Research Of Microcantilever Biochemical Sensing Technique

The goal to find biochemical sensors with high specificity, sensitivity and short response time are always pursued by people. Recently, the progress in the technology of Microelectromechanical System (MEMS) has brought some new ideas for this aim because of its advantages, such as large surface-area-to-volume ratio, very sensitive to surface effect, easy to realize array compact and low-cost. volume production.When a biochemical process taking place on a microcantilever surface, its surface stress changes and result in a cantilever deflection. Using this effect, an experimental system was established, and a simple-to-complex(from simple artificial PNIPAM macromolecule to complex natural Trypsin protein molecule) method was adopted to research experimentally the conformation transition of macromolecules. This investigation involves four aspects as bellow.(1) Taking a small molecule (11-mercaptoundecanoic acid, 11MUA) adsorption process as a control, the conformation transition of thiol-terminated poly(N-isopropylacrylamide) (HS-PNIPAM) in the adsorption-growth process on a microcantilever surface have been investigated. The results show that different from 11MUA whose growth process involves two phases, the growth process of HS-PNIPAM consists of three steps. By analysis, it is considered that the reason causing this difference is the conformational adjust mechanism which leads the HS-PNIPAM to form polymer brush finally.(2) Employing molecule self assembling method, PNIPAM molecules were grafted onto the surface of a microcantilever, and the cantilever deflections were detected by varying the surrounding (water solution) temperature in the range of 20°C —40℃. The results shown that the microcantilever deflects upon heating and an opposite deflection occurs upon cooling. This process corresponding to the conformation transition of PNIPAM, namely, transition between a coil conformation and a globule conformation. The deflection of the microcantilever is irreversible and shows a clear hysteresis during the whole experimental process. These phenomena are attributed to hydrogen bonding formed during the collapsing process.