Ratiometric sensing of metabolites using dual-emitting ZnS:Mn2+ quantum dots as sole luminophore via surface chemistry design

•Ratiometric sensing of metabolites is achieved using doped QDs as sole luminophore.•A triple-layer “filter screen” is designed for overcoming non-specific interactions.•The metabolites in serum can be directly assayed without any sample pre-treatment.

We herein present an effective and versatile platform for ratiometric sensing of metabolites using intrinsically dual-emitting ZnS:Mn2+ quantum dots (QDs) as sole reporter. To avoid notoriously non-specific interactions, a special triple-layer “filter screen” around the inorganic QD core is rationally constructed, which is made of oleic acid, cetyltrimethyl ammonium bromide and bio-enzymes. In the presence of the analytes, the in-situ enzymatic H2O2 molecules diffuse and pass through the “filter screen” along the molecule interspace, which then reacts with the inorganic core and leads to more dramatically quenching of the Mn2+ emission. The ratiometric signal readout is so distinct that can be observed by naked eyes (from orange to violet). In contrast, various coexisting bio-molecules, due to larger size, are well prevented from penetrating the filter screen by steric hindrance effect. So, various potential interfering substances do not disturb the assay. Under optimal conditions, five kinds of the corresponding substrates, namely glucose, cholesterol, lactate, xanthine and uric acid are well quantified by the emission intensity ratio of I470/I615, and the linear ranges are 0.1-200 µM, 0.1-200 µM, 1-200 µM, 1-200 µM and 1-200 µM, respectively. The detection limits can even reach quasi-picomole levels. Because of favorable analytical performances (excellent selectivity, appropriate sensitivity and broad linear range), the proposed system can direct assay the analytes in blood without any sample pre-treatment.

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