A highly structured hollow ZnO@Ag nanosphere SERS substrate for sensing traces of nitrate and nitrite species in pickled food

Abstract

A highly selective and sensitive surface-enhanced Raman scattering (SERS) sensor for nitrate and nitrite determination in foodstuffs has been developed using hollow ZnO@Ag nanosphere as a model SERS substrate. The principle of the work was based upon the significant SERS enhancement by traces of nitrite on the surface of hollow ZnO@Ag nanosphere substrate via its interaction with 4-aminothiophenol (4-ATP) and 1-naphthylamine (1-NA). This phenomenon was monitored with the emergence of a new enhanced peak at 1281 cm−1. Under the optimized experimental conditions, a wide linear range (1.0 × 10−8-1.0 × 10-3 mol L-1) for nitrite detection was obtained with lower limit of detection (LOD) 0.3 × 10−8 mol L-1. An enhancement factor for the proposed SERS substrate was found to be 3.17 × 108. Nitrate was also evaluated successfully with its environmental-friendly reduction to nitrite employing vanadium(III) chloride (3.0% VCl3 in 6.0 M HCl) reagent. TEM, FESEM, XRD, vibrational and electronic characterizations were performed. The method was applied successfully for the analysis of nitrate and nitrite in pickled radish samples. The relative standard deviation (RSD) calculated in the concentration range 0.0–30.0 μg g-1 was found lower than 14%. The proposed SERS sensors was further validated by the national standard method (GB 5009.33—2016, PR China) and the accuracy and precision were computed by students t- and F- tests at 95% confidence.