A substituent-modified new salicylaldehyde-diphenyl-azine based AIEgen: A promising skeleton for copper ion sensor

In this study, we have reported a novel 4-bromo-salicylaldehyde-diphenyl-azine (B-1), a new member of salicylaldehyde-diphenyl-azine (SDPA) family known for its excellent sensing properties. In contrast to the previously reported AIEgens, we found that the bromo-substitution at the 4th position of the salicylaldehyde moiety blue-shifted the emission by 10 and 15 nm as compared to the unsubstituted (Tong et.al 2017) and Bromo at the 5th position (Jain et.al 2023) respectively. Moreover, B-1 crystallizes instantly as the cooling process starts, which was not observed in the previously reported scaffolds. The sensing investigation again demonstrated the precise and ultrasensitive behavior of B-1 for copper ions. B-1 has a very low LOD value i.e. 29.2 x 10-8 M with a high association constant and binds with copper ion in 2:1 mode. This time we also analyzed the practical applicability in the solid phase using cotton swabs and performed the real-time estimation of copper ions in water and biological samples like urine and blood serum. The excellent percentage recovery and the RSD value suggest the precision of the experiments. Further, we also perform the sensing in living cancer HeLa cells. Altogether, we found that the SDPA skeleton is precise and ultrasensitive for copper ions and versatile which can be used variously to detect copper ions in the real world. This research will surely help in developing new specific skeleton-based AIEgens with desirable emission properties and precise applications in the future.

Hydrazide Schiff base Compound Containing Triphenylphosphonium Units for Fluorescence Sensing of Al3+ and its real Sample Applications

Al3+ excess in the body can cause many diseases. The development of chemosensors for the detection of Al3+ is therefore highly desirable. A hydrazide Schiff base compound containing triphenylphosphonium units (ER) was prepared and used as fluorescence turn-on sensor for the sensing of Al3+. Detection of Al3+ among various metals has been achieved successfully through the formation of Al3+-ligand coordination complexes. To detect Al3+, the "turn on" property of the fluorogenic chemosensor was investigated. Fluorescence sensing studies were carried out in CH3OH-Water (v/v, 9/1, pH 7.0) at λem = 528 nm. The LOD for sensing of Al3+ was found to be 0.129 µM. Using Job's graph, the stoichiometric ratio of ER- Al3+ was determined to be 1:1. The binding constant was determined to be 1.7 × 107 M-1 between Al3 + and the chemosensor ER. Finally, the determination of Al3+ in real herbal teas was carried out by using the sensing function of the chemosensor ER.

2-hydroxy-1- Naphthaldehyde Based Colorimetric Probe for the Simultaneous Detection of Bivalent Copper and Nickel with High Sensitivity and Selectivity

A neoteric colorimetric probe based on 2-hydroxy-1-naphthaldehyde (PMB3) was designed and synthesized for the real-time as well as on-site naked-eye detection of Cu2+/Ni2+ ions. Various physicochemical methods were employed to characterize the probe, and its colorimetric response to different metal ions was meticulously investigated. The probe, PMB3, exhibited a sensitive colorimetric response to Cu2+/Ni2+ ions among other competing metal ions, culminating in a prominent colour change from colourless to yellow. The stoichiometry of the ligand metal complexes was ascertained to be in a 1:1 ratio using Job's plot analysis, which was further corroborated by ESI-MS data. With detection limits of 4.56 µM for Cu2+ and 2.68 µM for Ni2+, the method was effectively extended to real sample analysis, ensuring propitious results that closely aligned with the actual values.

A piperazine- modified Schiff base sensor for highly selective detection of Zr (IV) ions: unveiling its antioxidant potential and regulatory effects on Zea mays growth

Piperazine functionalized Schiff bases 4(a-c) were synthesized by a condensation reaction which were thoroughly characterized by using various spectroscopic techniques like 1H NMR, 13C NMR, IR and mass spectrometry. X-ray crystallography was used to analyse synthesized compound 4b. The sensing capability of 4b was investigated towards the tetravalent form of the zirconium ion among other metal ions. The limit of detection and the association constant, were calculated to be 56.4 × 10-8 M and 5.36 × 105 M-1 respectively. The inclusion of additional metal ions had no effect on the selectivity of sensor 4b. The binding mechanism was clarified using 1HNMR spectroscopy, which was further verified computationally, using DFT. Also, the seed germination experiments were performed and effect of compound 4b was analyzed on the seedlings of Zea Mays. An investigation into molecular docking study using (5HQX) protein revealed that it had inhibitory effects on cytokinin oxidase. The protein and ligand effectively associate, as indicated by the lower binding energy of -9.69 kcal/mol. Therefore, compound 4b can act as a good, powerful inhibitor against cytokinin oxidase.

A highly selective and sensitive ICT-based Cu2+ fluorescent probe and its application in bioimaging

Cu²⁺ is an essential trace element for the organism, but its excess can also cause irreversible damage to the organism. As such, a "Turn-Off" fluorescent probe DPAP for the specific detection of Cu²⁺ was successfully constructed. DPAP exhibits large Stokes shift (120 nm), fast reaction speed (1 min), low detection limit (15.2 nM), low toxicity, and good cell permeability. Cu²⁺ quenches the fluorescence of DPAP by blocking its intramolecular charge transfer process to achieve the detection of Cu²⁺ and has been confirmed by HRMS, ¹H NMR and DFT calculations. Excitingly, the five-cycle detection of Cu²⁺ and the successful recovery of trace Cu²⁺ in environmental water samples fully demonstrate the potential of DPAP for practical applications. In particular, DPAP can observe the distribution and translocation patterns of exogenous Cu²⁺ in HeLa cells and zebrafish in real-time. This research concept has offered important theoretical support for the study of the environmental behavior of heavy metal ions.

A reversible and efficient probe for dual mode recognition of Al3+ and Cu2+ with logic gate behaviour: Crystal structure, theoretical and in-vivo bio-imaging investigations

This work presents the synthesis, characterization, crystal structure and spectroscopic investigations of isophthalohydrazide based probe. Among various tested metal ions, the probe selectively detects Al³⁺ and Cu²⁺ in aqueous ethanol via fluorometric and colorimetric methods, respectively. It displays a fluorescence "turn-on" response with Al³⁺ and visual colour change from colourless to yellow with Cu²⁺. Sensing mechanism is explored with UV-Vis, fluorescence spectroscopy and ¹H NMR titration, and confirmed with computational results. Suppression of CN isomerization and photo-induced electron transfer (PET) along with chelation enhanced fluorescence emission (CHEF) result in "turn-on" fluorescence with Al³⁺ while ligand to metal charge transfer (LMCT) accounts for visual colour change with Cu²⁺. Job's plot and HRMS confirm 1:2 (L:M) stoichiometry. The probe also exhibits efficient reversibility and reproducibility with EDTA which are successfully mimicked with combinatorial logic gate and truth table. Additionally, solid state applications and bio-imaging investigation on gut tissue of Drosophila 3rd instar larvae are performed.

Tetrazole conjoined organosilane and organosilatrane via the ‘click approach’: a potent Mycobacterium tuberculosis enoyl ACP reductase inhibitor and a dual sensor for Fe(iii) and Cu(ii) ions

This article includes the synthesis and characterization of tetrazole-allied organosilane and organosilatrane. The tetrazole-allied silatrane was explored for molecular docking and optical aspects.

Schiff base-functionalized silatrane-based receptor as a potential chemo-sensor for the detection of Al3+ ions

Excess Al³⁺ ions are considered toxic to living organisms.

Application of real sample analysis and biosensing: Synthesis of new naphthyl derived chemosensor for detection of Al3+ ions

A new chemosensor (NANH) based on naphthyl moiety was synthesized with good selectivity and sensitivity towards Al³⁺ ions via the inhibition by operating through dual mechanisms like photo-induced electron transfer (PET) and excited-state intramolecular proton transfer (ESIPT). The synthesized NANH was validated by various techniques such as ¹H, ¹³C NMR and mass spectrum. While prominent fluorescent enhancement was observed from the NANH upon binding with Al³⁺ ions, however, other metal ions have not responded in the emission spectrum. Detection limit and association constant of NANH for Al³⁺ were calculated as 1.2 × 10^-7 M and 4.09 × 10⁴ M^-1 by using fluorescence titration method. Binding ratio (1:1) of NANH with Al³⁺ ions were proved by Job's plot and DFT studies. Furthermore, aluminium in variety of water samples was determined, and NANH could be used for biosensing of Al³⁺ in living cells.

Multifunctional Receptor with Tunable Selectivity: A Comparative Recognition Profile of Organic Nanoparticles with Carbon Dots

The exponential growth in the research field of water pollution control demands the evolution of novel sensing materials for regulation and quantification of metals ions. Within this context, the current work reports a new strategy for the synthesis of carbon dots from the hydrothermal treatment of organic nanoparticles. The organic nanoparticles are found to be selective towards Cs(I) ions with a detection limit of 5.3 nM, whereas the highly fluorescent carbon dots are found to be selective towards Ag(I) ions with a detection limit of 4.8 nM. Both sensing systems illustrate rapid sensing with a working pH range from 4-9. The interfacial molecular restructuring of the sensing systems in the aqueous phase has been investigated in the absence and presence of targeted metal ions using a sum frequency generation vibrational spectroscopic tool. The practical applicability of the sensors was checked in environmental samples. This work opens new avenues for the exploration of temperature-guided sensing modulation in nanomaterials.

A multi-responsive crown ether-based colorimetric/fluorescent chemosensor for highly selective detection of Al3+, Cu2+ and Mg2

A novel multi-response chemosensor L based on coumarin-chalcone-crown ether was designed and synthesized, which exhibited a high selectivity for the colorimetric detecting Al³⁺ and Cu²⁺ and fluorescent recognizing Al³⁺ and Mg²⁺ in ethanol. L can monitor Al³⁺ and Cu²⁺ via distinct color changes from a slight yellow to pink and to orange, respectively. The sensor L can also monitor Al³⁺ and Mg²⁺ by fluorescence emission responses at 592 nm and 547 nm with low detection limits of 0.31 μM and 0.23 μM, respectively. The selectivity of L toward Al³⁺, Cu²⁺ and Mg²⁺ was not interfered by a large number of coexisting ions and was found to be reversible. By means of spectrometric titration, Job's plot, mass spectrometry, ¹H NMR titration and IR spectroscopy analysis, it was unanimously confirmed that the sensor L had a stoichiometric ratio of 1:1 with Cu²⁺ and Mg²⁺, and 1:2 with Al³⁺. The order of the stability of the complexes formed by L and Al³⁺, Cu²⁺, Mg²⁺ was as follows: L-Al³⁺ > L-Cu²⁺ > L-Mg²⁺. At the same time, some possible bonding modes and sensing mechanisms were further proposed, and the optimized structure of the sensor L and its sensing mechanism for Al³⁺, Cu²⁺ and Mg²⁺ were confirmed by the calculations of DFT/B3LYP and TD-DFT methods in a suite of Gaussian 09 programs.

Effect of n-alkyl substitution on Cu(ii)-selective chemosensing of rhodamine B derivatives

Rhodamine B hydrazide-based molecular probes (1-10) were synthesized by derivatization with n-alkyl chains of different lengths at the hydrazide amino end. These probes exhibited selective absorption (A∼557) and fluorescence (I∼580) 'off-on' signal transduction along with a colourless → magenta colour transition in the presence of Cu(ii) ions among all the competitive metal ions investigated. The effective coordination of these probes to Cu(ii) ions under the investigated environment forming [Cu·L]2+ (L = 1-5) and [Cu·L2]2+ (L = 6-10) complexes led to their spiro-ring opening, which in turn was expressed through signatory spectral peaks of ring-opened rhodamine. All these probes exhibited Cu(ii) selectivity in signalling despite structural modifications to the core receptor unit through variation of the nature of the alkyl substituents. However, the sensitivity of the signalling and kinetics of the spiro-ring opening varied and could be correlated with the number of carbon atoms present in the n-alkyl substituents. Structural elucidation with X-ray diffraction and X-ray photoemission spectroscopic analyses provided further insight into the structure-function correlation in their Cu(ii) complexes. These probes with Cu(ii) coordination showed selectivity in signalling, high complexation affinity (log Ka = 4.8-8.8), high sensitivity (LOD = 4.1-80 nM), fast response time (rate = 0.0017-0.0159 s-1) and reversibility with counter anions, which ascertained their potential utility as chemosensors for Cu(ii) ion detection.

Combined experimental and theoretical studies on a phenyl thiadiazole-based novel turn-on fluorescent colorimetric Schiff base chemosensor for the selective and sensitive detection of Al3+

A phenyl thiadiazole based receptor (L) has been presented for fluorescent colorimetric detection of Al³⁺ ion with very low detection limit in aqueous medium. The probe L can be applied for logic gate formation, recovery of contaminated water samples and smart-phone based analysis.

Coumarin based yellow emissive AIEE active probe: A colorimetric sensor for Cu2+ and fluorescent sensor for picric acid

A hydrazine derived ESIPT active Schiff base, 1-(8-methanylylidene-7-hydroxy-4-methyl-2H-chromen-2-one)-2-(2, 4-dihydroxybenzylidene) hydrazine, L was synthesized and characterized by elemental analysis and by various spectroscopic techniques. L exhibited a colourimetric response towards Cu²⁺ ion by changing from colorless to yellow with relatively a little or no interference of other common metal ions. The probe also showed good response for the detection of Cu²⁺ in real water samples. The H-aggregated L displayed AIEE property in acetonitrile/water mixture. The restriction of molecular motions endued the luminogen with a yellow fluorescence through ESIPT emission at 562 nm having relatively large Stock's shift of 205 nm. The scanning electron microscopic study was carried out to investigate the morphology of the nanoaggregate. The aggregated luminogen displayed it yellow emission in the pH range of 4-7 without affecting the intensity. The applicability of the probe for the detection of picric acid was also checked.

A dual-responsive colorimetric probe for the detection of Cu2+ and Ni2+ species in real water samples and human serum

The monitoring of heavy transition metals has increasingly attracted great attention because they pollute the environment and have unique physiological functions. Chemosensors are useful tools for monitoring heavy transition metals due to their simple visualization, excellent sensitivity and high selectivity. Herein, we have developed a novel chemosensor for the detection of water-soluble Cu2+ and Ni2+ species with different mechanisms, and low detection limits of 2.1 nM for Cu2+ and 1.2 nM for Ni2+ were obtained. The colorimetric probe CPH has been applied to qualitative and quantitative detection of Cu2+ and Ni2+ species in real samples.

Sequential Fluorescence Recognition of Molybdenum(VI), Arsenite, and Phosphate Ions in a Ratiometric Manner: A Facile Approach for Discrimination of AsO2 - and H2PO4. ACS OMEGA 2019;4:10877-10890. [PMID: 31460185 PMCID: PMC6648501 DOI: 10.1021/acsomega.9b00377]

An amide-based smart probe (L) is explored for nanomolar detection of Mo(VI) ion in a ratiometric manner, involving hydrogen-bond-assisted chelation-enhanced fluorescence process through inhibition of photoinduced electron transfer process. The recognition of Mo(VI) is associated with a 17-fold fluorescence enhancement and confirmed by single-crystal X-ray diffraction of the resulting Mo(VI) complex (M1). Further, M1 selectively recognizes arsenite through green emission of their adduct (C1) with an 81-fold fluorescence enhancement. Interestingly, dihydrogen phosphate causes dissociation of C1 back to free L having weak fluorescence. The methods are fast, highly selective, and allow their bare eye visualization at physiological pH. All of the interactions have been substantiated by time-dependent density functional theory calculations to rationalize their spectroscopic properties. The corresponding lowest detection limits are 1.5 × 10-8 M for Mo(VI), 1.2 × 10-10 M for AsO2 -, and 3.2 × 10-6 M for H2PO4 -, whereas the respective association constants are 4.21 × 105 M-1 for Mo(VI), 6.49 × 104 M-1 for AsO2 -, and 2.11 × 105 M-1 for H2PO4 -. The L is useful for efficient enrichment of Mo(VI) from aqueous solution, while M1 efficiently removes AsO2 - from environmental samples by solid-phase extraction.

A dual functional turn-on non-toxic chemosensor for highly selective and sensitive visual detection of Mg2+ and Zn2+: the solvent-controlled recognition effect and bio-imaging application

A new dual functional turn-on chemosensor, 2,6-diformyl-4-methylphenol-di(isoquinolinyl-1-hydrazone) (HL), has been developed, which could highly selectively discriminate Mg²⁺ and Zn²⁺ in different solvent systems. The chemosensor HL exhibits rapid visual turn-on fluorescence enhancing recognition toward Mg²⁺/Zn²⁺, which is not interfered by other cations, especially for respective congeners Ca²⁺/Cd²⁺. The remarkable fluorescence enhancement (71-fold or 11-fold) was observed after adding Mg²⁺ in acetonitrile or Zn²⁺ in DMF-H₂O solvent systems. Additionally such a solvent medium-controlled platform could achieve the quantitative determination of Mg²⁺ and Zn²⁺ quantitation with low detection limits of 2.97 × 10^-8 M and 3.07 × 10^-7 M, respectively. Furthermore, the turn-on fluorescence sensing mechanism is also investigated by ¹H NMR, FT-IR and ESI-MS spectroscopy. Density functional theory (DFT) calculations derive optimized geometries of HL and its complexes. Notably, non-toxic HL also can be successfully applied as a visual probe for the practical determination of Mg²⁺/Zn²⁺ in MCF-7 cells, Zebrafish larvae, syrup and water samples, which might provide extensive application in biology and medicine fields.

A dipodal molecular probe for naked eye detection of trivalent cations (Al3+, Fe3+and Cr3+) in aqueous medium and its applications in real sample analysis and molecular logic gates

A simple and low cost multifunctional colorimetric receptor L has been designed, synthesized and characterized by 1H-NMR, IR spectroscopy, ESI-MS spectrometry and elemental analysis. The chemosensor L can selectively detect three biologically and environmentally important trivalent metal ions (Al3+, Fe3+and Cr3+) both visually and spectrophotometrically in CH3CN-H2O (1 : 1, v/v) solution in the presence of other biologically relevant metal ions. The Job's plot analyses indicate the 2 : 2 binding stereochemistry for Al3+, Fe3+ and Cr3+ ions with L, which was further confirmed by 1H-NMR and ESI-MS studies. The binding constant values were found to be 2.9 × 104 M-1 for Al3+, 1.079 × 105 M-1 for Fe3+ and 1.366 × 105 M-1 for Cr3+ respectively. The detections limits of the sensor for Al3+ (2.8 × 10-7 M), Fe3+ (1.9 × 10-7 M) and Cr3+ (2.5 × 10-7 M) are far below than the limit set by the World Health Organization (WHO) for drinking water. Moreover, colorimetric test kits for rapid detection of Al3+, Fe3+, and Cr3+ could be successively applied for all practical purposes, indicating its potential use in environmental samples. It has also been used in building molecular logic gates.

Azine based smart probe for optical recognition and enrichment of Mo(vi )

Single crystal X-ray structure-characterized azine derivative (L) was explored for the selective detection of molybdenum (Mo(vi)) cations through green fluorescence emission. The Mo(vi) cation assisted inhibition of photo-induced electron transfer (PET) resulted in a 37-fold fluorescence enhancement via chelation enhanced fluorescence (CHEF) that allows detection of Mo(vi) with concentration as low as 2 × 10-9 M. The chelation of Mo(vi) cations by L has been confirmed by the single crystal X-ray structure of the resulting complex. The binding constant of L for Mo(vi) is fairly high (1.33 × 106 M-1). Moreover, L is very efficient for enrichment of Mo(vi) from aqueous solution. Density functional theoretical (DFT) studies substantiate the experimental results.

A highly selective and sensitive rhodamine-derived fluorescent probe for detection of Cu2

A novel water-soluble and reversible fluorescent probe was designed and synthesized based on a rhodamine B derivative. It was used for detection of Cu²⁺ in drinking water and in living cells with high sensitivity and excellent selectivity. The tested concentration range and the limit of detection (LOD) of the probe were 0-15.00μmolL^-1 and 0.085μmolL^-1, respectively. In addition, the mode of binding and mechanism of interaction between the probe and Cu²⁺ were analyzed by density functional theory (DFT) calculations.

Luminescent Functionalised Supramolecular Coordination Polymers Based on an Aromatic Carboxylic Acid Ligand for Sensing Hg2+ Ions

Two luminescent functionalised supramolecular coordination polymers, namely, [Zn(TPDC-2CH3)(H2O)2]·H2O (1) and [Cd(TPDC-2CH3)(H2O)4]·H2O (2), were successfully synthesised by the reaction of 2′,5′-dimethyl-[1,1′:4′,1″-terphenyl]-4,4″-dicarboxylic acid (H2TPDC-2CH3) with Zn2+ and Cd2+ ions, respectively. X-Ray crystallographic analysis reveals that both compounds 1 and 2 exhibit fascinating 3D supramolecular networks, in which metal ions are linked by ligands to form a 1D chain which further extends to a 3D structure through the interaction of hydrogen bonding. The use of 1 and 2 as luminescent sensors for the optical detection of metal ions: Na+, K+, Hg2+, Ag+, Ca2+, Co2+, Ni2+, Mn2+, Cu2+, Zn2+, Cd2+, Pb2+, Mg2+, Al3+, Fe3+, Fe2+, In3+, Bi3+, and Cr3+ was carried out in aqueous solution, and the results indicated that compound 1 could effectively detect Hg2+ ions among various cations at room temperature, with a detection limit of 3.6 × 10−15 M.

Fluorescent detection of multiple ions by two related chemosensors: structural elucidations and logic gate applications

Two related chemosensors L1 and L2 display selective detection of multiple ions (Cu²⁺, Al³⁺, Cd²⁺ and S²⁻) as a result of minor variation of functional groups at a remote arene ring.

Silver nanoclusters with enhanced fluorescence and specific ion recognition capability triggered by alcohol solvents: a highly selective fluorimetric strategy for detecting iodide ions in urine

Alcohol solvents can endow silver nanoclusters with enhanced red fluorescence and specific iodide recognition capability.

FRET based selective and ratiometric detection of Al(iii) with live-cell imaging

A cell permeable FRET based platform for dual mode ‘naked-eye’in vitroandin vivodetection of Al³⁺over other common ions (including trivalent ions).

The maiden report of a fluorescent-colorimetric sensor for expeditious detection of bifluoride ion in aqueous media

A fluorescent-colorimetric chemosensor L, for rapid detection of bifluoride ion has been developed based on a simple bis-Schiff base.