Aptamer-functionalized 3D gold nanodendrite platform for electrochemical detection of circulating tumor cells in breast cancer

Circulating tumor cells (CTCs) are critical biomarkers of breast cancer metastasis, yet their low abundance and phenotypic heterogeneity present formidable challenges for reliable detection. Here, we report the design and validation of an electrochemical biosensor based on three-dimensional gold nanodendrites (AuNDs) functionalized with dual aptamers targeting the epithelial cell adhesion molecule (EpCAM) and Mucin 1 (MUC1). The AuND platform, synthesized via potentiostatic electrodeposition, exhibited a mesoporous dendritic morphology with a specific surface area of 172.2 m² g^-1 and crystalline Au(111) facets, confirmed by SEM, TEM, XRD, BET, and XPS analyses. Stepwise assembly of the aptamer-modified electrode produced distinct electrochemical signatures, with charge transfer resistance (R_ct) increasing from ∼50 Ω for bare AuNDs to ∼2000 Ω after BSA blocking. Optimization identified 1.0 µM aptamer concentration and 60 min incubation as optimal sensing conditions. Using MCF-7 breast cancer cells as CTC-like model cells, the sensor achieved an exceptionally low detection limit of 3 cells per mL and displayed a wide dynamic range from 10 to 10⁶ cells per mL, with a linear regression equation of ΔI (µA) = 5.8 log[C_cell] + 2.5 (R² = 0.998). Selectivity tests showed negligible responses (<5%) toward HeLa and Jurkat cells, while reproducibility across five electrodes yielded a relative standard deviation of 3.5%. Stability evaluation demonstrated retention of 92.5% activity after 28 days of storage at 4 °C. Recovery studies in 10% human serum spiked with MCF-7 cells (as a model CTC system) showed excellent accuracy (96.5-104.2%) with RSD ≤ 4.5%. Collectively, these results demonstrate strong analytical performance for MCF-7 model CTCs in buffered suspensions and in a spiked (10%) serum matrix, supporting the AuND/dual-aptamer platform as a proof-of-concept CTC biosensing strategy; validation using patient-derived CTCs in whole-blood samples will be required in future studies to establish clinical utility.