Design and Fabrication of Nanofluidic Systems for Biomolecule Characterizations

Nanofluidic channel systems were designed and fabricated by combining MEMS microfabrication with AFM nanolithography. In the fabrication process flow, photolithography was first utilized to pattern microfluidic channels and reservoirs on a 4 Pyrex substrate. Subsequently, atomic force microscopy (AFM) based nanolithography was used to mechanically fabricate nanochannels to connect the microreservoirs which formed the inlet and outlet of the nanofluidic system. A Tap190 Diamond-Like Carbon (DLC) AFM tip with a force constant of 48 N/m and a radius of less than 15 nm was used as the nanolithography tool. The resultant nanochannel ranges from 20 to 80 µm in length and 10 to 100 nm in depth. After AFM, the Pyrex micro- and nanochannels were sealed off by a matching silicon capping piece using anodic bonding. Fluidic connectors are then attached to the inlet and outlet openings to complete the fabrication process. The relationship between the nanolithography parameters of the AFM and the resultant nanochannel dimensions was investigated in detail. A mostly linear trend was obtained between the AFM tip force and the nanochannel depth for a tip speed of 1 µm/s. This result was consistent with established nanotribological models and similar studies on silicon substrates. The relationship between the number of repeated scratches and the nanochannel depth was also investigated. The results indicated that the nanochannel depth increased with the number of scratches. A depth of about 20 nm was typically achieved with 25 scratches at a tip force of 25 µN. The width of the nanochannel also increased with the number of scratches. A typical nanochannel width of 120 nm was achieved for 25 scratches at 10 µN. Two different flow tests were conducted using the nanochannel system. In the first test, a fluorescent fluid, Fluorescein, was pumped through the nanochannel to demonstrate channel patency. To achieve this, a sequential wetting procedure was executed to modify the surface chemistry of the nanochannel system. Fluorescence microscopy confirmed the passage of fluid through a 40 µm long and 45nm deep channel. In the second test, negatively charged nanobeads, carboxylate-modified FluoSpheres, were translocated through the nanochannel using an externally supplied DC electric field