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

This communication presents a fluorescent chemosensor for detecting Pb(II) and Hg(II) in aqueous solutions. The sensor showed a turn-on response to Pb(II) by an enhancement of emission intensity at 380 nm and to Hg(II) by an enhancement of emission intensities at 380 and 475 nm. We have first characterized a unique function of tryptophan as a ligand as well as a quencher for recognition and fluorescent change by a metal binding event

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 (<b>1</b>) bearing tetraphenylethylene fluorophore showed an exclusively selective turn-on response to Hg²⁺ among 16 metal ions in aqueous buffered solution containing NaCl. The peptidyl chemosensor complexed Hg²⁺ 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 Hg²⁺, and about 1.0 equiv of Hg²⁺ was enough for the saturation of the emission intensity change. The detection limit (5.3 nM, <i>R</i>² = 0.99) of <b>1</b> for Hg²⁺ ions was lower than the maximum allowable level of Hg²⁺ in drinking water by EPA. Moreover, the peptidyl chemosensor penetrated live cells and detected intracellular Hg²⁺ ions by the turn-on response

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 (<b>Py12</b>; 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. <b>Py12</b> 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. <b>Py12</b> sensitively and ratiometrically detected nanomolar concentrations of heparin in biologically relevant samples containing human serum and human plasma, respectively. The detection limit of <b>Py12</b> was 34 pM (<i>R</i>² = 0.997) for heparin in an aqueous buffer solutions containing 5% human serum and 33 pM (<i>R</i>² = 0.994) for heparin in aqueous buffer solutions containing 5% human plasma. <b>Py12</b> 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

Highly Sensitive Ratiometric Fluorescent Chemosensor for Silver Ion and Silver Nanoparticles in Aqueous Solution

A pyrene derivative chemosensor (<b>Pyr-WH</b>) based on a dipeptide shows a highly sensitive ratiometric response to Ag(I) as well as silver nanoparticles in aqueous solution at physiological pH. <b>Pyr-WH</b> penetrated live HeLa cells and exhibits a ratiometric response to intracellular Ag(I). The binding mode of <b>Pyr-WH</b> with Ag(I) was characterized based on fluorescence changes in different pH, NMR, and ESI mass spectrometer experiments

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

Fluorescent chemosensors (<b>1</b> and <b>2</b>, Py–(Arg)_<i>n</i>GlyGlyGly­(Arg)_<i>n</i>Lys­(Py)–NH₂, <i>n</i> = 2 and 3) bearing two pyrene (Py) labeled heparin-binding peptides were synthesized for the sensitive ratiometric detection of heparin. The peptidyl chemosensors (<b>1</b> and <b>2)</b> 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, <b>1</b> and <b>2</b> 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 <b>2</b> 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