A highly sensitive and selective fluorescent "on-off-on" peptide-based probe for sequential detection of Hg2+ and S2- ions: Applications in living cells and zebrafish imaging

Mercury ions (Hg2+) and sulfur ions (S2-), have caused serious harm to the ecological environment and human health as two kinds of highly toxic pollutants widely used. Therefore, the visual quantitative determination of Hg2+ and S2- is of great significance in the field of environmental monitoring and medical therapy. In this study, a novel fluorescent "on-off-on" peptide-based probe DNC was designed and synthesized using dipeptide (Asn-Cys-NH2) as the raw material via solid phase peptide synthesis (SPPS) technology with Fmoc chemistry. DNC displayed high selectivity in the recognition of Hg2+, and formed non-fluorescence complex (DNC-Hg2+) through 2:1 binding mode. Notably, DNC-Hg2+ complex generated in situ was used as relay response probe for highly selective sequential detection of S2- through reversible formation-separation. DNC achieved highly sensitive detection of Hg2+ and S2- with the detection limits (LODs) of 8.4 nM and 5.5 nM, respectively. Meanwhile, DNC demonstrated feasibility for Hg2+ and S2- detections in two water samples, and the considerable recovery rate was obtained. More importantly, DNC showed excellent water solubility and low toxicity, and was successfully used for consecutive discerning Hg2+ and S2- in test strips, living cells and zebrafish larvae. As an effective visual analysis method in the field, smartphone RGB Color Picker APP realized semi-quantitative detections of Hg2+ and S2- without the need for complicated device.

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.

A novel ratiometric peptide-based fluorescent probe for sequential detection of Hg2+ and S2- ions and its application in living cells and zebrafish imaging

A new ratiometric peptide-based fluorescent probe DWPH was designed and synthesized, comprising dansyl fluorophore as a fluorescent dye, and tripeptide backbone (Trp-Pro-His-NH2) as a recognition group. The addition of Hg2+ caused the maximum emission peak of DWPH to blue shift from 560 nm to 510 nm. DWPH exhibited large Stokes shift (230 nm), satisfactory water solubility (100 % aqueous medium), good selectivity (only Hg2+), high sensitivity (24.6 nM), rapid response (within 50 s) and strong anti-interference ability for Hg2+ detection over a wide pH range (7-11). Additionally, the complex DWPH-Hg2+ as a relay response probe could also be applied to S2- according to displacement approach. Notably, the detection limit for S2- was calculated as 23.3 nM, exhibiting that DWPH showed great potential for environmental monitoring and bioimaging. In addition, DWPH were successfully used to determine Hg2+ and S2- in living cells and zebrafish based on excellent permeability and low cytotoxicity. What's more, the gradient concentration color changes of Hg2+ and S2- were combined with the smartphone APP to obtain red-green-blue (RGB) values, thus enabling rapid semi-quantitative detection of Hg2+ and S2- without expensive instruments.

Simultaneous detection of mercury and cadmium ions: A colorimetric method in aqueous media

Hg and Cd are the two most toxic heavy metal ions that could be found in aqueous solutions. In this study, a chemosensor based on 5-(4-((4-nitrophenyl) diazenyl) phenyl)-1,3,4-oxadiazole-2-thiol (DOT) was reported to detect these ions simultaneously. DOT showed high selectivity towards Hg ion by changing the color of the solution from beige to gold-yellow at different concentrations of Hg ion. In comparison, other relevant metals, such as Li+, Na+, K+, Cs+, Mg2+, Ca2+, Al3+, Fe2+, Ag+, Cu2+, Pb2+, Ni2+, Zn2+, Cr3+, Fe3+, Pb4+, Mn2+, and Cd2+ did not affect the color of the DOT solution as the interfering ions. Despite no changes in the color of DOT solution in the presence of Cd ion, a solution containing DOT-Hg complex was changed from gold-yellow to orange by adding Cd ion, providing an approach for detecting Hg and Cd ion simultaneously with UV-Vis and Fluorescent spectroscopy. DOT exhibited a high association constant with a detection limit of 0.05 μM for Hg and Cd ions in an aqueous solution. The results of quantum mechanics (QM) calculations were also consistent with the experimental observations, which indicated that changes in the band gap could explain the various colors of DOT complex with metal ions.

Cyanine-based fluorescent indicator for mercury ion and bioimaging application in living cells

A commercial cyanine dye IR-780 and a thioether-containing dicarboxylic acid ligand were used to construct the near-infrared fluorescent probe, which was used as a near-infrared fluorescent indicator for the determination of mercury ions in water and in living cells. This indicator displayed high specificity towards Hg²⁺ without any interference from other detecting species. Especially, the emission at 790 nm dramatically increased more than 25 times after interacting with Hg²⁺. The binding experiment showed that the indicator formed 1:1 complex with Hg²⁺. More, this indicator could be applied in the visualization of Hg²⁺ in living cells and measuring the Hg²⁺ concentration of tap-water sample.

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 vitro and in vivo studies of a chlorin-based carbon nanocarrier with photodynamic therapy features

Carbonaceous materials have long been developed to utilize "nano-spaces" and numerous guest species could be encapsulated. A remarkable fluorescence difference has been observed after newly designed pyropheophorbide-a-appended carbon nanohorns were incorporated in a cellular medium and confocal microscopy was employed for the determination of the intracellular localization. Our study supported the role of carbon nanohorns as carriers of photodynamic therapy (PDT) agents and their heating behavior was discussed. We have developed a theranostic platform based on photosensitizer-conjugated carbon nanostructures and this system has been applied in an animal model. In addition, a negligible toxicity of CNH-Pyro was found in body weight experiments and histopathological examination of the major organs.

Rhodamine–benzothiazole conjugate as an efficient multimodal sensor for Hg2+ ions and its application to imaging in living cells

A rhodamine B dye bearing a benzothiazole conjugate is designed and synthesized, it shows a highly selective and sensitive naked-eye color change and turn-on fluorescence response to Hg²⁺ ions.

Raposo MM, Costa SPG. Heterocyclic amino acids as fluorescent reporters for transition metals: synthesis and evaluation of novel furyl-benzoxazol-5-yl-l-alanines

Novel benzoxazol-5-yl-l-alanines with heterocyclic pendants were synthesized and investigated as fluorescent reporters for metal cations through spectrofluorimetric titrations.

A dual-mode turn-on fluorescent BODIPY-based probe for visualization of mercury ions in living cells

A novel turn-on fluorescent 8-amino BODIPY-based probe carrying a thiourea unit as the mercury ion recognition unit has been developed. Due to the cascade reaction processes, consecutive color changes reflecting the electronic absorption and emission responses were observed upon addition of increased concentrations of mercury(ii) ions. The likely sensing mechanism was proposed as mercury ion-promoted cyclization and subsequent hydrolysis. The probe displayed a selective response to mercury ions over other metal ions. Additionally, experiments with living Human Hepatoma SMMC-7721 cells to visualize intracellular mercury ions in biological systems were carried out with the probe.

NBD-based fluorescent chemosensor for the selective quantification of copper and sulfide in an aqueous solution and living cells

A fluorescent chemosensor (NL) has been developed for the selective quantification of copper and sulfide in aqueous solutions and living cells.