Real-time detection of the interaction between alpha-fetoprotein and its ssDNA aptamer by dual polarization interferometry

Abstract

Aptamers have recently been widely employed as recognition elements for the discovery and detection of protein biomarkers. Therefore a comprehensive and in-depth understanding of the interaction between aptamers and their target proteins is especially important. Herein we report a real-time and label-free strategy to detect the interaction between alpha-fetoprotein (AFP), a specific biomarker of hepatocellular carcinoma, and its specific ssDNA aptamer based on dual polarization interferometry (DPI). The ssDNA aptamer was immobilized on the surface of a sensor chip followed by AFP injection, while the changes of mass, thickness and density on the AFP–aptamer interface were monitored and recorded online by DPI. The experimental results showed that there were two different interaction patterns between AFP and the aptamer, which were specific binding and unspecific binding, and the former was found to be the dominant one. AFP binding makes the conformation of the aptamer change, resulting in an increase of mass/thickness and a decrease of density. The concentration of AFP is very important for the AFP–aptamer interaction, as a high AFP concentration will lead to a high probability of the aptamer capturing AFP and therefore a large binding amount and a high mass loading rate. The developed detection method proved effective to study the interaction behavior and mechanism between AFP and its aptamer, and will find wide applications in the detection and understanding of protein–aptamer interaction.