Tuning the number density of nanoparticles by multivariant tailoring of attachment pointson flat substrates

Abstract

We report on the organization of nanoparticles on a flat surface when there is strongyet tunable interaction between the particles and the surface. Specifically, wetailor the number density of citrate-stabilized gold nanoparticles on flat substratesby varying the concentration of the grafted amino groups on the surfaces andtheir degree of ionization. While the former effect is accomplished by decoratingsilica-based substrates with a molecular gradient of (3-aminopropyl)triethoxysilane(APTES), the latter effect is achieved by varying the degree of ionization of the−NH2 groups in APTES by varying the pH of the gold sol. We show that the measurement ofparticle number density on an APTES concentration gradient substrate at different pHvalues provides a simple, non-spectroscopic means to deduce the relative molecularconcentration profile of APTES on the substrate.