In this Letter, we demonstrate for the first time the experimental capability for the biochemical sensing of resonant nanopillars (RNPs) arrays. These arrays are fabricated over a glass substrate and are optically integrated from the backside of this substrate. The reflectivity profiles of the RNPs arrays are measured by infiltrating different ethanol fractions in water in order to evaluate the optical response for the different refractive indexes, which range from 1.330 to 1.342. A linear fit of the resonant modes shift is observed as a function of the bulk refractive index of the liquid infiltrated. For the type of transducer analyzed, a relative sensitivity of 10017  cm^−1/Refractive Index Unit (RIU) is achieved, allowing us to reach a competitive Limit of Detection (LoD) in the order of 1×10^−5  RIU.