"High-sensitivity gold-coated photonic crystal fiber (PCF) refractive index (RI) biosensor based on surface plasmon resonance (SPR) is proposed. To evaluate the sensing characteristics of the proposed sensor, the finite element method (FEM) is used. As a base material, silica is used and as a plasmonic material, 40-nm thickness gold layer is chosen. Resonance of electrons requires active plasmonic material. Gold is chosen because it has the highest plasmonic activity of all active plasmonic materials and offers the best resonance. The uppermost wavelength sensitivity response of 45,409.14 nm/RIU is obtained at RI 1.35. The maximum amplitude resolution, amplitude sensitivity response, birefringence, transmittance, coupling length, and dispersion of 2.52 × 10−05, 7679.06 RIU−1, 3.1 × 10−4, − 24.5 dB, 1,87,500 µm, and − 7000 ps/(nm-km) are obtained respectively. The proposed sensor is a strong contender for detecting microfluidic analytes in the biosensor field for its exceptional sensitivity response, compact structural design, and tunable performance.