A novel colorimetric chemosensor based on quinoline for the sequential detection of Fe3+ and PPi in aqueous solution

A pyridine dicarboxylate based hydrazone Schiff base for reversible colorimetric recognition of Ni2+ and PPi

A pyridine dicarboxylate Schiff-base DAS was synthesized for cascade colorimetric recognition of Ni²⁺ and PPi. The selectivity and sensitivity of chemosensor DAS was investigated through colorimetric and UV-vis studies in MeOH-PBS (5 : 1, v/v, pH = 7.4). The chemosensor formed a 2 : 1 complex with Ni²⁺ metal ions with a binding constant of K_a = 3.07 × 10³ M^-2. Besides, a plausible sensing mechanism is confirmed by single crystal X-ray diffraction (SC-XRD), Job's plot and Benesi-Hildebrand plot (B-H plot) experiments. Furthermore, the DAS-Ni²⁺ ensemble formed 'in situ' was used to selectively recognise PPi. The limit of detection (LOD) of DAS for Ni²⁺ was found to be 0.14 μM and that of the DAS-Ni²⁺ ensemble for PPi was found to be 0.33 μM. Also, the potential of the chemosensor has been applied for solid state detection of Ni²⁺ as well as to mimic the 'INHIBIT' logic gate on the addition of Ni²⁺ ions and PPi.

Colorimetric Sensing Strategy through the Coordination Chemistry between Ascorbic Acid 2-Phosphate and Copper Ions

The coordination chemistry between phosphorylated molecules and metal ions has been reported, while few studies focus on its sensing capability. Herein, we report a colorimetric sensing strategy through the coordination chemistry between ascorbic acid 2-phosphate (AAP) and copper ions. The phosphate group-containing AAP can coordinate with copper ions to induce a visible color change from blue to green in a rapid way, which can be easily read by the naked eye or a smartphone based on the blue-to-green (B/G) ratio. This coordination chemistry provides a facile and convenient strategy for designing colorimetric assays. Alkaline phosphatase can catalyze the hydrolysis of AAP to ascorbic acid (AA), thus modulating the AAP/AA transformation and the AAP-mediated coordination, offering a straightforward way for monitoring the enzymatic activity. This colorimetric sensing strategy shows good performances in stability, sensitivity, cost, and scale-up production, holding great promise as a point-of-care technique for diagnostic applications.

Novel Benzothiazole-Based Highly Selective Ratiometric Fluorescent Turn-On Sensors for Zn2+ and Colorimetric Chemosensors for Zn2+, Cu2+, and Ni2+ Ions

Metal ions play a very important role in environmental as well as biological fields. The detection of specific metal ions at a minute level caught much attention, and hence, several probes are available in the literature. Even though benzothiazole-based molecules have a special place in the medicinal field, only very few chemosensors are reported based on this moiety. The current work describes the design and synthesis of the benzothiazole-based chemosensor for a highly selective and sensitive detection of biologically important metal ions such as Zn2+, Cu2+, and Ni2+. The sensing studies of compound-1 showed a ratiometric as well as colorimetric response toward Zn2+, Cu2+, and Ni2+ ions and color changes from colorless to yellow and is found to be insensitive toward various metal ions (Cd2+, Cr3+, Mn2+, Pb2+, Ba2+, Al3+, Ca2+, Fe2+, Fe3+, Mg2+, K+, and Na+). Further, compound-1 exhibited ratiometric as well as turn-on-enhanced fluorescence response toward Zn2+ ions and turn off response for Cu2+ and Ni2+ ions. The Job plots revealed that the binding stoichiometry of compound-1 and metal ions is 2:1. The detection limits were found to be 0.25 ppm for Zn2+, while it was 0.30 ppm and 0.34 ppm for Ni2+ and Cu2+, respectively. In addition, density functional theory results strongly support the colorimetric response of metals, and the reversibility studies suggested that compound-1 can be used as a powerful chemosensor for the detection of Zn2+, Cu2+, and Ni2+ ions. The bioimaging data illustrated that compound-1 is a very effective ratiometric sensor for Zn2+ ions in live cells.

A Deferasirox Derivative That Acts as a Multifaceted Platform for the Detection and Quantification of Fe3+

Here, we report that ExSO3H, a synthetically accessible, water-soluble, non-toxic derivative of the clinical iron chelator deferasirox, acts as a colorimetric chemosensor that permits the detection and quantification of Fe3+ in aqueous samples at pH 2–5. In addition, we observed that a fluorescent turn-on response was produced when this chelator was allowed to interact with human serum albumin (HSA). This fluorescence was quenched in the presence of Fe3+, thus allowing us to monitor the presence of this biologically important metal cation via two independent methods.

C3-symmetric triaminoguanidine based colorimetric and fluorometric chemosensor: Sequential detection of Zn2+/PPi, its RGB performance for detection of Zn2+ ion and construction of IMPLICATION logic gate

In this work, new ethyl(E)-2-cyano-3-(1H-pyrrol-2-yl)acrylate appended C₃-symmetric star-shape triaminoguanidine based Schiff base (LH₃) was designed and synthesized from simple synthons. New probe, LH₃ was completely analyzed by ¹H NMR, ¹³C NMR and mass spectrum. In the present probe LH₃, effective π-conjugated ethyl(E)-2-cyano-acrylate unit was introduced on the periphery of the pyrrole-triaminoquanidine conjugates by using carefully chosen building units. The probe LH₃ shows high selectivity and sensitivity towards Zn²⁺ ion via colorimetric and fluorometric changes. The yellowish orange color of LH₃ solution turned to wine red color upon addition of Zn²⁺ solution, along with red shifted absorption maxima from 450 nm to 550 nm, this indicates the formation of LH₃-Zn²⁺ species. Job's plot and mass spectrum analysis confirms the formation of 1:3 stoichiometric complex between the LH₃ and Zn²⁺ ions. Further this ensemble shows selective detection towards PPi anion over the other anions based on displacement metal ion approach. Hence, reversible colorimetric/emission response of LH₃ towards Zn²⁺ and PPi ions via "on-off-on" manner could allow the construction of IMPLICATION logic gate functions. The practical efficacy of the probe LH₃ was established by utilization of the probe for the detection of Zn²⁺ ions in real water sample analysis. Further, the significant noticeable colorimetric changes of the probe LH₃ upon addition of Zn²⁺ ion have been successfully integrated with a smartphone app RGB color value to construct a real-time analysis of Zn²⁺ ions.

Thiophene-phenylquinazoline probe for selective ratiometric fluorescence and visual detection of Fe(iii) and turn-off fluorescence for I- and its applications

A 2,5-bis(4-phenylquinazolin-2-yl)thiophene (BQT) probe is designed, synthesized and explored for selective ratiometric fluorescence and visual detection of Fe³⁺ and as a turn-off fluorescence probe for I^- anion. BQT is colorless and has blue emission in CH₃CN solution. BQT selectively complexes with Fe³⁺, turns its solution from colorless to greenish yellow and enables the ratiometric sensing of Fe³⁺ with limit of detection (LOD) and limit of quantitation (LOQ) of 2 × 10^-8 M and 6.1 × 10^-8 M, respectively. Binding constant of BQT with Fe³⁺ is found to be 4.1 × 10^-4 M^-1. BQT is also able to sense I^- anion present in aqueous solution by selectively turning colorless to yellow and fluorescence quenching with a LOD of 1.7 × 10^-7 M and LOQ of 5.2 × 10^-7 M. BQT sensing ability is not influenced by the presence of other metal ions and anions in the vicinity. The BQT-Fe³⁺ complex is thoroughly characterized using MALDI-TOF, NMR and Job's plot. A reversibility experiment with EDTA suggests BQT is a reversible fluorescent chemosensor for Fe³⁺ ions. The spectroscopic data of BQT and its complexes are employed to construct a field test kit for qualitative analysis and INHIBIT logic gate.

Novel Quinoline-Based Thiazole Derivatives for Selective Detection of Fe3+, Fe2+, and Cu2+ Ions

New quinoline-based thiazole derivatives QPT and QBT were synthesized and characterized by various spectroscopic and single-crystal X-ray crystallographic studies. The metal-sensing properties of the probes were further examined by absorption and fluorescence spectrometry. The fluorescence intensity of QPT and QBT was remarkably quenched during the addition of Fe³⁺, Fe²⁺, and Cu²⁺ ions in THF/H₂O (1:1) at pH = 7.4 in HEPES buffer, while the addition of other metal ions did not affect the fluorescence intensity of the ligands. The detection ability of the probes QPT and QBT was further investigated by titration with various equivalents of metal ions, optimized pH ranges for detection, and reversibility with Na₂EDTA for biological applications.

A review on emerging principles and strategies for colorimetric and fluorescent detection of alkaline phosphatase activity

Alkaline phosphatase (ALP) is a natural enzyme that is able to catalyze the dephosphorylation of phosphate esters. It participates in a great number of biological processes ranging from various metabolisms to signal transduction and cellular regulation. Since the abnormality of ALP activity in body is closely associated with many diseases, it has become an important biomarker for clinical diagnosis and treatment. Besides, it is often utilized in enzyme-linked immunosorbent assays. Given these demands, in the last few years considerable interest has been focused on exploring new materials and methods for ALP activity detection. In this review, we first made a clear classification on the principles that could be used for ALP activity determination. After that, emerging colorimetric and fluorescent strategies designed on the basis of these principles were systematically summarized. Finally, some perspectives on ALP activity analysis were discussed, hoping to inspire future efforts in the field.

Selective Sensing of Iron by Pyrrolo[2,3-c]Quinolines

This paper reports development of an iron sensor, 2-(3H-pyrrolo[2,3-c]quinolin-4-yl)aniline (APQ). The fluorophore facilitates micromolar detection of Fe³⁺/Fe²⁺ in the presence of various cations, including well-known interfering cations Co²⁺and Cu²⁺ by the process of fluorescence quenching. Graphical Abstract.

A new “ON–OFF–ON” fluorescent probe for sequential detection of Fe3+ and PPi based on 2-pyridin-2-ylethanamine and benzimidazo [2,1-a]benz[de]isoquinoline-7-one-12-carboxylic acid

A new fluorescent probe X based on 2-pyridin-2-ylethanamine and benzimidazo[2,1-a]benz[de]isoquinoline-7-one-12-carboxylic acid was designed and synthesized for the detection of Fe³⁺ and PPi.

Sequential detection of Fe3+/2+ and pyrophosphate by a colorimetric chemosensor in a near-perfect aqueous solution

A colorimetric chemosensor was developed for Fe^3+/2+ and pyrophosphate with low detection limit and practical application for Fe³⁺ in water samples.

Synthesis and self-assembly of bent core polycatenar mesogens with binding selectivity to Hg2+

Target compounds can self-assemble into Cub_I/Pm3̄nLC phases and organogels, simultaneously; these compounds have binding selectivity to Hg²⁺.