Finite element calculations and fabrication of cantilever sensors for nanoscale detection

Finite element analysis (FEA) is used to study the effect of geometric variations on the properties of rectangular cantilevers and U-shaped Joule-heated cantilevers. Simulations of locally thinned cantilevers as well as of cantilevers modified by the implementing of a hole or a side cut are compared with fabricated cantilevers, which are tuned by focused ion beam (FIB) milling. By locally thinning the cantilevers, the resonance frequency and the spring constant are reduced. For a hole, the internal stress is increased while for a side cut, the lateral spring constant is decreased. Good agreement between the measured and the simulated resonance frequencies is observed. Simulations of the current density and the temperature distributions attained during the passage of current through a doped silicon layer are performed to optimize the design of Joule-heated cantilevers (U-shaped) for thermal gravimetric applications. A very uniform temperature distribution over a region near the apex can be realized by slitting the U-shaped cantilever. In such a way, the heating power can be minimized by effecting only a small variation in the geometry of a U-shaped cantilever. A simple fabrication process for the fabrication of Joule-heated cantilevers is presented, which consists mainly of a uniform conductive p-doped layer.

Neurite outgrowth on microstructured surfaces functionalized by a neural adhesion protein.

Designed networks of neurons are potentially very useful to investigate neural activities. Using photolithography microgrooves suited in size for single neurons have been produced on glass chips. Two conducting gold lanes ending in each microgroove allow extracelluar stimulation of the neurons and recording of their activity. A cell adhesive surface was created by functionalization of glass with the adhesion peptide RGDC. In addition, in order to optimize the contact of the neuronal cell membrane to the electrode surface axonin-1, a specific neural adhesion protein was used. A recombinant form of axonin-1 was produced and immobilized in a correct orientation on protected gold surfaces through a C-terminal cysteine residue. Neurite outgrowth of neurons cultured on chips derivatized with RGDC or axonin-1 were compared. The developed materials and methods represent a first step towards establishing designed functionalized glass surfaces for neurophysiological investigations.