In biological as well as chemical nano-technology of the future, a device that is capable of planting functional molecules within targeted regions of sub-micron to nanometer order will have broad applications in the future, e.g., as a new method of gene transfer, enzyme replacement, and local modifications of gels and surfaces. Knowing that pioneering effort has been made by several groups, we tried to use an atomic force microscope (AFM) as a nano-planting device of functional molecules in small regions such as the interior of organic gels or biological cells. A piece of ZnO whisker was glued to the free end of an AFM cantilever and coated with thin layers of gold film by sputtering. The whisker bearing cantilever was then modified with fluorescently labeled biological molecules through the photocleavable bi-functional cross-linker which was synthesized according to the method of Olejnik et al . The disulfide carrying cross-linker has the ability to react with gold by forming -Au-S- bonds. The cantilever was then mounted on an AFM and brought in contact with a thin layer of agarose gel. The cantilever was irradiated with light of 365 nm in wavelength to free the fluorescently labeled molecules. Examination of the gel revealed the presence of the fluorescent dye in the very confined region that was in contact with the whisker. We are now trying to transfer labeled molecules from the whisker to the interior of live fibroblast after piercing through the cell membrane with the modified whisker. Due to the increased mobility of the freed molecules, it has so far been difficult to identify a small number of functional molecules in the cell, but we believe that by using immobilization technique of the freed molecules we should be able to quantify the amount of the labeled molecules planted inside the live cell. In the future, a combined use of photo-cleavable and photo-activatable cross-linkers will enable us to simultaneously dissociate them from the AFM tip and covalently plant them in a new environment.
 J. Olejnik et al, Methods Enzymol. 291, 135-154 (1998)