Fabrication of microparticles with controllable internal woodpile structures for highly efficient sensing applications

Here, we report the fabrication of freestanding three-dimensional (3D) microparticles with internal woodpile structures via prism holographic lithography (HL) and a hot-embossing process. These internal woodpile structures with different reflectance peaks in the microparticles can act as encoded information carriers for multiplex immunoassays. Furthermore, due to the high surface area of the interconnected 3D structures, the HL-featured microparticles exhibited highly enhanced SERS signals, and fast analyte-adsorption binding kinetics coming from the interconnected nanopores that could enhance mass transport of target molecules from the bulk phase to the internal binding sites when they were decorated with silver nanoparticles. These particles overcome the limitation of substrate-based SERS detection methods in which the binding kinetics is slow because of their limited mobility, and these hierarchically-featured 3D porous microparticles could be used for high-sensitivity SERS-based detection. We further obtained a ten-fold increase in fluorescence signal from our HL-derived structures compared with 2D smooth structures. Overall, the designed high-throughput 3D microparticles with internal nanostructures could be used for high-sensitivity SERS or fluorescence based detection in microfluidic devices for biotechnology applications.