Polarization-dependent surface-enhanced Raman scattering (SERS) from microarrays.

The convergence between nanometric sensing (e.g. surface-enhanced Raman scattering - SERS) and lab-on-chip technologies has emerged as a potential revolutionary approach for a variety of "real-world" applications. Surface plasmons (SPs) can be excited on metal interfaces through light coupling to metallic surface gratings. The generation of SPs is a fundamental requirement for SERS. The work reported in this paper demonstrates a versatile procedure to prepare both large area (i.e. one inch2) and microarrays (μarrays) metallic gratings structures capable of supporting SP excitation (and SERS). Laser interference lithography (LIL), either alone or combined with traditional laser photolithography (LPL), was used to generate the periodic patterns. The fabrication procedure was simple, high-throughput, and reproducible, with array-to-array variations in geometrical parameters of less than 5%. Since the basic pattern of the nanostructures was a one-dimensional grating, the polarization anisotropy nature of the substrates was also explored. The use of these polarization-dependent properties to eliminate non-polarization sensitive interferences (e.g. spurious spectral background) was demonstrated. Lastly, the nanostructured gold μarrays were integrated on a chip for SERS detection of ppm-levels of 8-quinolinol, an emerging pharmaceutical contaminant in aquatic systems. A low-cost structure for fluid handling was realized by simply using perforated epoxy membranes. The results demonstrated that the procedure described here is suitable for the generation of simple integrated μarrays for SERS applications in environmental analysis.