Silicon Oxide Surface Functionalization by Self-Assembled Nanolayers for Micro-Cantilever Transducers

We developed a functionalization procedure for silicon oxide surfaces used in microcantilever-based sensors dedicated to the detection of food contaminants in fluid matrices. In particular we focused on the determination of heavy metal ions and of agricultural pesticides. The surface functionalization was obtained by direct self-assembly of long chain molecules bearing at one end a complexing moiety for metal ions. The selected chelating molecule, the nitrilotriacetic acid (NTA), was immobilized onto silicon oxide surfaces using a three-step process involving the consecutive addition of an organosilane, glutaraldehyde and a NTA derivative solutions. The formation of the self-assembled nanostructure (SAN) at the surface was traced by means of quartz crystal microbalance with dissipation monitoring (QCM) measurements as a function of time. The results indicated that the functionalized molecule forms a rigid self-assembled film on silicon dioxide. Data analysis provided the layer thickness and the molecular orientation of the chemisorbed layers at the interface. The optimized procedure was tentatively applied to functionalize the silicon oxide outer surface of an array of microwells each containing four microcantilevers. Quantitative determination of the metal ions complexation at the surface was achieved adding the desired solution in the QCM measuring chamber and recording the adsorbed mass change as a function of concentration.