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).     

A highly selective HBT-based “turn-on” fluorescent probe for hydrazine detection and its application

As one of the important industrial chemicals, hydrazine (N₂H₄) can be inhaled through the skin, leading to many serious health issues. In this paper, we constructed a novel turn-on fluorescent probe HBTM for N₂H₄ detection based on ESIPT and ICT mechanism by incorporating the methyl dicyanvinyl group to 2-(2′-hydroxylphenyl) benzothiazole (HBT) fluorophore. The probe showed the following advantages: high sensitivity with detection limit of 2.9 × 10^?7 M, high selectivity over other related interfering species, wide linear range of 0–140 μM and pH value adaptation. Moreover, the probe could detect N₂H₄ on paper strips and image N₂H₄ in living cells.     

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.     

Multiplex sensor for detection of different metal ions based on on–off of fluorescent gold nanoclusters

In this study, a multiplex fluorescence sensor for successive detection of Fe³⁺, Cu²⁺ and Hg²⁺ ions based on “on–off” of fluorescence of a single type of gold nanoclusters (Au NCs) is described. Any of the Fe³⁺, Cu²⁺ and Hg²⁺ ions can cause quenching fluorescence of Au NCs, which established a sensitive sensor for detection of these ions respectively. With the introduction of ethylene diamine tetraacetic acid (EDTA) to the system of Au NCs and metal ions, a restoration of fluorescence may be found with the exception of Hg²⁺. A highly selective detection of Hg²⁺ ion is, thus, achieved by masking Fe³⁺ and Cu²⁺. On the other hand, the masking of Fe³⁺ and Cu²⁺ leads to the enhancement of fluorescence of Au NCs, which in turn provides an approach for successive determination of Fe³⁺ and Cu²⁺ based on “on–off” of fluorescence of Au NCs. Moreover, this assay was applied to the successful detection of Fe³⁺, Cu²⁺ and Hg²⁺ in fish, a good linear relationship was found between these metal ions and the degree of quenched fluorescent intensity. The dynamic ranges of Hg²⁺, Fe³⁺ and Cu²⁺ were 1.96 × 10⁻¹⁰–1.01 × 10⁻⁹, 1.28 × 10⁻⁷–1.27 × 10⁻⁶ and 1.2 × 10⁻⁷–1.2 × 10⁻⁶ M with high sensitivity (the limit of detection of Fe³⁺ 2.0 × 10⁻⁸ M, Cu²⁺ 1.9 × 10⁻⁸ M and Hg²⁺ 2 × 10⁻¹⁰ M). These results indicate that the assay is suitable for sensitive detection of these metal ions even under the coexistence, which can not only determine all three kinds of metal ions successively but also of detecting any or several kinds of metal ions.     

Ultrasensitive detection of aliphatic nitro-organics based on “turn-on” fluorescent sensor array

The broad class of explosives includes nitro aromatics as well as challenging aliphatic nitro-organics whose detection is important from counter-terrorism and national security perspectives. Here we report a turn-on fluorescent sensor array based on aggregation-induced emission (AIE) fluorophores as receptors. To achieve a good sensing system with fast response, good sensitivity and low detection limit, three receptors with abundant chemical diversities for target analytes were synthesized. The turn-on response of the individual receptor showed highly variable and cross-reactive analyte-dependent changes in fluorescence. The excellent ability to identify a variety of explosives, especially the challenging aliphatic nitro-organics (2,3-dimethyl-2,3-dinitrobutane (DMNB), 1,3,5-trinitro-1,3,5-triazinane (RDX), cyclotetramethylene tetranitramine (HMX) and entaerythritol tetranitrate (PETN)), was demonstrated in qualitative and quantitative analyses with 100% accuracy. The fluorescence signal amplification in the presence of explosives allows for application of these receptors in a sensor microarray suitable for high-throughput screening. These results suggested that the cross-reactive sensor array based on AIE fluorophores could find a wide range of applications for sensing various analytes or complex mixtures.     

A selective coumarin-based “turn-on” fluorescent sensor for the detection of cysteine and its applications for bioimaging

A coumarin-based compound (1) was designed and synthesized as a new turn-on fluorescent probe for the detection of cysteine. The in vivo imaging of Hi5 cell and Caenorhabditis elegans had further confirmed the cysteine detection by compound 1.     

A highly sensitive ＂turn-on＂ fluorescent probe for bovine serum albumin protein detection and quantification based on AIE-active distyrylanthracene derivative

A sulfonated 9,10-distyrylanthracene derivative with aggregation-induced emission （AIE） property is designed and synthesized. It shows a highly sensitive and selective fluorescence enhancement property for bovine serum albumin （BSA） protein detection and quantification. Analysis on the interaction between the probe molecule and BSA reveals the essential role of the hydrophobic cavities of the protein folding structure.     

A highly selective colorimetric and “Off-On” fluorescence sensor for CN~- based on Zn(salphenazine) complex

The development of sensors for selective detection of cyanide ion(CN~-) is an important mission to accomplish because of the versatility and toxicity of CN~-. In the present work, an "ensemble"-based colorimetric and fluorescent sensor(L2-Zn~(2+)) for CN~-ion has been developed. The addition of cyanide ions removed Zn~(2+) from the ensemble(L2-Zn~(2+)) in aqueous medium, resulting in a color change of the solution from red to buff and a "turn-on" fluorescent response. Also, the sensitivity of both the fluorescenceand colorimetric-based assay is below the maximum allowable level of cyanide ions in drinking water set by the World Health Organization. In addition, test strips, which served as convenient and efficient CN~- test kits, were fabricated based on the sensor.Notably, the selective detection of cyanide with L2-Zn~(2+) for practical application was also performed in sprouting potatoes.     

Fluorescence “turn-on” chemosensor for the selective detection of zinc ion based on Schiff-base derivative

N,N′-phenylenebis(salicylideaminato) (L) has been used to detect trace amounts of zinc ion in acetonitrile–water solution by fluorescence spectroscopy. The fluorescent probe undergoes fluorescent emission intensity enhancement upon binding to zinc ions in MeCN/H₂O (1:1, v/v) solution. The fluorescence enhancement of L is attributed to the 1:1 complex formation between L and Zn(II), which has been utilized as the basis for selective detection of Zn(II). The linear response range for Zn(II) covers a concentration range of 1.6 × 10^?7 to 1.0 × 10^?5 mol/L, and the detection limit is 1.5 × 10^?7 mol/L. The fluorescent probe exhibits high selectivity over other common metal ions, and the proposed fluorescent sensor was applied to determine zinc in water samples and waste water.     

A new BODIPY-based fluorescent “turn-on” probe for highly selective and rapid detection of mercury ions

A new fluorescent sensor based on the BODIPY fluorophore and the carboxyl-thiol metal bonding receptor for Hg²⁺ was designed and synthesized. The sensor is highly selective for Hg²⁺ (about 630-fold fluorescence enhancement) over relevant competing metal ions, sensitive to ppb levels of Hg²⁺ (with detection limit of 5.7?nM), and fast response toward Hg²⁺ (within 30?s) in aqueous solution.     

An oxidative cyclization reaction based fluorescent “Turn-On” probe for highly selective and rapid detection of hypochlorous acid

A novel fluorescent turn-on probe, PHC1, for the detection of hypochlorous acid has been developed based on hypochlorous acid-initiated oxidative intramolecular cyclization. Endowed by the fast reaction rate, PHC1 features rapid detection kinetics, as well as high degree of selectivity and sensitivity for HClO.     

A highly selective and easy-to-synthesize Zn(Ⅱ) fluorescent probe based on 6-methoxyquinolin

A novel fluorescent Zn²⁺ probe based on 6-methoxyquinolin was synthesized in four steps from inexpensive starting materials.It exhibits very strong fluorescence responses and has a remarkably high selectivity to Zn²⁺ than other physiological relevant metal ions.This new compound could be used as low-priced yet high-quality Zn²⁺ probe.     

CuS–MWCNT based electrochemical sensor for sensitive detection of bisphenol A

The rapid and simple detection of bisphenol A is very important for the safety and reproduction of organisms. Here, a sensitive and reliable electrochemical sensor was established for bisphenol A detection based on the high amplification effect of copper sulfide-multi-walled carbon nanotube (CuS–MWCNT) nanocomposites. The flower-like CuS–MWCNT were successfully synthesized by a simple hydrothermal method accompanied by polyvinylpyrrolidone (PVP). Compared with bare glassy carbon electrode (GCE), CuS–MWCNT modified GCE could amplify the electrochemical signals in about ten times, which was attributed to the synergistic effect of CuS and MWCNT. The MWCNT could increase the specific surface area of electrodes and improve the electrode activity. The integration of CuS could further enhance the electrode conductivity as well as accelerate the electron transfer rate. Raman spectra and transmission electron microscope (TEM) were used to characterize the successful fabrication of CuS–MWCNT nanocomposites and its uniform and monodispersed morphology. Under optimizing conditions, the oxidation currents of bisphenol A via the differential pulse voltammetric (DPV) showed a good linear relationship with its concentration in a wide range of 0.5–100 μM, with a detection limit of 50 nM. This electrochemical sensor of bisphenol A provided a convenient and economical platform with high sensitivity and reproducibility, which had great potential in environmental monitoring.     

New coumarin-urea based receptor for anions: a selective off–on fluorescence response to fluoride

A novel fluorosensor for anions, 1,11-bis(4-methylcoumarin-7-yl)-6-methyl-1,3,6,9,11-pentaazaundeca-2,10-dione (L), which contains two coumarin–urea units spaced by a flexible diethylenetriamine fragment, was easily prepared in 65% yield by a one-pot two-step procedure. The binding ability of L toward several anions (G) was evaluated by ¹H NMR, UV–vis, and fluorescence titration. It was found that L forms stable [LG] and [LG₂] species in both DMSO and CH₃CN solvents. Furthermore, the fluorescence emission of L in the visible range (400 nm) is affected by the presence of anions; it is quenched by acetate, chloride, and pyrophosphate while it is enhanced by fluoride. Thus, this novel fluorosensor provides a selective off–on response to the presence of fluoride in solution.     

A novel resorufin based fluorescent “turn-on” probe for the selective detection of hydrazine and application in living cells

In this study, a resorufin derivative RTP-1, which is a novel fluorescent ‘‘turn-on' probe for sensitive detection of hydrazine within 30 min, is designed and synthesized. The selective deprotection of the ester group of the probe by hydrazine led to a prominent enhancement of fluorescent intensity, as well as a remarkable color change from colorless to pink, which could be distinguished by naked eye. The fluorescence enhancement showed decent linear relationship with hydrazine concentration ranging from 0 to 50 mmol/L, with a detection limit of 0.84 mmol/L. The specificity of RTP-1 for hydrazine to a number of metal ions, anions and amines is satisfactory. The sensing mechanism of RTP-1 and hydrazine was evaluated by HPLC, ESI mass spectrometry and density functional theory(DFT).Moreover, we have utilized this fluorescent probe for imaging hydrazine in living cells, and the fluorescence was clearly observed when the cells were incubated with hydrazine(100 mmol/L) for 30 min.     

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.     

Surface-imprinted core–shell Au nanoparticles for selective detection of bisphenol A based on surface-enhanced Raman scattering

Surface-imprinted core–shell Au nanoparticles (AuNPs) were explored for the highly selective detection of bisphenol A (BPA) by surface-enhanced Raman scattering (SERS). A triethoxysilane-template complex (BPA-Si) was synthesized and then utilized to fabricate a molecularly imprinted polymer (MIP) layer on the AuNPs via a sol–gel process. The imprinted BPA molecules were removed by a simple thermal treatment to generated the imprint-removed material, MIP-ir-AuNPs, with the desired recognition sites that could selectively rebind the BPA molecules. The morphological and polymeric characteristics of MIP-ir-AuNPs were investigated by transmission electron microscopy and Fourier-transform infrared spectroscopy. The results demonstrated that the MIP-ir-AuNPs were fabricated with a 2 nm MIP shell layer within which abundant amine groups were generated. The rebinding kinetics study showed that the MIP-ir-AuNPs could reach the equilibrium adsorption for BPA within 10 min owning to the advantage of ultrathin core–shell nanostructure. Moreover, a linear relationship between SERS intensity and the concentration of BPA on the MIP-ir-AuNPs was observed in the range of 0.5–22.8 mg L⁻¹, with a detection limit of 0.12 mg L⁻¹ (blank ± 3 × s.d.). When applied to SERS detection, the developed surface-imprinted core–shell MIP-ir-AuNPs could recognize BPA and prevent interference from the structural analogues such as hexafluorobisphenol A (BPAF) and diethylstilbestrol (DES). These results revealed that the proposed method displayed significant potential utility in rapid and selective detection of BPA in real samples.     

Chromogenic and fluorescent ‘‘turn-on' chemodosimeter for fluoride based on F~–-sensitive self-immolative linker

A new chromogenic and fluorescent ‘‘turn-on" chemodosimeter 3 was designed and synthesized by using a fluoride-sensitive self-immolative linker, in combination with the fluorescent dyes 7-hydroxy-4-trifluoromethyl coumarin. The chemodosimeter exhibited high selectivity and sensitivity toward fluoride anions through ‘‘turn-on" chromogenic and fluorogenic dual modes.