We report a novel optical platform based on SPR generation and confinement inside a defined three-dimensional microwell geometry that leads to background resonance-free SPR images. The array shows an exceptionally high signal-to-noise ratio (S/N > 80) for imaging analysis and subnanometric thickness resolution. An angular sensitivity of 1°/0.01 RIU has been achieved and the signal to background ratio (S/B) improves to 20, 1 order of magnitude higher than that of the best literature results. The design proves effective for probing-supported lipid membrane arrays in real time with a thickness resolution of 0.24 nm and allows for imaging analysis of microfluidic circuits where resonant spots are separated by only one pixel (∼7 μm). The high image quality and unique chip geometry open up new avenues for array screening and biomicrofluidics using SPRi detection.