A liquid-crystal aptasensing platform for label-free detection of a single circulating tumor cell

Circulating tumor cells (CTCs), which are shed from a primary site into the bloodstream and lead to distal metastases, are pivotal as a prognostic marker for evaluating the treatment response of cancer patients. One of the major challenges of detecting CTCs is their scarcity in blood. We report herein a label-free liquid crystal (LC) cytosensor by adopting an aptamer against epithelial cell adhesion molecule (EpCAM) to capture EpCAM-positive cancer cells. The optical and dielectric signals transduced from the interaction between LC and different numbers of captured breast cancer cells were investigated. A limit of detection (LOD) of 5 CTCs was resulted from the optical biosensing approach relying on texture observation and image analysis of the optical signal in polarizing micrographs. The LOD was further lowered to a single CTC in the dielectric approach by studying the real- and imaginary-part dielectric constants of LC at 1 kHz and 30 Hz as well as the relaxation frequency. The LC-based EpCAM-specific dielectric cytosensor was successfully applied to single-cell CTC detection in cancer cell-spiked human serum and whole blood. This platform demonstrates the potential of LC-based biosensing technologies in cellular-level detection and quantitation, which is crucial to the early diagnosis of cancer metastasis and progression.