A new biosensor for glucose determination in serum based on up-converting fluorescence resonance energy transfer

In this work, a new glucose sensor based on up-converting fluorescence resonance energy transfer (UC-FRET) was developed. Up-converting phosphors (UCPs, NaYF(4): Yb, Er), which were covalently labeled with Concanavalin A (ConA), were used as the energy donor with thiolated β-cyclodextrins (SH-β-CDs) functionalized gold nanoparticles as the energy acceptor. Due to the combination between ConA and SH-β-CDs, the energy donor and the acceptor were brought to close proximity, resulting in the quenching of the fluorescence of UCPs by gold nanoparticles. In the presence of glucose which competed with SH-β-CDs towards the binding sites of ConA, the biosensor (UCPs-ConA-SH-β-CDs-Au) was decomposed and the energy donor was separated from the acceptor. Therefore, the fluorescence of UCPs was restored dependent on the concentration of glucose. The increase of UCPs fluorescence intensity was proportional to glucose concentration within the range from 0.4 μM to 10μM in aqueous buffer, with a limit of detection (LOD) of 0.043 μM. A same linear range of glucose concentration was obtained in a human serum matrix (which was pretreated and thus contained no glucose) with a slightly higher LOD (0.065 μM). The glucose sensor was applied to real human serum samples with the results consistent with that of a classic hexokinase (HK) method, indicating that the UC-FRET biosensor was competent for directly sensing glucose in serum samples without optical interference, which benefited from the near infrared (NIR) excitation nature of UCPs. The results of this work suggested that the UC-FRET technique could be a promising alternative for detecting biomolecules in complex biological sample matrixes for diagnostic purposes.