Polarization and magnetic aggregation enhanced SERS recognition of nitrite in water by Ag/PEI/α-Fe2O3 porous nanorods.

How to improve surface-enhanced Raman scattering (SERS) performance for the detection of ultra-low concentration pollutants in water remains a critical research topic. Nitrite ions (NO2-), widely present and utilized in daily life, can readily enter aquatic environments. Once adsorbed onto organic matter, they pose serious threats to human health. Herein, we report a facile method to construct magnetic Ag/PEI/α-Fe2O3 porous nanorods to boost the SERS performance towards recognizing NO2- in water. The concentration of NO2- in water could be evaluated via surface-enhanced Raman scattering (SERS) in the range of 10-9-10-3 mol L-1 with a detection limit as low as 4.91 × 10-10 mol L-1, and the enhancement factor reaches approximately 1.95 × 107. The recovery range is 98%, while the relative standard deviation among the 10 samples is 7.14%. In addition, the application of an external magnetic field can increase the detection sensitivity by 2.54 times. The enhancement was ascribed to the enhanced polarization at the junction interface arising from the electron flow from Fe2O3 to Ag, together with the magnetic self-assembling effects. In addition, the porous structure could enhance the reflection times of laser light, which could further enhance the SERS performance. The sensor also demonstrates highly sensitive recognition of NO2- in real water and food samples. This work offers an approach for the design and fabrication of highly sensitive SERS sensors, and provides a comprehensive understanding of the enhancement mechanism, which may have application potential in NO2- detection and the design of high-performance sensors.