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.

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

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

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. In the present study, we synthesized a fluorescent probe (1) based on an unnatural peptide receptor containing sulfonamide groups with an aggregation-induced emission and twisted internal charge transfer (TICT)-active fluorophore, cyanostilbene. 1 exhibited a highly selective ratiometric response to Hg2+ among 14 metal ions tested by ratiometric red-emission at 600 nm, with a clear isoemissive point in purely aqueous solution containing 1% DMSO. The ratiometric response for Hg2+ ions was complete within 3 min and the ratiometric responses induced by Hg2+ ions did not suffer considerable interference from the other metal ions. The ratiometric response was complete for less than 7 µM Hg2+ and 1 had a potent binding affinity (7.42 × 10-6 M, R2 = 0.98) for Hg2+ and a nanomolar detection limit. 1 detected Hg2+ ions by ratiometric responses in aqueous buffered solutions over a wide range of pH (5.5-11.5). Binding mode studies using TEM, NMR, IR, and a mass spectrometer revealed that the sulfonamide groups of the unnatural peptide receptor played an important role in the complexation of Hg2+ and in the complexation-induced nano-sized aggregates, which resulted in a significant increase in emissions at 600 nm and a decrease in emissions at 535 nm. 1 quantified micro-molar concentrations (0-6 µM) of Hg2+ in tap water and groundwater by ratiometric detection. Furthermore, 1 passed through the lipid membranes of live cells and detected intracellular Hg2+ ions at 2 µM by a ratiometric red-emission change.

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

Indium is one of the most widely used scarce metals for manufacturing various electronic devices including notebooks, mobile phones, and PC monitors. Recent studies revealed that indium and its compound could cause several toxicities to human beings and animals. However, there is no report about ratiometric fluorescent detection of In(III) in aqueous solutions. We synthesized a fluorescent probe (1) for In(III) based on a phosphoserine as a receptor with a pyrene fluorophore using solid phase synthesis. 1 showed highly sensitive ratiometric response to In(III) in purely aqueous solutions by increasing excimer emission intensity at 476 nm with a concomitant decrease in monomer emission intensity at 395 nm. 1 showed sensitive ratiometric responses to In(III) over a wide range of pH (2 < pH < 8) and exhibited a highly selective ratiometric response to In(III) among 18 tested metal including Al(III) and Ga(III). Job's plot analysis indicated that 1 preferred to form a 2:1 complex with In(III) and the binding affinity for In(III) was measured to be 2.3 × 1012 M-2 ( R2 = 0.989). 1 showed linear ratiometric responses to nanomolar concentrations (0-750 nM) of In(III) and the detection limit was calculated to be 64 nM ( R2 = 0.992) in aqueous solution. The binding mode study using NMR, IR, and CD spectroscopies revealed that the phosphate and the amide groups of the receptor of 1 played an important role for the binding with In(III). Moreover, 1 was suitable for the ratiometric detection of In(III) in tap water and groundwater. 1 showed much better detection properties than those of the colorimetric methods using EDTA with Eriochrome black T (EBT) and 4-(2-pyridylazo) resorcinol (PAR) for the detection of In(III) in tap water and groundwater.

Ratiometric red-emission fluorescence detection of Al3+ in pure aqueous solution and live cells by a fluorescent peptidyl probe using aggregation-induced emission.

The development of a fluorescence method for the selective ratiometric detection of Al3+ ions in pure aqueous solutions and live cells is still a significant challenge. In the present study, we synthesized a new type of fluorescent probe using an Al3+-triggered self-assembly based on the dipeptide receptor and an aggregation-induced emission fluorophore. The fluorescent probe (1) bearing cyanostilbene with excitation by visible light detected Al3+ ions sensitively in pure aqueous buffered solution by ratiometric red-emission at 600 nm. 1 provided a highly selective ratiometric detection of Al3+ among 16 metal ions in aqueous solution. 1 exhibited sensitive ratiometric response to Al3+ in aqueous buffered solutions at pH ranging from 5 to 7.4. The detection limit (145 nM, R2 = 0.999) for Al3+ ions in pure aqueous solution was much lower than the maximum allowable level of Al3+ in drinking water demanded by the Environmental Protection Agency (EPA). The probe provided an efficient approach to detect low concentrations of Al3+ in ground water, tap water, and live cells by ratiometric red-emissions at 600 nm. The binding study using dynamic light scattering, NMR, IR, and TEM revealed that the complex between 1 and Al3+ self-assembled to form nanoparticles, resulting in the enhancement of the emission at 600 nm and a concomitant decrease in the emission at 535 nm.

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.

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.

Ethyl pyruvate inhibits HMGB1 phosphorylation and release by chelating calcium.

Ethyl pyruvate (EP), a simple aliphatic ester of pyruvic acid, has been shown to have antiinflammatory effects and to confer protective effects in various pathological conditions. Recently, a number of studies have reported EP inhibits high mobility group box 1 (HMGB1) secretion and suggest this might contribute to its antiinflammatory effect. Since EP is used in a calcium-containing balanced salt solution (Ringer solution), we wondered if EP directly chelates Ca(2+) and if it is related to the EP-mediated suppression of HMGB1 release. Calcium imaging assays revealed that EP significantly and dose-dependently suppressed high K(+)-induced transient [Ca(2+)]i surges in primary cortical neurons and, similarly, fluorometric assays showed that EP directly scavenges Ca(2+) as the peak of fluorescence emission intensities of Mag-Fura-2 (a low-affinity Ca(2+) indicator) was shifted in the presence of EP at concentrations of ≥7 mmol/L. Furthermore, EP markedly suppressed the A23187-induced intracellular Ca(2+) surge in BV2 cells and, under this condition, A23187-induced activations of Ca(2+)-mediated kinases (protein kinase Cα and calcium/calmodulin-dependent protein kinase IV), HMGB1 phosphorylation and subsequent secretion of HMGB1 also were suppressed. (A23187 is a calcium ionophore and BV2 cells are a microglia cell line.) Moreover, the above-mentioned EP-mediated effects were obtained independent of cell death or survival, which suggests that they are direct effects of EP. Together, these results indicate that EP directly chelates Ca(2+), and that it is, at least in part, responsible for the suppression of HMGB1 release by EP.

Efficient ensemble system based on the copper binding motif for highly sensitive and selective detection of cyanide ions in 100% aqueous solutions by fluorescent and colorimetric changes.

A peptide-based ensemble for the detection of cyanide ions in 100% aqueous solutions was designed on the basis of the copper binding motif. 7-Nitro-2,1,3-benzoxadiazole-labeled tripeptide (NBD-SSH, NBD-SerSerHis) formed the ensemble with Cu(2+), leading to a change in the color of the solution from yellow to orange and a complete decrease of fluorescence emission. The ensemble (NBD-SSH-Cu(2+)) sensitively and selectively detected a low concentration of cyanide ions in 100% aqueous solutions by a colorimetric change as well as a fluorescent change. The addition of cyanide ions instantly removed Cu(2+) from the ensemble (NBD-SSH-Cu(2+)) in 100% aqueous solutions, resulting in a color change of the solution from orange to yellow and a "turn-on" fluorescent response. The detection limits for cyanide ions were lower than the maximum allowable level of cyanide ions in drinking water set by the World Health Organization. The peptide-based ensemble system is expected to be a potential and practical way for the detection of submicromolar concentrations of cyanide ions in 100% aqueous solutions.

Highly sensitive colorimetric detection of Hg(II) and Cu(II) in aqueous solutions: from amino acids toward solid platforms.

A chemosensor (NBD-H) based on an amino acid with 7-nitro-2,1,3-benzoxadiazole was used for selective detection of Hg(II) and Cu(II) among 15 metal ions in aqueous solutions by a colorimetric change. NBD-H sensitively differentiated Hg(II) and Cu(II) in aqueous solutions by a color change; a pink color for Hg(II) and an orange color for Cu(II). NBD-H showed nanomolar detection limits for Hg(II) (176 nM, R2 = 0.996) and Cu(II) (163 nM, R2 = 0.996). The detection limit for Cu(II) was much lower than the maximum allowable level of Cu(II) in drinking water recommended by the U.S. EPA. The binding mode study showed that deprotonation of the NH group of NBD-H played a critical role in the binding and sensing of metal ions. NBD-H immobilized on PEG-PS resin maintained the potent binding affinity and sensing ability for the metal ions. The resin with NBD-H was recyclable for the detection of metal ions in 100% aqueous solutions.

Stimuli-responsive conformational conversion of peptide gatekeepers for controlled release of guests from mesoporous silica nanocontainers.

The use of peptides as gatekeepers for payloads of mesoporous silica nanoparticles would allow triggering the release of guests by various biological stimuli. We investigated the effect of peptide conformation on their gatekeeping capability by employing two model peptides with a turn or a random structure. The conformation-dependent gatekeeping properties provided an opportunity to utilize the conformational conversion of peptides as a valuable motif for stimuli-responsive gatekeepers. Based on that investigation, we demonstrated that Fmoc-CGGC-SS-Si, which exhibited a zero-release property without any stimuli due to a turn-like conformation induced by the intramolecular disulfide bond, can be triggered to release guests by converting its conformation to a random structure, induced by reduction of the disulfide bond upon addition of glutathione. We further demonstrated that the conformational conversion of Fmoc-CGGC by Zn(II) ion can also be utilized as a triggering motif.

Ratiometric detection of nanomolar concentrations of heparin in serum and plasma samples using a fluorescent chemosensor based on peptides.

A peptidyl fluorescent chemosensor for heparin was synthesized by conjugating a pyrene fluorophore with the heparin-binding peptide. The fluorescent chemosensor (Py12; pyrene-RKRLQVQLSIRT) showed a highly sensitive ratiometric response to nanomolar concentrations of heparin in aqueous solutions at physiological pH by increasing excimer emission intensity at 500 nm with a concomitant decrease in monomer emission intensity at 400 nm. Py12 showed a sensitive ratiometric response to heparin over a wide pH range (1.5 ≤ pH ≤ 11.5) and exhibited high selectivity for heparin compared to other biological competitors, such as hyaluronic acid and chondroitin sulfate. Py12 sensitively and ratiometrically detected nanomolar concentrations of heparin in biologically relevant samples containing human serum and human plasma, respectively. The detection limit of Py12 was 34 pM (R(2) = 0.997) for heparin in an aqueous buffer solutions containing 5% human serum and 33 pM (R(2) = 0.994) for heparin in aqueous buffer solutions containing 5% human plasma. Py12 had sufficient sensitivity and selectivity for ratiometrically detecting a nanomolar concentration of heparin, indicating that the peptide-base chemosensor provides a potential tool for monitoring heparin levels in clinical plasma samples.

Ratiometric fluorescence chemosensor based on tyrosine derivatives for monitoring mercury ions in aqueous solutions.

Ratiometric fluorescent chemosensors 1 and 2 were synthesized based on tyrosine amino acid derivatives with a pyrene fluorophore. 1 and 2 showed high selectivity for Hg(II) ions among 13 metal ions in aqueous solutions. Both 1 and 2 sensitively detected Hg(II) ions in aqueous solutions by ratiometric response without interference of any of the other tested metal ions including Cu(II), Cd(II), Pb(II), and Ag(I) ions. 1 and 2 had tight binding affinities (5.72 × 10(13) M(−2), 1.15 × 10(13) M(−2)) for Hg(II) with nano-molar detection limits. The binding mode was characterized with the help of organic spectroscopic data, which revealed that the methoxyphenyl moieties of 1 and 2 played a vital role in the coordination of Hg(II). The deprotonation of the sulfonamide group is not a critical process for the binding of mercury ions. The methoxyphenyl moiety, sulfonamide group, and the C-terminal amide moiety of 1 and 2 as ligands for Hg(II) played crucial roles in the stabilization of the 2:1 complexes.

A ratiometric fluorescent detection of Zn(II) in aqueous solutions using pyrene-appended histidine.

A fluorescent chemosensor, Py-His, based on histidine was easily synthesized in solid phase synthesis. Py-His displayed a highly sensitive ratiometric response to Zn(II) with potent binding affinity (Ka = 1.17 × 10(13)M(-2)) in aqueous solutions. The detection limit of Py-His for Zn(II) was calculated as 80.8 nM. Moreover, Py-His distinguished Zn(II) and Hg(II) by different ratiometric response type; the chemosensor showed a more enhanced increase of excimer emission intensity to Zn(II) than Hg(II). Upon addition of Ag(I) and Cu(II), Py-His showed a turn-off response mainly due to the quenching effect of these metal ions. The binding stoichiometry (2:1 or 1:1) of Py-His to target metal ions played a critical role in the fluorescent response type (ratiometric and turn off response) to target metal ions. The role of imidazole group of Py-His for ratiometric detection of Zn(II) was proposed by pH titration experiments.

A new peptidyl fluorescent chemosensors for the selective detection of mercury ions based on tetrapeptide.

A novel peptidyl chemosensor (PySO2-His-Gly-Gly-Lys(PySO2)-NH2, 1) was synthesized by incorporation of two pyrene (Py) fluorophores into the tetrapeptide using sulfonamide group. Compound 1 exhibited selective fluorescence response towards Hg(II) over the other metal ions in aqueous buffered solutions. Furthermore, 1 with the potent binding affinity (Kd=120 nM) for Hg(II) detected Hg(II) without interference of other metal ions such as Ag(I), Cu(II), Cd(II), and Pb(II). The binding mode of 1 with Hg(II) was investigated by UV absorbance spectroscopy, (1)H NMR titration experiment, and pH titration experiment. The addition of Hg(II) induced a significant decrease in both excimer and monomer emissions of the pyrene fluorescence. Hg(II) interacted with the sulfonamide groups and the imidazole group of His in the peptidyl chemosensor and then two pyrene fluorophores were close to each other in the peptide. The decrease of both excimer and monomer emission was mainly due to the excimer/monomer emission change by dimerization of two pyrene fluorophores and a quenching effect of Hg(II).

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 (Kd = 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 âˆ¼ 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.

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.

Development of peptide-based ratiometric fluorescent probe for sensing heparan sulfate and heparin in aqueous solutions at physiological pH and quantitative detection of heparan sulfate in live cells.

Heparan sulfate (HS) plays a critical role in various biological processes as a vital component of the extracellular matrix. In this study, we synthesized three fluorescent probes (1-3) comprising Arg-rich peptides as HS receptors and a fluorophore capable of exhibiting red-shifted emissions upon aggregation. All three probes demonstrated ratiometric responses to HS and heparin in aqueous solutions. Remarkably, probe 3 exhibited a unique ratiometric response to HS in both aqueous solutions at physiological pH and HS proteoglycans on live cells. Probe 3 displayed exceptional sensing properties, including high biocompatibility, water solubility, visible light excitation, a large Stokes shift for ratiometric detection and remarkable selectivity and sensitivity for HS (with a low limit of detection: 720 pM). Binding mode studies unveiled the crucial role of charge interactions between probe 3 and negatively charged HS sugar units. Upon binding, the fluorophore segments of the probes overlapped, inducing green and red emission changes through restricted intramolecular rotation of the fluorophore moiety. Importantly, probe 3 was effectively employed to quantify the reduction of HS proteoglycan levels in live cells by inhibiting HS sulfation using siRNA and an inhibitor. It successfully detected decreased HS levels in cells treated with doxorubicin and irradiation, consistent with results obtained from western blot and immunofluorescence assays. This study presents the first ratiometric fluorescent probe capable of quantitatively detecting HS levels in aqueous solutions and live cells. The unique properties of peptide-based probe 3 make it a valuable tool for studying HS biology and potentially for diagnostic applications in various biological systems.

Fluorescent dendron-cyclodextrin nanotubes with surface peptide spacer as a recyclable sensory platform.

Nanotube sensory platform: Dendron-cyclodextrin nanotubes with a surface coumarin unit attached by a GH dipeptide spacer were constructed by a combination of molecular recognition and self-assembly. These unique fluorescent nanotubes can serve as a recyclable metal ion sensory platform with high selectivity and sensitivity (see scheme).

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 (λex = 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).