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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]

Based on the controlled aggregation of quantum dots (QDs), a valid, reliable, and label-free fluorescence turn-on strategy is established for the detection of alkaline phosphatase activity. The aqueous solution of anionic QDs exhibits intense fluorescence. However, the addition of cationic polymer (poly-1) significantly quenched the fluorescence of the QDs via their induced aggregation. While short 3′-phosphorylated DNA (DNA-P) could not be extended by terminal deoxynucleotidyl transferase (TdT) and therefore, fluorescence of the QDs was recovered negligibly. The effective elimination of phosphate group of DNA-P in the presence of alkaline phosphatase (ALP) produced 3′-OH termini and the resulting DNA could be sufficiently extended by TdT. The presence of greater binding strength between the elongated DNA and poly-1 is very crucial to compete with the poly-1/QDs aggregates and release the QDs. Turned-on fluorescence emission is observed due to the efficient release of the QDs. A novel strategy for alkaline phosphatase detection is therefore established. Our method is quite sensitive and selective, as low as 0.1 mU/mL ALP can be easily detected. [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]

[Display omitted] • An innovative hydrostable perovskite-europium hybrid fluorescence sensor was designed and prepared. • The perovskite-europium nanosensor can realize TC sensing in various water samples. • The sensor had a good linear response in the range of 0–25 μM, and the LOD was 11.15 nM. • With a color-scanning application, the real-time intelligent detection of TC was realized. The development of real-time and efficient visual tetracycline sensors is helpful to evaluate the pollution status of tetracycline antibiotics in the environment. Considering the unique fluorescence properties of perovskite and rare earth elements, an innovative water-stable perovskite-europium hybrid fluorescence sensor MAPbBr 3 @PbBr(OH)@SiO 2 -Cit-Eu was fabricated. The introduction of tetracycline resulted in the increase of the fluorescence intensity of Eu complex, while the fluorescence intensity of perovskite quantum dots decreased slowly, accompanied by visual green-red switching. The sensor had good linear response in the range of 0–25 μM, and the detection limit was 11.15 nM. With the help of color analysis software in smart phones, the real-time intelligent detection of TC was realized. In addition, the wearable glove sensor obtained by fixing the nanosensor in the gel can realize the qualitative and semi-quantitative visual sensing of TC on the surface of many foods (eggs, apples, bananas, pears and oranges). It is believed that this work will open a new avenue for perovskite-europium hybrid nanosensors in intelligent sensing fields. [ABSTRACT FROM AUTHOR]