Synergistic integration of a rhodamine-labelled tripeptide into AIE-active fluorogenic probe: Enabling nanomolar detection of Al3+ ions through test strips, thin films, and Arduino-assisted optosensing platform

Peptide-fluorophore conjugates (PFCs) have been expeditiously utilized for metal ion recognition owing to their distinctive characteristics. Selective detection and quantification of aluminum is essential to minimize health and environmental risks. Herein, we report the synthesis and characterization of a new chemoprobe with aggregation-induced emission characteristics by chemically conjugating rhodamine-B fluorophore with a tripeptide. The probe revealed β-sheet secondary conformation in both solid and solution states, as confirmed by FT-IR, PXRD, and CD experiments. AIE characteristics of the probe in water-MeCN mixtures revealed the formation of spherically shaped nanoaggregates with an average size of 353 ± 7 nm, as confirmed by SEM, TEM, and DLS studies. The probe exhibited a large stokes shift (175 nm) and displayed selective colorimetric and fluorometric responses towards Al3+ ions with an extremely low detection limit (51 nm) and a fast response time (≤15 s). Comparative NMR studies confirmed the cleavage of spirolactam ring upon aluminum binding. The probe's practicality was enhanced through integration into test strips and thin films, allowing solid-phase detection of Al3+ ions. Furthermore, an RGB-Arduino enabled optosensing device has been developed to enable instant quantifiable analysis of aluminum concentrations in real-time conditions.

Hospital wastewater treatment using eco-friendly eugenol nanostructured lipid carriers: Formulation, optimization, and in vitro study for antibacterial and antioxidant properties

In this study, nano-formulation has been used to tackle one of the most important environmental problems which can be considered a major threat to human health. We prepared some eco-friendly nanostructured lipid carriers (NLCs) as delivery agents to properly deliver an antibacterial agent (eugenol) into hospital wastewater in order to control bacterial growth. Eugenol-loaded nanostructured lipid carriers were prepared by hot high-speed homogenization. Then, the prepared nanocarriers were characterized using different techniques such as transmission electron microscopy, Fourier transform infrared, and dynamic scanning calorimetry. The turbidity assay and colony counting method were used to determine the ability of the prepared eugenol-loaded nanostructured lipid carriers to inhibit bacterial growth rate in the culture media and hospital wastewater, respectively. The mean size and zeta potential of NLC-eugenol were 78.12 ± 6.1 nm and -29.43 ± 2.21 mV, respectively. The results showed that the highest inhibitory effect of NLC-eugenol in culture media was seen in standard and wild Staphylococcus aureus strains (43.42% and 26.41%, respectively) with a concentration of 0.125 μM. The antibacterial activity of NLC-eugenol in sterile wastewater on wild strains of bacteria showed that the most effective concentration to reduce bacterial amounts was 0.125 μM on wild S. aureus and Enterococcus faecalis strains (38% and 33.47%, respectively) at 37°C. The NLC-eugenol with a concentration of 0.125 μM showed the greatest effect of reducing total microbial agents by 28.66% in hospital wastewater at 25°C. The highest antibacterial effect achieved using the 0.125 μM concentration is due to the egel phenomenon. Also, the mechanism of action of NLC-eugenol is cell wall destruction and eventually cell death. The results showed that NLC-eugenol with a concentration of 0.125 μM can reduce wild bacterial strains in sterilized wastewater and hospital wastewater, which can prove the great potential of the prepared eugenol-loaded nanostructured lipid carriers to control bacterial growth. PRACTITIONER POINTS: NLC is one of the safest biodegradable and environmentally friendly carriers, which is nontoxic for humans and the environment. Eugenol is a natural compound, which makes it less toxic for the environment while being toxic for bacteria. Therefore, our method has the least side effect in comparison with existing methods for wastewater treatment. The gradual release of eugenol from NLC nanoparticles can effectively control the pathogenic factors of wastewater.

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...

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.

A dansyl-based fluorescent probe for sensing Cu2+ in aqueous solution

A fluorescent probe based on a glycyl-L-tyrosine-modified dansyl derivative (D-GT) is designed and synthesized. D-GT demonstrated great detection performance toward Cu²⁺ in an aqueous solution. Fluorescence quenching occurred due to the coordination of Cu²⁺ with D-GT. The sensitive detection of D-GT to Cu²⁺ was applied in aqueous solution within a wide pH span (6-12). A 1:1 coordinate stoichiometric way and an association constant of 6.47 × 10⁴ M^-1 between D-GT and Cu²⁺ were determined. The measured detection limit for Cu²⁺ in HEPES buffer solution (10 mM, pH 7.4) was 0.69 μM. The probe displayed an appropriate sensitivity toward Cu²⁺ in real drinking water samples and living cells, which reveals the potential applications of D-GT in complicated environments.

A label-free Exonuclease I-assisted fluorescence aptasensor for highly selective and sensitive detection of silver ions

Based on the specific interaction of Ag⁺ and cytosine-cytosine (C-C) base mismatch and using berberine (Ber) as the fluorescent probe and Exonuclease I (Exo I) as the background fluorescence reducing tool, a label-free Exo I-assisted fluorescence aptamer sensing platform was established for the detection of silver ions with high sensitivity and selectivity. Exo I reduced the fluorescence background of the Ber/Ag⁺-aptamer complex to a level similar to that of Ber itself in the absence of Ag⁺. After introducing Ag⁺ into the sensing system, it induces the aptamer rich in base C to form C-Ag⁺-C i-motif structure which are resistant to degradation mediated by Exo I. The concentration of Ber, Ag⁺-aptamer, Exo I and the temperature and reaction time for Exo I were all optimized. Under the optimal experimental conditions, the detection limit of Ag⁺ was 4.4 nM and the linear range was from 0.0059 μM to 235.48 μM with a coefficient of determination (R²) > 0.99. Moreover, the proposed strategy had been successfully applied to the detection of Ag⁺ in tap water and human serum with a good recovery ranging from 88.4% to 106.9%.

Bioinspired Luminescent Europium-Based Probe Capable of Discrimination between Ag+ and Cu. Inorg Chem 2021;60:10791-10798. [PMID: 34236828 DOI: 10.1021/acs.inorgchem.1c01486]

Due to their similar coordination properties, discrimination of Cu⁺ and Ag⁺ by water-soluble luminescent probes is challenging. We have synthesized LCC4^Eu, an 18 amino acid cyclic peptide bearing a europium complex, which is able to bind one Cu⁺ or Ag⁺ ion by the side chains of two methionines, a histidine and a 3-(1-naphthyl)-l-alanine. In this system, the naphthyl moiety establishes a cation-π interaction with these cations. It also acts as an antenna for the sensitization of Eu³⁺ luminescence. Interestingly, when excited at 280 nm, LCC4^Eu behaves as a turn-on probe for Ag⁺ (+150% Eu emission) and as a turn-off probe for Cu⁺ (-50% Eu³⁺ emission). Shifting the excitation wavelength to 305 nm makes the probe responsive to Ag⁺ (+380% Eu³⁺ emission) but not to Cu⁺ or other physiological cations. Thus, LCC4^Eu is uniquely capable of discriminating Ag⁺ from Cu⁺. A detailed spectroscopic characterization based on steady-state and time-resolved measurements clearly demonstrates that Eu³⁺ sensitization relies on electronic energy transfer from the naphthalene triplet state to the Eu³⁺ excited states and that the cation-π interaction lowers the energy of this triplet state by 700 and 2400 cm^-1 for Ag⁺ and Cu⁺, respectively. Spectroscopic data point to a modulation of the efficiency of the electronic energy transfer caused by the differential red shift of the naphthalene triplet, deciphering the differential luminescence response of LCC4^Eu toward Ag⁺ and Cu⁺.

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.

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.

A new chromogenic and fluorescent chemosensor based on a naphthol-bisthiazolopyridine hybrid: a fast response and selective detection of multiple targets, silver, cyanide, sulfide, and hydrogen sulfide ions and gaseous H2S

A novel chemosensor 1 based on a naphthol-bisthiazolopyridine hybrid was synthesized and characterized. Among the various screened cations and anions, chemosensor 1 selectively recognized Ag+ and CN- ions by relying on the color change and distinct absorption and emission changes. Moreover, the probe 1·Ag+ was well operable for the selective monitoring of S2-, HS- and H2S as evidenced by the different color and optical changes. The selective detection of all the anions was simply based on the breakage of the intramolecular hydrogen bonding of 1, followed by the protonation or deprotonation mechanism. In general, chemosensor 1 is a promising indicator in terms of its ease-of-use, selectivity, sensitivity, and rapid response (<1 s). Moreover, the visual detection and concentration determination of these analytes by solution or solid kits are the advantages for the practical applications of this sensor.

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 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.

Hg2+ and Cd2+ binding of a bioinspired hexapeptide with two cysteine units constructed as a minimalistic metal ion sensing fluorescent probe

Hg²⁺ and Cd²⁺ complexation of a short hexapeptide, Ac-DCSSCY-NH₂ (DY), was studied by pH-potentiometry, UV and NMR spectroscopy and fluorimetry in aqueous solutions and the Hg²⁺-binding ability of the ligand was also described in an immobilized form, where the peptides were anchored to a hydrophilic resin. Hg²⁺ was demonstrated to form a 1 : 1 complex with the ligand even at pH = 2.0 while Cd²⁺ coordination by the peptide takes place only above pH ∼ 3.5. Both metal ions form bis-ligand complexes by the coordination of four Cys-thiolates at ligand excess above pH ∼ 5.5 (Cd²⁺) and 7.0 (Hg²⁺). Fluorescence studies demonstrated a Hg²⁺ induced concentration-dependent quenching of the Tyr fluorescence until a 1 : 1 Hg²⁺ : DY ratio. The fluorescence emission intensity decreases linearly with the increasing Hg²⁺ concentration in a range of over two orders of magnitude. The fact that this occurs even in the presence of 1.0 eq. of Cd²⁺ per ligand reflects a complete displacement of the latter metal ion by Hg²⁺ from its peptide-bound form. The immobilized peptide was also shown to bind Hg²⁺ very efficiently even from samples at pH = 2.0. However, the existence of lower affinity binding sites was also demonstrated by binding of more than 1.0 eq. of Hg²⁺ per immobilized DY molecule under Hg²⁺-excess conditions. Experiments performed with a mixture of four metal ions, Hg²⁺, Cd²⁺, Zn²⁺ and Ni²⁺, indicate that this molecular probe may potentially be used in Hg²⁺-sensing systems under acidic conditions for the measurement of μM range concentrations.

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.

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

Metalloproteins are often a useful template for the design and development of peptide fluorescent probes. Herein, we report a novel and simple fluorescent probe L comprised of tetrapeptide and dansyl groups by the solid phase peptide synthesis (SPPS). As a multifunctional analytical probe, L exhibited a highly selective "turn-on" fluorescent response to zinc ions, and a selective "turn-off" fluorescent response to copper ions at an excitation wavelength of 330 nm. The high sensitivity of L was made possible photo-induced electron transfer (PET), and L exhibited very low detection limits for Zn²⁺ and Cu²⁺ of 4.9 nM and 15 nM in 100% aqueous solutions, respectively. Furthermore, L displayed very low biotoxicity and excellent cell permeability, and was successfully used for detection of Zn²⁺ and Cu²⁺ in living HeLa cells based on two different mechanisms. We believe that the probe L may have many potential applications in environmental and biological research.

A fluorescent dansyl-based peptide probe for highly selective and sensitive detect Cd2+ ions and its application in living cell imaging

We reported a novel and readily synthesized fluorescent "turn-on" probe L (Dansyl-Glu-Pro-Gly-Cys) based on dansyl group combine tetrapeptide. The probe L exhibited highly sensitive fluorescent recognition to Cd²⁺ ions in HEPES buffer solutions (10.0 mM, pH 7.4). The 2:1 binding stoichiometry of L with Cd²⁺ were determined based on fluorescence titration and the Job's plot investigation. The competitive experiments were found to be highly selective for the Cd²⁺ ions even in the existence of excess competing metal ions including Zn²⁺, Pb²⁺, Hg²⁺ and Cu²⁺ ions. The binding constant of the complex L-Cd was calculated to be 5.18 × 10¹⁰ M^-2, and showed great affinity compared to other probes. In addition, the detection limit of the probe L for Cd²⁺ ions was calculated to be 45 nM, which presented a pronounced sensitivity toward Cd²⁺ ions. Most importantly, the probe L had wide range of pH and good biocompatibility, and were successfully applied to selectively detected Cd²⁺ ions within pH range of 7-12 and bioimaging studies in live cells.

Dominant Role of Silver Ions in Silver Nanoparticle Toxicity to a Unicellular Alga: Evidence from Luminogen Imaging

Despite the extensive studies on silver nanoparticle (AgNP) toxicity, the contribution of released silver ions to the toxicity still remains debatable. This study investigated the toxicity of AgNPs with different sizes (20 and 60 nm) toward a phytoplankton Euglena gracilis, with a focus on evaluating the contributions of dissolved Ag to the toxicity by combining a newly developed aggregation-induced emission luminogen (AIEgen)-based imaging technique and a traditional inductively coupled plasma mass spectrometry (ICP-MS) method. Smaller AgNPs, which dissolved much faster, exhibited greater toxicity, as evidenced by lower 50% growth inhibition concentration (EC₅₀). However, the average Ag⁺ concentration at each EC₅₀ was comparable to the EC₅₀ of AgNO₃, and similar subcellular Ag distribution patterns were observed in both AgNPs and AgNO₃ exposed algae. More silver ions were internalized in algae treated with smaller AgNPs. With the application of luminogen imaging technology, we for the first time demonstrated that few Ag(I) were presented intracellularly in algae exposed to AgNPs when any released Ag in the medium was complexed by cysteine. Ag(I) was mainly distributed in cellular debris, organelles, and metal-rich granules fractions. No conclusive evidence for AgNP internalization was documented. Our results strongly suggested that Ag⁺ released from AgNPs extracellularly dominated the AgNP toxicity. The findings of this work provide new and useful insight into the toxicity of AgNPs in aquatic environments.

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.

Sensitive ratiometric detection of Al(iii) ions in a 100% aqueous buffered solution using a fluorescent probe based on a peptide receptor

The peptidyl bioprobe detected Al(iii) ions sensitively in a 100% aqueous buffered solution through ratiometric response.

A simple cost effective carbazole–thiobarbituric acid conjugate as a ratiometric fluorescent probe for detection of mercury(ii) ions in aqueous medium

A multimode ratiometric Hg²⁺ selective chemosensor based on a carbazole–thiobarbituric acid conjugate was developed. It responds to the presence of Hg²⁺ by colorimetry and by fluorescence. The sensor action is demonstrated in both aqueous homogeneous or microheterogeneous media.

Highly sensitive and selective detection of Al(III) ions in aqueous buffered solution with fluorescent peptide-based sensor

A fluorescent sensor based on a tripeptide (SerGluGlu) with a dansyl fluorophore detected selectively Al(III) among 16 metal ions in aqueous buffered solutions without any organic cosolvent. The peptide-based sensor showed a highly sensitive turn on response to aluminium ion with high binding affinity (1.84×10(4)M(-1)) in aqueous buffered solutions. The detection limit (230nM, 5.98ppb) of the peptide-based sensor was much lower than the maximum allowable level (7.41μM) of aluminium ions in drinking water demanded by EPA. The binding mode of the peptide sensor with aluminium ions was characterized using ESI mass spectrometry, NMR titration, and pH titration experiments.

Development of new peptide-based receptor of fluorescent probe with femtomolar affinity for Cu(+) and detection of Cu(+) in Golgi apparatus

Developing fluorescent probes for monitoring intracellular Cu(+) is important for human health and disease, whereas a few types of their receptors showing a limited range of binding affinities for Cu(+) have been reported. In the present study, we first report a novel peptide receptor of a fluorescent probe for the detection of Cu(+). Dansyl-labeled tripeptide probe (Dns-LLC) formed a 1:1 complex with Cu(+) and showed a turn-on fluorescent response to Cu(+) in aqueous buffered solutions. The dissociation constant of Dns-LLC for Cu(+) was determined to be 12 fM, showing that Dns-LLC had more potent binding affinity for Cu(+) than those of previously reported chemical probes for Cu(+). The binding mode study showed that the thiol group of the peptide receptor plays a critical role in potent binding with Cu(+) and the sulfonamide and amide groups of the probe might cooperate to form a complex with Cu(+). Dns-LLC detected Cu(+) selectively by a turn-on response among various biologically relevant metal ions, including Cu(2+) and Zn(2+). The selectivity of the peptide-based probe for Cu(+) was strongly dependent on the position of the cysteine residue in the peptide receptor part. The fluorescent peptide-based probe penetrated the living RKO cells and successfully detected Cu(+) in the Golgi apparatus in live cells by a turn-on response. Given the growing interest in imaging Cu(+) in live cells, a novel peptide receptor of Cu(+) will offer the potential for developing a variety of fluorescent probes for Cu(+) in the field of copper biochemistry.

Selective and Sensitive Detection of Heavy Metal Ions in 100% Aqueous Solution and Cells with a Fluorescence Chemosensor Based on Peptide Using Aggregation-Induced Emission

A fluorescent peptidyl chemosensor for the detection of heavy metal ions in aqueous solution as well as in cells was synthesized on the basis of the peptide receptor for the metal ions using an aggregation-induced emission fluorophore. The peptidyl chemosensor (1) bearing tetraphenylethylene fluorophore showed an exclusively selective turn-on response to Hg(2+) among 16 metal ions in aqueous buffered solution containing NaCl. The peptidyl chemosensor complexed Hg(2+) ions and then aggregated in aqueous buffered solution, resulting in the significant enhancement (OFF-On) of emissions at around 470 nm. The fluorescent sensor showed a highly sensitive response to Hg(2+), and about 1.0 equiv of Hg(2+) was enough for the saturation of the emission intensity change. The detection limit (5.3 nM, R(2) = 0.99) of 1 for Hg(2+) ions was lower than the maximum allowable level of Hg(2+) in drinking water by EPA. Moreover, the peptidyl chemosensor penetrated live cells and detected intracellular Hg(2+) ions by the turn-on response.

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.

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.

Pyrene Excimer-Based Peptidyl Chemosensors for the Sensitive Detection of Low Levels of Heparin in 100% Aqueous Solutions and Serum Samples

Fluorescent chemosensors (1 and 2, Py-(Arg)nGlyGlyGly(Arg)nLys(Py)-NH2, n = 2 and 3) bearing two pyrene (Py) labeled heparin-binding peptides were synthesized for the sensitive ratiometric detection of heparin. The peptidyl chemosensors (1 and 2) sensitively detected nanomolar concentrations of heparin in aqueous solutions and in serum samples via a ratiometric response. In 100% aqueous solutions at pH 7.4, both chemosensors exhibited significant excimer emission at 486 nm as well as weak monomer emission in the absence of heparin. Upon the addition of heparin into the solution, excimer emission increased with a blue shift (10 nm) and monomer emission at 376 nm decreased. The chemosensors showed a similar sensitive ratiometric response to heparin independent of the concentration of the chemosensors. The peptidyl chemosensors were applied to the ratiometric detection of heparin over a wide range of pH (1.5-11.5) using the excimer/momomer emission changes. In the presence of serum, 1 and 2 displayed significant monomer emission at 376 nm with relatively weak excimer emission and the addition of heparin induced a significant increase in excimer emission at 480 nm and a concomitant decrease in monomer emission. The enhanced ratiometric response to heparin in the serum sample was due to the interactions between the peptidyl chemosensors and serum albumin in the serum sample. The detection limits of 2 for heparin were less than 1 nM in 100% aqueous solutions and serum samples. The peptidyl chemosensors bearing two heparin-binding sites are a suitable tool for the sensitive ratiometric detection of nanomolar concentrations of heparin in 100% aqueous solutions and serum samples.

Peptide-based biosensors

Peptides have been used as components in biological analysis and fabrication of novel biosensors for a number of reasons, including mature synthesis protocols, diverse structures and as highly selective substrates for enzymes. Bio-conjugation strategies can provide an efficient way to convert interaction information between peptides and analytes into a measurable signal, which can be used for fabrication of novel peptide-based biosensors. Many sensitive fluorophores can respond rapidly to environmental changes and stimuli manifest as a change in spectral characteristics, hence environmentally-sensitive fluorophores have been widely used as signal markers to conjugate to peptides to construct peptide-based molecular sensors. Additionally, nanoparticles, fluorescent polymers, graphene and near infrared dyes are also used as peptide-conjugated signal markers. On the other hand, peptides may play a generalist role in peptide-based biosensors. Peptides have been utilized as bio-recognition elements to bind various analytes including proteins, nucleic acid, bacteria, metal ions, enzymes and antibodies in biosensors. The selectivity of peptides as an enzymatic substrate has thus been utilized to construct enzyme sensors or enzyme-activity sensors. In addition, progress on immobilization and microarray techniques of peptides has facilitated the progress and commercial application of chip-based peptide biosensors in clinical diagnosis.

Selective fluorescence sensing of salicylic acids using a simple pyrenesulfonamide receptor

The highest change in relative intensity of probe 3 among the probes 2–5 with 3,5-DNSA demonstrated the significance of sulfonamide N–H and imidazole C2–H with the highest association constant and complete quenching.

N-Unsubstituted-1,2,3-triazole-tethered, AIEE type conjugated polymer as a ratiometric fluorescence probe for silver ions

Selective fluorescence ratiometric detection of Ag⁺ was achieved by a N-unsubstituted-1,2,3-triazole decorated, aggregation-induced emission enhancement (AIEE) type conjugated polymer.

Highly selective colorimetric and fluorescent detection for Hg2+ in aqueous solutions using a dipeptide-based chemosensor

A dipeptide-based chemosensor selectively and sensitively detected Hg^II in aqueous solutions by colorimetric change and fluorescent change.

A novel peptide-based fluorescent chemosensor for measuring zinc ions using different excitation wavelengths and application in live cell imaging

A novel peptide-based fluorescent chemosensor containing both tryptophan and a dansyl fluorophore has been designed to detect Zn²⁺ in 100% aqueous solution and living cells via two pathways including fluorescence resonance energy transfer and chelation enhanced fluorescence.