| SUBJECT |
TARGETED SMART DUST HOW IT WORKS: In order to spontaneously assemble and orient the micron-sized porous Si "smart dust," we couple chemical modification with the electrochemical machining process used to prepare the nanostructures. The process involves two steps, see the scheme below. In the first step, a porous photonic structure is produced by etching silicon with an electrochemical machining process. This step imparts a highly reflective and specific color-code to the material, that acts like an address, or identifying bar-code for the particles. The second step involves chemically modifying the porous silicon photonic structure so that it will find and stick to the desired target. In the present case, we use chemistry that will target the interface between a drop of oil in water, but we hope to be able to apply the methodology to pollution particles, pathogenic bacteria, and cancer cells. The two steps (etch and modify) are repeated with a different color and a different chemistry, yielding two-sided films. The films are broken up into particles about the size of a human hair. With the chemistry shown below, the particles seek out and attach themselves to an oil drop, presenting their red surface to the outside world and their green surface towards the inside of the drop. Once they find the interface for which they were programmed, the individual mirrored particles begin to line up, or "tile" themselves on the surface of the target. As an individual, each particle is too small for one to observe the color code. However, when they tile at the interface, the optical properties of the ensemble combine to give a mirror whose characteristic color is easily observed. This collective behavior provides a means of amplifying the molecular recognition event that occurs at the surface of each individual particle. As a means of signalling their presence at the interface, the particles change color. As the nanostructure comes in contact with the oil drop, some of the liquid from the target is absorbed into it. The liquid only wicks into the regions of the nanostructure that have been modified with the appropriate chemistry. The presence of the liquid in the nanostructure causes a predictable change in the color code, signalling to the outside observer that the correct target has been located |
| UPDATE | 08.03 |
| AUTHOR | This data is not available for free |
| LITERATURE REF. | This data is not available for free |
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