Orange emissive carbon dots for fluorescent determination of hypoxanthine in fish.

Sensitive determination of hypoxanthine (HX), an indicator reflecting the degradation of meat and fish, is significantly important in monitoring food freshness. Herein, we design a novel sensor consisting of orange emissive carbon dots (O-CDs), nitrotetrazolium blue chloride (NTBC), and xanthine oxidase (XOD) for fluorescence turn-off detection of HX. O-CDs, possessing a high fluorescence quantum yield of 37%, are synthesized by hydrothermal treatment of 2,3-diaminopyridine in sulfuric acid. NTBC can react with HX/XOD-generated H2O2 and O2- to yield a violet-colored formazan, which remarkably quenches the orange fluorescence of O-CDs through inner filter effect. There is a linearity between the quenching efficiency and HX concentration in the range of 2-250 µM, and the limit of detection is 0.61 µM, lower than those of most reported HX sensors. In addition, the proposed method exhibits excellent selectivity, and can be applied to quantify HX in fish samples with satisfactory results.

Fluorescence detection of malachite green in fish tissue using red emissive Se,N,Cl-doped carbon dots.

Facile detection of malachite green (MG), a toxic dye, in aquaculture is urgently demanded for environment and food safety. Herein, we design a novel fluorescent probe, namely red emissive Se,N,Cl-doped carbon dots (CDs), to accurately determinate MG. CDs are prepared by hydrothermal treatment of selenourea and o-phenylenediamine in HCl solution. This material exhibits excitation-independent dual emissions at 625 and 679 nm, with a high quantum yield of 23.6%. A selective and sensitive fluorescent sensor toward MG is established based on inner filter effect, because both the excitation and emission light of CDs can be strongly absorbed by MG. The fluorescence quenching of CDs is linear to the MG concentration over the range of 0.07-2.50 µM with a low detection limit of 21 nM. Trace-level analysis of MG in fish tissue is successfully explored, demonstrating the great potential of the proposed sensor for MG monitoring in aquatic products.

Sensitive detection of Sudan dyes using tire-derived carbon dots as a fluorescent sensor.

In this paper, we exploit an innovative strategy to reuse waste rubber tires as a low-cost source for the fabrication of a high-value material, fluorescent carbon dots (CDs). In the hydrothermal condition, ammonium persulphate is utilized to oxidize the tires and offer nitrogen atom for doping, to produce CDs with a high quantum yield (QY) of up to 23.8%. Such a QY is outstanding among the reported waste-derived CDs. It is found that the fluorescence of CDs can be remarkably quenched by Sudan I-IV with negligible interference from other substances. The corresponding linear ranges are 0.5-60, 0.5-60, 1-70, and 1-70 µM, and limits of detection are 0.17, 0.21, 0.53, and 0.62 µM for Sudan I, II, III, and IV, respectively. Systematic investigations reveal that the fluorescence quenching mainly stems from the inner filter effect. Moreover, the CD-based sensor shows an excellent applicability for the assay of Sudan dyes in chili powder sample.

Yellow emissive Se,N-codoped carbon dots toward sensitive fluorescence assay of crystal violet.

Crystal violet (CV), a hazardous dye, poses a serious threat to the environment and human health. This motivates us to develop a facile method for its sensitive detection. Herein, we demonstrate a rapid sensing of CV using a novel fluorescent nanomaterial, yellow emissive Se,N-codoped carbon dots (CDs). CDs with an intense photoluminescence peak at 566 nm are synthesized by a hydrothermal technique using selenourea and o-phenylenediamine as precursors. This material shows a high quantum yield of up to 16.7 %. It is found that the yellow fluorescence of CDs can be selectively quenched by CV, which makes them promising for CV sensing. The linearity is obeyed in the range of 0.02-1.60 µM, and the limit of detection is as low as 7.3 nM. After detailed investigations, the inner filter effect is proposed to be the sensing mechanism. For practical usage, the newly built method is applied to determine the trace amount of CV in fish tissue samples, and satisfactory results are obtained.

Sewage sludge in microwave oven: A sustainable synthetic approach toward carbon dots for fluorescent sensing of para-Nitrophenol.

Million tons of sewage sludge produced yearly creates a severe pollution problem to environment, and thus needs either to be properly disposed of, or recovered. Here, we demonstrate a value-added utilization of sewage sludge by converting its contained organics into nanosized carbon dots (CDs) with microwave irradiation. This synthetic method, using waste resources as precursors and avoiding the requirement of hazardous reagents and complex procedures, has the great advantage of low cost, environmental friendliness, and easy scalability. The resultant CDs exhibit excellent fluorescence properties with a large quantum yield (QY) of up to 21.7%, higher than the most values of waste-derived CDs. It is found that CDs can serve as a sensitive and selective sensor to detect para-Nitrophenol (p-NP), a toxic pollutant, through fluorescence quenching, giving a linear detection range of 0.2-20 µM and a detection limit of as low as 0.069 µM. Systematic investigations suggest that the inner filter effect (IFE) is the dominant sensing mechanism. Moreover, the practical applications of CDs for p-NP assay in real water samples achieve good results.

Environmentally benign conversion of waste polyethylene terephthalate to fluorescent carbon dots for "on-off-on" sensing of ferric and pyrophosphate ions.

The increasing production of waste polyethylene terephthalate (PET) is a growing problem worldwide. Environmentally benign conversion of waste PET to valuable materials remains a substantial challenge. In this paper, we developed a green route to reuse waste PET for low-cost synthesis of fluorescent carbon dots (CDs) via air oxidation followed by hydrothermal treatment in aqueous H2O2 solution. No expensive, corrosive, or toxic reagents, or severe conditions were required in the synthetic process. The resultant CDs possessed abundant oxygenous groups and unique photoluminescence (PL) properties, which showed a highly selective and sensitive detection of ferric ion (Fe3+) through a PL quenching effect (on-off). The fluorescence of CDs quenched by Fe3+ could be restored specifically with pyrophosphate anion (PPi), rendering the CDs/Fe3+ sensor promising for PPi detection (off-on). The linear ranges for Fe3+ and PPi detections were 0.5-400 and 2-600 µM, and the limit of detections (LODs) were 0.21 and 0.86 µM, respectively. The sensing system applied for Fe3+ and PPi assays in real water samples and human urine achieved good results. After detailed investigations, a possible electron transfer process was proposed for explaining the "on-off-on" sensing mechanism.

Epitaxial Crystallization Behavior of Poly(butylene adipate) on Orientated Poly(butylene succinate) Substrate.

The crystallization behavior of poly(butylene adipate) (PBA) in the sheared PBS/PBA blend, as well as on highly orientated poly(butylene succinate) (PBS) substrate, was studied by means of DSC, POM, Raman microscopy, and XRD. The results showed that the pre-existing orientated PBS crystals exhibit a very strong nucleation ability toward PBA as reflected by the increased crystallization temperature and the occurrence of heteroepitaxy and transcrystallization of PBA on the PBS substrate. The epitaxial crystallization of PBA on the PBS substrate results in the formation of α-form PBA crystals in any crystallization conditions.