Surface plasmon resonance detection of small molecule using split aptamer fragments

It was difficult to detect small molecules directly using conventional surface plasmon resonance (SPR) biosensors since the changes of refractive index, which was resulted by binding small molecules, were usually small. In this paper, split aptamer fragments were used for the construction of SPR biosensor to determine small molecule such as adenosine with high sensitivity. An aptamer for adenosine was designed to be two flexible ssDNA pieces, one was tethered on Au film and the other was modified on Au nanoparticles (AuNPs). In the presence of adenosine, two ssDNA pieces reassembled into the intact aptamer structure and the AuNPs-labeled adenosine–aptamer complex was formed on the Au film. Then, the resonance wavelength shift was enhanced obviously, due to the electronic coupling between the localized plasmon of AuNPs and the surface plasmon wave associated with Au film. The results confirmed that this biosensor could detect adenosine with high sensitivity and selectivity. The limitation of detection (LOD) of this SPR biosensor was ca. 1.5 pM, which was an approximately ca. 2–3 order of magnitude lower than that of those SPR biosensors which utilized competitive methods.