## 3 Results and Discussion
Their size is typically above one micron. High-contrast SEM images support the assumption that these filamentous particles are formed by networks integrating macromolecular filaments and filament-bonded metal nanoparticles. Figure 6: Evolution of particle formation and assembly: (**a**) illustration of structural hierarchy in the formation and assembly of gold nanoparticles during their formation by the reduction of HAuCl4 with ascorbic acid; (**b**) example of temporal evolution reflecting the formation of single particles in the beginning (first measurement cycles) and later increasing long-wavelength absorption indicating the formation of particle clusters. The effect of poly-DADMAC is not limited to causing particle attachment. In addition, the application of these polycatonic molecules influences the particle nucleation and growth. The addition of a final concentration of 100 ppm poly-DADMAC leads to a significant reduction in the formation rate of small spherical or compact nanoparticles with the characteristic resonance at about 550 nm (Figure 7a) and to a significant enhancement of absorption in the NIR range (Figure 7b). In experiments with a reduced concentration of ascorbic acid of 60 \(\upmu\)M and 70 \(\upmu\)M HAuCl4, this long-wavelength absorption is related to the formation of nonspherical gold nanoparticles with higher aspect ratios (Figure 8a-d). In addition, it is remarkable that the increase of 550 nm absorption in the presence of poly-DADMAC occurs approximately linearly, which indicates a slow and nearly constant formation rate of small gold nanoparticles (1-min intervals in Figure 7c). In contrast, the absorption at 800 nm shows an increasing growth rate for the first measurement cycles (Figure 7c). This indicates an accelerated process. This can be interpreted as a comparatively low rate of nucleation for gold nanocrystals that are able to grow and as an acceleration of gold deposition on growing nanocrystals due to the increase in crystal surface area. Indeed, the formation of some flat, regular nanoprisms with side lengths above one micrometer has been observed in the related sample (Figure 8a). A further enhancement of poly-DADMAC concentration promotes the formation of fractal gold nanocrystals (Figure 8b-d). Highly fractal nanoparticles with a high specific surface area (Figure 1h) are formed by a combination of dendritic crystal growth and attachment of small gold nanoparticles on the crystal surface. The formation of highly structured particles with a typical size in the submicron range can be also generated by the common addition of small amounts of a polyanionic macromolecule PSS to the poly-DADMAC-containing solution (Figure 8e). It is assumed that the effect of the poly-DADMAC is mainly related to the electrostatic effect of macromolecules adsorbing onto the surface of growing nanoparticles. An excess of positive charge on particles during the growth process can lower the growth rates, on the one side. On the other side, it causes a self-polarization effect in the case of nonspherical particles. This could be the reason for the preferential edge- and corner-oriented growth of flat gold nanoprisms induced by an attractive Coulomb interaction between the positively polarized particle corners and the negatively charged tetrachlorourate. The formation of nonspherical, star-like and special-shaped crystalline gold nanoparticles [31; 32; 33] depends on the empirically optimized composition of reaction solutions and is known to be related to symmetry breaking during nanoparticle formation [47]. Figure 7: Cont. Figure 8: Typical nonspherical gold nanoparticles forming in the presence of poly-DADMAC: (**a**,**b**) 70 \(\mu\)M HAuCl\({}_{4}\), 60 \(\mu\)M ascorbic acid, 100 ppm poly-DADMAC; (**c**) 70 \(\mu\)M HAuCl\({}_{4}\), 60 \(\mu\)M ascorbic acid, 250 ppm poly-DADMAC; (**d**) 70 \(\mu\)M HAuCl\({}_{4}\), 60 \(\mu\)M ascorbic acid, 400 ppm poly-DADMAC; (**e**) 50 \(\mu\)M HAuCl\({}_{4}\), 100 \(\mu\)M ascorbic acid, 60 ppm poly-DADMAC, 10 ppm PSS.