Turn-on Fluorescent Chemosensor Based on an Amino Acid for Pb(II) and Hg(II) Ions in Aqueous Solutions and Role of Tryptophan for Sensing

Sulfonamides as Optical Chemosensors

Sulfonamides are auspicious chemosensors which are capable to bind with ionic species through various ways like complexation, charge transfer, proton transfer etc. and produce a detection signal in the form of an optical change either in visible or UV-light and for electronic as well as fluorimetric spectra. Sulfonamides have gained much attention of analytical chemists these days as these are inexpensive, robust, green in nature and some what sensitive and selective to many anionic and cationic species. Due to their promising versatility in sensing properties, these are under great consideration in forensic, environmental, analytical and biochemistry laboratories. This review narrates how sulfonamides are being used to optically sense ionic species.

Preparation, Physicochemical, and Cyto- and Genotoxic Characterisation of Polysaccharide Composites Containing Carbon Quantum Dots

Rapid industrial growth is associated with an increase in the production of environmentally harmful waste. A potential solution to significantly reduce pollution is to replace current synthetic materials with readily biodegradable plastics. Moreover, to meet the demands of technological advancements, it is essential to develop materials with unprecedented properties to enhance their functionality. Polysaccharide composites demonstrate significant potential in this regard. Polysaccharides possess exceptional film-forming abilities and are safe for human use, biodegradable, widely available, and easily modifiable. Unfortunately, polysaccharide-based films fall short of meeting all expectations. To address this issue, the current study focused on incorporating carbon quantum dots (CQDs), which are approximately 10 nm in size, into the structure of a starch/chitosan biocomposite at varying concentrations. This modification has improved the mechanical properties of the resulting nanocomposites. The inclusion of nanoparticles led to a slight reduction in solubility and an increase in the swelling degree. The optical characteristics of the obtained films were influenced by the presence of CQDs, and the fluorescence intensity of the nanocomposites changed due to the specific heavy metal ions and amino acids used. Consequently, these nanocomposites show great potential for detecting these compounds. Cellular viability assessments and comet assays confirm that the resulting nanocomposites do not exhibit any cytotoxic properties based on this specific analytic method. The tested nanocomposites with the addition of carbon quantum dots (NC/CD II and NC/CD III) were characterised by greater genotoxicity compared to the negative control. The positive control, the starch/chitosan composite alone, was also characterised by a greater induction of chromatin damage in mouse cells compared to a pure mouse blood sample.

Approaching Tryptophan-Derived Polynorbornene Fluorescent Chemosensors: Synthesis, Characterization, and Sensing Ability for Biomedical Applications as Biomarkers for Detecting Fe2+ Ions

We present a novel group of tryptophan (Trp)-based fluorescent polymeric probes synthesized via ring-opening metathesis polymerization (ROMP) of Trp-derived norbornene monomers. These probes, in mono- and disubstituted forms, incorporate amide and ester anchoring groups. The quantity of Trp substituents did not affect fluorescence selectivity but influenced quenching percentage. Poly-diamide-Trp, Poly-monoamide-Trp, Poly-diester-Trp, and Poly-monoester-Trp probes displayed selective detection of Fe2+ and Fe3+ ions with fluorescence on-off characteristics. Poly-diamide-Trp and Poly-monoamide-Trp exhibited a limit of detection (LOD) for Fe2+ and Fe3+ ions of 0.86-11.32 μM, while Poly-diester-Trp and Poly-monoester-Trp showed higher LODs (21.8-108.7 μM). These probes exhibited high selectivity over Fe2+, a crucial metal ion in the body known for its redox properties causing oxidative stress and cell damage. Cell cytotoxicity tests in various cell types confirmed biocompatibility. Additionally, Poly-diamide-Trp displayed excellent cell permeability and iron ion detection in EA.hy926 cells, suggesting potential for bioimaging and clinical applications.

Coumarin derivative-functionalized nanoporous silica as an on-off fluorescent sensor for detecting Fe3+ and Hg2+ ions: a circuit logic gate

A highly efficient fluorescent sensor (S-DAC) was easily created by functionalizing the SBA-15 surface with N-(2-Aminoethyl)-3-Aminopropyltrimethoxysilane followed by the covalent attachment of 7-diethylamino 3-acetyl coumarin (DAC). This chemosensor (S-DAC) demonstrates selective and sensitive recognition of Fe3+ and Hg2+ in water-based solutions, with detection limits of 0.28 × 10-9 M and 0.2 × 10-9 M for Hg2+ and Fe3+, respectively. The sensor's fluorescence characteristics were examined in the presence of various metal ions, revealing a decrease in fluorescence intensity upon adding Fe3+ or Hg2+ ions at an emission wavelength of 400 nm. This sensor was also able to detect ferric and mercury ions in spinach and tuna fish. The quenching mechanism of S-DAC was investigated using UV-vis spectroscopy, which confirmed a static-type mechanism for fluorescence quenching. Moreovre, the decrease in fluorescence intensity caused by mercury and ferric ions can be reversed using trisodium citrate dihydrate and EDTA as masking agents, respectively. As a result, a circuit logic gate was designed using Hg2+, Fe3+, trisodium citrate dihydrate, and EDTA as inputs and the quenched fluorescence emission as the output.

A selective and sensitive probes of chalcone derivative as a fluorescent chemosensor for the detection of Cr3+ ion

A new chalcone based chemosensor like 6-cinnamoylthiochroman-4-one (AZAN), has been designed and synthesized from 6-chlorothiochroman-4-one and cinnamaldehyde via keto ethylenic linkage. Its amino derivatives were synthesized by using urea (AZANU), thiourea (AZANTU) and 2,6-diamino pyridine (AZANPy) respectively and its metal ion sensing properties were investigated. The sensors can selectively recognize and sense the metal cations by showing different fluorescent characteristics at different concentrations. The fluorescence intensity shows remarkable enhancement by Cr3+ over other common metal ions (Cd2+, Hg2+ and Pb2+). The proposed mechanism can be confirmed by UV-Vis and emission titration. The newly synthesized receptor can sense the metal ions even in nano molar level. The binding or association constant and detection limit of chemosensor to Cr3+ are 1.684 × 105 M-1 and 0.2245 × 10-9 M respectively. A computation using the density functional theory was done to gain detailed insights into the electronic structures of the ligand and its derivatives. B3LYP function and 6-31G(d,p) basis set were used to optimize the ground-state geometry of the chemical and its derivatives.

Development of ratiometric fluorescent probes based on peptides for sensing Pb2+ in aquatic environments and human serum

The detection of Pb²⁺ ions in aquatic environments and biofluid samples is crucial for assessment of human health. Herein, we synthesized two fluorescent probes (1 and 2) consisting of the peptide receptor for Pb²⁺ and a benzothiazolyl-cyanovinylene fluorophore that exhibited excimer-like emission when it aggregated. The peptide-based probes sensitively detected Pb²⁺ in purely aqueous solution (1% DMF) through ratiometric fluorescent response with a decrease in monomer emission at 520 nm and an increase in excimer emission at 570 nm. Specially, probe 2 showed remarkable detection features such as high selectivity for Pb²⁺over 15 metal ions, high binding affinity (K_d = 5.83 × 10^-7 M) for Pb²⁺, significant emission intensity changes, low detection limit (3.8 nM) of Pb²⁺, high water solubility, and visible light excitation (450 nm). Probe 2 was successfully used to quantify nanomolar concentration (0 ∼ 800 nM) of Pb²⁺ in real water samples (ground water and tap water). Specially, 2 was successfully applied for the quantification of Pb²⁺ in human serum by combination of microwave-assisted human serum digestion and filtration of digested serum by anion exchange cartridge. We clearly investigated the binding mode of 2 with Pb²⁺ using ¹H NMR, IR spectroscopy, pH titration, confocal microscopy, and size analysis. The peptide-based fluorescent probe might have great application potential for sensing Pb²⁺ in aquatic environments and biofluid samples.

Construction of a novel ESIPT and AIE-based fluorescent sensor for sequentially detecting Cu2+ and H2S in both living cells and zebrafish

The development of effective methods for tracking Cu²⁺ and H₂S in living organisms is urgently required due to their vital function in a variety of pathophysiological processes. In this work, a new fluorescent sensor BDF with excited-state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE) features for the successive detection of Cu²⁺ and H₂S was constructed by introducing 3,5-bis(trifluoromethyl)phenylacetonitrile into the benzothiazole skeleton. BDF showed a fast, selective and sensitive fluorescence "turn off" response to Cu²⁺ in physiological media, and the situ-formed complex can serve as a fluorescence "turn on" sensor for highly selective detection of H₂S through the Cu²⁺ displacement approach. In addition, the detection limits of BDF for Cu²⁺ and H₂S were determined to be 0.05 and 1.95 μM, respectively. Encouraged by its favourable features, including strong red fluorescence from the AIE effect, large Stokes shift (285 nm), high anti-interference ability and good function at physiological pH as well as a low toxicity, BDF was successfully applied for the consequent imaging of Cu²⁺ and H₂S in both living cells and zebrafish, making it an ideal candidate for detecting and imaging of Cu²⁺ and H₂S in live systems.

Ratiometric Fluorescence Sensing System for Lead Ions Based on Self-Assembly of Bioprobes Triggered by Specific Pb2+-Peptide Interactions

Lead is one of the most toxic substances. However, there are few ratiometric fluorescent probes for sensing Pb2+ in aqueous solution as well as living cells because specific ligands for Pb2+ ions have not been well characterized. Considering the interactions between Pb2+ and peptides, we developed ratiometric fluorescent probes for Pb2+ based on the peptide receptor in two steps. First, we synthesized fluorescent probes (1-3) based on the tetrapeptide receptor (ECEE-NH2) containing hard and soft ligands by conjugation with diverse fluorophores that showed excimer emission when they aggregated. After investigation of fluorescent responses to metal ions, benzothiazolyl-cyanovinylene was evaluated as an appropriate fluorophore for ratiometric detection of Pb2+. Next, we modified the peptide receptor to decrease the number of hard ligands and/or to replace Cys with disulfide bond and methylated Cys for improving selectivity and cell permeability. From this process, we developed two fluorescent probes (3 and 8) among the probes (1-8) that exhibited remarkable ratiometric sensing properties for Pb2+ including high water solubility (≤2% DMF), visible light excitation, high sensitivity, selectivity for Pb2+, low detection limits (<10 nM), and fast response (<6 min). The binding mode study revealed that specific Pb2+-peptide interactions of the probes caused nanosized aggregates in which the fluorophores of the probes came close each other, exhibiting excimer emission. In particular, 8 based on tetrapeptide bearing a disulfide bond and two carboxyl groups with a good permeability successfully quantified intracellular uptake of Pb2+ in live cells through ratiometric fluorescent signals. The ratiometric sensing system based on specific metal-peptide interactions and excimer emission process could provide a valuable tool to quantify Pb2+ in live cells and pure aqueous solutions.

Highly Selective MOF-Based Turn-Off Luminescence Detection of Hg2+ Ions in an Aqueous Medium and Its Dual Functional Catalytic Activity toward Aldol Condensation and β-Enamination Reactions

A new organic ligand, 5-(carboxyformamido)isophthalic acid (5-CFIA), was prepared and employed for the synthesis of two compounds [M₃(C₁₀H₄O₇N₁)₂(8H₂O)]·H₂O (M = Cd, Mn). The compounds have three-dimensionally extended structures. Both the compounds were found to be luminescent at room temperature. The luminescence nature was exploited for the detection of Hg²⁺ ions in an aqueous medium with good selectivity. The interactions between Hg²⁺ ions and the compounds quench the luminescence intensity and act as a turn-off sensor. Both the compounds exhibited low limits for the detection of Hg²⁺ ions and in the range mandated by the WHO. The interactions between Hg²⁺ ions and the compound involve the -NH group, which was probed using Raman and IR spectroscopic techniques. These studies provide important pointers toward the mechanism of this turn-off luminescence behavior. The compounds were explored for base-catalyzed aldol condensation and Lewis acid-promoted β-enaminoester formation reactions. The aldol condensation reaction uses the -NH functionality as a base. The studies indicate that the electron-withdrawing group produces products with higher yields. The β-enaminoester reaction uses the Lewis acid centers, and the studies reveal that the electron-withdrawing groups produce lesser yields of the products. The catalytic nature of the reaction and recyclability of the catalysts were also established. The catalytic reactions employ ethanol (aldol condensation) and no solvent (β-enaminoester), which suggests that the reactions are green and environmentally friendly. The Mn compound was observed to be anti-ferromagnetic.

A novel peptide-based fluorescent probe for highly selective detection of mercury (II) ions in real water samples and living cells based on aggregation-induced emission effect

A new fluorescent probe TPE-GHK was synthesized containing a tetrastyrene (TPE) derivative as fluorophore and classical tripeptide (Gly-His-Lys-NH₂) as a receptor based on the aggregation-induced emission (AIE) mechanism. TPE-GHK displayed high selectivity and rapid fluorescent "turn-on" response to Hg²⁺ among other competitive metal ions. The 2:1 complex binding mechanism of TPE-GHK toward Hg²⁺ was verified by fluorometric titration, Job's plots, and ESI-HRMS spectra. The fluorescent emission showed a good linear response in the range of 0-1.0 μM with the low detection limit of 28.6 nM. Meanwhile, TPE-GHK exhibited the excellent biocompatibility and low toxicity and was successfully applied in monitoring Hg²⁺ in living CAKI 2 cells, which demonstrated its potential application in environment and biological science. More importantly, TPE-GHK could be used to detect Hg²⁺ in two real water samples and also was successfully designed as test strips.

Ratiometric fluorescent detection of lead ions in aquatic environment and living cells using a fluorescent peptide-based probe

Ratiometric fluorescent detection using dual emission bands is highly necessary to quantify Pb(II) in aquatic environment and live cells. We synthesized a ratiometric fluorescent peptidyl probe (1) by conjugation of a peptide receptor for Pb(II) with an excimer-forming benzothiazolylcyanovinylene fluorophore. The peptidyl probe dissolved well in aqueous solution and displayed an emission band at 538 nm (λ_ex = 460 nm). Upon addition of Pb(II) (0-20 μM), the emission maximum shifted from 538 nm to 575 nm and the emission intensity ratio (I₅₇₅ /I₅₃₈) increased significantly from 0.40 to 2.26. 1 exhibited a selective ratiometric response to Pb(II) over other metal ions. 1 with a low detection limit (1.2 ppb) of Pb(II) detected nanomolar concentrations (0-500 nM) of Pb(II) ions in groundwater and tap water. The cell-permeable probe detected intracellular Pb(II) by ratiometric fluorescent images. The binding mode study using NMR, IR and CD spectroscopy, and TEM revealed that the probe formed a 1:1 complex with Pb(II) and then formed red-emissive nanoparticles and fibrils. The probe exhibited desirable detection properties such as ratiometric detection, high solubility in water, visible light excitation, high selectivity and sensitivity for Pb(II), cell-permeability, and rapid response (< 6 min).

2,3-Diaryl-1,1,4,4-tetracyanobutadienes as colorimetric sensors for hydrogen sulfide ion in aqueous media

Two derivatives of tetracyanobutadienes are synthesized and used as colorimetric ion sensors in aqueous media. The key synthetic step involve a [2+2]-cycloaddition/retro-cycloaddition between electron-rich diaryl ethyne and the electron-deficient tetracyanoethene. The compound bearing two sulfonamide groups shows a good selectivity towards hydrogen sulfide ion with a detection limit of 15.5 μM. The use of this sensor for the quantitative analysis of hydrogen sulfide ion in real water samples is successfully demonstrated.

A bifunctional peptide-based fluorescent probe for ratiometric and "turn-on" detection of Zn(II) ions and its application in living cells

In this work, a bifunctional peptide-based fluorescent probe L containing a tetrapeptide scaffold (Pro-Gly-His-Trp-NH₂) and a dansyl group was synthesized using solid phase peptide synthesis (SPPS) technology. As designed, L, based on a FRET mechanism, exhibited high selectivity, excellent ratiometric signals, and fast response to Zn²⁺ in aqueous solutions at an excitation wavelength of 280 nm. In addition, when excited at 320 nm, L exhibited a fluorescent "turn-on" response towards Zn²⁺ based on PET mechanism. More importantly, the stoichiometry of L and Zn²⁺ was determined to be 2:1 by fluorescent titration, Job's plot method, and ESI-MS spectrometry. The association constant for Zn²⁺ ions was determined to be 6.26 × 10⁸ M^-2, while the limit of detection (LOD) of L was estimated as 5.43 nM, which is a much lower value than WHO and EPA guidelines for drinking water. Moreover, L was successfully applied to detect both Zn²⁺ and Cu²⁺ in living cells due to good biocompatibility and excellent low toxicity.

A novel peptide-based fluorescent probe with a large stokes shift for rapid and sequential detection of Cu2+ and CN- in aqueous systems and live cells

A novel fluorescent probe (DSD) was reasonably designed and synthesized with dansyl-labeled dipeptide (Dan-Ser-Asp-NH₂). DSD featured remarkably large Stokes shift (230 nm) and perfect water solubility, and exhibited high selectivity and rapid recognition toward Cu²⁺via fluorescence quenching. The detection limit of DSD for Cu²⁺ was 2.4 nM, indicated that DSD has excellent sensitivity. In addition, the stoichiometry between DSD and Cu²⁺ were detected as 1:1 by fluorescence titration, Job's plot and ESI-HRMS data. As designed, DSD-Cu²⁺ system was able to sequentially detect CN^- according to the displacement approach with fluorescence "off-on" response, and the detection limit for CN^- was calculated to be 41.9 nM. Specifically, the response time of DSD with Cu²⁺ and CN^- was less than 40 s, which rendered it suitable for real time detection in actual water samples. In addition, with the alternate addition of Cu²⁺ and CN^-, the reversible cycles could be repeated for at least 10 times, indicated that DSD was a promising reversibility probe. DSD showed low toxicity and good biocompatibility, and was successfully applied to detect Cu²⁺ and CN^- in living cells.

An electrochemical sensor–adsorbent for lead (Pb2+) ions in an aqueous environment based on Katiragum–Arginine Schiff base

A dual functional material fulfilling twin objectives; simultaneous sensing and adsorption of Pb2+ ions in an aqueous medium.

An “On-Off-On” fluorescent peptide probe for the specific detection of Cu2+ and S2- in living cells and zebrafish

Cu2+ plays an important role as the third of most abundant essential trace elements in normal physiological activities and metabolism of the organism. S2- participates in a variety of physiological...

The first tryptophan based turn-off chemosensor for Fe2+ ion detection

In this research work, we have designed and synthesized a novel Tryptophan-Quinoline conjugated turn-off chemosensor 4 for the selective detection of Fe²⁺ ion with high sensitivity (3.06 μM) among 21 metal cations such as Ag⁺, Ca⁺, Cs⁺, Cu⁺, K⁺, Na⁺, NH₄⁺, Ba²⁺, Ca²⁺, Cd²⁺, Co²⁺, Cu²⁺, Mn²⁺, Ni²⁺, Pb²⁺, Zn²⁺, Al³⁺, Au³⁺, Cr³⁺ and Fe³⁺ in DMF-HEPES (1 mM, pH = 7.0, 1:1, v/v) aqueous-organic solvent system. It showed a fluorescence quenching mechanism through the blocked PET process. The optical properties, binding mode of the metal ion with the receptor, plausible electron transfer mechanism, and its practical applications have been discussed. This work will open up a new avenue in amino acid-based Fe²⁺ ion sensors.

Recent Advances in Sensor-Based Detection of Toxic Dyes for Bioremediation Application: a Review

Extensive use of these harmful dyes has resulted in the surplus presence of these emerging pollutants in the environment, thus demanding an instant and sensitive detection method. Various synthetic dyes are illegitimately mixed into food and other consuming items for displaying bright colours that attracts consumers. The synthetic dyes cause a number of environmental health hazards and promote toxicity, mutagenicity and carcinogenicity in humans. Despite these serious health glitches, synthetic dyes are widely used due to their much lower cost. As a result, a faster, more selective and extremely sensitive technology for detecting and quantifying hazardous dyes in trace amount is urgently needed. This topic is currently in its initial phases of development and needs continuous refinements, such as explaining various sensing methods and potential future uses linked with dye detection technologies. The present review encompasses a comprehensive literature survey on detection of dyes and latest progress in developing sensors for dye detection and summarizes different detection mechanisms, including biosensor-, optical- and electrochemical-based sensors. Detection methodologies are examined with a focus on biosensor-based recent advancements in dye detection and the growing demand for more appropriate systems in terms of accuracy and efficiency.

A highly selective and sensitive Zn2+ fluorescent sensor based on zinc finger-like peptide and its application in cell imaging

Developing new chemosensors for detection of Zn²⁺ has attracted great attentions because of the important roles of Zn²⁺ in biological systems, and it will produce toxic effects with an excessive intake of zinc ion. Metalloproteins are often used as an effective template for the design and development of peptide-based fluorescent sensors. In this study, we designed a new and simple ratiometric fluorescent sensor for Zn²⁺, which was based on a zinc finger-like peptide and labeled with a dansyl group, i.e., Dansyl-His-Gln-Arg-Thr-His-Trp-NH₂ (D-P6), by using solid phase peptide synthesis (SPPS). The dimeric peptide has a high affinity for Zn²⁺ overothermetalions, as indicated by spectroscopic studies, as well as molecular modeling. Remarkably, the sensor exhibited a highly selective and sensitive ratiometric fluorescent response to Zn²⁺ by fluorescent resonance energy transfer effect between tryptophan residue and fluorophore dansyl group, with a very low detection limit of 33 nM in aqueous solution. Furthermore, the sensor displayed a very low biotoxicity, which allows successful detection of Zn²⁺ in living HeLa cells. We believe that the new sensor may have potential applications in biological science.

Controllable and reversible sensing cyanide ion using dual-functional Cu(II)-based ensemble

In this work, a dual-functional Cu²⁺-based ensemble (2S·Cu²⁺) was well designed and characterized. Then, the successional and discriminating sensing for CN^- over other competitive species (H₂PO₄^- and biothiols) was achieved based on the disaggregation of 2S·Cu²⁺ ensemble and the deprotonation of imidazole NH of regenerated sensor S in aqueous solution, respectively. The visual sensing mechanism could be clearly demonstrated by ¹H NMR, HRMS and energy changes between the HOMO-LUMO band gaps. Furthermore, the reversibility and reusability of S and 2S·Cu²⁺ upon alternating addition of CN^-/H⁺ and CN^-/Cu²⁺ were studied. Interestingly, the sequential sensing for biothiols (cysteine, glutathione and homocysteine) and CN^- was also realized through spectroscopic methodology and test paper strips. This work may provide a feasible strategy to discriminate CN^- over H₂PO₄^- and biothiols with high selectivity and sensitivity through Cu²⁺-based ensembles.

Highly selective fluorescent peptide-based chemosensors for aluminium ions in aqueous solution

Two novel fluorescent peptide-based chemosensors, including A (2-amino-benzoyl-Ser-Glu-Glu-NH₂) and B (2-amino-benzoyl-Ala-Glu-Pro-Glu-Ala-Glu-Pro-NH₂) were synthesized and characterized by nuclear magnetic resonance (NMR) spectra. These fluorescent probes exhibited excellent selective and sensitive responses to Al³⁺ ions over other metal ions in aqueous buffered solutions. The limits of detection for both chemosensors towards the Al³⁺ ions were in the order of ∼10^-7 M (A: 155 nM and B: 195 nM), which clearly indicates that these probes have significant potential for biological applications. They also displayed high binding affinity (1.3029 × 10⁴ M^-1 and 1.7586 × 10⁴ M^-1 relevant to A and B respectively). These two chemosensors are great analytical probes that produce turn-on responses upon binding to Al³⁺ ions through an intramolecular charge transfer (ICT) mechanism. In addition, the application of both chemosensors was examined over a wide range of pH. The fluorescent peptide-based probes and Al³⁺ form a 1:1 coordination complex according to the ESI-MS and Job's plot analysis. Notably, upon addition of Al³⁺ to these chemosensors, a fluorescence enhancement of approximately 8-fold was observed and the binding mode was determined using NMR titration and fluorescence emission data.

A dual-functional colorimetric and fluorescent peptide-based probe for sequential detection of Cu2+ and S2- in 100% aqueous buffered solutions and living cells

Highly sensitive and selectivite detection of copper ions (Cu²⁺) and hydrogen sulfide (H₂S) have become important research topics due to the potential harmful impacts of these chemicals to human health and the environment. In this study, we report the synthesis of a dual-functional peptide-based probe L (FITC-AhxSerSerHis), designed to mimic a copper-sulfur metalloprotein, and capable of continuous detection of Cu²⁺ and S^2- based on colorimetric and fluorescent methods. The new probe L displayed excellent "turn off" fluorescence response and good selectivity for Cu²⁺ ions via a modification of the tripeptide and fluorescein isothiocyanate group, and produced an obvious color change visible to the naked eye. Furthermore, as an excitable probe, the L-Cu complex could continuously detect S^2- with high selectivity and sensitivity in 100% aqueous buffered solutions. The detection limits for fluorescence titration measurements, calculated using the equation 3σ/k, were 76.7 nM (Cu²⁺) and 27.2 nM (S^2-), which were well below U.S. EPA safety levels. In addition, L could be cycled to alternately detect Cu²⁺ and S^2-, thereby making it a promising reversible probe. Moreover, L was successfully applied to monitoring Cu²⁺ and S^2- in live RKO cells through fluorescence imaging, exhibiting low cytotoxicity and good cell permeability.

A novel peptide-based fluorescent probe for sensitive detection of zinc (II) and its applicability in live cell imaging

In this work, we report SPSS synthesis of a new peptide-based fluorescent probe (L) capable of detecting Zn²⁺ with little interference in 100% aqueous solutions at physiological pH. Furthermore, L showed excellent sensitivity, with a detection limit of 26.77 nM. The 2:1 binding ratio between L and Zn²⁺ was determined using fluorometric titration, Job's plot and ESI-MS analyses. The "off-on-off" type fluorescence change of L was demonstrated by alternately adding Zn²⁺ and EDTA based on a formation-separation process of the complex, indicating that L could serve as a reversible probe. Moreover, MTT studies demonstrated that L has low biotoxicity, and could be successfully used for detection of Zn²⁺ and EDTA in live cells.

Water-soluble fluorescent sensor for Zn2+ with high selectivity and sensitivity imaging in living cells

A new water-soluble 4-amino-1, 8-naphthalimide based fluorescent sensor, with iminoacetic acid and iminoethoxyacetic acid as receptor contained two different arms, was developed. Under physiological pH conditions, it demonstrates good water solubility, high selectivity and sensitivity for sensing Zn²⁺ with about 20-fold enhancement in aqueous solution, with a characteristic emission band of 4-amino-1, 8-naphthalimide with a green color centered at 550 nm. It was applied successfully to detect Zn²⁺ in living cells.

Highly sensitive turn-on detection of mercury(II) in aqueous solutions and live cells with a chemosensor based on tyrosine

Herein, we reported a novel fluorescent chemosensor (DY) based on dansyl group and tyrosine by solid phase peptide synthesis (SPPS) for the detection of mercury(II) ions with excellent selectivity among 17 different metal ions. As designed, DY exhibited a sensitive fluorescence "turn-on" response to Hg²⁺ with low detection limits of 22.65 nM. A stoichiometric ratio (2: 1) of chemosensor DY and Hg²⁺ ions was determined by a Job's plot, fluorescent titration and the ESI-MS spectra. Especially, the reversible of DY-Hg with EDTA establishes the reuse of DY, and the circulation effect was very good. Furthermore, the wide pH range of 6-10 makes it capable of application in biological systems. Moreover, DY has been successfully applied to the detection of Hg²⁺ ions and EDTA in living HeLa and HK2 cells based on low cytotoxicity and good membrane permeability.

Fluorescent Detection of Methyl Mercury in Aqueous Solution and Live Cells Using Fluorescent Probe and Micelle Systems

It is highly challenging to develop fast and sensitive fluorescent methods for monitoring organic mercury in purely aqueous solutions as well as live cells. Especially, selective fluorescent detection of methylmercury over inorganic mercury ions has not been reported. We developed a fast and sensitive fluorescent detection method for Hg²⁺ ions as well as methylmercury using an amino acid-based fluorescent probe (1) and SDS micelles. The fluorescent probe in SDS micelles detected sensitively and selectively Hg²⁺ ions and methylmercury among 16 metal ions in purely aqueous solution by the enhancement of the red emission at 575 nm, and the detection of methylmercury was completed within 1 min. The probe in SDS micelles with EDTA showed highly sensitive and selective turn on detection for methylmercury over Hg²⁺. The limit of detection was 9.1 nM for Hg²⁺ (1.8 ppb, R² = 0.989) and 206 nM for CH₃Hg⁺ (R² = 0.997). 1 rapidly penetrated live cells and detected intracellular Hg²⁺ ions as well as CH₃Hg⁺ by the enhancement of both red emissions and green emissions. Subsequent treatment of EDTA into the cell confirmed the selective detection of methylmercury in the cells. The present work indicated that the fluorescent probe with micelle systems provided a fast, sensitive, and selective detection method for monitoring inorganic mercury as well as methyl mercury.

A novel fluorescent chemosensor for detection of mercury(II) ions based on dansyl-peptide and its application in real water samples and living LNcap cells

Mercury is one of the most hazardous pollutants, and mercury pollution is a serious hazard to our environment. Herein, we designed and synthesized a new peptide-based fluorescent chemosensor (L) based on a Fmoc-Lys (Fmoc)-OH backbone conjugated with two Serines and dansyl groups using solid phase peptide synthesis (SPPS) technology. L exhibited highly selective and excellent sensitive detection of Hg²⁺ ions in 100% aqueous solutions through fluorescence quenching. The chemosensor L forms a 2:1 stoichiometry with high binding constants (4.89×10⁶M^-1) and the detection limit for Hg²⁺ ions of the proposed assay was 7.59nM. In addition, the recovery test results of Hg²⁺ concentration in actual water samples showed that the quantitative detection of Hg²⁺ ions can be realized in two water samples. Moreover, L showed low cytotoxicity and excellent membrane permeability in HK2 cells, which has been successfully applied for monitoring Hg²⁺ ions in living LNCaP cells.

A water-soluble peptide fluorescent chemosensor for detection of cadmium (II) and copper (II) by two different response modes and its application in living LNcap cells

A novel peptide-based fluorescent chemosensor (DGC) based on dansyl-appended dipeptide (Gly-Cys-NH₂) was synthesized using SPPS technology. DGC exhibited highly sensitive detection of Cadmium (II) ions in 100% aqueous solutions through fluorescent "turn on" response and the detection limits of 14.5 nM. On the other hand, the fluorescence of DGC was almost completely quenched with fast response time when the addition of Cu²⁺ ions to DGC solutions, the detection limits for Cu²⁺ was 26.3 nM. In addition, the 2:1 binding stoichiometry of DGC with Cd²⁺ and Cu²⁺ were confirmed by Job's plot, fluorescent titration and HR-MS data. More importantly, MTT assays and fluorescence imaging experiments suggested that DGC has outstanding membrane permeability and hypotoxicity, and could be an efficient fluorescent chemosensor for Cd²⁺ and Cu²⁺ detection by two different response modes in living LNcap cells.

A novel bimacrocyclic polyamine-based fluorescent probe for sensitive detection of Hg2+ and glutathione in human serum

Detection of glutathione in human serum is of great importance for clinical diagnosis of various diseases, such as AIDS, diabetes mellitus, Alzheimer disease and cancer. In this work, a new water-soluble bismacrocyclic polyamine-derived compound, namely L, which contains two molecules of 4-nitro-1,2,3-benzoxa-diazole as the fluorophores, was designed and prepared. The experiments of selectivity of L toward metal ions showed it could rapidly and sensitively detect Hg²⁺ with a detection limit of 27 nM. Furthermore, the cell imaging and co-staining experiments in HeLa cells demonstrated that the L-Hg²⁺ probe had selectivity for the Golgi apparatus to a certain degree. Moreover, it had excellent selectivity for biothiols, especially for glutathione. Finally, the probe was successfully applied to sensitively detect glutathione (GSH) in human serum and fetal bovine serum.

A novel fluorescent chemosensor for detection of Zn(II) ions based on dansyl-appended dipeptide in two different living cells

This paper describes a new fluorescent chemosensor (DSH) based on dipeptide conjugated with dansyl group, which was synthesized by solid phase peptide synthesis (SPPS) technology. DSH exhibited a highly selective and sensitive toward Zn²⁺ ions by "turn-on" response based on generation of monomer-excimer mechanism in aqueous solutions, and the detection limit was calculated at 11.2 nM. In addition, the reversible of DSH-Zn with Na₂EDTA establishes the reuse of DSH, and the circulation effect was very good. Moreover, DSH had good water solubility, and was successfully applied to bioimage intracellular Zn²⁺ ions and Na₂EDTA in two different living cells with exciting cellular permeability and low cytotoxicity, which indicated that DSH had great potential in the application of biological imaging.

Fluorescence study of 5-nitroisatin Schiff base immobilized on SBA-15 for sensing Fe3+

N’-(5-nitro-2-oxoindolin-3-ylidene) thiophene-2-carbohydrazide (NH) was successfully synthesized as a ligand, then grafted onto the surface of mesoporous silica SBA-15via an aminopropyl bridge. The successful grafting of ligand NH onto the hybrid nanomaterial (SBA-15/APTES-NH) was confirmed by infrared spectroscopy. On excitation at 276 and 370 nm, the ligand NH and the hybrid nanomaterial SBA-15/APTES-NH showed a strong and narrow emission peak centered at 533 nm. By dispersing SBA-15/APTES-NH in an aqueous solution containing metal ions, the resulting solid materials showed a higher binding of NH sensing site to Fe3+ ions as compared to the others with a quench of the emission intensity up to 84%. This result showed that the hybrid nanomaterial is a potential chemosensor that requires development for the detection of metal ions.

A sequential and reversibility fluorescent pentapeptide probe for Cu(II) ions and hydrogen sulfide detections and its application in two different living cells imaging

In this study, we report a sequential and reversibility fluorescent probe (DP5) based on pentapeptide conjugated with dansyl groups using the solid phase peptide synthesis (SPPS) technology. DP5 showed immediate "turn off" response toward Cu²⁺ ions at an excitation wavelength of 330 nm with detection limits of 23.5 nM. The 2:1 binding ratio between DP5 and Cu²⁺ were confirmed using Job's plot method and fluorescence titration study, and DP5-Cu complex was observed with an association constant of 6.76 × 10⁸ M^-2. As designed, DP5-Cu complex as a promising analytical probe exhibited highly selective for H₂S detection in aqueous solutions. The detection limit for H₂S was obtained to be 17.2 nM, and lower than EPA and WHO guidelines. In addition, the reversibility and cyclicity were imparted to the DP5 during the detection of Cu²⁺ and H₂S, and cycle effect is very good. Furthermore, DP5 displayed better biocompatibility and low biotoxicity, and sequential fluorescence "on-off-on" responses of DP5 to Cu²⁺ and H₂S were successfully applied in two different living cells.

A novel peptide-based fluorescent chemosensor for Cd(II) ions and its applications in bioimaging

Nowadays, it is of great significance to develop a novel fluorescent chemosensor for Cd(II) ions detection with cost-effective, rapid, facile and applicable to environment and biological milieus. Herein, we report a new peptide-based fluorescent chemosensor DSC (Dan-Ser-Cys-NH₂) based on dipeptide (Ser-Cys-NH₂) conjugated with dansyl group, which was synthesized using solid phase peptide synthesis (SPPS) technology. As designed, DSC exhibited fluorescent "turn-on" response for Cd²⁺ in 100% aqueous solution over a wide range of pH values based on photoinduced electron transfer (PET). The stoichiometry binding of DSC and Cd²⁺ was determined to be 2:1 by Job's plot and ESI-MS analysis. Furthermore, DSC showed highly sensitive for Cd²⁺ and a low detection limit of 13.8 nM. What's more, DSC has cell permeability and low cytotoxicity, and fluorescence imaging experiments demonstrated that DSC was capable of monitoring Cd²⁺ in living HK2 cells by confocal microscopy.