Selective fluorescent probes based on CN isomerization and intramolecular charge transfer (ICT) for zinc ions in aqueous solution

AIE-based fluorescent probe designed with xanthone as a π-bridge for detecting of ClO- in pericarp and living cells

The role of ClO- in the physiological functioning of organisms is significant. In this paper, the four fluorescent probes HONx (HON1, HON2, HON3 and HON4) were prepared based on oxyanthracene through the introduction of different substituents, and their photophysical properties were investigated, among which the AIE effect of HON1 was the most significant, and therefore the fluorescent "turn-off" ClO- probe HON1-CN was chosen to be prepared by constructing the ClO- recognition site hydrazone bond at HON1. The ClO- recognises the hydrazone group in the probe HON1-CN, and when the hydrazone bond is broken, the aldehyde group is released, generating HON1 with yellow fluorescence. The probe HON1-CN is highly selective and stable for the detection of ClO- with a detection limit of 0.48 μM and a more than 10-fold increase in fluorescence intensity when the fluorescence is 'switched on', and to a lesser extent, the probe is also very good for the detection of hypochlorite ClO- in the pericarp. Finally, HON1-CN has also been used to detect the presence of ClO- in HeLa cells and zebrafish.

Anthraquinone Based Sensors for the Selective Detection of Cyanide Ion with Turn on Fluorescence with Logic Gate & Real Sample Applications

In recent years, there is an increasing interest in finding better and more efficient ways to detect CN- ions. Most of the anthraquinone-based probes show less fluorescence This paper presents the design and synthesis of a new anthraquinone based imine probe with good colorimetric sensing property and fluorescent turn on behavior toward CN- ion. Herein, we report a receptor with both colorimetric and fluorescent enhancement of cyanide ion in DMSO medium is synthesized. The synthesized receptor shows an immediate color change from orange to pink when cyanide is added; and it can be readily observed visually due to the presence of diverse p-conjugated systems in the receptor. These studies were confirmed by UV-Visible, PL studies, DFT, HRMS and 1H NMR titration. Moreover, this receptor shows 1:1 stoichiometry and micromolar detection limit. Further the receptor was applied to a real sample in finger millet (Eleusine Coracana) to detect the presence of cyanide ion. Moreover, the receptor is applicable toward INHIBITION, IMPLICATION logic gates with two input systems.

Advancements in the development of fluorescent chemosensors based on CN bond isomerization/modulation mechanistic approaches

The CN bond isomerization/modulation as a fluorescence signalling mechanism was explored by studying the photophysical properties of conformationally restricted molecules. From the beginning, the CN bond isomerization method has attracted the attention of researchers owing to its simplicity, high selectivity, and sensitivity in fluorescence evaluation. Continuous developments in the field of sensing using CN bond-containing compounds have been achieved via the customization of the isomerization process around the CN bond in numerous ways, and the results were obtained in the form of specific discrete photophysical changes. CN isomerization causes significant fluorescence enhancement in response to detected metal cations and other reactive species (Cys, Hys, ClO-, etc.) straightforwardly and effectively. This review sheds light on the process of CN bond isomerization/modulation as a signalling mechanism depending on fluorescence changes via conformational restriction. In addition, CN bond isomerization-based fluorescent sensors have yet to be well reviewed, although several fluorescent sensors based on this signalling mechanism have been reported. Therefore, CN-based fluorescent sensors are summarized in this review.

A Comprehensive Review on Thiophene Based Chemosensors

The recognition and sensing of various analytes in aqueous and biological systems by using fluorometric or colorimetric chemosensors possessing high selectivity and sensitivity, low cost has gained enormous attention. Furthermore, thiophene derivatives possess exceptional photophysical properties compared to other heterocycles, and therefore they can be employed in chemosensors for analyte detection. In this review, we have tried to explore the design and detection mechanism of various thiophene-based probes, practical applicability, and their advanced models (design guides), which could be thoughtful for the synthesis of new thiophene-based probes. This review provides an insight into the reported chemosensors (2008-2020) for thiophene scaffold as effective emission and absorption-based chemosensors.

Designed Synthesis of Fluorescence 'Turn-on' Dual Sensor for Selective Detection of Al3+ and Zn2+ in Water

1-(Pyridin-2-yl-hydrazonomethyl)-naphthalen-2-ol (PNOH) is a naphthalene-based fluorescence dual chemo-sensor for Al³⁺ and Zn²⁺. The probe (PNOH) is spectroscopically characterised and the chemo-sensing mechanism has been demonstrated through ¹H NMR, absorption and both steady state and time resolved fluorescence study. The 'turn-on' luminescence property of PNOH is used for the selective detection of trace amount of Al³⁺and Zn²⁺via chelation enhanced fluorescence (CHEF) through complex formation. The 1:1 stoichiometry of each sensor-metal complex is observed from Job's plot based on UV-Vis titration. Most promising advantage of the probe (PNOH) is its application in the one-pot detection of Al³⁺ (λem- 460 nm) and Zn²⁺ (λ_em- 510 nm) exciting at same wavelength (λ_ex- 420 nm) while high intense emission appears at two different wavelengths. Limit of detection (LOD) of PNOH towards Al³⁺ & Zn²⁺ are found to be 60 nM & 365 nM respectively. Real water sample analysis has also been demonstrated by using the probe PNOH.

The recent development of fluorescent probes for the detection of NADH and NADPH in living cells and in vivo

Reduced nicotinamide adenine dinucleotide (NADH) and its phosphate ester (NADPH) participate in numerous metabolic processes in living cells as electron carriers. The levels of NADH and NADPH in a cell are closely related to its metabolic and pathological state. It is important to monitor the levels of NADH and NADPH in living cells and in vivo in real-time. This review mainly focuses on fluorescent probes developed for monitoring NADH and NADPH in living cells and in vivo, and classifies them according to the recognition units. These fluorescence probes can rapidly respond to changes in NADH and NADPH levels without interference from other biomolecules, both in cell culture and in vivo. These probes have been employed to monitor NADH and NADPH levels in living cells, tumor spheroids, and in vivo; moreover, some of them can be used to discriminate normal cells from cancer cells, and detect cancer cell death due to reductive stress induced by natural antioxidants. This review is expected to inspire the generation of novel fluorescent probes for the detection of NADH and NADPH, and stimulate more attention in the development of fluorescent probes based on carbon dots and nanoparticles, as well as metal complex-based, time-gated luminescent probes for monitoring NADH and NADPH in both living cells and in vivo.

A novel sensitive and selective chemosensor for fluorescent detection of Zn2+ in cosmetics creams based on a covalent post functionalized Al-MOF

A material was fabricated based on the Schiff base reaction to achieve covalent attachment of NH₂-MIL-53(Al) and 3-formylsalicylic acid for fluorimetric detection of Zn²⁺ ions based on inhibition and destruction of CN isomerization and ESIPT.

A new 1,2,3-triazole-decorated imino-phenol: selective sensing of Zn2+, Cu2+ and picric acid under different experimental conditions

A new 1,2,3-triazole-based imino-phenol 1 is synthesized. It selectively senses Zn²⁺ in CH₃CN–H₂O with a detection limit of 1.8 × 10⁻⁶ M. Further, the selective sensing of Cu²⁺ and picric acid is achieved by the ensemble 1.Zn²⁺ in CH₃CN–H₂O.

Synthesis of new cyclotriphosphazene derivatives bearing Schiff bases and their thermal and absorbance properties

In this study, a series of cyclotriphosphazene derivatives containing a Schiff base (3a-3d) were synthesized by the reactions of hexachlorocyclotriphosphazene (1) with bis-aryl Schiff bases ( 2a - 2d ) having different terminal groups (H, F, Cl, and Br). The products ( 3a - 3d ) were characterized by elemental and mass analyses, FT-IR, and ¹ H, ¹³ C, and ³¹ P NMR spectroscopies. Furthermore, the structure of compound 3a was also determined by X-ray crystallography. The thermal behaviors and the spectral properties of the new cyclotriphosphazene compounds ( 3a - 3d ) were investigated and the results were compared in the series.

BODIPY-Derived Polymeric Chemosensor Appended with Thiosemicarbazone Units for the Simultaneous Detection and Separation of Hg(II) Ions in Pure Aqueous Media

Developing a simple and cheap analytical method for the selective detection and quantitative separation of toxic ions present in aqueous media is the biggest challenge faced by the chemosensing research community. Here, a 5,5-difluoro-1,3,7,9-tetramethyl-10-phenyl-5 H-dipyrrolo-diazaborinine-derived water-soluble polymer integrated with thiosemicarbazone units was rationally designed and synthesized for the simultaneous detection and separation of Hg(II) ions in pure aqueous solution. The water-soluble polymer scaffold poly( N, N'-dimethyl acrylamide- co-5,5-difluoro-1,3,7,9-tetramethyl-10-phenyl-5 H-dipyrrolo-diazaborinine-2-carbaldehyde) was synthesized by reversible addition-fragmentation chain transfer polymerization, followed by post-polymerization modification with thiosemicarbazide, leading to the formation of the target probe, P1. The nonemitting P1 exhibited bright yellow emission upon exposure to Hg(II) ions, with a limit of detection as low as 0.37 μM. This turn-on emission behavior triggered by Hg(II) ions might originate from the suppression of isomerization around the C═N bond of the thiosemicarbazone moiety caused by the formation of a coordination complex between P1 and Hg(II) ions. In addition, P1 displayed excellent selectivity toward Hg(II) ions over other metal cations. Finally, the selective removal of Hg(II) ions from an aqueous solution containing various metal ions was achieved by precipitation, which is probably caused by the fact that coordination complexes whereby Hg(II) ions acted as bridgeheads between P1 molecules had formed.

An azine-based carbothioamide chemosensor for selective and sensitive turn-on-off sequential detection of Zn(II) and H2PO4-, live cell imaging and INHIBIT logic gate

Hydrazino-carbothioamide, 1, serves as a turn-on fluorescent chemosensor to Zn²⁺ and the mixture shows green emission (λ_em 492) in presence of large number of ions with impressive limit of detection (LOD), 0.59 nM. Intense fluorescence of Zn-complex is selectively turn-off upon adding H₂PO₄^- only to the limit of detection, 26 μM, while other anions remain silent. The sensing mechanism of 1 is established by suppressing the ESIPT of 1 and complexation with Zn²⁺ (CHEF) is supported by Job's plot, ¹H NMR, and HR-MS data. Turn-on-off sequential detection of Zn²⁺ and H₂PO₄^- also have successfully been employed for the engineering of INHIBIT molecular logic gate. The sensor is non-toxic and has been used in identifying Zn²⁺ in the intracellular region of African green monkey kidney cells (Vero cells).

A multi-analyte responsive chemosensor vanilinyl Schiff base: fluorogenic sensing of Zn(ii), Cd(ii) and I−

A single fluorescence probe recognizes multiple ions and grabs the great attention of scientists.

Highly selective and sensitive recognition of Zn(ii) by a novel coumarinyl scaffold following spectrofluorometric technique and its application in living cells

A biocompatible coumarinyl Schiff base scaffold (H2L), a nontoxic probe and a fluorescent sensor to Zn²⁺, with an LOD of 11 nM, was used for living cell imaging.

Triphenylamine based lab-on-a-molecule for the highly selective and sensitive detection of Zn2+ and CN− in aqueous solution

A triphenylamine based lab-on-a-molecule TATP was designed and synthesized as a bifunctional sensor for the detection of Zn²⁺ and CN⁻ through fluorescence and UV-Vis absorption channels, with detection limits of 14 nM and 0.37 μM, respectively.

Colorimetric chemosensor for multiple targets, Cu2+, CN−and S2−

New Schiff-base was developed as colorimetric sensor for Cu²⁺, CN⁻and S²⁻with the detection limits lower than the given guidelines.

Selective and sensitive colorimetric sensor for CN− in the absence and presence of metal ions (Cu2+/Ni2+): mimicking logic gate behaviour

Enone based anion sensors have significance due to their colorimetric reaction upon deprotonation and variable occurrence in the conjugated moiety.

A new Schiff base and its metal complex as colorimetric and fluorescent–colorimetric sensors for rapid detection of arginine

A new Schiff base (L) and its Pb²⁺-complex have been utilized for rapid detection of arginine in aqueous medium.Lexhibits an excellent selective colorimetric response whereas its Pb²⁺-complex exploits fluorescent-colorimetric response towards arginine with very low detection limits.

Coumarinyl thioether Schiff base as a turn-on fluorescent Zn(ii) sensor and the complex as chemosensor for the selective recognition of ATP, along with its application in whole cell imaging

A Zn²⁺ sensor, coumarinyl thioether Schiff base shows the LOD 0.068 μM. The fluorogenic complex, [ZnL] recognizes ATP in presence of other anions and the LOD, 6.7 μM, is the lowest in literature. Ligand is used for fluorescence cell imaging process.

A colorimetric chemosensor based on a Schiff base for highly selective sensing of cyanide in aqueous solution: the influence of solvents

A new highly selective colorimetric chemosensor 1 shows exclusive response toward cyanide by a color change in aqueous solution.

A new multifunctional Schiff base as a fluorescence sensor for Al3+ and a colorimetric sensor for CN− in aqueous media: an application to bioimaging

A new multifunctional Schiff-base receptor 1 which exhibits an excellent cell-permeable fluorescence for Al³⁺ and a color change for CN⁻ in aqueous media has been prepared.