With current micro and nanofabrication techniques such as photolithography and nano-imprinting, it can be difficult to control the location of nanostructures in three dimensions, due to the two-dimensional nature of the various processes. Researchers at the University of Texas at Austin, US, have been working on the problem and propose an alternative method for selectively growing gold nanoparticles in a 3D polymer microstructure. The technique could have a great impact on the development of biosensing devices, novel photonic materials and nanomaterial functionalized active micro-systems, where both the nanostructures and the 3D features play important roles.
The group's microstructure was fabricated using DPP. The system features a programmable digital micro-mirror device (DMD) for cross-section pattern definition during the layer-by-layer polymerization part of the process. A material switching step was introduced to fabricate a heterogeneous microstructure with two different liquid monomers. As shown in the figure above, the microstructure was made into a woodpile. The polymer material present in the coloured rods contains charged molecular groups, while the uncoloured ones are neutral.
Amine-bearing polyelectrolyte, branched poly(ethylenimine) (BPEI) was attached to the coloured rods exclusively due to the electrostatic force between the charged molecule groups in BPEI and the rods. The BPEI acted as both a reducing and a protective agent for the synthesis of dispersed gold nanoparticles on the coloured rods.
The microstructure was analysed using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The 3D selective decoration of the gold nanoparticles on the microstructure has been confirmed.
The selective growth method can be applied to a wide variety of nanostructured materials and their supporting microstructures. The resolution for selective growth of nanoparticles is defined by the smallest feature that the multi-material DPP technique can fabricate without the incorporation of impurities.
The researchers presented their work in Nanotechnology.