In recent years, the confinement of light within metamaterials and plasmonic graded structures, often referred to as 'rainbow' trapping, has offered novel possibilities for downsizing spectrometers, a development crucial for advancing on-chip spectral analysis. One particular challenge, especially in imaging-based spectroscopic sensing, lies in accurately determining spatial shifts. In this presentation, we introduce a plasmonic metasurface designed for 'rainbow' trapping to enhance on-chip spectrometers and sensors. By extracting the numerical centroid of the trapped surface plasmon waves, we demonstrate a miniaturized imager-based platform capable of super-resolution displacement spectroscopic sensing for specific biomedical applications. The ability to detect nanometric displacements in both spatial position and wavelength domains is pivotal in realizing ultra-sensitive on-chip imaging and sensing technologies. Furthermore, through advanced post-processing algorithms, we leverage the chip's spectral response to reconstruct incident spectral information, making it valuable for colorimetric sensing applications.