A label-free and ultrasensitive EIS cytosensor was developed to detect CTCs. The viable HepG-2 cells were captured to the senor by a multivalent Gal-ASGP-R binding. The nanostructured GNI has an enhanced electro-transfer rate and a low LOD of 30 cell mL− 1. The EIS biosensor has a good reproducibility with the RSD of 1.9% in blood samples. It provides a versatile and noninvasive sensing platform for early diagnosis of tumor.