Facile fabrication of silver nanoparticle decorated α-FeO nanoflakes as ultrasensitive surface-enhanced Raman spectroscopy substrates.

Although great progress has been made on designing noble metal nanoparticle aggregates/assemblies as surface-enhanced Raman spectroscopy (SERS) substrates, an ever increasing research interest has focused on fabrication of hierarchical nanostructures for superior SERS performance. Here, we report effective decoration of silver nanoparticles (AgNPs) onto vertically and densely grown α-FeO nanoflakes (NFs) as SERS active substrates. The SERS substrate was prepared by thermally annealing Fe foil at 450 °C to grow α-FeO NFs and electroless deposition of AgNPs onto α-FeO NFs, with excellent ability to control the particle size and density. The AgNP-decorated α-FeO NFs offer high density hot spots and exhibited high SERS performance with enhancement factor of 8.1 × 10. Integration of α-FeO nanostructure functions as intrinsic internal standard and selective binder for specific analytes like the toxic arsenic. The substrate was successfully used for quantitative detection of arsenic with spatial uniformity (relative standard deviation, RSD, 8.8%) and good reproducibility (RSD, 9.7%). The Raman signal of α-FeO integrated to the SERS substrate was utilized as internal standard which significantly improves reproducibility. The substrate exhibited a high sensitivity for arsenic detection with a limit of detection down to 1.5 μg L, which is much lower than permissible limit (10 μg L) set by the WHO. Moreover, the SERS substrates showed excellent practicability and selectivity for determination of arsenic in environmental waters which is valuable for environmental and human health protection.