| In the past decade, the fabrication of fluorescent quantum dots(QDs)-based biosensors/chemosensors has become an active research field and attracted great attention. In this work, we creatively developed two kinds of CdTe QDs-based sensing mechanisms for glucose and Cu2+ visual detection under a UV lamp.Firstly, a novel kind of versatile dual-emission microhybrids(DEMBs) is fabricated in this study whose fluorescence will be ratiometrically responsive to H2O2 produced from the glucose oxidase(GOD)-catalyzed oxidation of glucose, which allows simple and sensitive visual detection of glucose in serum. Herein, green-emitting rhodamine-embedded silica microbeads(MBs) are used as the core of the DEMBs while an outer shell of CdTe quantum dots of red fluorescence are attached on the surface of MBs through a layer-by-layer strategy as the signal report unit. So the as-fabricated DEMBs exhibit two well-resolved emission bands under a single wavelength excitation. The red fluorescence of CdTe is susceptible to H2O2 produced by the glucose/GOD reaction while the inner green fluorescence of the MBs is inert. Therefore, with the assistance of GOD, increased glucose levels can lead to variations of the two fluorescence intensity ratios of DEMBs accompanied with continuous color changes from red to green under a 365 nm UV lamp, which can be easily and distinctly identified by naked eye. Moreover, quantitative analysis of glucose is also realized because the intensity ratios of the two emission bands of DEMBs(I555 nm/I650 nm) are linearly proportional to glucose concentrations in the range of 5~2000 ?M. This ratiometric strategy possesses a built-in correction that can remarkably increase the sensing accuracy. So this DEMBs-based sensing strategy can be directly used for assaying glucose in serum and the results agree well with those measured by commercial glucose meter, indicating this glucose sensing system is not only simple, sensitive, but also reliable and suitable for practical applications. More importantly, since many oxidases-based enzymatic reactions can all produce H2O2, the proposed design may serve as a generic platform for probing of H2O2-generating oxidases as well as their substrates.Copper ions play important roles in either environmental or biological systems, so simple, sensitive and selective determination of copper ions is of great significance. Herein, based on the interesting phenomenon that copper ions may lead to the fluorescence band shift of CdTe quantum dots(QDs), we have developed a new colorimetric strategy that allows for visual detection of Cu2+. In this study, with the increasing dosage of Cu2+, the fluorescence color of CdTe QDs can be tuned gradually from green to yellow and then red under the irradiation of a UV lamp, which can be clearly identified by naked eye without requirement of any instrument. Furthermore, quantitative determination of Cu2+ is also achieved because the band shift value of the maximum fluorescence wavelength of CdTe(??max) is proportional to the Cu2+ concentration in the range of 0.1~5 ?M. In this new strategy, although a variety of metal ions can lead to the fluctuation of fluorescence intensity of the CdTe QDs, fascinatingly, only Cu2+ arouses a remarkable fluorescence band shift accompanied with a distinct color change that can be easily identified visually, suggesting an ultrahigh selectivity of the proposed strategy towards Cu2+. |
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