A homogeneous biosensor for Human Epididymis Protein 4 based on upconversion luminescence resonance energy transfer

Abstract

Human epididymis protein 4 (HE4) is a widely used biomarker for the early diagnosis of ovarian cancer. Luminescence resonance energy transfer (LRET) is a homogeneous assay technique with great simplicity and specificity, which shows a significant advantage in a bioassay. Lanthanide-doped upconverting nanoparticles (UCNPs) were an ideal material to construct LRET-based probes, because their near-infrared (NIR)-excitable property can effectively eliminate the interference from autoluminescence of biosamples. Herein, a HE4 nanoprobe was fabricated based on LRET strategy, in which UCNPs was employed as an energy donor. The commercial organic dye BHQ-1, whose absorption overlaps well with the blue emission of Tm3+-doped UCNPs, was chosen as an energy acceptor. The two components were tagged with the two ends of a molecular beacon (MB) containing HE4 aptamer sequence. Due to the proximity and spectral overlap of UCNPs and BHQ-1, 82% of upconversion luminescence (UCL) can be quenched through LRET. In presence of HE4, the hairpin structure was opened for the strong interaction between HE4 and its aptamer sequence, which leads to the separation of UCNPs and BHQ-1 and inhibition of LRET. There is a good linear relationship between UCL intensity and the logarithm of HE4 concentration in the range from 0.4 ng/mL to 7.0 ng/mL, with a LOD of 0.021 ng/mL in HEPES buffer. This probe exhibits excellent selectivity and stability, and can also be successfully applied in HE4 quantification in human serum. It might be a reliable method for the early diagnosis of ovarian cancer.