Preparation and SERS study of triangular silver nanoparticle self-assembled films

We report a novel type of self-assembly of triangular silver nanoparticles onto a quartzose substrate with a monolayer of poly(diallyldimethyl ammonium chloride). Attractive electrostatic interactions between the negatively charged nanoparticles and the positively charged polyelectrolyte are responsible for the self-assembly. Surface morphology and optical properties of the triangular, silver nanoparticle self-assembly film were studied by atomic force microscopy (AFM) and ultraviolet-visible (UV-vis) spectroscopy, and then compared with those of the spherical silver nanoparticle self-assembly film. It was found from the AFM measurement that most of the spherical and triangular silver nanoparticles were assembled directly onto the substrate rather than aggregated to each other. The UV-vis spectrum of the triangular, silver nanoparticle self-assembled film is quite different from that of the colloid of silver nanoparticles. A peak at 697 nm assigned to the in-plane dipole plasmon resonance shows a blue shift by 55 nm after the triangular silver nanoparticles are immobilized onto the substrate. The triangular, silver nanoparticle self-assembly film can be used as a surface-enhanced Raman scattering (SERS) substrate, and Rhodamine 6G as a Raman probe to evaluate its enhancement ability. It was found that the enhancement ability of the triangular, silver nanoparticle film is remarkable but somewhat lower than that of the spherical silver nanoparticle film. The reason for this is discussed from the point of electromagnetic mechanism and chemical mechanism. Copyright (C) 2008 John Wiley & Sons, Ltd.