This study introduces a novel photonic crystal fiber sensor with a modified D-shaped structure, which utilizes the surface plasmon resonance (SPR) phenomenon. The sensor is intended for detection of various analytes with refractive indices within the range of 1.31 to 1.39. To incorporate the surface plasmon resonance phenomenon, gold (Au) is taken as plasmonic layer due to its chemical stability. Gold is deposited on the external flat polished surface of the photonic crystal fiber (PCF) sensor, and an external sensing mechanism is considered to detect the analyte. The performance analysis of the proposed PCF sensor encompasses an investigation of both the approaches of wavelength and amplitude interrogation. The highest sensitivities for wavelength and amplitude are determined to be 22,000 nm/RIU and 316 RIU−1, respectively. The sensor that has been proposed exhibits finer resolution, figure of merit (FOM), and full width at half maximum (FWHM) values of 4.54 × 10–6 RIU, 185 RIU−1, and 118.9 nm, respectively. The sensor under consideration demonstrates exceptional sensing capabilities. Additionally, the sensor exhibits a high degree of suitability for efficient manufacturing processes owing to its uncomplicated design. Therefore, the proposed sensor exhibits potential applicability in the detection and analysis of diverse bio-analytes and chemicals due to its vast sensing capabilities, uncomplicated structure, and exceptional sensing efficacy.