This paper presents a novel Mach-Zehnder interferometer (MZI) integrated with a surface plasmon resonance (SPR) biosensor to enhance the detection of biomolecular interactions in a simplified and cost-effective manner. Traditional SPR sensors rely on broadband light sources and high-resolution spectrum analyzers to detect resonance wavelength shifts, increasing system complexity and cost. Our proposed architecture eliminates these requirements by employing a monochromatic laser source tuned to the SPR resonance wavelength, a phase shifter, a variable optical attenuator, and a power detector. By optimizing the phase and amplitude in the MZI reference arm, the system achieves -30 dBm output power in the absence of the target analyte, enabling sensitive detection of minute refractive index changes through power variations. The output power increases dramatically from -30 dBm to -3.3 dBm for a refractive index change from 1.33 to 1.34, facilitating real-time, label-free biomolecular analysis. This compact, low-cost design offers a robust platform for biomedical diagnostics.