Rapid and Efficient Dual Detection Of Zn2+ Ions and Oxytetracycline Hydrochloride Using a Responsive Fluorescent "On-Off" Sensor Based on Simple Salen-Type Schiff Base Ligand

This research has progressed to an effective detection chemosensor of zinc, aluminum ions and oxytetracycline hydrochloride antibiotic based on the fluorescence technique. A straightforward method utilizing microwave irradiation was employed to synthesize the salen-type Schiff base ligand N,N'-bis(salicylaldehyde)4,5-dichloro-1,2-phenylenediamine (H2I), providing a good 70 % yield. In ethanol, the H2I sensor demonstrated remarkable rapidity, selectivity, and sensitivity in detecting zinc ions. The fluorescence spectrum exhibited a 44-fold substantial enhancement at 522 nm and achieved a low limit of detection (LOD) of 1.47 μM. Furthermore, the H2I probe's emission intensity increased by 124 times when compared to the ligand's ability to detect Al3+ ions at 494 nm with a LOD value of 7.4 μM. Additional research was done using the H2I probe's effective Zn2+ detection capability. The ability to recognize zinc ions in different real water samples demonstrated a recovery rate of 98.67 % to 103.31 %. Interestingly, a naked-eye visible fluorescence color of H2I solution impregnated filter papers turned colorless into yell ow under UV irradiation by adding Zn2+ ions, renders it suitable for developing a practical zinc ion detection kit test. In particular, the I-Zn2+ complex effectively quenched the fluorescence toward oxytetracycline hydrochloride (OTC) with a LOD value of 1.49×10-2 μM in DMSO:H2O (6 : 4, v/v). This is a novel and effective procedure for sensing OTC antibiotic by the I-Zn2+ complex. These findings hold immense potential for the development of dual fluorescent probes, thereby enhancing sensitivity and specificity in identifying metal ions and antibiotics in a wide range of applications.

A pyrene-induced PET-based chemosensor for biologically important Zn(II) ions: application in test strips and live cell imaging studies

Cation and anion sensing is vital owing to their universal dispersion in ecosystems and biological functions. It has been shown that fluorescent receptors based on organic platforms are efficient for detecting a number of ions and have many advantages such as low cost, superior sensitivity and simplicity in installation. This study demonstrates the design and synthesis of a novel receptor (E)-3-[(3,5-di-tert-butyl-2-hydroxybenzylidene)amino]-2-(pyren-1-yl)-2,3-dihydroquinazolin-4(1H)-one (DTQ) for the rapid recognition of Zn(II) ions. DTQ exhibited a significant fluorometric "turn-on" characteristic towards Zn(II) at λmax 444 nm in aqueous acetonitrile by inhibiting the photo-induced electron transfer (PET) and -CN- process. The ESI-MS analysis and Job's plot experimental results confirmed stoichiometric 1 : 1 complex formation between DTQ and Zn(II). Fluorometric investigations revealed the detection limit and association constant of DTQ towards Zn(II), which were found to be 13.4 nM and 1.47 × 105 M-1, respectively. DTQ was employed to sense Zn(II) on low-cost test strips. The present research findings imply that DTQ can function as an effective sensor for Zn(II).

Variation of the Emission Efficiency and Wavelength from Fluorescent Zinc Salen Complexes upon Systematic Structural Modifications

Understanding the photophysical properties of metal salen complexes is not straightforward because the emission efficiency is altered irregularly upon structural modifications. The present study prepared zinc salen complexes with systematic structural variations to pinpoint critical factors to determine the emission efficiency. One of the important experimental observations is the regiochemistry of a phenolate substituent affecting emission efficiency from a salicylidene fluorophore, which is nicely assigned as arising from the photoexcited electronic structure of metal salen complexes. Another significant finding is the thermal fluctuation of a salen ligand arising from the mismatched ligand-metal interaction, which has a significant impact on fluorescence lifetime. The present study sheds light on hidden factors that alter photophysical properties of a metal salen complex, which provide valuable insights into designing new photoactive salen ligands.

Fluorescence detection of malachite green and cations (Cr3+, Fe3+ and Cu2+) by a europium-based coordination polymer

Due to remarkable fluorescence characteristics, lanthanide coordination polymers (CP) have been widely employed in fluorescence detection, but it is rarely reported that they act as multifunctional luminescent probes dedicated to detecting malachite green (MG) and various metal ions. A europium-based CP fluorescent probe, Eu(PDCA)2(H2O)6 (PDCA = 2,6-pyridinedicarboxylic acid), has been synthesized and exhibited excellent recognition ability for malachite green and metal cations (Cr3+, Fe3+ and Cu2+) among 11 metal cations, 13 anions and six other compounds. The recognition was achieved by fluorescence quenching when MG, Cr3+, Fe3+ and Cu2+ were added to a suspension of Eu(PDCA)2(H2O)6 respectively. Eu(PDCA)2(H2O)6 is a multifunctional luminescent probe, and displayed high quenching efficiencies K sv (2.10 × 106 M-1 for MG; 1.46 × 105 M-1 for Cr3+; 7.26 × 105 M-1 for Fe3+; 3.64 × 105 M-1 for Cu2+), and low detection limits (MG: 0.039 μM; Cr3+: 0.539 μM; Fe3+: 0.490 μM; Cu2+: 0.654 μM), presenting excellent selectivity and sensitivity, especially for MG. In addition, Eu(PDCA)2(H2O)6 was also made into fluorescent test strips, which can rapidly and effectively examine trace amounts of MG, Cr3+, Fe3+ and Cu2+ in aqueous solutions. This work provides a new perspective for detecting malachite green in fish ponds and heavy metal ions in waste water.

Selective Detection of Picric Acid and Pyrosulfate Ion by Nickel Complexes Offering a Hydrogen-Bonding-Based Cavity

This work describes the synthesis and characterization of three mononuclear nickel complexes supported with amide-based pincer ligands. All three complexes presented an H-bonding-based cavity due to the migration of amidic protons to the appended heterocyclic rings that formed H-bonds with the metal-ligated solvent molecule(s). These complexes functioned as the nanomolar chemosensors for the detection of picric acid and pyrosulfate ion as inferred by the detailed absorption and emission spectral studies while further supported with FTIR, NMR, and mass spectra of the isolated products. We also illustrate a few practical detection methods for the sensing of picric acid in the solution state as the naked-eye colorimetric methods and in the solid state by employing polystyrene films.

Unraveling the Origin of Differentiable 'Turn-On' Fluorescence Sensing of Zn2+ and Cd2+ Ions with Squaramides

A squaramide ring conjugated with Schiff-bases decorated with hydroxy and methoxy functional groups differentially senses zinc and cadmium ions, which turn on the fluorescence. The feebly emitting free ligands light up in the presence of zinc and cadmium acetates, with the acetate ion playing a pivotal role as a conjugate anion. The selective and differentiable emission responses for zinc and cadmium ions make these ligands efficient multi-analyte sensing agents. Furthermore, these ligands could be used to differentially sense zinc and cadmium ions even in aqueous environments. The NMR investigations reveal marginal differences in the binding of zinc and cadmium ions to the ligands, whereas density functional theory calculations suggest the different extent of ligand-to-metal charge transfer (LMCT) contributes to the differential behavior. Finally, comparison of the excited-state dynamics of free ligand and the metal complexes reveal the appearance of longer lifetime (about 500-700 ps) component with complexation, due to rigidified molecular skeleton, thereby impeding the non-radiative processes.

A novel switch on and reversible optical sensor as an efficient, selective receptor for Zn(II) ion and its biological application

In the present study, a promising optical sensor (TR) was designed, synthesized, characterized and its chemosensing mechanism has been explored through ¹H NMR, ESI-MS, UV-Vis absorption and emission spectral studies. This compound exhibits a drastic change in its optical properties when treated with Zn²⁺, whereas other metal ions do not respond. This provides a naked eye detection for Zn²⁺ ion. In methanolic medium, Zn²⁺ ion induces strong fluorescence in TR with large Stokes shifts up to ∼132 nm. A 5-fold increase in fluorescence intensity of TR in presence Zn²⁺ ion is due to inhibition of ESIPT (Excited State Intramolecular Proton Transfer) and -C=N isomerization with large increase in the ICT (Intramolecular Charge Transfer) character of TR in the excited state. The Job's plot and BH plots reveal the formation of 1: 1 stoichiometry with an estimated binding constant of 3.9 × 10⁷ M^-1. The detection limit of TR was found to be 3.85 nM. The TR could be regenerated by adding EDTA solution to the complex formed during interaction. The pH studies indicate that TR could render pH dependent fluorescence measurements in a live physiological environment. Computational technique was used to optimize the structures and the theoretical results are correlated with the experimental results. The possible utilization of TR as bio-imaging fluorescent sensor with 98.57% cell viability to detect Zn²⁺ in HeLa cells was also explored by fluorescent cell imager.

An imidazole derivative-based chemodosimeter for Zn2+ and Cu2+ ions through “ON–OFF–ON” switching with intracellular Zn2+ detection

Imidazole derivative-based chemodosimeter (HL) for selective detection of Zn²⁺ and Cu²⁺ metal ions and intracellular Zn²⁺ sensing.

Monitoring ADP and ATP in vivo using a fluorescent Ga(iii)-probe complex

A naphthol-based sensor (L) was designed and synthesized for the specific recognition of Ga3+ using fluorescence enhancement. An in situ generated L-Ga3+ ensemble detected ADP and ATP more selectively through a fluorescence "switch off" response, which was confirmed both in cells and in adult zebrafish.

Highly efficient fluorescence sensing of phosphate by dual-emissive lanthanide MOFs

The detection of phosphate (Pi) under physiological conditions is a very important issue in environmental and biological sciences. Herein, a unique fluorescent probe {[EuL(H2O)1.35(DMF)0.65]·1.9DMF}n (1) was prepared through the organic-inorganic hybridization between asymmetrical tricarboxylate ligands and Eu2O2 clusters under solvothermal conditions. The as-prepared sample 1 exhibited excellent fluorescence properties and could be designed as a self-calibrating fluorescent probe for sensitively and selectively detecting Pi which served as an essential substance in aquatic ecosystems and biological systems. The different responses of the two emission peaks caused by the addition of Pi resulted in a continuous fluorescence color change, which could be clearly observed with the naked eye under UV light lamp illumination at 302 nm. Typically, a good linearity existed between the ratio of dual fluorescence intensities and the Pi contents ranging from 0.1 μM to 15 μM with a low detection limit of 52 nM (S/N = 3). It is noteworthy that the prepared self-calibrating fluorescent probe displayed specific recognition towards Pi anions with satisfactory recovery ranging from 92.8% to 100.6% in water samples and biological fluids. Thus, we can envision that this work may open a new avenue for the detection of many other bioactive ions in environmental and biological samples.

A highly selective and sensitive chemosensor forl-tryptophan by employing a Schiff based Cu(ii) complex

Construction of a new Cu(ii) complex (1) based modified glassy carbon electrode (1-GCE) for highly selective and sensitive detection ofl-tryptophan (l-Trp).

A versatile optical assay plate fabricated from e-waste and its application towards rapid determination of Fe3+ ions in water

Fabricating an optical assay plate from e-waste and demonstrating its applicability towards one-step assays.

The development of fluorescence turn-on probe for Al(III) sensing and live cell nucleus-nucleoli staining

The morphology of nucleus and nucleolus is powerful indicator of physiological and pathological conditions. The specific staining of nucleolus recently gained much attention due to the limited and expensive availability of the only existing stain "SYTO RNA-Select". Here, a new multifunctional salen type ligand (L1) and its Al3+ complex (1) are designed and synthesized. L1 acts as a chemosensor for Al3+ whereas 1 demonstrates specific staining of nucleus as well as nucleoli. The binding of 1 with nucleic acid is probed by DNase and RNase digestion in stained cells. 1 shows an excellent photostability, which is a limitation for existing nucleus stains during long term observations. 1 is assumed to be a potential candidate as an alternative to expensive commercial dyes for nucleus and nucleoli staining.

Multicolour fluorescent carbon nanoparticle probes for live cell imaging and dual palladium and mercury sensors

Carbon based nanomaterials are emerging as a desirable alternative to semiconducting quantum dots due to their unique optical properties and biocompatibility. The present study demonstrates the design and synthesis of highly fluorescent carbon nanoparticles (CNPs). The CNPs are investigated for their biocompatibility and henceforth successfully employed as promising multicolor bioimaging probes in A375 and DU145 cell lines. Furthermore, a "turn off" mode has been established for the detection of noble metal palladium (Pd²⁺) and heavy metal mercury (Hg²⁺) by quenching the fluorescence of CNPs. The CNP sensor responded to the detection of Pd²⁺ (5-100 μM) and Hg²⁺ (1-18 μM) in a wide range with the limit of detection (LOD) of 58 nM for Pd²⁺ and 100 nM for Hg²⁺. The CNP sensor was employed for the detection of Pd²⁺ and Hg²⁺ in real water samples and detection of leftover palladium catalysts in a model reaction system. Also, the CNPs were successfully employed as intracellular mercury and palladium sensors using confocal microscopy.

Varying structural motifs in the salen based metal complexes of Co(ii), Ni(ii) and Cu(ii): synthesis, crystal structures, molecular dynamics and biological activities

Four new metal complexes which demonstrates varying structural motifs from monomeric to dimeric to tetrameric complexes by slightly altering the reaction conditions and their biological applications.