Highly selective and sensitive detection of Zn(II) and Cu(II) ions using a novel peptide fluorescent probe by two different mechanisms and its application in live cell imaging

A Dipeptide-derived Dansyl Fluorescent Probe for the Detection of Cu2+ in Aqueous Solutions

A novel dansyl-based fluorescent probe (DG) was designed via the introduction of a dipeptide, glycyl-L-glutamine. DG showed good selectivity and sensitivity towards Cu2+ in aqueous solutions in the pH span of ~ 6-12. The coordination of Cu2+ with the dipeptide moiety led to the fluorescent quenching of the dansyl fluorophore. The association constant value for Cu2+ was 0.78 × 104 M- 1 in a 1 to 1 stoichiometric ratio. The detection limit in HEPES buffer solution (10 mM, pH 7.4) was 1.52 µM. DG also showed strong anti-interference capability in the presence of other metal ions. It was worth noting that DG maintained the detection ability towards Cu2+ in real water samples and cell imaging, implying the potential application opportunities in complicated environments.

Progress in the Development of Biosensors Based on Peptide-Copper Coordination Interaction

Copper ions, as the active centers of natural enzymes, play an important role in many physiological processes. Copper ion-based catalysts which mimic the activity of enzymes have been widely used in the field of industrial catalysis and sensing devices. As an important class of small biological molecules, peptides have the advantages of easy synthesis, excellent biocompatibility, low toxicity, and good water solubility. The peptide-copper complexes exhibit the characteristics of low molecular weight, high tenability, and unique catalytic and photophysical properties. Biosensors with peptide-copper complexes as the signal probes have promising application prospects in environmental monitoring and biomedical analysis and diagnosis. In this review, we discussed the design and application of fluorescent, colorimetric and electrochemical biosensors based on the peptide-copper coordination interaction.

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 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.

Effect of Collagen Peptide-Chelated Zinc Nanoparticles From Pufferfish Skin on Zinc Bioavailability in Rats

Small-molecular-weight collagen peptides (CPs) with high zinc-chelating ability were extracted from pufferfish skin. Chelation of CPs with zinc was performed to prepare novel CP-chelated zinc (CP-Zn) nanoparticles. CP-Zn nanoparticles were spherical, regular, and well dispersed with an average size of ∼100 nm. The zeta potential assay was used to explore the stability of CP-Zn nanoparticles. CP-Zn nanoparticles were much more stable in the pH range of 3-8. The structural properties of CP-Zn nanoparticles were characterized by matrix-assisted laser desorption-ionization time-of-flight mass spectrometry, Fourier transform infrared spectroscopy, and ¹H nuclear magnetic resonance spectroscopy. The results indicated that CPs were chelated with Zn ions through the amino nitrogen and oxygen atoms from the carboxyl groups. Furthermore, the animal experiment results showed that CP-Zn nanoparticles were more effective in improving zinc bioavailability of Zn-deficient rats than zinc gluconate and zinc sulfate. The study demonstrated that CP-Zn nanoparticles were ideal for zinc supplementation.

Chirality in peptide-based materials: From chirality effects to potential applications

Chirality is ubiquitous in nature with primary cellular functions that include construction of right-/left-handed helix and selective communications among diverse biomolecules. Of particularly intriguing are the chiral peptide-based materials that can be deliberately designed to change physicochemistry properties via tuning peptide sequences. Critically, understanding their chiral effects are fundamental for the development of novel materials in chemistry and biomedicine fields. Here, we review recent researches on chirality in peptide-based materials, summarizing relevant typical chiral effects towards recognition, amplification, and induction. Driven forces for the chiral discrimination in affinity interaction as well as the handedness preferences in supramolecular structure formation at both the macroscale and microscale are illustrated. The implementation of such chirality effects of artificial copolymers, assembled aggregates and their composites in the fields of bioseparation and bioenrichment, cell incubation, protein aggregation inhibitors, chiral smart gels, and bionic electro devices are also presented. At last, the challenges in these areas and possible directions are pointed out. The diversity of chiral roles in the origin of life and chirality design in different organic or composite systems as well as their applications in drug development and chirality detection in environmental protection are discussed.

A smartphone-integrated ratiometric fluorescence sensor for visual detection of cadmium ions

A novel fluorescence sensing platform was fabricated for visual detection of cadmium ions (Cd²⁺) with excellent stability and portability. In this protocol, dual-emission ratiometric fluorescence probe were constructed based on silicon oxide-coated copper nanoclusters (CuNCs@SiO₂) as a signal reference and cadmium telluride quantum dots (CdTe QDs) as signal response, thereby greatly improving the accuracy of test results. The level of Cd²⁺ can be reported within a wide linear range from 0.010 mg·L^-1 to 2.0 mg·L^-1 with a sensitive detection limit of 1.1 μg·L^-1 (2.75 μg·kg^-1) and a quick sample-to-answer monitoring time of 6 min, which was quite qualified for regularly monitoring Cd²⁺. Moreover, aiming to attain portable analysis, the smartphone as colorimetric reader and analyzer were also utilized for rapidly analyzing Cd²⁺ by capturing the change in fluorescence color. Additionally, benefiting from the strong combination of 1, 10-phenanthroline (Phen) and Cd²⁺, the fluorescence probe showed excellent anti-interference activities for Cd²⁺ assay in complex oyster matrix. Overall, the sensing platform had significant stability, specificity and sensitivity, offering a promising potential for conveniently evaluating the quality of marine bivalves polluted with Cd²⁺.

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.

Organic-Inorganic Two-Dimensional Hybrid Networks Constructed from Pyridine-4-Carboxylate-Decorated Organotin-Lanthanide Heterometallic Antimotungstates

Six organic-inorganic hybrid pyridine-4-carboxylate-decorated organotin (OT)-lanthanide (Ln) heterometallic antimotungstates [Ln(H₂O)₆(pca)]H[Sn(CH₃)₂(H₂O)]₃[B-β-SbW₉O₃₃]·12H₂O [Ln = La³⁺ (1), Ce³⁺ (2), Pr³⁺ (3), Nd³⁺ (4), Sm³⁺ (5), Eu³⁺ (6); Hpca = isonicotinic acid] have been prepared with the help of the structure-directing effect of the trivacant [B-α-SbW₉O₃₃]^9- segment toward [(CH₃)₂Sn]²⁺ and Ln³⁺ ions in an acidic water medium. The prominent architecture characteristic is that their structural units consist of a trivacant [B-β-SbW₉O₃₃]^9- segment stabilized by three [Sn(CH₃)₂(H₂O)]²⁺ groups and a [Ln(H₂O)₆(pca)]²⁺ cation, which are interconnected to propagate an intriguing two-dimensional (2D) network. For all we know, 1-6 stand for the first 2D OT-Ln heterometallic polyoxometalates. Furthermore, luminescence performances of solid-state 3-6 were deeply surveyed at ambient temperature. Energy migration from [B-β-SbW₉O₃₃]^9- and pca^- to Sm³⁺ centers in 5 was also studied. Comparative studies demonstrate that the contribution of [B-β-SbW₉O₃₃]^9- sensitizing the emission of Sm³⁺ is prominently larger than that of pca^- sensitizing the emission of Sm³⁺ in the emission process of 5. Most interestingly, 6 as a fluorescence probe exhibits high selectability and sensitivity for recognizing Zn²⁺ and Cu²⁺ in water.

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.

Copper nanoclusters @ nitrogen-doped carbon quantum dots-based ratiometric fluorescence probe for lead (II) ions detection in porphyra

A novel ratiometric fluorescence probe was proposed for detecting lead (II) ions (Pb²⁺) in porphyra, the approach was based on copper nanoclusters and nitrogen-doped carbon quantum dots (CuNCs-CNQDs). In this probe, the CuNCs delivered the response signal, the fluorescence of which was enhanced by Pb²⁺ due to the aggregation-induced emission enhancement (AIEE) between Pb²⁺ and CuNCs. The CNQDs provided the self-calibration signal, whose fluorescence remained almost unchanged in coexistence with Pb²⁺. According to the change of fluorescence intensity ratio between the fluorophores, CuNCs-CNQDs nanohybrid was used as ratiometric probes for the sensitive detection of Pb²⁺ in the range of 0.010-2.5 mg L^-1, with a detection limit of 0.0031 mg L^-1. Finally, the probe was successfully applied to detect Pb²⁺ in porphyra with relative standard deviations (RSDs) lower than 5%. This study provides a straightforward, stable, and sensitive approach for detecting Pb²⁺ in porphyra.

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 Pentapeptide with Tyrosine Moiety as Fluorescent Chemosensor for Selective Nanomolar-Level Detection of Copper(II) Ions

Herein, we have investigated principally with the use of UV and fluorescence (steady-state and time-resolved) spectroscopy the interactions between selected pentapeptides with tyrosine residue (EYHHQ, EHYHQ, EHHQY, and KYHHE) and various metal ions (Cu²⁺, Mn²⁺, Co²⁺, Ni²⁺, Zn²⁺, Cr³⁺, Cd²⁺, Ag⁺, Pb²⁺, Sr²⁺, Ba²⁺, Ca²⁺, Mg²⁺, Al³⁺, Fe²⁺, and Ga³⁺) in order to establish the relationship between the position of a tyrosine residue in the peptide sequence and the metal ion-binding properties. Among the peptides studied, EHYHQ was evaluated as an efficient and selective ligand for developing a chemosensor for the detection of copper(II) ions. While significant fluorescence emission quenching was observed for that peptide in the presence of Cu²⁺ cations, other metal cations used at the same and at considerably higher concentrations caused a negligible change of the fluorescence emission spectrum, indicating a high selectivity of EHYHQ for Cu²⁺ ions. Under optimum conditions, fluorescence intensity was inversely proportional to the concentration of Cu²⁺ ions. The limit of detection of Cu²⁺ ions with the use of EHYHQ was determined at the level of 26.6 nM. The binding stoichiometry of the complexes of the studied peptides with Cu²⁺ ions was evaluated spectrophotometrically and fluorimetrically (as in the case of EHYHQ confirmed by mass spectrometry) and found to be 1:2 (Cu²⁺-peptide) for all the investigated systems. Furthermore, the stability constant (K) values of these complexes were determined. The reversibility of the proposed Cu²⁺ ions sensor was confirmed, the pH range where the sensor acts was determined, while its analytical performance was compared with some other reported recently fluorescent sensors. The mechanism of the interactions between EHYHQ and Cu²⁺ was proposed on the basis of NMR spectroscopy investigations.

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.

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.