Silver/Alumina Core/Shell Nanopatterned Films for In-Field Detection of Soil and Water Phosphorus Using Surface Enhanced Raman Spectroscopy

In this paper, results of our running work on a sensitive and efficient detection of phosphates are presented. We develop a testing kit for rapid chemical detection based on surface-enhanced Raman scattering (SERS). We combine highly SERS active silver layer with a thin overlayer of alumina that is able to adsorb phosphorus compounds, in the form of silver/alumina core/shell nanopatterned film. In the first step, the silver layer was prepared by physical vapor deposition, followed by thermal annealing to form silver nanodots. Subsequently, alumina film was deposited over the silver nanodots using atomic layer deposition to form the silver/alumina core/shell nanopatterned surface. The prepared Ag/Al2O3 films can vary in overall thickness from 4 to 10 nm by changing the deposition parameters. The produced Ag/Al2O3 nanodots exhibit high SERS activity and significant adsorption of phosphate anions on these nanofilms has been confirmed under 532 nm excitation, which produced characteristic phosphate bands in the Raman spectra. The method will be further applied for quantitative detection of inorganic phosphates as well as organophosphates in real pond water samples.