Asymmetric split ring resonators (A-SRRs) are formed when two separate metallic arcs of different lengths share the same centre-of-curvature. The resonances of the two arcs interact to produce steep slopes in the reflection spectrum. Due to their size they are also known as nano antennas. By depositing very thin films of poly-methyl-methacrylate (PMMA), a shift in resonance reflection spectra is obtained. Similarly, it is known that the spectral position of the A-SRR resonances can be tuned with size. We show that, when PMMA is used as an organic probe (analyte) on top of an A-SRR array, the phase and amplitude of a characteristic molecular bond resonance associated with PMMA changes the appearance of the observed Fano resonance, according to the spectral position of the plasmonic reflection peaks. This effect can be utilized to give characteristic signatures for the purpose of detection. We also show the effectiveness of localizing different blocks of PMMA at different places on the A-SRR array to detect very small amounts of non-uniformly distributed analytes. Finally we show that even though the resonance Q-factor is much smaller when compared to values achievable in photonic crystal microcavities, the plasmonic nano-antenna arrays can be used to provide highly sensitive detection of organic compounds.