Low-wettable Nanopatterned SERS Platform for Sub-ppt-level Detection of Xanthene Food Additive

Surface-enhanced Raman spectroscopy (SERS) is a label-free analytical technique for real-time trace-level detection. In this study, we report the formation of a monolayer SERS substrate of gold nanorods (GNRs) to detect hazardous and nonpermitted xanthene food additive dye, Rose Bengal (RB). The optimized aspect ratio of GNRs produced by a novel method is found to be an excellent candidate for the SERS substrate. Moreover, we demonstrate that a low wettability of nanometer-scale smooth (Rrms ∼0.3 nm) substrate allows a tip–tip large-area assembly of GNRs. The electromagnetic field enhancement by the assembled GNRs is further revealed by the finite-difference time-domain calculation, which enables 0.1 pM detection of RB in an aqueous medium with an analytical enhancement factor of ∼1010. The large-area homogeneity of the SERS substrate is established through Raman imaging with a standard deviation of ∼9.15%. The practical viability of the substrate is also upheld by ppb-level detection of RB in a commercial brown product.