Search

A novel fluorescence “turn-on” assay for protease activity based on controlled aggregation of a tetraphenylethene probe is reported. A tetraphenylethene derivative (TPE-2+) with two positive charges is used in this study. TPE-2+ has no emission in an aqueous solution. Heparin is an anionic polymer, which can induce aggregation of TPE-2+. Strong aggregation-induced fluorescence emission (AIE) is observed. Histone is a cationic protein, it binds with heparin via electrostatic attractive interactions, which hinders the binding of TPE-2+ to heparin. TPE-2+ is released, and a decreased emission signal is detected. Upon the addition of a protease, histone is hydrolyzed into small fragments, which weakens its competitive binding to heparin. Free heparin induces aggregation of TPE-2+. A turn-on emission signal is recorded. An efficient and convenient fluorescence assay for protease activity is therefore established. [ABSTRACT FROM AUTHOR]

Bis(difluoroboron)-1,2-bis[(1H-pyrrol-2-yl)methylene]hydrazine (BOPHY) is a new class of highly fluorescent organoboron compound. The new symmetric structural motif, the unusual absorption and emission properties, and better photostability have attracted considerable attentions for the development of various functional chromophores. In the present work, a novel BOPHY derivative (BOPHY-NNBOH) for the selective sensing of Cu 2+ was synthesized. BOPHY-NNBOH shows very weak fluorescence. However, it displays significant fluorescence enhancement in the presence of Cu 2+ . The method is sensitive and selective, and sensing of Cu 2+ ions in HeLa cells is also demonstrated. To our knowledge, the present work is the first application of BOPHY derivatives in bioanalysis. [ABSTRACT FROM AUTHOR]

Polyaniline (PANI) is one of the most studied conducting polymers. It could adopt a number of chemical forms depending on the redox states of the assay solution. It was observed that the emeraldine base form of PANI could be reduced by common antioxidants (such as glutathione and ascorbic acid), which resulted in clear changes of the solution color and the UV–vis absorption spectra. In addition, it was observed that the fluorescence of CdTe quantum dots could be efficiently quenched by PANI, and the fluorescence quenching could not take place by the addition of antioxidants. The intensity of the quantum dots fluorescence could be directly related to the amount of antioxidant added to the assay solution, thus a sensitive fluorescent turn-on sensor for antioxidant was established. The detection limits for glutathione and ascorbic acid were estimated to be 50 nM and 100 nM, respectively. Our assay is simple, sensitive, and label-free, we envision it could facilitate the antioxidant sensing related applications. [ABSTRACT FROM AUTHOR]

An ultrasensitive dihydroxybenzene (DHB) quantitative detection method was developed based on the fluorescent graphene quantum dots (GQDs). In the presence of H 2 O 2 and horse radish peroxidase (HRP), DHB could be oxidized to the corresponding benzoquinone which could efficiently quench the fluorescence of GQDs. The fluorescence intensity ratio of GQDs ( I / I 0 ) was proportional to the concentration of o-dihydroxybenzene (o-DHB), m-dihydroxybenzene (m-DHB) and p-dihydroxybenzene (p-DHB) in the concentration ranges of 0.5–250, 1–120, and 0.5–90 nM, respectively. The detection limits are 2.0 × 10 −10 mol/L, 8.0 × 10 −10 mol/L and 3.0 × 10 −10 mol/L, which were much more sensitive than previous reports. In addition, the present method could be used for DHB sensing in rainwater and tap-water samples, and had a potential application for detecting various analytes which can be translated into benzoquinone in aqueous solution. [ABSTRACT FROM AUTHOR]

• A sensor array for the discrimination of metal ions and drinking waters. • Two novel functionalized fluorescent perylene probes were utilized. • The sensor array is based on perylene monomer-excimer emission transition. A new type of sensor array is developed for the highly efficient differential sensing of metal ions and drinking waters. Two functionalized fluorescent perylene probes (Pery-1 and Pery-2) were employed. These probes could interact with metal ions via electrostatic and coordinate bonding interactions. As a result, the probe monomer fluorescence was quenched, and the appearance of distinct excimer emission was observed. Depending on the metal ion used, various degrees of quenching of probe monomer fluorescence, and the generation of excimer emission were observed. For example, quenching of monomer fluorescence was observed when Cu2+ and Fe3+ ions were tested. However, quenching of monomer fluorescence and generation of excimer fluorescence were both observed when Pb2+, Zn2+ and Al3+ ions were employed. And it was also observed that Ni2+, Mn2+ and Cr3+ ions interacted differently with Pery-1 and Pery-2. These differences formed the basis of the metal ion sensor array. The sensor array was used for differentiation of eleven metal ions, and it was also capable of discrimination of metal ions at different concentrations, as well as the discrimination of metal ion mixtures. The array was further successfully used for the distinction of drinking waters, different brands of commercial mineral water, and evaluation of the quality of drinking water. We envisage that the monomer and excimer emission transition of the perylene probe could be easily adopted for efficient sensor array development for various sensing applications. [ABSTRACT FROM AUTHOR]

A facile fluorescence turn-on approach for the detection of l -ascorbic acid (AA) and alkaline phosphatase (ALP) activity was designed based on graphene quantum dots (GQDs). It is found that the fluorescence intensity of GQDs can be efficiently quenched by para-benzoquinone (BQ). And a turn-on fluorescence signal can be observed if BQ is reduced by AA. In addition, ALP can hydrolyze l -ascorbic acid-2-phosphate (AAP) to produce AA, which also results in the recovery of the GQDs fluorescence. The recovered fluorescence intensity of GQDs was proportional to the concentration of AA or ALP in the concentration ranges of 5.0 × 10 −7 to 2.0 × 10 −5 mol/L and 1.0–90 U/L, respectively. The detection limit for AA and ALP were 2.0 × 10 −7 mol/L and 0.45 U/L. The established method showed a high selectivity for ALP activity compared with other interference components. Furthermore, the detection system as a fluorescence probe has great potential in the development of sensors for widely detecting various analytes with AA producing process. [ABSTRACT FROM AUTHOR]