A rapid selective colorimetric and ‘On–Off’ fluorimetric sensor for detecting Cu2+ ions in aqueous media based on a simple bis-schiff-base derivative

A simple colorimetric and fluorimetric ‘On–Off’ sensor L (3,3′-dimethyl -[1,1′-biphenyl]-4,4′-diyl)bis(azanylylidene)bis(methanylylidene)bis(naphthalen-2-ol) for Cu²⁺ ions bearing o-tolidine substituents has been designed and synthesised, and exhibits significant fluorimetric and colorimetric response for Cu²⁺ in DMSO/H₂O (8:2, v/v) HEPES buffer (pH 7.2) solution. The detection limit of the sensor towards Cu²⁺ is 7.25 × 10^? 8 M and the association constant K_a of 9.86 × 10⁴ M^? 1 was determined. Furthermore, other anions, including Fe³⁺, Hg²⁺, Ag⁺, Ca²⁺, Co²⁺, Ni²⁺, Cd²⁺, Pb²⁺, Zn²⁺, Cr³⁺ and Mg²⁺ have almost no influence on the probe's behaviour. Test strips based on the sensor L were fabricated, which could act as convenient and efficient Cu²⁺ test kits.     

A biacylhydrazone-based chemosensor for fluorescence ‘turn-on’ detection of Al3+ with high selectivity and sensitivity

A simple Al³⁺ fluorescent chemosensor (1) based on diacylhydrazone has been designed and synthesized by the condensation reaction of 2-hydroxy naphthaldehyde and metaphthalic hydrazide. The chemosensor 1 displays a specific and sensitive response to Al³⁺ over other cations in DMSO solution. Upon the addition of DMSO solution of Al³⁺, the sensor 1 shows an immediate fluorescence ‘turn-on’ response and emitting strong blue emission with visible color change from colorless to green. The fluorescence quantum yield enhanced from 7.24% to 48.68%. Meanwhile, the fluorescence and UV absorption spectra detection limits of the chemosensor 1 for Al³⁺ were 2.0 × 10^?7 M and 5.6 × 10^?7 M respectively, indicating the high sensitivity of 1 to Al³⁺. Furthermore, test strips based on 1 were fabricated, which could be used as a convenient test kit for the detection of Al³⁺ and an efficient Al³⁺ controlled fluorescent security display materials.     

A fluorescence “on–off” sensor for the highly selective and sensitive detection of Cu2+ ion

In an attempt to obtain a model of copper(II) ion-selective sensors, a new 1,8-naphthalimide-based fluorescence chemosensor, N-allylamine-4-[(E)-4-(([2-aminoethyl]imino)methyl) benzene-1,3-diol]-1,8-naphthalimide (NABN), was designed and synthesized. The sensor NABN is fully characterized by melting point analysis, fourier transform infrared spectra, Ultraviolet–visible (UV–vis) spectra, fluorescence spectra, ¹H NMR and ¹³C NMR spectroscopy, and mass spectrometry. NABN showed an unrivaled sensing behavior and an ardent selectivity toward copper(II) ion over other competitive metal ions tested in solution (N,N-Dimethylformamide (DMF)/Tris–HCl buffer, 1:1, v/v, pH = 7.2). The sensor showed a linear fluorescence quenching toward copper(II) ion in the range 0–50 μM, with a detection limit of 1.92 × 10⁻⁷ M estimated. Job's method indicated the formation of a 2:1 coordinative mode of the sensor with copper(II) ion with a high threshold of binding constant of 4 × 10¹² M⁻¹. Combining the above results, the quenching response of NABN toward Cu(II) ions could be ascribed to the strong, intrinsic paramagnetic behavior of Cu(II).     

Two types of rhodamine–naphthalimide-based fluorescence sensors for different ratiometric detection of Hg(II) or Fe(III)

Two types of rhodamine–naphthalimide sensors 1a–1c and RND with different polyamine linkers and terminal chains were designed and synthesized for different ratiometric detection of Fe(III) or Hg(II). The fluorescent properties including response time, pH effect, selectivity, anti-interference, fluorescence titration and reproducibility were investigated and compared in details. Sensor RND possessing two recognition groups of rhodamine and 1-(pyridin-2-ylmethyl)piperazine displayed good response and selectivity to Hg(II) with a detection limit of 1.72 μmol/L, whereas 1a–1c with piperidine instead of 1-(pyridin-2-ylmethyl)piperazine showed quite different recognition to Fe(III) and the detection limit of 1b was the lowest (1.92 μmol/L). The Hg(II)/Fe(III) chelation-induced dual/single recognition mechanisms as well as the structure–fluorescence properties relationships (SFPRs) were discussed in detail with the aid of quantum chemical density functional theory (DFT) calculations. Through adjusting the linker and introducing other recognition groups to rhodamine- naphthalimide system, novel sensors with selective recognition of different metal ions should be achieved.

     

A highly selective fluorescent chemosensor for successive detection of Fe3+ and CN− in pure water

A water-soluble fluorescent chemosensor (D) based on 1, 8-naphthalimide derivative has been designed and synthesised as a new fluorescent sensor for successive detection of Fe³⁺ and CN^?. Fluorescence measurements show that chemosensor D has excellent fluorescent-specific selectivity and high sensitivity for Fe³⁺ over many other metal ions in pure water. Moreover, the complex of D and Fe³⁺ (D–Fe³⁺) displayed high sensitivity for CN^? over many other anions in the same medium. Even more important, the recognition of the sensor D for Fe³⁺ and D–Fe³⁺ complex for CN^- could be used successfully in pure water. The test strips based on D and D–Fe³⁺ exhibited good selectivity to Fe³⁺ and CN,^- respectively, we believe the test strips could serve as convenient and efficient Fe³⁺ and CN^? test kits.     

Naphthalene thiourea derivative based colorimetric and fluorescent dual chemosensor for F− and Cu2+/Hg2+ ions

A structurally simple (Z)-2-(naphthalen-2-ylmethylene)-N-phenylhydrazinecarbothioamide (R1) was used as a colorimetric and fluorescent sensor for both F^?  and Cu²⁺/Hg²⁺ ions. R1 selectively recognised F^?  ions as indicated by colour change from colourless to green. Fluorescence spectral data reveal that R1 is an excellent fluorescence chemosensor for Cu²⁺ ions. Finally, R1 was successfully applied to the bioimaging of Cu²⁺ ions in RAW 264.7 macrophage cells.     

Turn-on fluorescence probe for selective detection of Hg(Ⅱ)by calixpyrrole hydrazide reduced silver nanoparticle: Application to real water sample

A simple and quick method for the synthesis of water dispersible stable silver nanoparticles has been developed. Calix[4]pyrrole octahydrazide(CPOH), has been successfully used as a reducing as well as stabilizing agent for the synthesis of silver nanoparticles. CPOH-AgNps have been duly characterized by SPR, PSA, TEM and EDX-ray. The ability of CPOH-AgNps as selective and sensitive sensor for various ions(Pb(Ⅱ), Cd(Ⅱ), Mn(Ⅱ), Fe(Ⅲ), Ni(Ⅱ), Zn(Ⅱ), Hg(Ⅱ), Co(Ⅱ), Cu(Ⅱ)) by colorimetry and spectrofluorimetry has been explored. CPOH-AgNps were found to be selective only for Hg(Ⅱ) ions. Nanomolar concentration of Hg(Ⅱ) ions can also be determined by spectrofluorimetry by increase in fluorescence intensity. Linear range of detection of Hg(Ⅱ) ions in water was found to be from 1 nmol/L to 1 μmol/L. The method has been successfully applied for determination of Hg(Ⅱ) ions in ground water and industrial effluent waste water samples.     

A dual chemosensor for Cu2+ and Fe3+ based on π-extend tetrathiafulvalene derivative

A new dual chemosensor (TTF-PBA) for Fe³⁺ and Cu²⁺ in different signal pathways was designed and synthesized. The absorption spectrum, fluorescence spectrum and cyclic voltammograms changed in the presence of Cu²⁺ and Fe³⁺. The optical color changed within 5 s from yellow to orange upon the addition of Cu²⁺, and it changed to dark yellow when Fe³⁺ existed. The cyclic voltammogram of Cu²⁺/TTF-PBA changed from E_ox = 0.50 V, E_red = 0.32 V to E_ox = 0.64 V, E_red = 0.80 V (vs Ag/AgCl) upon the addition of 2.0 equiv. Cu²⁺. As for Fe³⁺/TTF-PBA, its oxidation wave disappeared, and its reduction wave appeared at E_red = ?0.59 V (vs Ag/AgCl) upon the addition of 4.0 equv. Fe³⁺. The sensor displayed high selectivity for Cu²⁺ and Fe³⁺ over other ions including Pb²⁺, Zn²⁺, Ni²⁺, Ag⁺, Cr³⁺, Mn²⁺, Al³⁺, Co²⁺, Pd²⁺, Hg²⁺, Fe^2+, Cd²⁺, Ce³⁺, Bi³⁺ and Au³⁺, the detection limits for Cu²⁺ and Fe³⁺ ion reached as low as 5.33 × 10^?7 mol/L and 5.34 × 10^?7 mol/L, respectively. Furthermore, when Fe³⁺ existed, Cu²⁺ can be detected sequentially by the sensor through the absorption spectrum and the color change observed by naked-eyes.     

A New ‘Off–On’ System Based on Core-Substituted Naphthalene Diimide with Dimethylamine for Reversible Acid–Base Sensing

A new ‘Off–On’ system designed and synthesised by functionalisation of a naphthalene diimide (NDI) core with dimethylamine produces 4,9-bis(dimethylamino)-2,7-dioctylbenzo[lmn][3,8]-phenanthroline-1,3,6,8-(2H,7H)-tetraone, abbreviated as DDPT ( 1 ). DDPT 1 was synthesised using a simple strategy, namely aromatic nucleophilic substitution using Br₂-NDI with dimethylamine at 110 °C. DDPT was characterized by ¹H and ¹³C NMR spectroscopy, ESI mass spectrometry and elemental analysis. DDPT 1 was then used for optical studies through protonation of its dimethylamine core with trifluoroacetic acid (TFA), blue-shifting the absorption band from 600 nm to 545 nm in solution. Interestingly, the fluorescence of DDPT 1 is weak in solution with a quantum yield Φ=0.09, which is significantly enhanced to Φ=0.78 upon addition of TFA. The limit of detection (LOD) was determined to 2.77 nm . Furthermore, DDPT 1 can be used for naked eyed detection not only under UV light (365 nm) but also using visible light, as clear changes can be clearly seen upon addition of TFA. The binding constant of DDPT was calculated to 2.1×10⁻³ m ⁻¹. Importantly, DDPT 1 showed reversible switching by alternative addition of acid (TFA) and base (triethylamine) without loss of activity. Immobilised on paper, DDPT 1 can be used for strip-test sensing in which the colour changes from blue to reddish when expose to TFA vapours and reverse in the presence of triethylamine vapours.     

A novel colorimetric and “turn-on” fluorescent sensor for selective detection of Cu2+

In this work, a new highly selective and sensitive fluorescent sensor for detecting Cu²⁺ was developed based on rhodamine fluorophore. It displayed strong fluorescence “turn-on” effect upon addition of Cu²⁺, and possessed the function of naked eye recognition. The fluorescence enhancement also enabled the sensor to quantitatively analyze Cu²⁺ due to the formation of a stable 1:1 metal–ligand complex in a short time, and the complex possesses relatively good pH stability. In addition, the density functional theory calculations were adopted to investigate the molecular orbitals as well as the spatial structure. Simultaneously, the cell imaging and zebra fish experiments provided a broader application prospect in biological system.     

Rhodamine-linked pyridyl thiourea as a receptor for selective recognition of F–, Al3+ and Ag+ under different conditions

A new rhodamine-labelled pyridyl thiourea-based compound 1 has been designed and synthesised. While the receptor selectively recognises F^– and Al³⁺ ions in CH₃CN, Al³⁺ and Ag⁺ ions are selectively screened from other cations in CH₃CN/water (4/1, v/v; 10 μM Tris–HCl buffer, pH 6.8) by observing different emission characteristics and colour changes. While Ag⁺ is sensed through an increase in emission at 416 nm, Al³⁺ is detected by a ratiometric change in emission of 1 with a band at 585 nm. The receptor shows in vitro detection of both the ions in human cervical cancer (HeLa) cells.     

Nanostructured Fe2O3–graphene composite as a novel electrode material for supercapacitors

Nanostructured Fe₂O₃–graphene composite was successfully fabricated through a facile solution-based route under mild hydrothermal conditions. Well-crystalline Fe₂O₃ nanoparticles with 30–60?nm in size are highly encapsulated in graphene nanosheet matrix, as demonstrated by various characterization techniques. As electrode materials for supercapacitors, the as-obtained Fe₂O₃–graphene nanocomposite exhibits large specific capacitance (151.8?F?g^?1 at 1?A?g^?1), good rate capability (120?F?g^?1 at 6?A?g^?1), and excellent cyclability. The significantly enhanced electrochemical performance compared with pure graphene and Fe₂O₃ nanoparticles may be attributed to the positive synergetic effect between Fe₂O₃ and graphene. In virtue of their superior electrochemical performance, they will be promising electrode materials for high-performance supercapacitors applications.     

Synthesis and spectral properties of π-extended rhodamine hydrazide probe for the detection of Hg2+EI北大核心CSCD

The π-extended rhodamine derivative aminobenzopyranoxanthene ABPX was synthesized by condensation of 2-4-diethylamino-2-hydroxybenzoylbenzoic acid with resorcinol in H2 SO4 solutionthen the derivative reacted with hydrazine monohydrate to obtain ABPX-hydrazideABPX-hyand its structure was characterized by ESI-MSFT-IR and NMR spectroscopy. The UV-Vis adsorption spectra at 500-600 nm tended to increase in the presence of Hg2+ in ABPX-hy ethanol solutionand the color of the solution changed from colorless to pink and gradually deepenedenabling visual colorimetric detection of Hg2+ by naked eye. Under the coexistence of 10 common metal ionsthe recognition of Hg2+ at 533 nm showed good anti-interference sensing performance. The absorption intensity of ABPX-hy had a good exponential relationship with the addition of Hg2+. The continuous coordination of Hg2+ to the N and O binding sites of ABPX-hy formed 21 stoichiometry of the ABPX-hy-Hg2+ complex. The orbital energy and spatial distribution levels of the closed-cycle to the open-cycle form were obtained by density functional theoryDFTcalculation. © 2022, Youke Publishing Co.,Ltd. All rights reserved.     

Microwave-assisted sol-gel synthesis of CeO2–NiO nanocomposite based NO2 gas sensor for selective detection at lower operating temperature

The progress in the development of gas sensors has considerably grown using some novel nanomaterials of metal, metal oxide and composite. In the current study, we intended and evaluated the properties of nanomaterials like CeO₂, NiO, and CeO₂–NiO composite and its application as NO₂ gas sensor. Sensing of low concentration of NO₂ gas at optimum functional temperature was succeeded using CeO₂–NiO nanocomposites (NCs) film. The working temperature ranges in between 100 and 225 ?°C. Highly crystalline nanomaterials (CeO₂, NiO and CeO₂–NiO) have been prepared by applying microwave-assisted sol-gel route. The as-prepared nanomaterials are characterized for their structure, size, morphology and constitution by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray analysis. XRD studies of nanoparticles reveal the formation of nanoscale CeO₂ and NiO with crystallite size 26, 23 ?nm, respectively. Both are having a face centered cubic structure. The nanocomposite (NC) Ce:Ni ?= ?60:40 has crystallite size of 13 ?nm. XRD study of NCs shows assimilation of Ni metal into the ceria and proves physical similarities of two phases. It can be observed from SEM that prepared NC has a porous surface which enables more surface active sites for adsorbing oxygen. The optical properties are measured with the help of UV–Vis. Spectroscopy. Optical band gaps of 3.19, 3.41 and 2.9 ?eV were observed for CeO_2, NiO nanoparticles (NPs) and CeO₂–NiO NC, respectively. Gas sensing properties state that the NC material shows a higher gas response % of 67.34% for NO₂ gas (25 ?ppm) at comparatively low operating temperature (125 ?°C). It gives response time as (～28 ?s) and the recovery (～54 ?s). NiO incorporation in CeO₂ results in a decline of operating temperature of NC and improves the sensing features.     

A reversible fluorescence “ON–OFF–ON” sensor for sequential detection of F− and Cu2+ ions and its application as a molecular-scale logic device and security keypad lock

A new azoimine receptor, R₁, was synthesized by Schiff base condensation of 4-(4-butylphenyl) azophenol and 2,6-diaminopyridine and acts as a colorimetric and fluorometric chemosensor for F^? and also toward Cu²⁺ ions in aqueous environment. UV–Vis absorption and fluorescent emission spectra were employed to study the sensing process. Emission study was performed to examine the dual sensing ability of the obtained probe with sequential addition of F^? followed by Cu²⁺ and vice versa. The receptor is an efficient “ON–OFF” fluorescent probe for the fluoride ion. Also, R₁ + F^? operated as an “OFF–ON” fluorescent sensor for Cu²⁺ ions. Considering emission intensity and absorption wavelength for F^? and Cu²⁺ ions, a molecular system was developed with the ability to mimic the functions of XNOR logic gating on the molecular level. In addition, R₁ behaved as a molecular security keypad lock with F^? and Cu²⁺ inputs. The keypad lock operation is particularly important, as the output of the system depends not only on the proper combination but also on the order of input signals, creating the correct password that can be used to “open” this molecular keypad lock through strong fluorescence emission at 460?nm.     

A multi-responsive diarylethene-rhodamine 6G derivative for sequential detection of Cr3+ and CO32−

A new unsymmetrical diarylethene derivative (1o) with rhodamine 6G as a functional group has been designed and synthesized. It displayed good physicochemical properties induced by lights and chemical stimuli. 1o could sensitively detect towards Cr³⁺ with a 1:1 stoichiometry, and exhibit an obviously fluorescence (from dark to light cyan) and color (from colorless to pink) changes during the recognition process. The limit of detection was determined to be 27?nM and 8.5?nM via UV/vis and fluorescence methods, respectively. More importantly, the resulting complex 1o-Cr³⁺ (1o') could be served as a potential fluorescent probe to selectively and sensitively recognize toward CO₃^2?, the limit of detection was determined to be 0.88?μM and 0.26?μM via UV/vis and fluorescence methods, respectively. Moreover, the quenching of fluorescence intensity can reach 95% due to the perfect FRET processes between the excited open-ring rhodamine 6G moiety and the closed-ring diarylethene unit.     

Improved catalytic activity and N2 selectivity of Fe–Mn–O x catalyst for selective catalytic reduction of NO by NH3 at low temperature

Research on Chemical Intermediates - FeO x , MnO x and Fe–Mn–O x catalysts were prepared by the co-precipitation method and used for the selective catalytic reduction (SCR) of NO x by...     

CdS quantum dots as fluorescence probes for the sensitive and selective detection of highly reactive HSe<Superscript>−</Superscript> ions in aqueous solution

Water-soluble cadmium sulfide (CdS) quantum dots (QDs) capped by mercaptoacetic acid were synthesized by aqueous-phase arrested precipitation, and characterized by transmission electron microscopy, spectrofluorometry, and UV-Vis spectrophotometry. The prepared luminescent water-soluble CdS QDs were evaluated as fluorescence probes for the detection of highly reactive hydrogen selenide ions (HSe⁻ ions). The quenching of the fluorescence emission of CdS QDs with the addition of HSe⁻ ions is due to the elimination of the S²⁻ vacancies which are luminescence centers. Quantitative analysis based on chemical interaction between HSe⁻ ions and the surface of CdS QDs is very simple, easy to develop, and has demonstrated very high sensitivity and selectivity features. The effect of foreign ions (common anions and biologically relevant cations) on the fluorescence of the CdS QDs was examined to evaluate the selectivity. Only Cu²⁺ and S²⁻ ions exhibit significant effects on the fluorescence of CdS QDs. With the developed method, we are able to determine the concentration of HSe⁻ ions in the range from 0.10 to 4.80 μmol L⁻¹, and the limit of detection is 0.087 μmol L⁻¹. The proposed method was successfully applied to monitor the obtained HSe⁻ ions from the reaction of glutathione with selenite. To the best of our knowledge, this is the first report on fluorescence analysis of HSe⁻ ions in aqueous solution. Figure CdS quantum dots as fluorescence probes for the sensitive and selective detection of highly reactive HSe- ions in aqueous solution     

Thin films of ��-Fe2O3 nanoparticles using as nonmetallic SERS-active nanosensors for submicromolar detection

A new kind of nonmetallic nanosensors based on surface-enhanced Raman spectroscopy (SERS) have been successfully prepared by the assembly of α-Fe₂O₃ nanoparticles (NPs) onto clean quartz surface via the cross-linker of hexamethylene diisocyanate (HDI). The resultant substrates have been characterized by electron micrographs, which show that the α-Fe₂O₃ NPs distribute on the modified surface uniformly with a monolayer or sub-monolayer structure. 4-mercaptopyridine (4-Mpy) and 2-mercaptobenzothiazole (2-MBT) molecules have been used as SERS probes to estimate the detection efficiency of the α-Fe₂O₃ thin films. The SERS experiments show that it is possible to record high quality SERS spectra from probe molecules on the α-Fe₂O₃ thin films at sub-micromolar ( < 10⁻⁶ mol/L) concentration. These results indicate that the highly ordered, uniformly roughed, highly sensitive and low-cost α-Fe₂O₃ thin films are excellent candidates for nonmetallic SERS-active nanosensors.