Ultrasensitive label-free optical microfiber coupler biosensor for detection of cardiac troponin I based on interference turning point effect.

Sensitive detection of cardiac biomarkers is critical for clinical diagnostics of myocardial infarction (MI) while such detection is quite challenging due to the ultra-low concentration of cardiac biomarkers. In this work, a label-free immunosensor based on optical microfiber coupler (OMC) has been developed for the ultrasensitive detection of cardiac troponin I (cTnI), a selective and highly sensitive biomarker of acute myocardial infarction (AMI). CTnI monoclonal antibodies were immobilized on the surface of the fiber through polyelectrolyte layer using layer-by-layer deposition technique. For refractive index sensing characterization, an ultra-high sensitivity of 91777.9 nm/RIU was achieved when the OMC works around the dispersion turning point, which is the highest experimental demonstration in the field of fiber-optic evanescent biosensors. For biosensing, the immunosensor with good specificity showed a linear wavelength shift in the range of 2-10 fg/mL and an ultra-low detection limit of 2 fg/mL. Such immunosensors have huge application potential for the detection of cardiac biomarkers of myocardial infarction due to simple detection scheme, quick response time, ease of handling and miniaturation.