Attomolar SERS detection of organophosphorous pesticides using silver mirror–like micro-pyramids as active substrate

Surface-enhanced Raman spectroscopy (SERS) is gaining importance as an ultrasensitive analytical tool for routine high-throughput analysis of a variety of molecular compounds. One of the main challenges is the development of robust, reproducible and cost-effective SERS substrates. In this work, we study the SERS activity of 3D silver mirror–like micro-pyramid structures extended in the z-direction up to 3.7 μm (G0 type substrate) or 7.7 μm (G1 type substrate), prepared by Si-based microfabrication technologies, for trace detection of organophosphorous pesticides, using paraoxon-methyl as probe molecule. The average relative standard deviation (RSD) for the SERS intensity of the peak displayed at 1338 cm⁻¹ recorded over a centimetre scale area of the substrate is below 13% for pesticide concentrations in the range 10⁻⁶ to 10⁻¹⁵ mol L⁻¹. This data underlies the spatial uniformity of the SERS response provided by the microfabrication approach. According to finite-difference time-domain (FDTD) simulations, such remarkable feature is mainly due to the contribution on electromagnetic field enhancement of edge plasmon polaritons (EPPs), propagating along the pyramid edges where the pesticide molecules are preferentially adsorbed. [Figure not available: see fulltext.]