A selective fluorescence-on reaction of spiro form fluorescein hydrazide with Cu(II)

Shedding Light on Heavy Metal Contamination: Fluorescein-Based Chemosensor for Selective Detection of Hg2+ in Water

This article discusses the design and analysis of a new chemical chemosensor for detecting mercury(II) ions. The chemosensor is a hydrazone made from 4-methylthiazole-5-carbaldehyde and fluorescein hydrazide. The structure of the chemosensor was confirmed using various methods, including nuclear magnetic resonance spectroscopy, infrared spectroscopy with Fourier transformation, mass spectroscopy, and quantum chemical calculations. The sensor's ability in the highly selective and sensitive discovery of Hg2+ ions in water was demonstrated. The detection limit for mercury(II) ions was determined to be 0.23 µM. The new chemosensor was also used to detect Hg2+ ions in real samples and living cells using fluorescence spectroscopy. Chemosensor 1 and its complex with Hg2+ demonstrate a significant tendency to enter and accumulate in cells even at very low concentrations.

Influence of ortho group in rhodamine B hydrazide based Schiff base for selective recognition of Cu2+ and Fe3+ ions: A mechanistic approach by DFT and colorimetric studies

Herein we have implemented a computational approach in designing sensor molecules for the selective recognition of Cu²⁺ and Fe³⁺ ions. Seven rhodamine B hydrazide-based Schiff base derivatives were designed and analysed their chemosensing properties against Cu²⁺ and Fe³⁺ ions in ethanol solution theoretically. The theoretical calculations revealed that the selective recognition of Cu²⁺ and Fe³⁺ ions takes place via spirolactam ring-opening and there is a pivotal role of ortho substituents and N-heteroatoms. The two best chemosensors were synthesised and used for the detection of Cu²⁺ and Fe³⁺ ions by colorimetric methods.

Fluorescein Based Fluorescence Sensors for the Selective Sensing of Various Analytes

Fluorescein molecules are extensively used to develop fluorescent probes for various analytes due to their excellent photophysical properties and the spirocyclic structure. The main structural modification of fluorescein occurs at the carboxyl group where different groups can be easily introduced to produce the spirolactam structure which is non-fluorescent. The spirolactam ring opening accounts for the fluorescence and the dual sensing of analytes using fluorescent sensors is still a topic of high interest. There is an increase in the number of dual sensors developed in the past five years and quite a good number of fluorescein derivatives were also reported based on reversible mechanisms. This review analyses environmentally and biologically important cations such as Cu2+, Hg2+, Fe3+, Pd2+, Zn2+, Cd2+, and Mg2+; anions (F-, OCl-) and small molecules (thiols, CO and H2S). Structural modifications, binding mechanisms, different strategies and a comparative study for selected cations, anions and molecules are outlined in the article.

Synthesis and Photophysical Properties of Fluorescein Esters as Potential Organic Semiconductor Materials

Fluorescein (1), a known fluorescent tracer in microscopy with high photophysical properties, was esterified to have fluorescein ethyl ester (2) and O-ethyl-fluorescein ethyl ester (3) in excellent yields. All of them were investigated for the photophysical and electrochemical properties as potential organic semiconductor materials. Absorptions and emission spectra were taken in various solvents, compound 2 showed emission maxima at λ_max = 545 and compound 3 showed λ_max = 550 nm. Optical band gap energy (E_g) was calculated for 1-3 and the values were found in between 2.34 - 2.39 eV. Possibility of shifting emission maxima was studied in various pH (5-9) buffers, and finally the thermal stability was examined using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Increasing of conjugation system of 2 and 3 were studied by HOMO and LUMO distributions of 1-3. Experimental results showed that compounds 2 and 3 have excellent photophysical and electrochemical properties hence can be used as excellent organic semiconductor materials.

Detection of Cu2+ and S2- with fluorescent polymer nanoparticles and bioimaging in HeLa cells

Novel spherical polymer nanoparticles were synthesized by hyperbranched polyethylenimine (hPEI) and 6-hydroxy-2-naphthaldehyde (HNA) via Schiff base reaction (one-pot reaction), which had great advantages in water solubility and green synthesis. Meanwhile, probe PEI-HNA could quickly detect Cu²⁺ in the range of 0-60 μM in 30 s with the detection limit of 243 nM. The fluorescence of PEI-HNA-Cu²⁺ could be recovered by the addition of S^2- in 50 s with the detection limit of 227 nM. Based on the excellent optical properties, PEI-HNA has been used in the bioimaging of living cells with excellent cell penetrability and low toxicity. More importantly, PEI-HNA has been doped into filter paper, hydrogel, and nanofibrous film to prepare solid-phase sensors, displaying rapid response and excellent sensitivity. Moreover, the low-cost and simple preparation of these sensors offers great potential and possibilities for industrialization, which could help accelerate the development of sensors in environmental and biological fields.

Corrosion Monitoring Effect of Rhodamine-Ethylenediamine on Copper Relics under a Protective Coating

Fluorescence spectroscopy is a common technique used to monitor early metallic corrosion. The fluorescence response characteristics of rhodamine-ethylenediamine toward Cu²⁺ have been studied using fluorescence and infrared spectroscopy. Fluorescence microscopy and electrochemical impedance spectroscopy were used to study the monitoring effect of rhodamine-ethylenediamine on the corrosion of copper relics protected by an epoxy coating. The results showed a strong fluorescent response and selectivity toward Cu²⁺ that existed using rhodamine-ethylenediamine. Early metallic corrosion of copper relics can be effectively monitored upon adding 0.8 wt % rhodamine-ethylenediamine to an epoxy coating. When the soaking time was increased, the fluorescence intensity of the fluorescent area on the coating became stronger. In addition, the area of the luminous coating reached ∼0.06 mm² and the area of corrosion under the protective coating was ∼0.008 mm², which was about 1/10 of the fluorescence area observed on the coating.

A rhodamine-based fluorescent sensor for selective detection of Cu2+ in aqueous media: synthesis and spectroscopic properties

Two new chemosensors, rhodamine B derivative bearing 3-formyl-6-nitrochromone (L ₁ ) and 3-formyl-6-methylchromone (L ₂ ) units were designed and synthesized using microwave irradiation for the selective detection of Cu²⁺ in aqueous media. Copper triggers the formation of highly fluorescent ring-open spirolactam. The fluorescence intensity was remarkably increased upon the addition of Cu²⁺ within a minute, while the other metal ions caused no significant effect. More importantly, the resulting complexes can be used as a reversible fluorescence sensor for CN^-. The recognition ability of the sensors was investigated by fluorescence titration, Job's plot, ¹H NMR spectroscopy and density functional theory (DFT) calculations.

Bifunctional Cu2+/Fe3+ Probe with Independent Signal Outputs Based on a Photochromic Diarylethene with a Dansylhydrazine Unit

A novel dual-response fluorescent sensor based on a diarylethene photoswitching unit and a dansylhydrazine functional group has been synthesized. The compound exhibited high selectivity for Fe³⁺ and Cu²⁺ with independent fluorescence signal outputs. In the presence of Fe³⁺, the sensor formed a 1:1 metal complex, resulting in a remarkable "turn-off" fluorescence signal. On the other hand, its fluorescence intensity was notably enhanced (turn-on) and a color change from bright yellow to bright blue was observed when the sensor interacted with Cu²⁺, which was due to the hydrolysis reaction of the dansyl acid dye, as confirmed by high-resolution mass spectrometry-electrospray ionization and infrared spectrum. The detection limits were 9.73 × 10^-8 mol L^-1 for Fe³⁺ and 3.49 × 10^-7 mol L^-1 for Cu²⁺, respectively. From the unimolecular platform, two molecular logic circuits were constructed using the fluorescence emission intensity at 557/494 nm (Fe³⁺/Cu²⁺) as the outputs and the combined stimuli of Fe³⁺/ethylenediaminetetraacetic acid, Cu²⁺, and UV/vis as the inputs. In addition, the sensor was successfully used to determine Fe³⁺ in water samples from Ganjiang River and soil samples from Nanchang fields.

Fluorescent Sensors for the Detection of Heavy Metal Ions in Aqueous Media

Due to the risks that water contamination implies for human health and environmental protection, monitoring the quality of water is a major concern of the present era. Therefore, in recent years several efforts have been dedicated to the development of fast, sensitive, and selective sensors for the detection of heavy metal ions. In particular, fluorescent sensors have gained in popularity due to their interesting features, such as high specificity, sensitivity, and reversibility. Thus, this review is devoted to the recent advances in fluorescent sensors for the monitoring of these contaminants, and special focus is placed on those devices based on fluorescent aptasensors, quantum dots, and organic dyes.

Potentially toxic elements and environmentally-related pollutants recognition using colorimetric and ratiometric fluorescent probes

A safer detection or sensing of toxic pollutants is one among several environmental contamination issues, across the globe. The ever-increasing industrial practices and controlled or uncontrolled release of toxic pollutants from various industrial sectors is a key source of this environmental problem. Significant research efforts have been or being made to tackle this problematic issue to fulfill the growing needs of the modern world. Despite many useful aspects, heavy metals are posing noteworthy toxicological concerns and human-health related issues at various levels of the ecosystem. In this context, notable efforts from various regulatory authorities, the increase in the concentration of these toxic heavy metals in the environment is of serious concern, so real-time monitoring is urgently required. Herein, we reviewed fluorescent sensor based models and their potentialities to address the detection fate of hazardous pollutants including chromium, manganese, cobalt, nickel, copper, and zinc as model elements. The novel aspects of turn-on/off fluorescent sensors have also been discussed from a state of the art viewpoint. In summary, comprehensive literature regarding fluorescent sensor based models and their potentialities to detect various types of toxic pollutants is reviewed.

Paper-Based Sensor Chip for Heavy Metal Ion Detection by SWSV

Heavy metal ion pollution problems have had a terrible influence on human health and the environment. Therefore, the monitoring of heavy metal ions is of great practical significance. In this paper, an electrochemical three-electrode system was fabricated and integrated on nitrocellulose membrane (NC) by the use of magnetron sputtering technology, which exhibited a uniform arrangement of porous structure without further film modification. This paper-based sensor chip was used for Cu²⁺ detection by square-wave stripping voltammetry (SWSV). Within the ranges of 5–200 μg·L⁻¹ and 200–1000 μg·L⁻¹, it showed good linearity of 99.58% and 98.87%, respectively. The limit of detection was 2 μg·L⁻¹. On the basis of satisfying the detection requirements (10 μg·L⁻¹), the integrated sensor was small in size and inexpensive in cost. Zn²⁺, Cd²⁺, Pb²⁺ and Bi³⁺ were also detected by this paper-based sensor chip with good linearity.

A novel fluorescein-based colorimetric probe for Cu2+ detection

A new colorimetric probe, 5-chlorosalicylaldehyde fluorescein hydrazone (CSFH), has been synthesized and characterized by, FT-IR, NMR, mass elemental analysis and X-ray single crystal diffraction.

Fluorescent magnetic nanosensors for Zn2+ and CN− in aqueous solution prepared from adamantane-modified fluorescein and β-cyclodextrin-modified Fe3O4@SiO2via host–guest interactions

A novel multifunctional fluorescent chemosensor has been constructed with a highly selective “off–on” behavior, recoverability and recyclability.

A highly selective and sensitive single click novel fluorescent off–on sensor for copper and sulfide ions detection directly in aqueous solution using curcumin nanoparticles

Graphical representation of the binding of CURNPs to Cu²⁺(fluorescence off) and release of CURNPs (fluorescence on) by the reaction of S²⁻with copper bound to CURNPs.

Fluorescein hydrazones as novel nonintercalative topoisomerase catalytic inhibitors with low DNA toxicity

Fluorescein hydrazones (3a-3l) were synthesized in three steps with 86-91% overall yields. Topo I- and IIα-mediated relaxation and cell viability assay were evaluated. 3d inhibited 47% Topo I (camptothecin, 34%) and 20% Topo II (etoposide 24%) at 20 μM. 3l inhibited 61% Topo II (etoposide 24%) at 20 μM. 3d and 3l were further evaluated to determine their mode of action with diverse methods of kDNA decatenation, DNA-Topo cleavage complex, comet, DNA intercalating/unwinding, and Topo IIα-mediated ATP hydrolysis assays. 3d functioned as a nonintercalative dual inhibitor against the catalytic activities of Topo I and Topo IIα. 3l acted as a Topo IIα specific nonintercalative catalytic inhibitor. 3d activated apoptotic proteins as it increased the level of cleaved capase-3 and cleaved PARP in a dose- and time-dependent manner. The dose- and time-dependent increase of G1 phase population was observed by treatment of 3d along with the increase of p27(kip1) and the decrease of cyclin D1 expression.

A colorimetric and luminescent dual-modal assay for Cu(II) ion detection using an iridium(III) complex

A novel iridium(III) complex-based chemosensor bearing the 5,6-bis(salicylideneimino)-1,10-phenanthroline ligand receptor was developed, which exhibited a highly sensitive and selective color change from colorless to yellow and a visible turn-off luminescence response upon the addition of Cu(II) ions. The interactions of this iridium(III) complex with Cu2+ ions and thirteen other cations have been investigated by UV-Vis absorption titration, emission titration, and 1H NMR titration.

Probing oxidative stress: Small molecule fluorescent sensors of metal ions, reactive oxygen species, and thiols

Oxidative stress is a common feature shared by many diseases, including neurodegenerative diseases. Factors that contribute to cellular oxidative stress include elevated levels of reactive oxygen species, diminished availability of detoxifying thiols, and the misregulation of metal ions (both redox-active iron and copper as well as non-redox active calcium and zinc). Deciphering how each of these components interacts to contribute to oxidative stress presents an interesting challenge. Fluorescent sensors can be powerful tools for detecting specific analytes within a complicated cellular environment. Reviewed here are several classes of small molecule fluorescent sensors designed to detect several molecular participants of oxidative stress. We focus our review on describing the design, function and application of probes to detect metal cations, reactive oxygen species, and intracellular thiol-containing compounds. In addition, we highlight the intricacies and complications that are often faced in sensor design and implementation.

Self-assembled coordination nanoparticles from nucleotides and lanthanide ions with doped-boronic acid-fluorescein for detection of cyanide in the presence of Cu2+ in water

The sensor molecule, F-oBOH, containing boronic acid-linked hydrazide and fluorescein moieties was synthesized. For anion sensing applications, F-oBOH was studied in aqueous media. Unfortunately, F-oBOH was found to be hydrolyzed in water. Therefore, a new strategy was developed to prevent the hydrolysis of F-oBOH by applying self-assembly coordination nanoparticles network (F-oBOH-AMP/Gd(3+) CNPs). Interestingly, the nanoparticles network displayed the enhancement of fluorescent signal after adding Cu(2+) following by CN(-). The network, therefore, possessed a high selectivity for detection of CN(-) compared to other competitive anions in the presence of Cu(2+). Cyanide ion could promote the Cu(2+) binding to F-oBOH incorporated in AMP/Gd(3+) CNPs to give the opened-ring form of spirolactam resulting in the fourfold of fluorescence enhancement compared to Cu(2+) complexation without CN(-). Additionally, the log K value of F-oBOH-AMP/Gd(3+) CNPs⊂Cu(2+) toward CN(-) was 3.97 and the detection limits obtained from naked-eye and spectrofluorometry detections were 20μM and 4.03μM, respectively. The proposed method was demonstrated to detect CN(-) in drinking water with high accuracy.

Toward the development of prochelators as fluorescent probes of copper-mediated oxidative stress

A fluorescent sensor prochelator, FlamB (fluorescein hydrizido 2-imidophenylboronic ester), has been developed that selectively probes for copper under conditions of oxidative stress. High levels of hydrogen peroxide trigger the release of a boronic ester masking group from the prochelator to unveil a metal chelator, FlamS (fluorescein hydrizido 2-imidophenol), that provides a modest fluorescence increase in response to Cu(2+) but not other metal ions. X-Ray crystal structures of FlamB, FlamS, and Cu-bound FlamS are all reported. The fluorescence turn-on results from opening of a fluorescein spirolactam ring upon Cu(2+) binding to FlamS in aqueous solution. Oxidation of the aryl boronic ester of FlamB to the metal-binding phenol of FlamS proceeds in organic solvents. However, in aqueous solution a competing mechanism occurs due to hydrolytic instability of the masked prochelator. Hydrolysis of FlamB leads to formation of fluorescein hydrazide, which interacts with copper or H(2)O(2) to produce fluorescein and a significant fluorescence increase.

Fluorophotometric determination of hydrogen peroxide and other reactive oxygen species with fluorescein hydrazide (FH) and its crystal structure

Methods for the fluorophotometric determination of hydrogen peroxide (H(2)O(2)) and other reactive oxygen species (ROS) were proposed by using the fluorescence reaction between H(2)O(2) or other ROS and fluorescein hydrazide (FH). In the determination of H(2)O(2), the calibration curve exhibited linearity over the H(2)O(2) concentration range of 2.1-460 ng ml(-1) at an emission wavelength of 527 nm with an excitation of 460 nm and with the relative standard deviations (n=6) of 4.06%, 1.78%, and 2.21% for 3.1 ng ml(-1), 30.8 ng ml(-1), and for 308 ng ml(-1) of H(2)O(2), respectively. The detection limit for H(2)O(2) was 0.7 ng ml(-1) due to three blank determinations (rho=3). The calibration curves for ROS-related compounds were also constructed under the optimum conditions. This method was successfully applied in the assay of H(2)O(2) in human urine. In addition, we performed the characterization of FH, and interesting information was obtained with regard to the relationship between the chemical structure and fluorescence.