A peptide-based fluorescent chemosensor for measuring cadmium ions in aqueous solutions and live cells

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.

Applications of Material-Binding Peptides: A Review

Material-binding peptides (MBPs) are functionalized adhesive materials consisting of a few to several dozen amino acids. This affinity between MBPs and materials is regulated by multiple interactions, including hydrogen bonding, electrostatic, hydrophobic interactions, and π-π stacking. They show selective binding and high affinity to a diverse range of inorganic and organic materials, such as silicon-based materials, metals, metal compounds, carbon materials, and polymers. They are used to improve the biocompatibility of materials, increase the efficiency of material synthesis, and guide the controlled synthesis of nanomaterials. In addition, these can be used for precise targeting of proteins by conjugating to target biomolecules. In this review, we summarize the main designs and applications of MBPs in recent years. The discussions focus on more efficient and functional peptides, including evolution and overall design of MBPs. We have also highlighted the recent applications of MBPs, such as functionalization of material surfaces, synthesis of nanomaterials, drug delivery, cancer therapy, and plastic degradation. Besides, we also discussed the development trend of MBPs. This interpretation will accelerate future investigations to bottleneck the drawbacks of available MBPs, promoting their commercial applications.

A phenazine-imidazole based ratiometric fluorescent probe for Cd2+ ions and its application in in vivo imaging

A new phenazine-imidazole based Schiff base (PIS) fluorescent probe has been developed for the ratiometric detection of Cd²⁺ ions in aqueous media at physiological pH. PIS upon binding with Cd²⁺ ions shows red shifted fluorescence and thereby, permits ratiometric detection of Cd(II) ions. A detection limit down to 2.10 × 10^-8 M was determined for Cd²⁺ quantitation. Also, the accompanying apparent fluorescence color change (from yellow to orange red) is noticeable to the naked eye under a UV-lamp. The sensing mechanism could be attributed to the 1 : 1 PIS-Cd complexation, followed by extension of the conjugation due to better planarity and modulation of the charge transfer efficiency in the probe. This was complemented by solvatochromism and density functional theory calculations. Furthermore, PIS was used to detect Cd²⁺ in Oxya chinensis cells, zebrafish larvae and live tissues of Arabidopsis thaliana under a fluorescence microscope, showing great potential in analyzing living biosystems.

Ultrasensitive mercury ion and biothiol detection based on Dansyl-His-Pro-Gly-Asp-NH2 fluorescent sensor

Mercury is an environmental contaminant, which is highly toxic even at extremely low concentrations. Long-term accumulation of mercury in human body will damage the central nervous system or digestive tract system. Here, a new fluorescent chemical sensor Dansyl-His-Pro-Gly-Asp-NH₂ (D-P4) was synthesized for the determination of Hg²⁺. The D-P4 sensor exhibits excellent selectivity and sensitivity to Hg²⁺ in aqueous solution with a 'turn-off' fluorescence response. Furthermore, D-P4-Hg system displays a good 'turn-on' fluorescence response to biothiols. The calculated binding constant for the 1:1 complex of D-P4 with Hg^{2 +} is 1.07 × 10⁵ M^-1, which also confirms the high affinity of D-P4 for Hg²⁺. Results indicate that the detection limit of D-P4 for Hg²⁺ is 61.0 nM, and that of D-P4-Hg system for Cys is as low as 80.0 nM.

A Highly Selective and Sensitive Peptide-Based Fluorescent Ratio Sensor for Ag. J Fluoresc 2020;31:237-246. [PMID: 33215317 DOI: 10.1007/s10895-020-02653-5]

A fluorescence ratio sensor based on dansyl-peptide, Dansyl-Glu-Cys-Glu-Glu-Trp-NH₂ (D-P5), was efficiently synthesized by Fmoc solid phase peptide synthesis. The sensor exhibits high selectivity and sensitivity for Ag⁺ over 16 metal ions in 100 mM sodium perchlorate and 50 mM 2-[4-(2-hydroxyethyl)piperazin-1-yl]ethanesulfonic acid buffer solution by fluorescence resonance energy transfer. The 1:1 binding stoichiometry of the sensor and Ag⁺ is measured by fluorescence ratio response and the job's plot. The dissociation constant of the sensor with Ag⁺ was calculated to be 6.4 × 10^-9 M, which indicates that the sensor has an effective binding affinity for Ag⁺. In addition, the limit of detection of the sensor for Ag⁺ was determined to be 80 nM, which also indicates that the sensor has a high sensitivity to Ag⁺. Result showed that the sensor is an excellent Ag⁺ sensor under neutral condition. Furthermore, this sensor displays good practicality for Ag⁺ detection in river water samples without performing tedious sample pretreatment, as well as for silver chloride detection.

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 peptide-based fluorescent sensor for selective imaging of glutathione in living cells and zebrafish

Monitoring and imaging glutathione (GSH) in living systems is an essential tool to determine the key roles of GSH in biological pathways, but most fluorescent sensors can only be used in vitro because of their potential biotoxicity. Here, a peptide-based fluorescent sensor, FP, has been successfully designed and synthesized based on the biocompatibility of the peptide backbone and low toxicity. The design strategy of FP contains a specific spatial structure of the peptide sequence which selectively binds to Cu²⁺, triggering fluorescence quenching. Interestingly, the fluorescence of FP can be fully restored by GSH, due to the strong binding between Cu²⁺ and the GSH sulfhydryl groups. Finally, the sensor is highly sensitive and selective for imaging GSH both in vitro and in vivo with low toxicity. Thus, FP with its strong "on-off-on" fluorescence changes is a powerful way to image GSH both in cells and zebrafish larvae to study the GSH pathway.

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.

Reducing methylmercury accumulation in fish using Escherichia coli with surface-displayed methylmercury-binding peptides

Seafood consumption is widely considered as the primary route for human exposure to the neurotoxin methylmercury (MeHg) that is produced by certain anaerobic microorganisms and can bioaccumulate to high concentration levels in natural aquatic food webs. In this study, a novel methylmercury-binding peptide with seven amino acids was displayed on the cell surfaces of Escherichia coli strain W-1, which was isolated from fish feces and fused with ice nucleation protein. These cells exhibited high affinity and selectivity toward methylmercury. They efficiently removed more than 96% of 12 μM methylmercury, and accumulation of methylmercury in the engineered strain was four times higher than that in the wild type. Transmission electron microscopy confirmed methylmercury accumulation on cell membranes. Carassius auratus was fed by engineered bacteria, which showed a decrease in methylmercury concentration in muscles of about 36.3 ± 0.7%; whereas an increase in methylmercury concentration was observed in the feces (36.7 ± 0.8%) in comparison to the control group. The engineered strain in the gut captured methylmercury and prevented it's absorption by muscles, while some bacteria with methylmercury were excreted in the feces. The surface-engineered E. coli effectively protected fish from methylmercury contamination.

Hg2+-binding peptide decreases mercury ion accumulation in fish through a cell surface display system

Mercury is a potentially toxic trace metal that poses threats to aquatic life and to humans. In this study, a mercury-binding peptide was displayed on the surface of Escherichia coli cells using an N-terminal region ice nucleation protein anchor. The surface-engineered E. coli facilitated selective adsorption of mercury ions (Hg²⁺) from a solution containing various metal ions. The Hg²⁺ adsorption capacity of the surface-engineered cell was four-fold higher than that of the original E. coli cells. Approximately 95% of Hg²⁺ was removed from solution by these whole-cell sorbents. The transformed strains were fed to Carassius auratus, so that the bacteria could colonize fish intestine. Engineered bacteria-fed C. auratus showed significantly less (51.1%) accumulation of total mercury when compared with the group that had not been fed engineered bacteria. The surface-engineered E. coli effectively protected fish against the toxicity of Hg²⁺ in aquatic environments by adsorbing more Hg²⁺. Furthermore, the surface-engineered E. coli mitigated microbial diversity changes in the intestine caused by Hg²⁺ exposure, thereby protecting the intestinal microbial community. This strategy is a novel approach for controlling Hg²⁺ contamination in fish.

Selective red-emission detection for mercuric ions in aqueous solution and cells using a fluorescent probe based on an unnatural peptide receptor

The selective ratiometric red-emission detection of Hg²⁺ions in aqueous buffered solutions and live cells is still a significant challenge.

A selective and sensitive peptide-based fluorescent chemical DSH sensor for detection of zinc ions and application in vitro and in vivo

Here we report the design and synthesis of a peptide-based fluorescent chemical sensor (DSH sensor: Dansyl-Ser-Pro-Gly-His-Trp-Gly) for detecting Zn²⁺, based on fluorescence resonance energy transfer (FRET) from tryptophan (donor) to the dansyl fluorophore (acceptor).

A differentially selective probe for trivalent chemosensor upon single excitation with cell imaging application: potential applications in combinatorial logic circuit and memory devices

A new rhodamine 6G-benzylamine-based sensor (L1) shows selective recognition of trivalent metal ions with advanced level molecular logic gate and bio-imaging applications.

A quinoline-based fluorescence "on-off-on" probe for relay identification of Cu2+ and Cd2+ ions

A novel fluorescent probe based 8-hydroxyquinoline (8-HQ) has been designed and synthesized. The probe 1 exhibits fast relay recognition performance for Cu²⁺ and Cd²⁺ via a fluorescence "on-off-on" response signal. The probe 1 itself has a strong emission peak at 471 nm in EtOH/H₂O (v/v = 1:9) solution with a blue fluorescence. The addition of Cu²⁺ immediately results in the quenching of fluorescence and the limit of detection is 2.7 × 10^-8 M. Moreover, the formation of [1-Cu²⁺] complexes can also serve as a new efficient probe system for the relay recognition of Cd²⁺ with the emergence of a new fluorescence signal under the same conditions. The study also found that the probe 1 has high selectivity for target ions in the presence of other competing ions. The probe 1 has been successfully applied to detect and analyze the trace amount of Cu²⁺ and Cd²⁺ in environmental water samples.

High selective and sensitive detection of Zn(II) using tetrapeptide-based dansyl fluorescent chemosensor and its application in cell imaging

The zinc ions (Zn²⁺) play extremely irreplaceable role in the organism and the environment, the design and synthesis of a biomolecule-based fluorescence chemosensor for the detection of Zn²⁺ with high sensitivity is very important. Herein, a novel tetrapeptide-based dansyl fluorescent "turn-on" response chemosensor (L) has been designed and synthesized by solid phase peptide synthesis (SPPS). As designed, L can detect Zn²⁺ ions with specifically and sensitively based on photo-induced electron transfer (PET) mechanism in 100% aqueous solutions, and other metal ions do not interfere with Zn²⁺ ions recognition. The stoichiometric ratio of L with Zn²⁺ ions was 2:1, which matches with fluorescence titration and Job-plot assay. In addition, the reversibility and circularly process of the detection of L was confirmed by adding bonding agent Na₂EDTA. Moreover, L exhibits excellent biocompatibility and low biotoxicity with the limit of detection (LOD) for Zn²⁺ about 18 nM, and has been successfully utilized for fluorescence imaging of Zn²⁺ ions in living HeLa cells under physiological conditions.

A novel fluorescent chemosensor based on tetra-peptides for detecting zinc ions in aqueous solutions and live cells

A novel fluorescent chemosensor (HL) based on tetra-peptides conjugated with dansyl groups has been designed and synthesized, which is a promising analytical tool for detecting Zn²⁺ in aqueous solutions and live cells.

Highly selective ratiometric peptide-based chemosensors for zinc ions and applications in living cell imaging: a study for reasonable structure design

The relationship between the structure and activity for the fluorescent sensing of zinc ions with H₂L peptides has been studied experimentally and computationally.

A selective fluorescent probe for the detection of Cd2+ in different buffer solutions and water

A fluorescent probe NHQ, which exhibited excellent selectivity toward Cd²⁺ in different buffer solutions such as Tris-HCl buffer solution, HEPES buffer solution, and PBS buffer solution, and even in water, was developed.

Fluorescence “on–off–on” peptide-based chemosensor for the selective detection of Cu2+ and S2− and its application in living cell bioimaging

A novel fluorescence chemosensor L based on a tetra-peptide conjugated with dansyl groups has been designed as a promising analytical tool for detecting Cu²⁺ and S²⁻ in 100% aqueous solutions and living cells.

A new quinoline-based fluorescent probe for Cd2+ and Hg2+ with an opposite response in a 100% aqueous environment and live cell imaging

A new quinoline-based dual fluorescent probe L was synthesized for the detection of Cd²⁺ (turn-on) and Hg²⁺ (turn-off) in a 100% aquatic system. Its in vivo sensitivities to Cd²⁺ and Hg²⁺ were demonstrated in the EC9706 cell line.