Measuring cancer biomarkers at ultralow detection limit and high sensitivity could be a promising tool for early diagnosis, monitoring treatment and post-treatment recurrence. Soluble CD44 is a promising diagnostic and prognostic biomarker in several types of cancer including gastric, colon and breast cancer. Several highly sensitive biosensors have been built to measure this important biomarker. However, they did not reach attomolar level of detection. The aim of this work was to build a biosensor capable of detecting CD44 concentrations down to attomolar (aM) level while measuring it in a wide concentration range. Herein, we demonstrate a biosensor that offers 4 key advantages over existing platforms for CD44 detection: 1) detection of CD44 was carried out in a diluted serum down to attomolar level (4.68 aM) which is about 6 orders of magnitude lower than that of a traditional ELISA; 2) fabrication of the sensor is done in a fast way using inexpensive materials making it a disposable fiber optic biosensor; 3) detection of CD44 was performed in a wide dynamic range previously not shown in other similar biosensors; 4) a proof-of-concept experiment was performed using the biosensor to embed it in a catheter to measure the protein in flow conditions.
Keywords: Attomolar detection; Ball resonator; Biomarker; CD44 protein; Optical fiber biosensor; Real-time sensing.
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