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Development of inexpensive and environmentally friendly chemical sensors can help improve the global ecological environment and reduce pollutant emissions. In this work, asphaltene of coal liquefaction by-product was employed as the carbon source to fabricate carbon dots (CDs) by straightforward microwave radiation. The asphaltene-based CDs gave out blue emission under UV light excitation. Interestingly, the CDs are highly lipophilic because of its carbonized structure and insufficient hydrophilic groups. Based on these findings, an outstanding fluorescent sensor for 2,4,6-trinitrophenol (TNP) was developed by loading asphaltene-based CDs into polymeric micelles. The micelle formed by nonionic tri-block copolymers exhibited a hydrophobic inner cavity and hydrophilic surface. Due to the protection of the micelles, the emission of asphaltene-based CDs was enhanced by 2.89 times. But the fluorescence was significantly quenched by TNP through energy transfer and electron transfer mechanism, showing high sensitivity to TNP with a detection limit of 0.21 μM. The findings presented here provide a green method to synthesize fluorescent CDs and a promising strategy to design fluorescent probes. [ABSTRACT FROM AUTHOR]

This paper reported a dual-mode probe for D-penicillamine on the basis of pH-mediated gold nanoparticles aggregation and fluorescence resonance energy transfer (FRET) from carbon dots. D-penicillamine is a zwitterionic compound and has different forms depending on specific pH ranges. The thiol group of D-penicillamine has high affinity towards the surface of gold nanoparticles and can replace other surface ligands. When pH values were close to its isoelectrical point (pH(I)), the D-penicillamine capped gold nanoparticles aggregated through hydrogen bonding or electrostatic interactions, resulting in the releasing of carbon dots from gold nanoparticles. The dual-mode probe consisted of fluorescent carbon dots and gold nanoparticles, and the fluorescence of carbon dots was quenched by the attached gold nanoparticles due to the FRET. Then, the fluorescence can be recovered in presence of D-penicillamine due to the gold nanoparticles aggregation in specific pH range. Under the optimum conditions, the probe has linear response for D-penicillamine in the 0.25-1.5 μM concentration range with a detection limit of 0.085 μM. This method provides a potential application in sensitive detection of D-penicillamine. [ABSTRACT FROM AUTHOR]

In this study, we have developed a facile method for preparation of highly fluorescent Au nanoclusters (AuNCs) using 11-mercaptoundecanoic acid (MUA) as both the reducing and stabilizing agent. The as-prepared MUA functionalized AuNCs (MUA-AuNCs) have good water solubility, excellent photostability, and strong fluorescence emission at 610 nm with a quantum yield of 7.28% in water. The fluorescence of MUA-AuNCs was first quenched by copper ions through electron transfer, subsequently caused obvious restoration by competitive effect after adding penicillamine, making it a potential fluorescent sensor for penicillamine with a detection limit of 0.08 μM. Furthermore, the newly designed fluorescence “on-off-on” assay was explored for the measurement of penicillamine in complex real water and urine samples with satisfactory results. [ABSTRACT FROM AUTHOR]

This paper describes the synthesis of fluorescent copper nanoclusters (CuNC) with a fluorescence quantum yield as high as 2.3% after modification with cysteamine. The modified CuNC are shown to be viable probes for the determination of picric acid (PA). Fluorescence drops with increasing concentration of PA which can be detected fluorometrically with a 0.14 μM limit of detection. This is much lower than required by the People’s Republic of China Surface Water Environmental Quality Standard (2.2 μM). The probe was successfully applied to the determination of PA in spiked tap water, lake water and river water.Copper nanoclusters (CuNC) have weak fluorescence but after the modification with cysteamine, the fluorescence of CuNC is strongly enhanced. The fluorescence of such cysteamine-coated copper nanoclusters (CuNC-CA) is reduced upon the addition of picric acid (PA) through an inner filter effect (IFE). [ABSTRACT FROM AUTHOR]

A ratiometric probe is described for the fluorometric determination of Cu(II) ions based on their quenching effect on the luminescence of dually-emitting quantum dots (QDs). ZnS QDs were doped with Mn(II) and subsequently modified with mercaptopropionic acid to give the QD probe which consists of a  sole fluorophore but has two emission peaks (at 430 and 590 nm under 310 nm excitation, respectively). On addition of Cu(II) ions, the 590 nm band is quenched while the 430 nm band exhibits a little change. The changes in the intensity ratios of the yellow and the purple bands increases linearly in the 0 to 3.0 μM Cu(II) concentration range, and the detection limit reached 14 nM. The QD probe was validated and successfully applied to the determination of Cu(II) in spiked real water samples.Mn-doped ZnS (ZnS:Mn(II)) quantum dots were synthesized with yellow fluorescence. After the modification of 3-mercaptopropionic acid (MPA), ZnS:Mn(II) was transferred to aqueous phase and became MPA modified Mn-doped ZnS (MPA- ZnS:Mn(II)). The fluorescence was changed to purple upon the addition of copper ions because the yellow band was largely quenched while the purple band only changed a little. [ABSTRACT FROM AUTHOR]