Design and fabrication of nanofluidic devices by surface micromachining

Using surface micromachining technology, we fabricated nanofluidic devices with channels down to 10 nm deep, 200 nm wide and up to 8 cm long. We demonstrated that different materials, such as silicon nitride, polysilicon and silicon dioxide, combined with variations of the fabrication procedure, could be used to make channels both on silicon and glass substrates. Critical channel design parameters were also examined. With the channels as the basis, we integrated equivalent elements which are found on micro total analysis (mu TAS) chips for electrokinetic separations. On-chip platinum electrodes enabled electrokinetic liquid actuation. Micro-moulded polydimethylsiloxane (PDMS) structures bonded to the devices served as liquid reservoirs for buffers and sample. Ionic conductance measurements showed Ohmic behaviour at ion concentrations above 10 mM, and surface charge governed ion transport below 5 mM. Low device to device conductance variation (1%) indicated excellent channel uniformity on the wafer level. As proof of concept, we demonstrated electrokinetic injections using an injection cross with volume below 50 attolitres (10^-18 l).