Ultra‐Sensitive Cancer Cell Detection Based on the Vernier Effect of Taper‐In‐Taper Structured Optical Fibers

ABSTRACT Early diagnosis of cancer is the key to improving the cure rate, but traditional detection methods (such as tissue biopsy and imaging examinations) often have problems such as strong invasiveness, insufficient sensitivity, or high cost. In this work, an ultrasensitive microfiber interferometer biosensor is proposed for cancer cell detection. An ultra‐high refractive index (RI) sensitivity of 15225.665 nm/RIU was achieved by cascading two taper‐in‐taper structured fiber (TITF). TITF that is functionalized with biotin was employed to identify the biotin receptor protein (streptavidin) and the cancer cell exhibiting overexpression of surface biotin receptors (Human Hepatocellular Carcinoma Cells, HepG2). The results of the experiments indicate that in the standard buffer sample, the detected concentrations of streptavidin (SA) were 11, 23, 46, and 92 pM, respectively, with a detection limit of 1.4 pM. The log‐linear concentrations of HepG2 cells are 10, 10 2 , 10 3 , and 10 4 cells/mL, respectively, with a detection limit of 4 cells/mL. The specificity test revealed that TITF showed a lack of sensitivity to normal cells, particularly human acute monocytic leukemia cells (THP‐1) and human colorectal adenocarcinoma epithelial cells (HCT116). The proposed biosensor has good selectivity and sensitivity, providing a feasible method for the early diagnosis of cancer.