Fig. 1. Schematic diagram of (a) conventional SMS coupler and (b) tapered SMS coupler; (c) the photomicrograph of the taper transition and taper waist area; (d) the SEM image of the taper waist area.

Fig. 2. Experimentally observed RI sensitivity of the tapered SMS coupler in different RI ranges: (a) 1.33, (b) 1.37, and (c) 1.42.

Fig. 3. Dip-1 and dip-2 of the spectrum.

Fig. 4. (a) Spectral response of the sensor at different RIs and (b) wavelength shift versus RI for dip-1 and dip-2.

Fig. 5. (a) Spectral response of dip-1 at different temperatures; (b) spectral response of dip-2 at different temperatures; (c) wavelength shift versus temperature for dip-1 and dip-2.

Fig. 6. (a) Surface modification and Ab immobilization procedure; (b) zoomed fiber waist region showing RI change caused by the bonding of hCG on the fiber surface, immobilized with hCG-β Ab; (c) functionalized fiber sensor for hCG detection.

Fig. 7. Stability test of the sensor in PBS.

Fig. 8. Summary of captured Ab concentration on the capability of the fiber surface to detect hCG in the entire sample range from 0.05 to 500 mIU/mL.

Fig. 9. Summary of captured Ab concentration on the capability of the fiber surface to detect hCG in the entire sample range from 0.05 to 500 mIU/mL.

Fig. 10. Selectivity test for the sensor by immersing into a solution of Escherichia coli (7×105cfu/mL) and Staphylococcus aureus (4×106cfu/mL).