A label-free cardiac biomarker immunosensor based on phase-shifted microfiber Bragg grating

Fiber optics evanescent field based biosensor is an excellent candidate for label-free detection of cardiac biomarkers which is of great importance in rapid, early, and accurate diagnosis of acute myocardial infarction (AMI). In this paper, we report a compact and sensitive cardiac troponin I (cTn-I) immunosensor based on the phase-shifted microfiber Bragg grating probe which is functionalized. The fine reflective signal induced by the phase shift in modulation significantly improves the spectral resolution, enabling the ability of the sensor in perceiving an ultra-small refractive index change due to the specific capture of the cTn-I antigens. In buffer, a log-linear sensing range from 0.1 to 10 ng/mL and a limit of detection (LOD) of 0.03 ng/mL (predicted to be as low as 10.8 pg/mL) are obtained. Furthermore, with good specificity, the sensor can be applied in test of cTh-I in human serum samples. The proposed sensor presents superiorities such as improved integratability and portability, easy fabrication and operation, and intrinsic compatibility to the fiber-optic network, and thus has a promising prospect in "point-of-care" test for cardiac biomarkers and preclinical diagnosis.