Fig: The geometrical profile of fiber optic spherical tip sensor (548–544 µm) used to detect CD44 protein in this work. (a,b) Two-sided profilometry of the fiber optic tips obtained from Fujikura splicer as measured by its inner microscope; where diameter on the horizontal and vertical axes (x, y) for each position along the fiber axis (z) is shown; (a) actual sensor (fabricated and used in experiments) and (b) actual sensor vs. target (i.e. designed profile for the splicing fabrication).(c,d) 3D profiles extrapolated from profilometry data by reconstructing the elliptical meshes of the tips: (c) actual sensor and (d) actual sensor vs. target; Ellipticity548-544 µm = 0.1206.
Increased level of CD44 protein in serum is observed in several cancers and is associated with tumor burden and metastasis. Current clinically used detection methods of this protein are time-consuming and use labeled reagents for analysis. Therefore exploring new label-free and fast methods for its quantification including its detection in situ is of importance. This study reports the first optical fiber biosensor for CD44 protein detection, based on a spherical fiber optic tip device. The sensor is easily fabricated from an inexpensive material (single-mode fiber widely used in telecommunication) in a fast and robust manner through a CO2laser splicer. The fabricated sensor responded to refractive index change with a sensitivity of 95.76 dB/RIU. The spherical tip was further functionalized with anti-CD44 antibodies to develop a biosensor and each step of functionalization was verified by an atomic force microscope. The biosensor detected a target of interest with an achieved limit of detection of 17 pM with only minor signal change to two control proteins. Most importantly, concentrations tested in this work are very broad and are within the clinically relevant concentration range. Moreover, the configuration of the proposed biosensor allows its potential incorporation into an in situ system for quantitative detection of this biomarker in a clinical setting.
Bekmurzayeva, A., Ashikbayeva, Z., Myrkhiyeva, Z. et al. Label-free fiber-optic spherical tip biosensor to enable picomolar-level detection of CD44 protein. Sci Rep 11, 19583 (2021). https://doi.org/10.1038/s41598-021-99099-x