Fabrication of large-area metal nanoparticle arrays by nanosphere lithography for localized surface plasmon resonance biosensors

The localized surface plasmon resonance (LSPR) phenomenon that is characteristic of gold and silver nanoparticles has applications in areas such as portable and remote chemical and biological sensing. However, fabrication of metal nanoparticle arrays with high uniformity and repeatability, at a reasonable cost, is difficult. Nanosphere lithography (NSL) has been used to produce inexpensive nanoparticle arrays, through the use of monolayers of self-assembled microspheres as a deposition mask. However, lack of control over the location and size of the arrays, as well as poor uniformity over large areas, limits its use to research purposes. Here, we present large-area fabrication of nanoparticle arrays through both convective self-assembly NSL (CSANSL) and our new method, geometrically confined NSL (GCNSL). In GCNSL, microsphere assembly is confined to geometric patterns defined in photoresist. We show that 400nm polystyrene microspheres can be assembled inside of large arrays of photoresist trenches from 4-20 mu m in width and 500 mu m in length, with high uniformity, repeatability, and quality. Compared to CSANSL, GCNSL allows precise patterning of nanoparticle arrays for use in practical LSPR sensing devices, while still remaining inexpensive.