Two-photon fabrication of three-dimensional silver microstructures in microfluidic channels for volumetric surface-enhanced Raman scattering detection

We report on the nonlinear photochemistry fabrication of three-dimensional silver (Ag) microstructures in microfluidic channels for volumetric surface-enhanced Raman scattering (3D SERS). The fabrication of high resolution 3D Ag microstructures is obtained by a two-photon induced reduction process of silver cations, which is restricted at the focal point of a Q-switched Nd:YAG microlaser (sub-nanosecond pulses at 1064 nm). Firstly, 3D Ag micro-pillars made on cover glass showed a 3D SERS detection limit of Oxazine 720 as low as 10-8 M. Secondly, we directly fabricated 3D microstructures within microfluidic channels, and demonstrated their 3D SERS capability. The micro-cube geometry gave a significantly larger 3D SERS signal than the micro-pillar geometry. This result demonstration is paving the way for further optimization routes by varying the geometry, the size, and the density of complex 3D structures which can be obtained by direct laser writing based on two-photon induced chemistry. (C) 2016 Optical Society of America