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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.

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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.

Synthesis of a novel pyrene derivative sensor (Py-Met) based on amino acid and its fluorescent behavior for Hg(II) in water was investigated. Upon Hg(II) binding, the Py-Met-bearing sulfonamide group exhibited a considerable excimer emission at 480 nm along with a decrease of monomer emission at 383 nm. Py-Met allows a selective and sensitive ratiometric detection of Hg(II) without any interference from other metal ions.

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.

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