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A new tool for sorting molecules

Researchers solve a hurdle of bionanotechnology

Oeiras, 10.01.11

Separating objects of different sizes and shapes may seem like a child play but things do get difficult at the nanoscale, where a difference of 0.000002 milimeters may mean twice as big. In fact, the coated gold nanoparticles promising for so many bionanotechnological applications often vary in size, shell composition, and morphology and determining their properties is limited to bulk averaging. Now Yann Astier and collaborators have devised a detection scheme to make characterizations on single-particle basis. The work in published in Small.

One can picture this detection scheme as a glass sieve with very tiny and regular pores; the nanopores are obtained by using a high resolution transmission electron microscope to beam electrons on a silicon nitrate surface. To make this sieve useful for biological applications, pores are coated with biocompatible molecules. The sieve can thus be tailored to have a functionalized pore diameter of 3.2 to 6.5 nanometers (one nanometer is a millionth of a millimeter).

Coated gold nanoparticles of different sizes are filtered through this nanosieve; the particles are negatively charged, and thus applying an electrical potential to the sieve makes particles move through it, generating a measurable current. What researchers observed, is that the mere interaction of coated gold particles with the pore affects this current. If the particle actually moves through the pore, the blockage is higher. So, by simply examining the current variations it is possible to determine how many molecules are in solution and their size distribution. And as different particle surfaces affect current differently, the sieve can also determine morphology. This means researchers have now a tool for quickly sorting molecules one by one. This monomolecular method can give up to 5,000 measurements in a few minutes.

But things get even more interesting for researchers. Current blockages are a result of the type of dynamic molecular binding - hydrogen bridges and hydrophobic (water hating) interactions – that regulate protein-protein interactions. This opens a new door to study interactions in the living world: one by one.

Original Article

Article first published online DOI: 10.1002/smll.201002113

Artificial Surface-Modified Si3N4 Nanopores for Single Surface-Modified Gold Nanoparticle Scanning

Yann Astier, Lucien Datas, Randy Carney, Francesco Stellacci, Francesco Gentile, Enzo DiFabrizio

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