Cu²⁺ and Al³⁺ ions were discussed detailed. To the best of our current knowledge, this will be the first research work on the simultaneous determination of Cu²⁺ and Al³⁺ using D-CDs as fluorescent probes.

D-CDs with strong red emission and weak blue emission as an effective colorimetric and ratiometric fluorescence sensing probe are employed to realize the simultaneous detection of Cu²⁺ and Al³⁺ ions without any interference effect.     

Zn2+ detection of a benzimidazole 8-aminoquinoline fluorescent sensor by inhibited tautomerization

A new fluorescent chemosensor based on 8-aminoquinoline L1 bearing a benzimidazole moiety was synthesized, which exists as two predominant tautomers L1A and L1B in diluted DMSO-d₆ solution. Among various metal ions, L1 showed a highly selective and sensitive turn-on fluorescence response to the presence of Zn²⁺ ions in methanol. The detection limit for Zn²⁺ by L1 was calculated to be 1.76 × 10⁻⁷ M. The 1 : 1 complexation ratio of the L1–Zn complex was confirmed through Job plot measurements. Complexation studies were performed by FT-IR, NMR and HR-ESI MS measurements and DFT calculations. With the gained insight, it was possible to successfully apply L1 in water sample analysis.

The sensor shows a high selectivity and sensitivity toward zinc cations, accompanied by a distinct green fluorescence emission.     

Two novel colorimetric fluorescent probes: Hg2+ and Al3+ in the visual colorimetric recognition environment

Two new dual channel Schiff base fluorescent probes, Tri-R6G and Tri-Flu, were synthesized, and can detect Hg²⁺ and Al³⁺, respectively. The two probes were characterized by FTIR, ¹H NMR, ¹³C NMR and HRMS, and their optical properties were detected by UV and FL. Test results showed the probes'' detection of Hg²⁺ and Al³⁺ compared to other metal ions (Ag⁺, Co²⁺, Cd²⁺, Mg²⁺, Cu²⁺, Ni²⁺, Ba²⁺, Pb²⁺, Cr³⁺, Al³⁺, Zn²⁺, Hg²⁺, K⁺, Ga²⁺ and Fe³⁺), respectively. Besides, the detection limits were determined to be 1.61 × 10⁻⁸ M and 1.15 × 10⁻⁸ M through the standard curve plot, respectively. The photoelectron transfer (PET) mechanism was guessed by the Job''s plot and the infrared titration. Corresponding orbital electron distribution and molecular geometry configurations of the compounds were predicted by density functional theory (DFT). In addition, the prepared test paper changed from white to pink when the target ion was detected. The color changed from colorless to pink in a solution having a concentration of 10⁻⁵ M.

Two new dual channel Schiff base fluorescent probes, Tri-R6G and Tri-Flu, were synthesized, and can detect Hg²⁺ and Al³⁺, respectively.     

Fluorescence detection of malachite green and cations (Cr3+, Fe3+ and Cu2+) by a europium-based coordination polymer

Due to remarkable fluorescence characteristics, lanthanide coordination polymers (CP) have been widely employed in fluorescence detection, but it is rarely reported that they act as multifunctional luminescent probes dedicated to detecting malachite green (MG) and various metal ions. A europium-based CP fluorescent probe, Eu(PDCA)₂(H₂O)₆ (PDCA = 2,6-pyridinedicarboxylic acid), has been synthesized and exhibited excellent recognition ability for malachite green and metal cations (Cr³⁺, Fe³⁺ and Cu²⁺) among 11 metal cations, 13 anions and six other compounds. The recognition was achieved by fluorescence quenching when MG, Cr³⁺, Fe³⁺ and Cu²⁺ were added to a suspension of Eu(PDCA)₂(H₂O)₆ respectively. Eu(PDCA)₂(H₂O)₆ is a multifunctional luminescent probe, and displayed high quenching efficiencies K_sv (2.10 × 10⁶ M⁻¹ for MG; 1.46 × 10⁵ M⁻¹ for Cr³⁺; 7.26 × 10⁵ M⁻¹ for Fe³⁺; 3.64 × 10⁵ M⁻¹ for Cu²⁺), and low detection limits (MG: 0.039 μM; Cr³⁺: 0.539 μM; Fe³⁺: 0.490 μM; Cu²⁺: 0.654 μM), presenting excellent selectivity and sensitivity, especially for MG. In addition, Eu(PDCA)₂(H₂O)₆ was also made into fluorescent test strips, which can rapidly and effectively examine trace amounts of MG, Cr³⁺, Fe³⁺ and Cu²⁺ in aqueous solutions. This work provides a new perspective for detecting malachite green in fish ponds and heavy metal ions in waste water.

A europium-based CP fluorescent sensor was synthesized and exhibited excellent recognition ability for malachite green (MG) and metal cations (Cr³⁺, Fe³⁺ and Cu²⁺).     

Synthesis,characterisation and ion-binding properties of oxathiacrown ethers appended to [Ru(bpy)2]2+. Selectivity towards Hg2+, Cd2+ and Pb2+

A series of complexes with oxathiacrown ethers appended to a [Ru(bpy)₂]²⁺ moiety have been synthesized and characterised using ¹H NMR, ¹³C NMR, IR, electronic absorption and emission spectroscopies, mass spectrometry and elemental analyses. The complexes exhibit strong MLCT luminescence bands in the range 608–611 nm and one reversible metal centred oxidation potential in the range 1.00–1.02 V. Their selectivity and sensitivity towards Hg²⁺, Cd²⁺ and Pb²⁺ metal ions have been investigated using electronic absorption, luminescence, cyclic and differential pulse voltammetry titrations. Their responses towards selected cations and anions have also been investigated using electronic absorption and luminescence. While the complexes are selective towards Hg²⁺ and Cd²⁺ ions, none of them is selective towards Pb²⁺ ions. In particular, complex 2 gives a selective change in the UV/Vis absorbance with Hg²⁺ making it possible to detect mercury down to a detection limit of 68 ppm. The binding constants and limits of detection of the complexes have been calculated, with values ranging from 4.37 to 5.38 and 1.4 × 10⁻³ to 6.8 × 10⁻⁵ for log K_s and LOD respectively.

Oxathiacrown ether modified ruthenium complex 2 facilitates a selective naked-eye detection of Hg²⁺ with an instrumental detection limit of 68 ppm.     

A colorimetric and ratiometric fluorescent sensor for sequentially detecting Cu2+ and arginine based on a coumarin–rhodamine B derivative and its application for bioimaging

In this work, a colorimetric and ratiometric fluorescent sensor based on a coumarin–rhodamine B hybrid for the sequential recognition of Cu²⁺ and arginine (Arg) via the FRET mechanism was designed and synthesized. With the addition of Cu²⁺, the solution displayed a colorimetric change from pale yellow to pink which is discernible by the naked eye. Additionally, the fluorescence intensities of the sensor exhibited ratiometric changes for the detection of Cu²⁺ at 490 and 615 nm under a single excitation wavelength of 350 nm, which corresponded to the emissions of coumarin and rhodamine B moieties, respectively. The fluorescence color change could be visualized from blue to pink. The limits of detection were determined to be as low as 0.50 and 0.47 μM for UV-vis and fluorescence measurements, respectively. More importantly, the sensor not only can recognize Cu²⁺ and form a sensor-Cu²⁺ complex but can also sequentially detect Arg with the resulting complex. The detection limits for Arg were as low as 0.60 μM (UV-vis measurement) and 0.33 μM (fluorescence measurement), respectively. A fluorescence imaging experiment in living cells demonstrated that the fabricated sensor could be utilized in ratiometric fluorescence imaging towards intracellular Cu²⁺, which is promising for the detection of low-level Cu²⁺ and Arg with potentially practical significance.

A FRET-based colorimetric and ratiometric coumarin–rhodamine B fluorescent sensor was designed, and its sensing behaviors for sequentially detecting Cu²⁺ and arginine were studied systematically.     

A sensitive OFF–ON–OFF fluorescent probe for the cascade sensing of Al3+ and F− ions in aqueous media and living cells

A simple Schiff-base ligand 2-hydroxy-1-naphthaldehyde semicarbazone (HNS) was synthesized and characterized. Based on the combined effect of inhibition of CH N isomerization and chelation-enhanced fluorescence (CHEF), HNS functions as a fluorescence “turn on” sensor for Al³⁺ in buffered aqueous media. Based on the strong affinity of Al³⁺ to F⁻ ions, the in situ generated Al³⁺–HNS complex can also be utilized as an effective chemosensor for F⁻ sensing by metal displacement approach, ensuing quenching of fluorescence by the reversible return of HNS from Al³⁺–HNS complex. Thus a method using a single probe for the detection of both Al³⁺ and F⁻ ions is developed. The system exhibits high selectivity and sensitivity for Al³⁺ and F⁻ ions and the detection limits were found to be as low as 6.75 × 10⁻⁸ M and 7.89 × 10⁻⁷ M, respectively. Furthermore, the practical applicability of this probe has been examined in living cells.

A simple Schiff-base ligand 2-hydroxy-1-naphthaldehyde semicarbazone (HNS) was synthesized and applied to the sequential sensing of Al³⁺ and F⁻ ions in aqueous media and live cells.     

Ratiometric fluorescence probe of Cu2+ and biothiols by using carbon dots and copper nanoclusters

A novel dual-emission ratiometric fluorescent probe based on N-doped yellow fluorescent carbon dots (y-CDs) and blue fluorescent copper nanoclusters (CuNCs) was established for quantitative determination of Cu²⁺ and biothiols. In this work, the Cu²⁺-(y-CDs) complexes formed by the chelation of y-CDs with Cu²⁺, showed an absorption peak at 430 nm that not only enhanced the fluorescence of y-CDs through inhibiting photoinduced electron transfer (PET) but also effectively quenched the fluorescence of CuNCs due to Förster resonance energy transfer (FRET). In addition, the chelation of y-CDs with Cu²⁺ could be inhibited by biothiols that prevented the fluorescence of y-CDs from being enhanced and the fluorescence of CuNCs from being quenched. On account of the changes of ratiometric signal, a dual-emission fluorescence probe for Cu²⁺ and biothiols determination was achieved. The proposed method exhibited high sensitivity for Cu²⁺ and biothiols in the ranges of 0.5–100 μM and 0.8–50 μM and the limits of detection (LODs) of Cu²⁺, glutathione (GSH), cysteine (Cys) and homocysteine (Hcy) were 0.21 μM, 0.33 μM, 0.39 μM and 0.46 μM, respectively. Subsequently, the established strategy presented an application prospect for the detection of Cu²⁺ and biothiols in real samples.

A dual-mechanism ratiometric fluorescent probe based on N-doped yellow fluorescent carbon dots (y-CDs) and blue fluorescent copper nanoclusters (CuNCs) was established for the first simultaneous determination of Cu²⁺ and biothiols.     

A new fluorescent and colorimetric chemosensor for Al3+ and F−/CN− based on a julolidine unit and its bioimaging in living cells

A novel multifunctional chemosensor HL bearing a julolidine unit and a Schiff base unit has been synthesized. As a fluorescent sensor, HL exhibited excellent selectivity and high sensitivity to Al³⁺ and F⁻/CN⁻ with a low detection limit in acetonitrile. Moreover, HL also showed good colorimetric selectivity to F⁻/CN⁻; a solution color change from colorless to light yellow in acetonitrile was observed by the ‘naked-eye’. The properties of HL with Al³⁺ and F⁻/CN⁻ were studied by UV-vis absorption spectroscopy, fluorescence spectroscopy, high-resolution mass spectrometry and ¹H NMR titration. Furthermore, the cell imaging experimental results indicated that the chemosensor HL could be applied for the detection of Al³⁺ in living cells.

A novel multifunctional chemosensor HL bearing a julolidine unit and a Schiff base unit has been synthesized.     

An ‘‘off–on–off’’ sensor for sequential detection of Cu2+ and hydrogen sulfide based on a naphthalimide–rhodamine B derivative and its application in dual-channel cell imaging

A novel colorimetric and fluorometric sensor with unique dual-channel emission to sequentially detect Cu²⁺ and hydrogen sulfide (H₂S) was synthesized from naphthalimide–rhodamine B through the PET and FRET mechanism. The sensor showed a selective “off–on” fluorescence response with a 120-fold increase toward Cu²⁺, and its limits of detection were 0.26 μM and 0.17 μM for UV-vis and fluorescence measurements, respectively. In addition, 1–Cu²⁺ was an efficient “on–off” sensor to detect H₂S with detection limits of 0.40 μM (UV-vis measurement) and 0.23 μM (fluorescence measurement), respectively. Furthermore, the sensor can also be used for biological imaging of intracellular staining in living cells. Therefore, the sensor should be highly promising for the detection of low level Cu²⁺ and H₂S with great potential in many practical applications.

A novel colorimetric and fluorometric sensor with unique dual-channel emission to sequentially detect Cu²⁺ and hydrogen sulfide (H₂S) was synthesized from naphthalimide–rhodamine B through the PET and FRET mechanism.