Highly Sensitive Ratiometric Fluorescent Detection of Indium(III) Using Fluorescent Probe Based on Phosphoserine as a Receptor

A rapid and specific fluorescent probe based on aggregation-induced emission enhancement for mercury ion detection in living systems

Mercury is a harmful heavy metal that seriously threatens the environment and organisms. In this study, we combined the aggregation-induced emission mechanism and the advantages of peptides to design a novel tetraphenylene (TPE)-based peptide fluorescent probe, TPE-Cys-Pro-Gly-His (TPE-CPGH), in which the sulfhydryl group of Cys in the peptide chain and the imidazolium nitrogen provided by His were used to mimic the Hg2+ binding site of metalloproteins. The β-fold formed by Pro-Gly was used to promote the spatial coordination of the probe with Hg2+ and the formation of the coordination complex aggregates, these changes led to the "turn on" response to Hg2+. The detection of Hg2+ by TPE-CPGH not only showed high specificity and sensitivity (LOD=46.2 nM), but also had the advantages of fast response and applicability for detection over a wide pH range. Additionally, TPE-CPGH effectively detected Hg2+ in environmental samples, living cells and organisms due to its low cytotoxicity, high water solubility and cell membrane permeability. More interestingly, TPE-CPGH was also mitigated Hg2+ exposure-induced oxidative stress toxicity in vitro and in vivo.

A Dual-target Fluorescent Chemosensor for Detecting Indium (III) and Hypochlorite with High Selectivity

A dual-target fluorescent chemosensor BQC (((E)-N-benzhydryl-2-(quinolin-2-ylmethylene)hydrazine-1-carbothioamide) was synthesized for detecting In3+ and ClO-. BQC displayed green and blue fluorescence responses to In3+ and ClO- with low detection limits (0.83 µM for In3+ and 2.50 µM for ClO-), respectively. Importantly, BQC is the first fluorescent chemosensor capable of detecting In3+ and ClO-. The binding ratio between BQC and In3+ was determined to be a 2:1 through Job plot and ESI-MS analysis. BQC could be successfully utilized as a visible test kit to detect In3+. Meanwhile, BQC showed a selective turn-on response to ClO- even in the presence of anions or reactive oxygen species. The sensing mechanisms of BQC for In3+ and ClO- were demonstrated by 1 H NMR titration, ESI-MS and theoretical calculations.

Ethyl 3-aminobenzo[b]thiophene-2-carboxylate Derived Ratiometric Schiff Base Fluorescent Sensor for the Recognition of In3+ and Pb2

An ethyl 3-aminobenzo[b]thiophene-2-carboxylate derived ratiometric Schiff base fluorescent sensor R was devised and synthesized. R exhibited a highly sensitive and selective ratiometric response to In3+ in DMF/H2O tris buffer solution. R exhibited a colorimetric/fluorescent dual-channel response to In3+. More importantly, R can distinguish In3+ from Ga3+ and Al3+ in less than 5 min. R exhibited a good linear correlation with the concentration of In3+ in the 5-25 μM range and the limit of detection for In3+ was found to be 8.36 × 10-9 M. According to the job`s plot and MS spectra, R formed a complex with In3+ at 1:2 with a complexation constant of 8.24 × 109 M2. Based on Gaussian theory calculations, the response mechanism of R to In3+ can be explained by photo-induced electron transfer (PET) and intramolecular charge transfer (ICT) mechanisms. In addition, R can be used for the detection of indium in tap water with satisfactory recoveries. Meanwhile, R displayed a linear relationship to micromolar concentrations (0-50 μM) of Pb2+ and recognized Pb2+ in a ratiometric response with a detection limit of 8.3 × 10-9 M.

Fluorescent detection of tartrazine based on the supramolecular self-assembly of cationic perylene diimide

A cationic perylene probe was designed and synthesized for sensitive determination of tartrazine. In the presence of tartrazine, the fluorescence of the perylene probe was quenched by efficient supramolecular self-assembly of the perylene derivate. The quenching is caused by the synergistic effect of noncovalent interactions including static electricity, π-π stacking, and hydrophobic interaction. Benefiting from these advantages, the probe exhibited excellent sensing performance to tartrazine within 2 min. The detection and quantification limit of tartrazine are as low as 2.42 and 8.07 nmol L-1, respectively, with a wide linear operation range from 15 to 500 nmol L-1. Most importantly, due to the high binding affinity (3.22 × 107 mol L-1) between the perylene probe and tartrazine, the sensing system shows great anti-interference capacity. Subsequently, the visualization application of the approach was evaluated by portable device, and the limits of detection for visual detection for test strip, membrane, and hydrogel were 0.5, 0.5, and 5 μmol L-1, respectively. The approach has been applied to monitor tartrazine in various food condiments with recoveries in the range 91.29-108.83%. As far as we know, this is the first report of using perylene-based probe for tartrazine determination, offering a promising strategy for the construction of perylene-based detection system in the field of food safety.

Compounds Derived from 9,9-Dialkylfluorenes: Syntheses, Crystal Structures and Initial Binding Studies (Part II)

New representatives of 2,4,7-trisubstituted 9,9-dialkyl-9H-fluorenes were prepared and used for crystallographic investigations as well as initial binding studies towards metal ions and carbohydrates. The binding studies, which included ¹ H NMR spectroscopic titrations and fluorescence measurements, demonstrated the ability of the tested fluorene-based compounds to act as complexing agents for ionic and neutral substrates. Depending on the nature of the subunits of the fluorene derivatives, "turn on" or "turn off" fluorescent chemosensors can be developed. Compounds composed of 4,6-dimethylpyridin-2-yl-aminomethyl moieties have the potential to be used as sensitive "turn-on" chemosensors for some metal ions.

A new Schiff base derived from 5-(thiophene-2-yl)oxazole as "off-on-off" fluorescence sensor for monitoring indium and ferric ions sequentially and its application

A new Schiff base sensor (E)-N'-((8-hydroxy-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-9-yl)methylene)-5-(thiophen-2-yl)oxazole-4-carbohydrazide (TOQ) was synthesized and found to emit yellowish green fluorescence upon introduction of In³⁺. Furthermore, the resulting complex TOQ-In³⁺ was quenched selectively by Fe³⁺. The detection limits of TOQ for In³⁺ and Fe³⁺ were 1.75 × 10^-10 M and 8.45 × 10^-9 M, respectively. The complex stoichiometry of TOQ with target ions was determined to be 1:2 via Job's plot analysis, which further was verified by ESI-MS titration and theoretical calculations. Moreover, TOQ can be used for the determination of target ions in environmental water samples. A portable paper sensor of TOQ was successfully developed for detecting In³⁺ to assess its applicability.

Rapid Detection of Cd2+ Ions in the Aqueous Medium Using a Highly Sensitive and Selective Turn-On Fluorescent Chemosensor

Herein, a novel optical chemosensor, (CM1 = 2, 6-di((E)-benzylidene)-4-methylcyclohexan-1-one), was designed/synthesized and characterized by ¹H-NMR and FT-IR spectroscopy. The experimental observations indicated that CM1 is an efficient and selective chemosensor towards Cd²⁺, even in the presence of other metal ions, such as Mn²⁺, Cu²⁺, Co^2+, Ce³⁺, K⁺, Hg²⁺,^, and Zn²⁺ in the aqueous medium. The newly synthesized chemosensor, CM1, showed a significant change in the fluorescence emission spectrum upon coordination with Cd²⁺. The formation of the Cd²⁺ complex with CM1 was confirmed from the fluorometric response. The 1:2 combination of Cd²⁺ with CM1 was found optimum for the desired optical properties, which was confirmed through fluorescent titration, Job's plot, and DFT calculation. Moreover, CM1 showed high sensitivity towards Cd²⁺ with a very low detection limit (19.25 nM). Additionally, the CM1 was recovered and recycled by the addition of EDTA solution that combines with Cd²⁺ ion and, hence, frees up the chemosensor.

Detection of Heavy Metal Ions by Ratiometric Photoelectric Sensor

In recent years, heavy metal pollution has become increasingly serious. Heavy metals exist in an environment mainly in the form of ions (heavy metal ions, HMs). They can contaminate food, water, soil, and the atmosphere, leading to serious harm to plants and animals. With high bioavailability and nonbiodegradability, HMs can accumulate through biomagnification. Consequently, heavy metal pollution has become the cause of many fatal diseases threatening human health and ecological environment. Therefore, the accurate detection of HMs is vital and necessary. In this paper, the harm and limit standards of heavy metals were systematically summarized and the common analysis methods were overviewed and compared. Specifically, the latest research progress of ratiometric photoelectric sensor, including optical and electrical sensor, were mainly described. The research status and advantages and disadvantages of a photoelectric sensor were summarized. Furthermore, the future directions were proposed, which provided the reference for the further research and application of the ratiometric photoelectric sensor.

Rational synthesis of a pyridyl-imidazoquinazoline based multifunctional 3D Zn(II)-MOF: structure, luminescence, selective and sensitive detection of Al3+ and TNP, and its semiconducting device application

In the age of sustainable development, the exploration of multifunctional materials is of high priority due to their economic benefits and environmental suitability. A stable luminescent coordination polymer, [Zn₂(tdc)₄(pdiq)₃] (1), (pdiq = pyridyl-imidazoquinazoline; H₂tdc = 2,5-thiophenedicarboxylic acid) has been prepared and structurally confirmed by single-crystal X-ray diffraction analysis. The 3D framework consists of a distorted octahedral geometry with a ZnO₄N₂ coordination sphere where four carboxylato-O donations come from two tdc^2- as bridging ligands and two pyridyl-Ns come from two pdiq. The π⋯π interactions between the imidazolium and phenyl groups bestow robustness on the architecture. The compound is chemically stable to water, shows tolerance to acid/base aqueous solutions (pH = 2-12), and is stable to the impact of organic solvents. The high dispersibility of Zn-MOF (1) in acetonitrile may enhance the fluorescence intensity compared to that in water, which prompted fluorescence measurements in the former solvent and it is used for the efficient and selective turn-off ratiometric sensing of Al³⁺ ions (LOD, 1.39 × 10^-7 M). In addition, the fluorescence emission of 1 is instantly quenched by trinitrophenol (TNP) and the LOD is 1.54 × 10^-7 M. The Tauc's plot is used to measure the semiconducting band gap (3.33 eV) and the electrical conductivity is significantly increased upon illumination (Λ: 1.14 × 10^-3 S m^-1 (dark), 5.35 × 10^-3 S m^-1 (light)) and the energy barrier declines marginally (FB: 0.57 (dark), 0.49 (light)). Transit time (τ) and diffusion length (L_D) at the quasi-Fermi level were analyzed to offer information on the charge transport mechanism of the compound. The better performance on photo-irradiation signifies the enhanced charge transfer kinetics of a Zn-MOF coated thin-film device (TFD 1), which encourages its application in semiconductor devices.

A fiber optic photoacoustic sensor for real-time heparin monitoring

Heparin is a common anticoagulant, but heparin overdose is a common intensive care unit (ICU) medication error due to the narrow therapeutic window of heparin. Conventional methods to monitoring heparin suffer from long turnaround time, the need for skilled personnel, and low frequency of sampling. To overcome these issues, we describe here a fiber optic photoacoustic (PA) sensor for real-time heparin monitoring. The proposed sensor was validated with in vitro testing and in a simulated in vivo model using the following samples: (1) phosphate-buffered saline (PBS), (2) spiked human plasma, (3) spiked whole human blood, and (4) clinical samples from patients treated with heparin. Samples were validated by comparing the PA signal to the activated partial thromboplastin time (aPTT) as well as the activated clotting time (ACT). Importantly, the proposed sensor has a short turnaround time (3 min) and a limit of detection of 0.18 U/ml in whole human blood. The PA signal is linear with heparin dose and correlates with the aPTT value (Pearson's r = 0.99). The PA signal from 32 clinical samples collected from eight patients linearly correlated with ACT values (Pearson's r = 0.89, in vitro; Pearson's r = 0.93, simulated in vivo). The PA signal was also validated against the cumulative heparin dose (Pearson's r = 0.94, in vitro; Pearson's r = 0.96, simulated in vivo). This approach could have applications in both in vitro and real-time in vivo heparin monitoring.

A two fluorescent signal indicator-based ratio fluorometric alkaline phosphatase assay based on one signal precursor

Two fluorescent signal indicators were simply converted from one organic precursor system by using the superior oxidation capability of manganese dioxide (MnO2) nanosheets for the first time, finally resulting in the successful fabrication of a ratio fluorometric bioassay of alkaline phosphatase (ALP).

The influence of linker substitution on the fluorescence responsive sensing of isostructural coordination polymers: visual turn-on, ratiometric, and turn-off sensing in water

Linker substituents show great impacts on the luminescence properties and sensing performances of isostructural coordination polymers, causing turn-on or ratiometric sensing of Fe³⁺, Al³⁺, and Cr³⁺ and turn-off sensing of CrO₄²⁻ and Cr₂O₇²⁻.

A Schiff base sensor for relay monitoring of In3+ and Fe3+ through “off–on–off” fluorescent signals

A Schiff base N′-(3-ethoxy-2-hydroxybenzylidene)-4,5-dihydronaphtho[1,2-b]thiophene-2-carbohydrazide (LB2) was designed and synthesized and could be used as a sensor to identify In³⁺ and Fe³⁺ through fluorescence ‘off–on–off’ behavior.

Selective ratiometric red-emission detection of In3+ in aqueous solutions and in live cells using a fluorescent peptidyl probe and metal chelating agent

Indium has been regarded as one of the most rarely used metal ions; however, the consumption of indium has increased intensively due to its increasing use in electrodes of liquid crystal displays (LCDs). In recent years, warnings have been issued about the toxicity of indium to aquatic ecosystems and humans. Thus, the development of efficient and selective detection methods for In³⁺ in aquatic environments as well as in live cells is highly required. However, the selective and sensitive detection of In³⁺ in the presence of trivalent metal ions and other metal ions is highly challenging. In the present study, we synthesized a fluorescent probe (1) for In³⁺ and Al³⁺ based on an unnatural peptide receptor and an aggregation-induced emission fluorophore and developed a selective fluorescent detection method for In³⁺ in aqueous solutions and live cells using the probe and a metal chelating agent. 1 recognized In³⁺ and Al³⁺ selectively among 19 metal ions in aqueous solutions depending on pH by the enhancement of the red emission at 600 nm and decrease in the green emission at 530 nm. 1 sensitively detected In³⁺ and Al³⁺ by ratiometric response in a wide pH range (3.5-7.4), and the ratiometric response was complete within 20 seconds in an aqueous buffered solution at pH 5.0. Interestingly, the addition of EDTA to the complex of 1 with In³⁺ or Al³⁺ did not induce the Al³⁺-free spectrum but instead induced the In³⁺-free spectrum; thus, In³⁺ and Al³⁺ could be easily differentiated. The detection limit of 1 for In³⁺ ions was 211 nM (R² = 0.981) in purely aqueous solutions. The fluorescence ratiometric detection method using 1 could quantify low concentrations of In³⁺ in ground water and tap water. Fluorescence cell image studies revealed that the probe was cell-permeable, and low concentrations of In³⁺ inside the cells could be recognized by the enhancement of the red emission at 600 nm. The binding mode study via NMR, IR, and CD spectroscopy revealed how the peptide receptor of 1 interacted with In³⁺ and resulted in the enhancement of the red emission in an aqueous solution.

Red-Emitting Carbon Dots as a Dual Sensor for In3+ and Pd2+ in Water

We have demonstrated the synthesis, characterization, and application of nitrogen-doped red-emitting carbon dots (NRCDs) for dual sensing of indium (In3+) and palladium (Pd2+) in water. The detection of In3+ was associated with "turn-on" fluorescence response with a red shift, while in the presence of Pd2+, the fluorescence intensity of NRCDs was quenched to show a "turn-off" response. The interaction of NRCDs with the metal ions was investigated using 1H nuclear magnetic resonance and Fourier-transform infrared spectroscopy studies. The synthesized nanoprobes possessed good biocompatibility and photostability and were found to be suitable candidates for bioimaging due to their emission profiles in the near-infrared (NIR) window. Applicability of the as-prepared NRCDs was demonstrated in the NIR region when they were loaded in vesicle membranes with and without cations and subjected to confocal imaging successfully.

Reduced texaphyrin: A ratiometric optical sensor for heavy metals in aqueous solution

We report here a water-soluble metal cation sensor system based on the as-prepared or reduced form of an expanded porphyrin, texaphyrin. Upon metal complexation, a change in the redox state of the ligand occurs that is accompanied by a color change from red to green. Although long employed for synthesis in organic media, we have now found that this complexation-driven redox behavior may be used to achieve the naked eye detectable colorimetric sensing of several number of less-common metal ions in aqueous media. Exposure to In(III), Hg(II), Cd(II), Mn(II), Bi(III), Co(II), and Pb(II) cations leads to a colorimetric response within 10 min. This process is selective for Hg(II) under conditions of competitive analysis. Furthermore, among the subset of response-producing cations, In(III) proved unique in giving rise to a ratiometric change in the ligand-based fluorescence features, including an overall increase in intensity. The cation selectivity observed in aqueous media stands in contrast to what is seen in organic solvents, where a wide range of texaphyrin metal complexes may be prepared. The formation of metal cation complexes under the present aqueous conditions was confirmed by reversed phase high-performance liquid chromatography, ultra-violet-visible absorption and fluorescence spectroscopies, and high-resolution mass spectrometry.

A fluorescence probe based on 6-phenylimidazo[2,1-b]thiazole and salicylaldehyde for the relay discerning of In3+ and Cr3+

A new fluorescence probe, (E)-N′-(2-hydroxybenzylidene)-6-phenylimidazo[2,1-b]thiazole-3-carbohydrazide (LB1), based on 6-phenylimidazo[2,1-b]thiazole and salicylaldehyde was designed and synthesized.

Double Schiff base from thiophene-2,5-dicarboxylic acid as an “off–on–off” fluorescence sensor for the sequential detection of In3+ and PPi

A double Schiff base T as acceptor for metal ions derived from thiophene-2,5-dicarboxylic acid was designed and synthesized, and showed a high selectivity for In³⁺ in a DMF/H₂O buffer solution.

A hydrazono-quinoline-based chemosensor sensing In3+ and Zn2+via fluorescence turn-on and ClO−via color change in aqueous solution

A multi-target sensor, based on hydrazono-quinoline, was developed for fluorescence turn-on detection of In³⁺ and Zn²⁺ and colorimetric detection of ClO⁻.