Exosomes are important mediators of intercellular communications and carry parent cell-specific cargos of proteins, lipids, and genetic materials. Every cell releases exosomes as part of its cellular process. Different cell types, including normal cells and cancer cells, produce a heterogeneous mixture of exosomes in body fluids. Exosomes derived from cells with abnormal conditions can be exploited as a potential biomarker for the respective disease condition. While these exosomes carry various biomarkers, they share a common biomarker called CD63. Therefore, CD63 can be used as an analyte to track exosomes. Toward this endeavor, this work reports a fiber-optic sensor functionalized with anti-CD63 to measure the exosomes by quantifying exosomal CD63 in real-time. For this purpose, an anti-CD63 antibody functionalized surface plasmon resonance (SPR)-based fiber-optic sensor was developed that measured variations in localized SPR due to the changes in local refractive index in response to CD63 binding onto the fiber. Gold-thiol chemistry was used to covalently functionalize the fiber-optic probe with anti-CD63, wherein the antigen-binding sites of anti-CD63 were uniquely exposed to target CD63 molecules. In our preliminary experiment, the fiber-optic sensor exhibited a sensitivity of 2.83 % light reflection variations per Log(ng ml-1 ) concentration of CD63 per cm2 sensing area and a detection limit of 2.64 ng ml-1 . Protein concentrations in culture media were used to calibrate the sensor for precision measurements. Considering excellent dynamic detection range and sensitive thiol chemistry, the developed sensor could hold promises in future in-vivo probe development, significantly impacting real-time monitoring and therapeutic planning.
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