This paper presents a biosensor utilizing a whispering gallery mode (WGM) resonator characterized by azimuthal symmetry and crescent-shaped coatings of silver. The study investigates the impact of the coupling gap on the extinction ratio and Q-factor of the setup. The resonator is coated with silver in crescent shapes, ranging from 40 nm to 65 nm in thickness. Coupling is achieved with a silica waveguide, simulating the tapered fiber coupling method. Notably, the resonator exhibits a maximum sensitivity of 220 nm/RIU when coated with 55-nm-thick silver in conjunction with a 4-nm-thick layer of thiol-tethered deoxyribonucleic acid (DNA). This biosensor holds promise for biomolecule detection applications.