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 NaYF₄ nanoparticles (NaYF₄:Tb) and deformable aptamers terminated with BHQ1 were sequentially introduced onto superparamagnetic silica-decorated Fe₃O₄ nanoparticles. Prior to target binding, emission from NaYF₄:Tb at 543 nm was partially quenched due to the fluorescence resonance energy transfer (FRET) from NaYF₄: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 NaYF₄:Tb at 543 nm was then utilized as the detection signal (I₁), while the less changed emission at 583 nm served as the reference signal (I₂), further reporting the self-ratiometric values of I₁ and I₂ (I₁/I₂) to illustrate the epithelial cancerous features of exosomes while ignoring possible sample loss. Consequently, over a wide range of exosome concentrations (2.28 × 10²–2.28 × 10⁸ particles per mL), the I₁/I₂ ratio exhibited a linear increase with exosome concentration [Y(I₁/I₂) = 0.166 lg (N_exosomes) + 3.0269, R² = 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.