Pan Mao, Anthony G. Balducci, Michael Previte, Peter T.C. So

Hindered transport of macromolecules in liquid-filled pores is important to biological membrane processes associated with cell biology and medical physiology, chromatography, separation, and heterogeneous catalysis. It is highly desirable to conduct well-controlled, model-based studies of molecular and fluidic transport process in a confined space. Compared to nanoporous track-etched membranes, micromachined nanofluidic structures offer unique advantages, including well-controlled physical and chemical properties and compatibility with various single molecule detection methods.

We propose a combination of fluorescence microscopy and well-defined geometries to study transport of ions or molecules confined in nanoscale space which approaches molecular dimensions, as shown in Fig 1. Fluorescence microscopy allows us to visualize the motion and conformational change of molecules (especially large flexible molecules like DNA) in a nanochannel, thus enabling the study of polymer statics and dynamics of single molecules in confined environments(1, 2). In addition, fluorescence correlation spectroscopy (FCS) has a unique ability in observing single molecules at molecular level, extracting valuable information about molecular dynamics and biochemical reactions3. The effects of spatial confinement and surface boundary layer on the diffusivity of small biomolecules (such as DNA and protein) within a nanochannel are being investigated by two-photon FCS. The potential impact of this research would be significant both scientifically and technologically by offering a better understanding of molecular diffusion and transport in confined environments as well as generating new concepts of molecular sorting and manipulation technology.

Figure 1 (A) Schematic diagram of a single, large DNA molecule confined to a slit glass nanochannel with a depth of H, examined by epifluorescence video microscopy. (B) Schematic diagram of detecting single, small molecules by two-photo FCS in a slit nanochannel with vertical confinement.

References

1. Chen, Y.-L. et al. "Conformation and dynamics of single DNA molecules in parallel-plate slit microchannels," Physical Review Letters E 70, 060901.1-4 (2004).
2. Tegenfeldt, J. O. et al. "The dynamics of genomic-length DNA molecules in 100-nm channels," Proceedings of the National Academy of Sciences of the United States of America 101, 10979-10983 (2004).
3. Foquet, M., Korlach, J., Zipfel, W. R., Webb, W. W. & Craighead, H. G. "Focal Volume Confinement by Submicronmeter-sized Fluidic Channels," Analytical Chemistry 76, 1618-1626 (2004).