Organized Gold Polycation Multilayers

In [55-56], the self-assembly of 15-nm-diameter gold particles in alternation with polycation PAH was demonstrated. Gold alternation with the polycation was possible because of negative nanoparticle charge (surface potential -35 mV) due to the synthesis procedure. The saturation time needed for the formation of close-packed gold nanoparticle mono-layer (full coverage) was 2 h because of the low particle concentration in solution [55]. An approach to a spatial separation of nanoparticle layers in such sandwich-like films was elaborated: three- to five polycation/polyanion interlay-ers were assembled between gold layers (e.g., Au/{PAH + (PSS/PAH)3-5}/Au). The gold surface (with a roughness of the order of the radius of nanoparticles) was covered and smoothed by the 6-10 nm polyion layer. Further "sandwiching" of gold nanoparticles with the thick polyion interlayers resulted in the ordered gold/polymer heterostructure. The low-angle, X-ray reflectivity of these samples gave 2-3 orders of Bragg reflections with the spacing corresponding to such a complex unit cell. We think that this is a general approach to creating ordered inorganic/organic heterostructure multilayers, and we have used it also for the formation of pro-tein/polyion heterostructures [77, 79].

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