Detection of the self-assembly of poly-（N-isopropylacrylamide） on gold based on microcantilever sensor

Abstract

A microcantilever sensor platform is used for detecting the self-assembly of poly-（N-isopropylacrylamide） （HS-PNIPAM） on gold surface. The change of the interaction between molecules caused by conformation transition will change the surface stress of the microcantilever which causes its bending. The kinetic curves of self-assembly can be obtained by real-time monitoring the deflection of the microcantilever using the optical lever read-out technique. HS-PNIPAMs of different molecular weight were used to study the self-assembly process, and the results showed that the kinetic curves can be divided into three stages corresponding to different conformations, respectively. The first stage cor responds to physical adsorption of HS-PNIPAM on gold-coated side. The second and third stages correspond to chemical adsorption on gold-coated side with conformation transition. The kinetic curves fit Langmuir adsorption isotherm well. The results also show that the reaction rate κ of HS-PNIPAM is far less than that of small molecules and decreases exponentially with the molecular weight; while the time of HS-PNIPAM’s self-assembly is far greater than that of small molecules and proportional to the molecular weight. The change of the surface stress is linear to the molecular weight of HS-PNIPAM.