Sensitive and selective colorimetric detection of Cu(2+) in aqueous medium via aggregation of thiomalic acid functionalized Ag nanoparticles.

A simple and effective colorimetric method for determination of Cu(2+) in real samples was developed. In this method, thiomalic acid functionalized silver nanoparticles (TMA-AgNPs) were prepared and changes in solution color, induced by the aggregation of TMA-AgNPs in the presence of Cu(2+), were employed for quantitative analysis. The surface plasmon resonance (SPR) band of our synthesized TMA-AgNPs was located at 392 nm and shifted to a longer wavelength after aggregation due to the interactions between carboxylate and Cu(2+). A band intensity ratio of A455/(A392-A455) was constructed and used to correlate with the concentration of Cu(2+). A linear relationship was found with a linear response up to 50 nM of Cu(2+). Due to the formation of a stable carboxylate Cu(2+) complex, highly sensitive detection of Cu(2+) was achieved with the estimated detection limit approaching 1 nM. Moreover, the formation of the stable complex leads to high selectivity in the detection of Cu(2+), which was verified by examination of 12 other metal ions. In the detection of Cu(2+) in real samples, results indicated that our proposed method is simple, sensitive and selective for application in such measurements.

A highly selective ratiometric fluorescent chemosensor for Cu(ii) based on dansyl-functionalized thiol stabilized silver nanoparticles.

A fluorescent chemosensor for Cu2+ ions based on dansyl-functionalized thiol stabilized silver nanoparticles containing 2-aminothiophenyl units as the Cu2+ binding sites is developed. A decrease in fluorescence at 497 nm and an increase in fluorescence at 410 nm with an isoemissive point at 445 nm upon the addition of Cu2+ ions is attributed to the formation of a Cu2+ complex in aqueous acetonitrile based on an energy transfer mechanism. This sensor has excellent sensitivity and selectivity over other metal ions and has a detection limit as low as 5.0 × 10-10 mol L-1.

An acyclic, dansyl based colorimetric and fluorescent chemosensor for Hg(II) via twisted intramolecular charge transfer (TICT).

An efficient fluorescent chemosensor for Hg(2+) ion, based on 5-(dimethylamino)-N-(2-mercaptophenyl)naphthalene-1-sulfonamide, has been developed. It exhibits Hg(2+)-selective on-off fluorescence quenching behavior via twisted intramolecular charge transfer (TICT) mechanism, which is rationalized by time dependent density functional theory (TD-DFT) calculations. The system exhibits visible color change from colorless to gray upon Hg(2+) binding with very high selectivity and sensitivity (as low as 5.0×10(-10)molL(-1)) over other metal ions such as K(+), Na(+), Ag(+), Mn(2+), Ca(2+), Ba(2+), Fe(2+), Zn(2+), Pb(2+), Cu(2+), Sn(2+), Cd(2+), Ni(2+) and Co(2+). The present sensing system is also successfully applied for the detection of Hg(2+) ion in real samples.

An intramolecular charge transfer (ICT) based chemosensor for silver ion using 4-methoxy-N-((thiophen-2-yl)methyl)benzenamine.

4-Methoxy-N-((thiophen-2-yl)methyl)benzenamine was found to be a highly selective chemosensor for Ag(+) ion in methanol-water (1 : 1 v/v) mixture over other metal ions such as Na(+), K(+), Li(+), Cu(+), Ba(2+), Cd(2+), Co(2+), Cu(2+), Fe(2+), Hg(2+), Mn(2+), Ni(2+), Pb(2+) and Zn(2+) with a limit of detection (LOD) is 5.0 × 10(-6) mol L(-1). Upon binding to Ag(+) ion, a strong fluorescent enhancement is observed which is attributed to an increase in intramolecular charge transfer (ICT). The proposed mechanism is strongly supported by TD-DFT calculations.

Autofluorescence in BrdU-positive cells and augmentation of regeneration kinetics by riboflavin.

The earthworm, Eudrilus eugeniae, has a prodigious ability to regenerate lost segments. The skin of the worm has an outermost epidermal layer followed by a thick circular muscle layer and an innermost thin longitudinal cell layer. During the process of regeneration, the circular muscle layer decreased in thickness, and longitudinal cell layer increased. The histological analysis of the regenerated worm shows that the longitudinal cell layer forms the regeneration blastema. BrdU-labeling retention assay confirmed that the circular muscle and longitudinal cell layers have BrdU-positive cells, which migrate from the adjacent segments to the regeneration blastema. In addition, it was noted that the cells of the earthworm, E. eugeniae, have the property of autofluorescence. Autofluorescence was found in the cytoplasm, but not in the nucleus. It has been also found that the major source for autofluorescence is riboflavin. Further, it was also demonstrated that supplementation with riboflavin increases the rate of regeneration, while regeneration was hampered by reduced levels of riboflavin. The importance of riboflavin in regeneration was also confirmed by rescue assay. In addition, it was also identified that BrdU-positive cells are highly fluorescent compared to the surrounding cells.

Alginate stabilized silver nanocube-Rh6G composite as a highly selective mercury sensor in aqueous solution.

Alginate-stabilized silver nanocubes are synthesized via a reduction method and are characterized by UV-Vis and fluorescence spectroscopies, SEM, AFM and HRTEM analyses. A silver nanocubes (Ag NCbs) based sensor for detecting Hg2+ ions in aqueous solution has been developed using Rh6G as an external spectroscopic probe. Using this system, Hg2+ ions (as low as 1×10(-10) mol L(-1)) are recognized in aqueous media via a colorimetric method with very high selectivity and sensitivity over other metal ions namely Fe2+, Zn2+, Pb2+, Cu2+, Sn2+, Cd2+, Ni2+, and Co2+.