We have demonstrated two types of size separation of biomolecules using a nanostructured matrix artificially fabricated using electron-beam lithography: sieve-type separation using a regular pillar array structure and size exclusion chromatography (SEC) type separation using a structure with narrow and wide gaps. With these devices, samples of double-stranded DNA molecules (2, 5, and 10 k base pairs) were clearly separated into bands; smaller molecules eluted earlier in the sieve type while they eluted later in the SEC type. The nanostructured matrix enables various types of molecular separation by changing the design of the nanostructure. Moreover, it should be easy to integrate the matrix with other biomolecular fluidic devices because it does not require a filling medium.

We numerically investigated contact characteristics of a contact pad with a rough disk surface and the possibility of contact/near-contact sliders, using a single-degree-of-freedom (1-DOF) slider and a random wavy surface model with random roughness. Contact characteristics of a contact pad are numerically calculated based on a modified Greenwood-Williamson model, considering the bulk deformation of the surface due to all other asperity contact forces. It was found that contact stiffness and other characteristics are mainly determined by asperity contact, to the extent that the contact pad penetrates into the upper standard deviation of asperity peak height. However, the contact stiffness tends to approach a constant value as the pad penetrates into the average asperity height because the bulk deformation becomes predominant. From the numerical simulations of a 1-DOF air bearing slider model in contact and near-contact regimes over a random wavy surface with random roughness, a typical example of design condition of disk surface waviness in terms of the tracking ability and wear durability are shown, and the possibility and difficulty of a contact/near-contact slider is discussed. Finally, we analyzed meniscus effects on the contact characteristics and found a hysteresis process of the touch down and take off of a slider due to the meniscus force.

We have achieved the size separation of DNA molecules on a biochip using an anodic porous alumina as a separation matrix in electrophoresis. The bottom of the microfluid channel on the chip was made of a porous alumina membrane that has uniform nanoscale pores on its surface. Since smaller molecules are much more frequently trapped by nanopores than larger ones, larger molecules elute earlier than smaller molecules. This type of separation is the same process as that resulting from size-exclusion chromatography. When two kinds of DNA samples (3.2 and 0.3 kilobases) were applied to the biochip, they were clearly separated into two bands, with the larger molecules (3.2 kilobases) eluting earlier. Since nanopore formation does not require any nanolithography, the fabrication is easy and inexpensive. The matrix can be integrated with other biomicroelectromechanical systems reactors on a micro total analysis system chip.

No abstract

No abstract