Magnetic lanthanide sensor with self-ratiometric time-resolved luminescence for accurate detection of epithelial cancerous exosomes

Fluorescence-based LB (liquid biopsy) offers a rapid means of detecting cancer non-invasively. However, the widespread issue of sample loss during purification steps will diminish the accuracy of detection results. Therefore, in this study, we introduce a magnetic lanthanide sensor (MLS) designed for sensitive detection of the characteristic protein, epithelial cell adhesion molecule (EpCAM), on epithelial tumor exosomes. By leveraging the inherent multi-peak emission and time-resolved properties of the sole-component lanthanide element, combined with the self-ratiometric strategy, MLS can overcome limitations imposed by manual operation and/or sample complexity, thereby providing more stable and reliable output results. Specifically, terbium-doped NaYF 4 nanoparticles (NaYF 4 :Tb) and deformable aptamers terminated with BHQ1 were sequentially introduced onto superparamagnetic silica-decorated Fe 3 O 4 nanoparticles. Prior to target binding, emission from NaYF 4 :Tb at 543 nm was partially quenched due to the fluorescence resonance energy transfer (FRET) from NaYF 4 :Tb to BHQ1. Upon target binding, changes in the secondary structure of aptamers led to the fluorescence intensity increasing since the deconfinement of distance-dependent FRET effect. The characteristic emission of NaYF 4 :Tb at 543 nm was then utilized as the detection signal ( I 1 ), while the less changed emission at 583 nm served as the reference signal ( I 2 ), further reporting the self-ratiometric values of I 1 and I 2 ( I 1 / I 2 ) to illustrate the epithelial cancerous features of exosomes while ignoring possible sample loss. Consequently, over a wide range of exosome concentrations (2.28 × 10 2 -2.28 × 10 8 particles per mL), the I 1 / I 2 ratio exhibited a linear increase with exosome concentration [ Y ( I 1 / I 2 ) = 0.166 lg ( N exosomes ) + 3.0269, R 2 = 0.9915], achieving a theoretical detection limit as low as 24 particles per mL. Additionally, MLS effectively distinguished epithelial cancer samples from healthy samples, showcasing significant potential for clinical diagnosis. The structure of MLS and its working principle for detection of exosomal EpCAM.