Nitrogen-doped carbon nanodots-based "off-on" fluorescent sensor for the detection of breast cancer-derived exosomes and early diagnosis.

Breast cancer is a leading cause of cancer death in women, requiring non-invasive early diagnostic tools. Exosomes are promising liquid biopsy biomarkers that reflect tumor-derived molecular information. Here, we developed an "off-on" fluorescent sensor using nitrogen-doped carbon nanodots (N-CNDs) for sensitive detection of breast cancer-derived exosomes. The sensor uses a magnetic bead-based aptamer complex (MBs-Apt-P1-P2) for target capture. P1 and P2 probes contain both EpCAM-recognition and Poly-T sequences. In the absence of targets, Ag+ quenches N-CNDs fluorescence. Upon target introduction, aptamers bind exosomal EpCAM, competitively releasing P1/P2 probes. After magnetic separation, the released Poly-T sequences capture Ag+ via T-Ag+-T coordination, restoring N-CNDs fluorescence. Each exosome can release two probes, providing dual signal amplification. Under optimal conditions, the sensor responded linearly to 1 × 109-4 × 1011 particles/mL with a detection limit of 35 particles/mL, showing excellent sensitivity for EpCAM-positive breast cancer exosomes. Clinical testing on 11 serum samples (6 patients, 5 healthy donors) distinguished patients with an AUC of 0.94, compared with ELISA (AUC = 0.88). This sensor offers a promising platform for breast cancer detection with high sensitivity and accuracy, warranting further validation in large-scale clinical studies.