A simple method for phosphate (Pi) detection is established by developing an off-on fluorescence probe of europium-adjusted carbon dots (CDs), which has been successfully applied to the detection of Pi in very complicated matrixes such as artificial wetlands system.

It is known that localized surface plasmon resonance (LSPR) is responsible for the surface-enhanced spectroscopic processes of metallic nanoparticles and thus LSPR spectroscopy has become a powerful technique for chemical and biological purposes. In this contribution, we present a simple homogeneous Hg2+ assay by measuring enhanced LSPR scattering signals resulted from Hg(2+)-DNA complex induced aggregation of gold nanoparticles (AuNPs). In a medium of pH 7.4 tris-HCl buffer containing 0.05 M NaCl, single-stranded oligonucletides with the sequence of 5'-d(T6)-3' (poly-T6 ssDNA), can be selectively adsorbed onto the surface of gold colloids, stabilizing the AuNPs against aggregation. If Hg(2+)-DNA complex via Hg(2+)-mediated thymine-Hg(2+)-thymine (T-Hg(2+)-T) is formed, however, the adsorption of poly-T6 ssDNA onto the surface of gold colloids gets reduced, and then aggregation of the AuNPs occurs owing to the decrease of the electrostatic repulsion between AuNPs. Consequently, strong LSPR scattering signals resulting from the aggregates of AuNPs could be visually observed under a dark field microscope and easily be measured with a common spectrofluorometer. The LSPR scattering intensities characterized at 556.0 nm were found to be proportional to the concentration of Hg2+ ions in the range of 4.0 x 10(-8) to 6.0 x 10(-7) M with the limit of determination (3sigma) of 1.0 nM. Compared with reported colorimetric methods, our present approaches display the advantages of higher sensitivity.

A comparative reaserch of the assembly of different porphyrin molecules on graphene oxide (GO) and reduced graphene oxide (RGO) was carried out, respectively. Despite the cationic porphyrin molecules can be assembled onto the surfaces of graphene sheets, including GO and RGO, to form complexes through electrostatic and π-π stacking interactions, the more obvious fluorescence quenching and the larger red-shift of the Soret band of porphyrin molecule in RGO-bound states were observed than those in GO-bound states, due to the differenc of molecular flattening in degree. Further, more interesting finding was that the complexes formed between cationic porphyrin and GO, rather than RGO sheets, can facilitate the incorporation of iron (III) ions into the porphyrin moieties, due to the presence of the oxygen-contained groups at the basal plane of GO sheets served as auxiliary coordination units, which can high-efficiently obstruct the electron transfer from excited porphyrin to GO sheets and result in the occurrence of fluorescence restoration. Thus, a fluorescence sensing platform has been developed for iron (III) ions detection in this contribution by using the porphyrin/GO nanohybrids as an optical probe, and our present one exhibited rapid and sensitive responses and high selectivity toward iron (III) ions.

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Water-soluble fluorescent silver nanoclusters (AgNCs) with almost seven and nine silver atoms and a quantum yield (QY) of 5.38 ± 0.25% were successfully prepared via one-pot hydrothermal synthesis using polymethacrylic acid sodium salt (PMAA-Na) as a template. The as-prepared PMAA-AgNCs displayed a mono-distribution, they were uniform in size and the color of the fluorescence, emitting at 579 nm, was orange when excited at 502 nm. What is more, we found that the as-prepared PMAA-AgNCs could be quenched by sulfides based on the formation of a metal-ligand bond Ag-S, and thus sulfides could be sensitively detected by spectrofluorometry. As proof of concept, thiourea (TU) and other sulfides including cysteine (Cys), glutathione (GSH) and dl-methionine could be detected. For example, the color of the orange fluorescent AgNCs solutions darkened upon the addition of TU and the fluorescence of PMAA-AgNCs was quenched. The detection limit for TU was 6.10 μM in the linear range from 8.57 μM to 2.29 mM.