Gold nanorod gradient surfaces

• A method for the preparation of gold nanorod gradient surfaces was developed. • The gradient surfaces exhibited a linear increase in gold nanorod surface coverage along the support. • The materials’ optical and photothermal properties were evaluated as a function of nanoparticle surface coverage. • Under near-infrared (NIR) irradiation, a temperature gradient was demonstrated, correlating with the increased surface coverage of gold nanorods. Materials based on solid-supported nanoparticles are used in a range of applications, spanning from catalysis to sensing. Controlling the inter-nanoparticle distance is essential in property optimization of these materials. To achieve such control, nanoparticle gradient surfaces, where nanoparticles are attached in a number density gradient on the support, show great promise. This study presents a tunable method for the preparation of gold nanorod gradient surfaces, exploiting nanoparticle adsorption kinetics to control the surface coverage. The method involves immersing a mercapto silane-functionalized substrate in a gold nanorod suspension, which is then withdrawn at a fixed rate. We show that the gradient dynamics can be tuned by changing the withdrawal rate, and that the gradients exhibit a linear increase in surface coverage along the distance of the support. The changes in optical properties and influence of plasmon coupling with the surface coverage of gold nanorods were evaluated using extinction spectroscopy. Additionally, by assessing the photothermal properties of the gradients upon irradiation with a near-infrared laser, through thermal imaging and in situ X-ray diffraction, we show that a temperature gradient is achieved, correlating with the increased surface coverage of gold nanorods