Label-free optical fiber biosensor for the detection of CD44-expressing breast cancer cells

Increased level of CD44, transmembrane glycoprotein, is observed in several cancers such as breast, colorectal, head and neck, gastric, and ovarian cancer. Current methods for analyzing CD44 expressing cells are time-consuming, semi-quantitative, use labeled reagents for analysis or are not suitable for in situ analysis. Therefore exploring novel methods which are label-free and fast with the in situ detection capability for the quantification of these cells is of importance. Using optical fiber as a sensing element in biosensors offers low cost, high sensitivity, chemical inertness, and immunity to electromagnetic interference, and possibility of being used in in situ applications. This study reports the first label-free optical fiber biosensor for detection of CD44-expressing cancer cells. A fiber-optic ball resonator (BR) sensor was fabricated and then functionalized with CD44 antibodies. Different concentrations of the cells were incubated with the biosensor to measure the reflected light using optical backscatter reflectometer. The biosensor was able to detect cancer cells with a limit of detection of 335 cells/mL. The presence of the cells on the sensor surface was demonstrated by fluorescent and scanning electron microscope analysis. The work is the first proof-of-concept biosensor based on optical fibers for CD44 cancer cells and acts as a promising tool for in situ detection of cancer cells.