A highly selective benzildihydrazone based Schiff base chromogenic chemosensor for rapid detection of Cu2+ in aqueous solution

Luminous Insights: Exploring Organic Fluorescent "Turn-On" Chemosensors for Metal-Ion (Cu+2, Al+3, Zn+2, Fe+3) Detection

There are several metal ions that are vital for the growth of the environmental field as well as for the biological field but only up to the maximum limit. If they are present in excess, it could be hazardous for the human health. With the growing technology, a series of various detection techniques are employed in order to recognize those metal ions, some of them include voltammetry, electrochemical methods, inductively couples, etc. However, these techniques are expensive, time consuming, requires large storage, advanced instrumentation, and a skilled person to operate. So, here comes the need of a sensor and it is defined as a miniature device which detects the substance of interest by giving response in the form of energy change. So, from past few decades, many sensors have been formulated for detecting metal ions with some basic characteristics like selectivity, specificity, sensitivity, high accuracy, lower detection limit, and response time. Detecting various metal ions by employing chemosensors involves different techniques such as fluorescence, phosphorescence, chemiluminescence, electrochemical, and colorimetry. The fluorescence technique has certain advantages over the other techniques. This review mainly focuses on the chemosensors that show a signal in the form of fluorescence to detect Al+3, Zn+2, Cu+2, and Fe+3 ions.

A quinazolin-based Schiff-base chemosensor for colorimetric detection of Ni2+ and Zn2+ ions and 'turn-on' fluorometric detection of Zn2+ ion

Herein, we have reported a novel quinazolin-based Schiff base chemosensor (E)-2-benzamido-N'-(1-(pyridin-2-yl)ethylidene)benzohydrazide (L). L has been designed, synthesised and characterised by ¹H-NMR, IR spectroscopy, ESI-MS spectrometry and theoretical studies. The receptor showed appreciable colorimetric λ _max shift for both Ni²⁺ and Zn²⁺ ions and fluorometric "turn on" response in presence of only Zn²⁺ ion. The Jobs plot analysis revealed that receptor forms 2 : 1 complex with both the ions Ni²⁺ and Zn²⁺, further confirmed by ESI-MS analysis. The single crystal structure of L-Ni²⁺ complex (1) has also been determined. The colorimetric detection limits were calculated to 7.9 nM and 7.5 nM respectively for Ni²⁺ and Zn²⁺ in methanol-Tris-HCl buffer medium (10 mM, pH 7.2, 1 : 1 v/v). The chemosensor L can be applied for the recovery of contaminated water samples.

A label-free fluorescent peptide probe for sensitive and selective determination of copper and sulfide ions in aqueous systems

A label free fluorescent peptide probe (HDSGWEVHH) was used for Cu2+ and S2- determination in aqueous solution. Our results demonstrated that HDSGWEVHH is highly selective and sensitive for monitoring free Cu2+ concentration via quenching of the probe fluorescence upon Cu2+ binding. The mechanism of the complexation is investigated with Cyclic Voltammetry (CV), 1H nuclear magnetic resonance (NMR), electron paramagnetic resonance (EPR) spectroscopy and computational techniques. Theoretical calculation results indicated the binding ratio of the probe to Cu2+ is 2 : 1 and the binding constant was obtained as 1.72 × 10 8 M-1. Cu2+ concentration can be detected with the detection limit of 16 nM. Free Cu2+ concentration released from the metallothionein-Cu complex at different pH values was detected. Cu2+ concentration in real water and tea samples was also detected, and the results were consistent with the ones monitored by atomic absorption spectrometer. Because of the exceedingly small K sp value of CuS (1.27 × 10-36), S2- can sequester Cu2+ from HDSGWEVHH to restore the tryptophan (W) fluorescence. Thus the HDSGWEVHH-Cu2+ complex can also be used for S2- detection. The S2- concentrations can be monitored with a detection limit of 19 nM. The assay is also amenable to measurement of S2- concentration in pure water samples. Thus the probe designed herein is sensitive, label free, low cost, and environmentally friendly for Cu2+ and S2- determination in aqueous solutions.

A novel near-infrared turn-on fluorescent probe for the detection of Fe3+ and Al3+ and its applications in living cells imaging

In this study, a new hemicyanidine-based colorimetric-fluorescent probe L has been synthesized and characterized by X-ray single crystal diffraction, NMR, HRMS and other technologies. The probe L serves as a "turn-on" probe for the detection of Fe³⁺ and Al³⁺ ions in DMF-HEPES system with a high sensitivity and an excellent selectivity. The probe L manifesting the color of the solution containing L turns red on the addition of Fe³⁺, and turns pink on the addition of Al³⁺. The fluorescence turn-on detection of Fe³⁺ and Al³⁺ ions is attributed to the photo-induced electron transfer (PET) process and the exertion of the chelation-enhanced fluorescence effect (CHEF) mechanism. The results of thin layer silica gel plate coloration experiments also present the same characteristics. Additionally, we further demonstrate that the probe L exhibit good cell permeability and could be employed to monitor Fe³⁺ and Al³⁺ ions in the living cells.

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.

Diaminomaleonitrile-based Fluorophores as Highly Selective Sensing Platform for Cu2

A colorimetric and turn-on fluorescent chemodosimeter 1 based on diaminomaleonitrile was synthesized for Cu²⁺ detection. It showed high selectivity and sensitivity towards Cu²⁺ over the other tested metal ions. Probe 1 in acetonitrile exhibited a strong absorption band at 530 nm and weak fluorescence emission when excited at 480 nm, while the addition of Cu²⁺ could lead to a 30-nm blue shift of the absorption band and a remarkable fluorescence enhancement. Moreover, the detection limit of probe 1 for Cu²⁺ was calculated to be 28 nM. Quite different from the reported mechanism based on a metal-complexation induced fluorescence enhancement, the sensing mechanism was proved to be based on the Cu²⁺-promoted hydrolysis reaction, which was confirmed by ¹H NMR, ¹³C NMR and mass spectrum analysis. Studies on probe 2 were carried out to verify the universality of this sensing mechanism.

A novel hydrazide-based selective and sensitive optical chemosensor for the detection of Ni2+ ions: applications in live cell imaging, molecular logic gates and smart phone-based analysis

A novel hydrazide-based optical sensor for Ni²⁺ ions was designed, which can be applied for recovery of contaminated water samples, smart phone-based analysis and live cell imaging.

A dual-mode highly selective and sensitive Schiff base chemosensor for fluorescent colorimetric detection of Ni2+ and colorimetric detection of Cu2

In this paper, a novel flexible Schiff base chemosensor N'-(2-hydroxy-3-methoxybenzylidene)-2-(benzamido)benzohydrazide (L) has been designed, synthesised and characterised by 1H-NMR, IR spectroscopy, ESI-MS spectrometry and single crystal XRD analysis. A significant fluorescence enhancement of L was observed only in the presence of Ni2+ ions with a detection limit of 3.64 μM whereas Cu2+ induced fluorescence quenching, although both the metals showed colorimetric responses in methanol-Tris-HCl buffer (10 mM, pH 7.2) solution (1 : 1, v/v). The single crystal structure of L-Cu2+ has also been determined. No major interference by the other effective background cations (Fe3+, Fe2+, Co2+, Zn2+, Cd2+, Hg2+, Pb2+, Cr3+, Ag+, Al3+ and Mn2+) was observed even at a higher concentration of analytes. The experimental results were further supported by DFT studies. The chemosensor L can be applied to the formation of binary logical devices, recovery of contaminated water samples and living intracellular media.

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.

Novel selective and sensitive optical chemosensor based on phenylfluorone derivative for detection of Ge(IV) ion in aqueous solution

A water soluble chemosensor for Ge⁴⁺ ion based on fluorone derivative containing 3,4-bis(2-(diethylamino)-2-oxoethoxy)phenyl (R8) has been synthesized. The binding abilities between R8 and 10 equiv. of Na⁺, K⁺, Ca²⁺, Fe²⁺, Cu²⁺, Cd²⁺, Hg²⁺, Pb²⁺, Al³⁺, Cr³⁺, Fe³⁺ and Ge⁴⁺ ions in 1% v/v EtOH-water (tris-buffer pH 7.0) were studied using UV-vis and fluorescence spectrophotometry. When observed by naked-eyes, the color of R8 changed from yellow-orange to pink and the fluorescent color changed from green to non-fluorescence when complexed with Ge⁴⁺ ion. The spectral analysis showed that UV-vis absorption and fluorescence emission intensity of R8 decreased dramatically when Ge⁴⁺ ion was added comparing with other ions. To explain this behavior, the quantum calculation was performed using the hybrid density functional at B3LYP /LanL2DZ level of theory. The calculated orbital energies indicated that the decreasing of UV-vis absorption and the quenching of fluorescence were due to the complexation induced metal to ligand charge transfer. The association constants (K_a) of R8-Ge⁴⁺ complexes calculated from Benesi-Hildebrand equation was 6.21 × 10⁵ M^-1. The UV-vis detection limit for Ge⁴⁺ was 4.40 × 10^-7 M which was three orders of magnitude lower than those of Al³⁺, Cd²⁺, Cu²⁺ and Na⁺ ion.

A new Schiff-base chemosensor for selective detection of Cu2+ and Co2+ and its copper complex for colorimetric sensing of S2- in aqueous solution

A new Schiff-base colorimetric chemosensor 1 was developed for the detection of Cu²⁺, Co²⁺ and S^2-. Sensor 1 could simply monitor Cu²⁺ and Co²⁺ by a color change from colorless to yellow. The binding modes of 1 to Cu²⁺ and Co²⁺ were determined to be a 2 : 1 complexation stoichiometry through Job's plot and ESI-mass spectrometry analysis. The detection limits (0.02 μM and 0.63 μM) for Cu²⁺ and Co²⁺ were lower than the recommended values (31.5 μM and 1.7 μM) by the World Health Organization (WHO) for Cu²⁺ and the Environmental Protection Agency (EPA) for Co²⁺, respectively. Importantly, 1 could detect and quantify Cu²⁺ in real water samples. In addition, the Cu²⁺-2·1 complex could be used as a highly selective colorimetric sensor for S^2- in the presence of other anions without any interference. Moreover, the sensing mechanisms of Cu²⁺ and Co²⁺ by 1 were explained by theoretical calculations.

Quantum chemical insight into the molecular structure of L-chemosensor 1,3-dimethyl-5-(thien-2-ylmethylene)-pyrimidine-2,4,6-(1H,3H,5H)-trione: Naked-eye colorimetric detection of copper(II) anions

A sensitive colorimetric L-chemosensor 1,3-dimethyl-5-(thien-2-ylmethylene)-pyrimidine-2,4,6-(1[Formula: see text]-trione was developed by Knoevenagel combination of barbituric acid with thiophene aldehyde chelating moiety. The sensor displayed a high colorimetric Cu(II)X2 response; a dramatic methanol color change was recorded depending on anion type ([Formula: see text], Cl[Formula: see text], ClO[Formula: see text], NO[Formula: see text], OAc[Formula: see text], and SO[Formula: see text]. Off-on-off decolorized halochromism of the L-chemosensor/CuBr2 was recorded in an acidic medium. The structure of the L-chemosensor was confirmed by single-crystal X-ray diffraction, elemental analysis, and molecular spectroscopic tools such as UV–Vis, Fourier transform infra-red, 1H, and [Formula: see text]C nuclear magnetic resonance (NMR) spectroscopy. The thermal stability of the L-chemosensor was experimentally evaluated by thermogravimetric analysis. The structural optimized parameters of the ligand matched the crystallographic data, and the intermolecular forces were computed by Hirshfeld surface analysis. Electronic absorption in several solvents and 1H NMR were correlated with the computed spectra in the gaseous state. The HOMO/LUMO, global reactivity descriptor quantum parameters, Mulliken charge population, and molecular electrostatic potential of the L-chemosensor were also computed.

Colorimetric detection of iron and fluorescence detection of zinc and cadmium by a chemosensor containing a bio-friendly octopamine

A chemosensor containing a bio-friendly octopamine was developed for the colorimetric detection of iron and fluorescence detection of zinc and cadmium.