Nanoelectronics on a molecular length scale is an emerging high technology and bound to particular electrical properties of molecular structures. It has found in semiconducting carbon nanotubes (CNT's) a construction element, that allows to combine traditional microelectronics fabrication technology (mainly nanoscale lithography) with dimensional requirements of a future integrated circuit family. Nevertheless, it lacks properties of self-organization, which is intrinsic only to biological systems. Comparing geometrical and durability properties, the Tobacco Mosaic Virus (TMV) shows similitude to carbon nanotubes, but as a microbiological object it intrinsically displays self-organization properties, which are useful in future nanobiosystems and needed particularly in bioelectronics applications. TMV is a rigid rod-shaped virus of 2R=18 nm outer diameter and about 2L=60....1000 nm of length, the latter determined from electron-microscopic viewgraphs of a TMV ensemble. The radius-to-length ratio e=R/L extents over more than one order of magnitude between e=0.018...0.300. This turns out to be an useful property for a dielectrophoretic sorting of virus populations of different size. The technique of dielectrophoretic separation is based on intrinsic dielectric properties of cells and particles and has been applied to cell discrimination of diverse nature. Little is known about electrical properties of TMV and their dependence on length extension of the virus. Natural populations with its length variety between 60 and 1000 nm need to be separated in subgroups of size in order to be analyzed or further cultured. We develop in the present paper a theoretical framework, which allows to separate TMV of different lengths by means of a dielectrophoretic process in a microcontact array. A size-selective separation can be achieved, given correct medium permittivity and conductivity, as well as frequency of the applied electric field. The induced electrical polarization of the tiny objects is the essential property in this process and enters the equation of field force. While the modeling of larger TMV columns as general ellipsoids is feasible, an approximation procedure for short TMV as dielectric bodies of cylindrical shape is necessary. The dipole moment of TMV with a variable radius-to-length relation gives rise to the separation process. It is shown in this paper, that an experimental separation protocol can be established.
Alfred F. K. Zehe
Facultad de Cs. Físico-Matemáticas
Benemérita Universidad Autónoma de Puebla
Puebla, Pue. 72000 Mexico
Phone: +52 222 2295500 ext. 7851 Fax: +52 222 2402197