A silane terminated poly (3-benzyloxycarbonyl-L-lysine) was synthesized and deposited as a self-assembled monolayer on the pre-colored silica substrate which was fabricated by Langmuir-Blodgett (LB) method. The monolayer was covalently attached to silica surface through terminal silane groups. The secondary structure of polymer, a-helix, was confirmed by circular dichroism spectroscopy. Furthermore, the conversion of the monolayer surface from non-ionic to cationic was accomplished by removal of 3-benzyloxycarbonyl group (Z group). The uniform monolayer on silica substrate and the changes occurring in the tethered monolayer were analyzed by atomic force microscopy (AFM). RNA aptamer with 72 sequences of nucleotides could be immobilized on the poly (L-lysine) cationic surface through electrostatic interaction. The superior recognition capability of RNA aptamer with specific microorganism is becoming a promising candidate in detection of bacteria. In this study, the binding of target bacteria, Sphingobium yanoikuyae, to the resulting RNA probe leads to a color change at the surface which is visually observed by real-time and confirmed through UV-reflective spectrophotometer. The RNA probes can be used as a high efficiency and versatile tool to visually sense the bacterial contamination in the food products. q