An LF-NMR Biosensor for the Detection of Circulating Tumor Cells Based on Target-Triggered Bioorthogonal Chemistry and Click Chemistry

Circulating tumor cells (CTCs), crucial biomarkers for monitoring cancer metastasis and prognosis, present significant challenges for detection technologies due to their extremely low abundance in peripheral blood. This study introduces a low-field nuclear magnetic resonance (LF-NMR) biosensor leveraging the synergistic effect of biorthogonal chemistry and click chemistry for CTC detection by a sol-gel phase-transition strategy. Initially, CTCs were targeted and enriched using mucin 1-specific aptamers. Subsequently, Cys-GO@CuO nanoprobes were assembled quantitatively on captured CTCs through target-triggered bioorthogonal chemistry: sialic acid molecules on the cell membrane were oxidized by NaIO₄ to generate aldehyde groups, enabling their covalent coupling with thiol/amino groups of nanoprobes via thiazolidine bond formation. Then, acidolysis reduction of CuO released Cu⁺ ions, catalyzing azide-alkyne cycloaddition click reactions to drive sol-gel phase transitions. Quantitative CTC analysis was achieved by monitoring LF-NMR-derived transverse relaxation time (T₂) signal changes. Under optimal conditions, the detection limit for MCF-7 cells is as low as 5 cells/mL, with satisfactory precision and accuracy for real samples. This integrated platform offers a sensitive, accurate, stable, and operationally simple method for CTC detection, showcasing promising applications for liquid biopsy and precision medicine.