Rapid and sensitive detection of cardiac markers using plasmonic gold nanostar-engineered microfiber Bragg grating biosensor

Fiber-optic grating biosensor offers compelling advantages such as compact footprint and nature of signal reflection, and thus becomes a particularly apt candidate for cardiovascular biomarker determination. However, limit of detection (LOD), test speed, and maneuverability of such biosensor should be substantially improved before conferring those advantages into application. Herein, we reported a fiber Bragg grating written in a unilateral fiber taper to enhance the sensitivity while reducing the manufacturing difficulty. The chirped grating fabricated on the diameter-variated fiber taper also provided the narrow linewidth signal, which was mediated by the localized Fabry-Perot effect, to enhance the spectral resolution for the interrogation. Furthermore, the modification of the plasmonic gold nanostar (AuNSt) on the grating sensor allowed additional sensitivity improvement due to the star-like nanotip- induced electromagnetic field enhancement and significantly accelerated the test speed mediated by the electrostatic attraction. The proposed biosensor could respond to the cardiac troponin-I (cTn-I) with the concentration of under 10 ng/mL and held an LOD of 3 pg/mL in buffer and 11.9 pg/mL in clinical serum. More importantly, the required test duration could be cut down to approximately 5 min. Results of tests on the clinical serum samples further validated the effectiveness of the biosensor, which may fuel the “lab-to-fab” twist and holds tantalizing prospect for Point-of-care test (POCT) of emergency and severe diseases.