Development of a Label-Free Optical Biosensor Using Porous Anodic Alumina (PAA) Layer Chip

The hybridization of probe DNA with target DNA will lead to changes in the mass, electrical charge, or optical properties of the immobilized DNA layer, which can be detected by microgrativimetric, potentio-metric, amperometric or optical transducers. For this reason, we developed a new Localized Surface Plasmon Resonance (LSPR) based label-free optical biosensor in connection with a Porous Anodic Alumina (PAA) layer chip. For the fabrication of PAA layer chip, a double oxidation step method was developed, which used oxalic acid as oxidizing agent at an oxidation voltage of 40 V. In our sensor, the absorbance at surface of PAA layer chip resulted in an interferometric pattern that was related to the LSPR optical properties of bio-molecules. All absorbance spectra were taken from 400 to 850 nm on the UV-visible spectrophotometer at room temperature. The absorbance strength increased with the formation of double-helix with the probe target DNA hybridization. The reaction of mismatch DNA did not cause a significant increase in the absorbance, but only a slight bathochromic shift was observed. However, the binding of match DNA caused a significant bathochromic shift and increase in the absorbance indicating the complete hybridization. We expect that this detection method using LSPR based label-free optical biosensor can be used for analysis conveniently with high sensitivity, because there is no necessity of labeling such as the enzymes and the fluorescent dye.