A closer look at the surface modification of silicon nanowire sensors

Silicon nanostructures are currently being discussed for various applications including drug delivery or biosensing. In order to modify the surface of such nanostructures, usually short organosilanes, such as 3-mercaptopropyltrimethoxysilane (MPTMS), are used. Although a multitude of protocols for silanization reactions are reported, most of them suffer from incompatibilities with resists used for microfabrication, from extended reaction times, and from difficulties in sample handling. We tried and overcame these challenges and developed an innovative experimental set-up suitable for the modification of a wide variety of surfaces, with a main emphasis on silicon nanostructures used in liquid-gate field effect transistors or other lab-on-chip systems. Besides planar silicon model substrates, silicon nanowires embedded into a microfabricated chip design were modified with MPTMS using our new set-up. The MPTMS layers resulting from this gas phase reaction were thoroughly analyzed chemically, and in situ I/V measurements were performed to gain insight on modification procedure. Additionally, surface changes at various pH conditions in buffer solutions were examined using the unmodified and MPTMS modified sensor.