Highly Selective Visible and Near-IR Sensing of Cu2+ Based on Thiourea-Salicylaldehyde Coordination in Aqueous Media

Carbohydrazone/Thiocarbohydrazone-Based Dual-Responsive Probes for Highly Selective Detection of Cu2+/Fe3+ Cations and F-/ClO4 - Anions, and Their Application in Bioimaging of Live Cells and Zebrafish Larvae

Four dual-responsive probe molecules 1,5-bis(thiophene-2-carbaldehyde)carbohydrazone (R1), 1,5-bis(thiophene-2-carbaldehyde)thiocarbohydrazone (R2), 1,5-bis(indole-3-carbaldehyde)carbohydrazone (R3), and 1,5-bis(indole-3-carbaldehyde)thiocarbohydrazone (R4) were synthesized, characterized, and investigated for their sensing efficacy. The initial sensing behavior of the probes was tested by colorimetric signaling, followed by spectral and theoretical techniques, which supported the dual-sensing ability of the selected inorganic ions. The probes exhibited highly selective optical recognition for Cu2+/Fe3+ cations and F-/ClO4 - anions compared to the tested cations and anions. Interestingly, the addition of Cu2+ and F- ions to the probes resulted in "turn-on" fluorescence responses. Job's plot studies showed 1:2 stoichiometry between the probe molecules and cations and 1:1 stoichiometry between the probe molecules and anions. The binding constant of the probe molecules with the sensed ions was determined by the Benesi-Hildebrand equation and was found to be between 7.08 × 104 and 7.44 × 106 M-1 with a limit of detection between 0.11 and 0.80 μM, in CH3CN:DMF (9:1, v/v). Density functional theory calculations established the nature of the interaction between the probe molecules and sensed ions. Further, the practical utility of the probes was successfully demonstrated with paper strip experiments, fluorescence imaging of Cu2+ ions in DrG cells and zebrafish larvae, as well as in the development of molecular logic gates.

A Series of Lanthanide Coordination Polymers as Luminescent Sensors for Selective Detection of Inorganic Ions and Nitrobenzene

Seven new lanthanide coordination polymers, namely [Ln(cpt)3H2O)]n(Ln = La (1), Pr (2), Sm (3), Eu (4), Gd (5), Dy (6), and Er (7)), which were synthesized under hydrothermal conditions using 4'-(4-(4-carboxyphenyloxy)phenyl)-4,2':6',4'-tripyridine (Hcpt) as the ligand. The crystal structures of these seven complexes were determined using single-crystal X-ray diffraction, and they were found to be isostructural, crystallizing in the triclinic P1- space group. The Ln(III) ions were nine-coordinated with tricapped trigonal prism coordination geometry. The Ln(III) cations were coordinated by carboxylic and pyridine groups from (cpt)- ligands, forming one-dimensional ring-chain structures. Furthermore, the luminescent properties of complexes 1-7 were investigated using fluorescent spectra in the solid state. The fluorescence sensing experiments demonstrated that complex 4 exhibits high selectivity and sensitivity for detecting Co2+, Cu2+ ions, and nitrobenzene. Moreover, complex 3 shows good capability for detecting Cu2+ ions and nitrobenzene. Additionally, the sensing mechanism was also thoroughly examined through theoretical calculations.

Fluorescence Variation in Selective Sensing of Hg2+and Cu2+ Ions By Coumarin-xanthene Fused Optical Probe

The fluorescent moieties coumarin and xanthene (R6GCP) combined in a single molecule was designed and synthesized. The colorimetric and fluorescent variation of the probe towards the copper and mercury ions sensing is examined. With the added copper/mercury ions to the solution of R6GCP in DMF:H2O (2:8, v/v), the probe showed deep red color from yellow color. The probe showed turn-off and turn-on fluorescence for copper and mercury ion respectively. In the presence of other competing metal ions, the probe showed better sensitivity towards copper and mercury ions. The probe's detection limit found to be 5.29 × 10^-6 M and 1.24 × 10^-5 M for Cu²⁺ and Hg²⁺ ion respectively by the UV-visible spectral measurement. Fluorescence measurement, the detection limit for the Cu²⁺ and Hg²⁺ ions detection by this probe is 1.91 × 10^-7 M, and 1.32 × 10^-8 M respectively. 1:1 binding stoichiometry was confirmed between the probe and Cu²⁺/Hg²⁺ ions from jobs plot by UV-visible spectral technique. Moreover, R6GCP combined filter paper were prepared. These test paper containing probe could detect Cu²⁺/Hg²⁺ ions in real-time with a spontaneous color change.

On the synthesis and performance of a simple colorimetric and fluorescent chemosensor for Cu2+ with good reversibility

A colorimetric and fluorescent chemosensor (CS1) for Cu²⁺ based on the mechanism of internal charge transfer (ICT) has been successfully designed and prepared by simple condensation of 4^_(diethylamino)salicylaldehyde and oxalyl dihydrazide. Cu²⁺ in solution (DMSO/H₂O = 7:3, v/v) by 5 mM NaAc-HAc at pH 7.0 was determined through dual channels: (1) "naked-eye" observation, a visually dramatic color change from light green to orange, which can be used for qualitative determination of Cu²⁺; (2) spectrofluorometry, which can quantificationally assay Cu²⁺. It provides a simple-to-use platform for reliable detection of Cu²⁺ at concentrations ranging from 5.0 × 10^-7 to 1.1 × 10^-5 M with detection limit of 1.2 × 10^-7 M, which is nearly 2 × 10² times lower than the maximum allowable level of inorganic Cu²⁺ in drinking water (1.3 ppm, ∼20 µM) permitted by the EPA (Environmental Protection Agency), and the sensing detection of Cu²⁺ ions was reversible.

Colorimetric detection of fluoride ions in aqueous medium using thiourea derivatives: a transition metal ion assisted approach

This work explores the position of the hydroxyl moiety and its participation in intramolecular H-bonding towards dictating the fluoride selective colorimetric response in functionalized thiourea derivatives. The study reveals the pivotal aspect of the hydroxyl moiety in C2 towards attaining selectivity for fluoride over acetate and dihydrogenphosphate ion. Furthermore, a methodology employing stabilization of deprotonated thiourea through metal ion (Ni²⁺ and Cu²⁺) coordination is proposed for the colorimetric sensing of fluoride in water medium. The mechanism of interaction is thoroughly studied by UV-Vis, ¹H NMR, ESR spectroscopy, electrochemical techniques and further validated by DFT calculations. This study reveals the formation of an in situ Ni²⁺ complex that shows greater stability in aqueous medium. The methodology is applied in the detection of fluoride in groundwater samples.

A multi-functional picolinohydrazide-based chemosensor for colorimetric detection of iron and dual responsive detection of hypochlorite

A novel effective chemosensor HPHN, (E)-6-hydroxy-N'-((2-hydroxynaphthalen-1-yl)methylene) picolinohydrazide, was synthesized. HPHN sensed Fe^3+/2+ with the changes of color from yellow to orange without obvious inhibition from other cations. In addition, HPHN could detect ClO^- by both the color change from yellow to colorless and the fluorescence quenching. The binding modes of HPHN with Fe^3+/2+ and ClO^- were determined to be 1:1 with Job plot and ESI-mass analysis. HPHN displayed low detection limits of 0.29 μM for Fe³⁺ and 0.77 μM for Fe²⁺. For ClO^-, the detection limit was 6.20 μM by colorimetric method and 3.99 μM by fluorescent one, respectively. Moreover, HPHN can be employed to quantify Fe³⁺ and ClO^- in environmental samples and apply to cell imaging for ClO^-.

A new highly selective colorimetric Schiff base chemosensor for determining the copper content in artisanal cachaças

This work demonstrated the feasibility of applying the Schiff base 5-bromo-2-salicyl-beta-alanine as a colorimetric chemosensor for the spectrophotometric quantification of the copper content in artisanal cachaças. For this, the experimental conditions were optimized to obtain an efficient, sensitive, reversible, and highly selective chemosensor to Cu²⁺ ions. The complex stoichiometry was 1:1, with a formation constant of 5.82 × 10² L mol^-1 and molar absorptivity of 5.82 × 10³ mol L^-1 cm^-1. Then, a spectrophotometric analytical method was developed and validated according to the Brazilian legislation. The linearity of the analytical curve was demonstrated by ANOVA, at a confidence level of 95%. The limits of detection and quantification were 0.0659 and 0.200 mg L^-1, respectively. The coefficients of variation for both the intra- and inter-day precisions were lower than 3.83%, and the accuracy presented a mean recovery of 100.55 ± 2.87%. The absence of a matrix effect was confirmed by the standard addition method, and the copper content in three artisanal cachaças from different geographical origins was estimated as lower than 2.93 mg L^-1. This result was in accordance with the Brazilian legislation but reinforces the need to carry out stricter quality control to achieve exportation standards. Therefore, the proposed method can be considered a simple, selective, linear, precise, and accurate tool that involves only a simple complexation reaction through the addition of the chemosensor solution in a buffered medium. As a consequence, the simplicity, practicality, rapidity, and low cost of synthesis of the proposed Schiff base chemosensor are highlighted.

Exploring the Chelating Potential of an Easily Synthesized Schiff Base for Copper Sensing

The present study deals with the investigation of Cu2+, Ni2+ and Pd2+ chelating potential of the Schiff base, (E)-N-(2-((2-hydroxybenzylidene)amino)benzyl)-4-methylbenzenesulfonamide (H2SB). Crystal structures of Ni(HSB)2, Pd(HSB)2 and Cu(HSB)2 have been elucidated from single crystal X-ray diffraction data. NMR spectroscopy showed the presence of two conformers of Pd(HSB)2 in solution, both with an E configuration of the ligand. The determination of binding constants by fluorescence quenching showed that affinity of H2SB to Cu2+ in solution is higher than for Ni2+ and Pd2+. Since there is a high demand for selective, sensitive, rapid and simple methods to detect copper in aqueous samples (both as Cu2+ ions and as CuO NPs), we have explored H2SB as an optical chemosensor. H2SB interacts with increasing concentrations of Cu2+ ions, giving rise to a linear increase in the absorbance of a band centered at about 392 nm. H2SB displays a high selectivity toward Cu2+, even in the presence of the most common metal ions in water (Ca2+, Mg2+, Na+, K+, Al3+ and Fe3+), and some heavy transition metal ions such as the soft acids Pd2+ and Cd2+. H2SB also interacts with increasing concentrations of CuO NPs, which gives rise to a linear decrease in its fluorescence intensity (λem = 500 nm, λex = 390 nm). Quenching has occurred as a result of the formation of a non-fluorescent ground-state surface complex H2SB–CuO NPs. The limits of detection and quantification of CuO NPs were 9.8 mg/L and 32.6 mg/L, respectively. The presence of TiO2, Ag and Au NPs does not interfere with the determination of CuO NPs.

A novel imidazole derived colorimetric and fluorometric chemosensor for bifunctional detection of copper (II) and sulphide ions in environmental water samples

Herein, a novel "ON-OFF" colorimetric and fluorometric chemosensor; 1N-allyl-2-(2, 5-dimethoxyphenyl)-4, 5-diphenyl-1H-imidazole (ADPPI), was constructed for sequential determination of Cu²⁺ and S^2- ions in aqueous media. The interaction between chemosensor ADPPI and different metal cations was investigated using UV-VIS and fluorimetric spectroscopy. ADPPI showed a favorable and good interaction with Cu²⁺ ions producing blue colored solution peaked at 610 nm with blue fluorescence at λ_em. = 447 nm. The produced complex between Cu²⁺ ions and ADPPI can be used as a cascade probe for detection of S^2- ions. The detection limits (LODs) were 1.01 nM and 1.25 μM for Cu²⁺ and S^2- ions, respectively (the lowest between the family of colorimetric and fluorometric chemosensors). To further increase the applicability of the proposed method, Cu²⁺ and S^2- ions concentrations were measured in environmental water samples.

Unambiguous Detection of Elevated Levels of Hypochlorous Acid in Double Transgenic AD Mouse Brain

Alzheimer's disease (AD) is one of the most prevalent forms of dementia. The current diagnosis methods based on the behavior and cognitive decline or imaging of core biomarkers, namely, amyloid-β (Aβ) plaques and neurofibrillary tangles (NFTs), in the brain offer poor to moderate success. Detection and imaging of biomarkers that cause additional traits of pathophysiological aberrations in the brain are invaluable to monitor early disease onset and progression of AD pathology. The pathological hallmark of AD is associated with generation of excessive reactive oxygen species (ROS) in the brain, which aggravate oxidative stress and inflammation. ROS production involves elevated levels of hypochlorous acid (HOCl) and can serve as one of the potential biomarkers for the diagnosis of AD. We report the design, synthesis, and characterization of switchable coumarin-morpholine (CM) conjugates as off-on fluorescence probes for the specific detection of HOCl produced and proximally localized with amyloid plaques. The nonfluorescent thioamide probe CM2 undergoes regioselective transformation to fluorescent amide probe CM1 in the presence of HOCl (∼90-fold fluorescence enhancement and 0.32 quantum yield) with high selectivity and sensitivity (detection limit: 0.17 μM). The excellent cellular uptake and blood-brain barrier (BBB) crossing ability of CM2 allowed unambiguous and differential detection, imaging, and quantification of HOCl in cellular milieu and in the wild type (WT) and AD mouse brains. This study demonstrates the elevated level of HOCl in the AD mouse brain and the potential to expand the repertoire of biomarkers for the diagnosis of AD.

A new hydrazone-based colorimetric chemosensor for naked-eye detection of copper ion in aqueous medium

A new hydrazone-based colorimetric Cu2+ chemosensor is synthesized. Its structure was confirmed by single-crystal X-ray diffraction. Its binding properties towards various metal ions are examined through absorption spectroscopy. In aqueous THF solution, the chemosensor exhibits selective recognition towards Cu2+ over other metal ions with a colour change from colourless to pink. The complex formed between the chemosensor and Cu2+ ions forms a 2:1 stoichiometry with an association constant of 2.46 × 108M−2. The analytical detection limit for Cu2+ by the naked eye is as low as 10.0 μM.

A fluorescent and colorimetric Schiff base chemosensor for the detection of Zn2+ and Cu2+: Application in live cell imaging and colorimetric test kit

A novel Schiff base chemosensor HMID, ((E)‑1‑((2‑hydroxy‑3‑methoxybenzylidene)amino)imidazolidine‑2,4‑dione), have been designed and synthesized. Sensor HMID showed a selectivity to Zn²⁺ through fluorescence enhancement in aqueous solution. Its detection limit was analyzed as 11.9 μM. Importantly, compound HMID could be applied to image Zn²⁺ in live cells. Detection mechanism of Zn²⁺ by HMID was suggested to be an effect of chelation-enhanced fluorescence (CHEF) by DFT calculations. Moreover, HMID could detect Cu²⁺ with a change of color from colorless to pink. The selective detection mechanism of Cu²⁺ by HMID was demonstrated to be the promotion of intramolecular charge transfer band by DFT calculations. Additionally, HMID could be employed as a naked-eye colorimetric kit for Cu²⁺. Therefore, HMID has the ability as a 'single sensor for dual targets'.

Unprecedented thiocarbamidation of nitroarenes: a facile one-pot route to unsymmetrical thioureas

A one-pot synthesis of unsymmetrical thiourea compounds was achieved by the reaction of nitroarenes with in situ generated dithiocarbamate anions.

A dual-response sensor based on NBD for the highly selective determination of sulfide in living cells and zebrafish

A dual chemosensor, 1-NO₂, showing fluorogenic and colorimetric responses was developed for the detection of sulfide in vitro and in vivo.

Nitrogen-doped carbon quantum dots for fluorescence detection of Cu2+ and electrochemical monitoring of bisphenol A

Nitrogen-doped carbon dots were applied in the fluorescence detection of Cu²⁺ and electrochemical detection of BPA.

Detection of cyanide ions in aqueous solutions using cost effective colorimetric sensor

Cyanide (CN̄) is one of the most toxic material to the human and environment. It is very important to develop the diagnostic tools for the detection of CN̄ ions. Moreover, detection of the ions in an aqueous medium is a challenging task as water molecules interfere with the sensing mechanism. In this context, we prepared chemical sensor, S1, having anthraquinone as a signaling unit and thiourea as a binding site. This sensor exhibited distinct visual color and spectral changes in response to CN̄ ion over other testing anions in 50% aq. DMSO solution. However, in 20% aq. DMSO solution, S1 exhibited obvious spectral and color changes in response to CN̄, fluoride (F̄), acetate (Ac̄) and benzoate (Bz̄). Another sensor, S2, having a same signaling unit with that of S1, but a different binding site of urea group. In contrast to S1, S2 exhibited obvious spectral and color changes to F̄ in 2.5% aq. DMSO solution. NMR titration results suggested that the spectral and colorimetric responses were due to the formation of host-guest complex and deprotonation events. Finally, economically viable paper-based colorimetric "test stripes" of S1 were fabricated to detect the CN̄ ions in 100% aqueous solution.

Highly Selective Bifunctional Luminescent Sensor toward Nitrobenzene and Cu2+ Ion Based on Microporous Metal-Organic Frameworks: Synthesis, Structures, and Properties

Two metal-organic frameworks (MOFs), namely, [Ni(DTP)(H₂O)]_n (I) and [Cd₂(DTP)₂(bibp)_1.5]_n (II) (H₂DPT = 4'-(4-(3,5-dicarboxylphenoxy) phenyl)-4,2':6',4″-terpyridine; bibp = 1,3-di(1H-imidazol-1-yl)propane), that present structural diversity were solvothermally prepared. Single-crystal X-ray diffraction analysis indicates that they consist of {NiN₂O₄} building units (for I) and {CdO₄N₂} and {CdO₃N₃} building units (for II), which are further linked by multicarboxylate H₂DPT to construct microporous three-dimensional frameworks. The remarkable character of these frameworks is that coordination polymer II demonstrates highly selective and sensitive bifunctional luminescent sensor toward nitrobenzene and Cu²⁺ ion. The fluorescence quenching mechanism of II caused by nitrobenzene is ascribed to electron transfer from electron-rich (II) to electron-deficient nitrobenzene. The result was also evidenced by the density functional theory. Furthermore, anti-ferromagnetic as well as electrochemical characters of Ni-MOF (I) were also investigated in this paper.

A highly selective “ON–OFF” probe for colorimetric and fluorometric sensing of Cu2+in water

A new diformyl phenol based probe for selective detection of Cu²⁺in aqueous medium, applicable for cell imaging in Vero cells. Theoretical studies were performed to establish the underlying keto–enol tautomerism and optimization of the Cu²⁺complex.

A single fluorescent chemosensor for multiple targets of Cu2+, Fe2+/3+ and Al3+ in living cells and a near-perfect aqueous solution

A naphthol-based chemosensor 1 was developed for detection of Cu²⁺ and Fe^2+/3+ by fluorescence quenching and Al³⁺ by fluorescence emission change.

A new Schiff-based chemosensor for chromogenic sensing of Cu2+, Co2+and S2−in aqueous solution: experimental and theoretical studies

A new Schiff-based multifunctional colorimetric chemosensor1was developed for the detection of various analytes (Cu²⁺, Co²⁺and S²⁻).

Rhodamine 6G hydrazone with coumarin unit: a novel single-molecule multianalyte (Cu2+ and Hg2+) sensor at different pH value

An effective colourimetric and ratiometric fluorescent probe for Cu²⁺ in neutral aqueous media was synthesised. Moreover, the probe could sense Hg²⁺ with fluorescence enhancement at high pH.

A colorimetric chemosensor for sulfide in a near-perfect aqueous solution: practical application using a test kit

A selective chemosensor with practical applications was developed for the colorimetric detection of S²⁻ in a near-perfect aqueous solution.