Depletion-Mediated Uniform Deposition of Nanorods with Patterned, Multiplexed Assembly

Device-scale, uniform, and controllable deposition of nanoparticles on various substrates is fundamentally important not only for the fabrication of thin-film devices but also for the large sample statistics of single-particle performances. However, it is challenging to obtain such predefined depositions using a simple and efficient method. Here, we present a novel strategy for obtaining the uniform and particle density/spacing-tunable deposition of nanorods on a linker-free substrate. The deposition is driven by the tailored particle-substrate depletion attraction owing to the size-matched design of the substrate roughness and the nanorod diameter. Both gold nanorods and upconversion nanorods were applied to demonstrate the generality of the method. The high particle density of more than 21 per μm² and correspondingly the small particle spacing of fewer than 0.3 μm were achieved on a scalable substrate template. On this basis, orientational ordering and pattern-selective deposition of nanorods were realized by controlling the liquid flow rate and employing the substrate with patterned roughness areas, respectively. With the roughness-directed density-tunable depositions of nanorods integrated onto a single platform, multiplexed gold nanorod assembly and programmable surface-enhanced Raman mapping were achieved, with a promising prospect in information encoding by using the Raman signals as the translation units. The thermal stability and related transition temperature of about 160 °C of gold nanorods were also revealed as an application of single-particle statistics. This practical method could be extended to wide ranges of potential applications in plasmonic coupling devices, cryptography, or single-particle performance statistics with the feature of the high-throughput, low-cost, and scalable fabrication.