A modified solid-core photonic crystal fiber (PCF)-based plasmonic sensor is proposed where light propagation through the PCF is controlled by scaling down of air holes. The modified core facilitates the easy excitation of the plasmonic surface, resulting in improved sensor performance. The chemically stable gold is externally coated on the PCF surface, which helps to establish surface plasmon resonance phenomena. The response of the sensor is analyzed based on the numerical method, and the design parameters are optimized to enhance the sensing performance. The asymmetric fiber-core structure provides the polarization controllability and significantly suppresses the 𝑦$y$-polarized response to achieve a dominant 𝑥$x$-polarized response and additional functionalities. The sensor exhibits a maximum wavelength sensitivity of 11,000 nm/RIU (refractive index unit) and sensing resolution of 9.09×10−6$9.09\times 10-6$ RIU in the 𝑥$x$-polarized mode. Also, the sensor exhibits maximum amplitude sensitivity of 631RIU−1$631RIU-1$, and a good figure of merit is 157RIU−1$157RIU-1$. Furthermore, the sensor can detect the unknown analytes’ refractive index (RI) in the sensing analyte RI range of 1.33 to 1.40, which will lead to finding the potential applications in biomolecules, organic chemicals, and environment monitoring.