Estudo do uso de nanopartículas metálicas (NPM) e filmes finos metálicos em amostras de grãos para o aprimoramento da performance analítica da técnica de Espectroscopia de Emissão Óptica Induzida por Laser (LIBS)

Abstract

The agricultural sector is responsible for nearly ¼ of Brazil’s GDP, and consolidates the country as one of the largest producers of food globally. Given this scenario, the need for analysis techniques regarding the composition, which envisions the quality control of grains, is proving to be more and more necessary. Between all of the analytic techniques, the LIBS (Laser Induced Breakdown Spectroscopy) technique has proven to be relevant because of its versatility, ease of application, robustness, multi-element analysis capability, among other benefits. Despite all of the advantages of this technique, there are still many efforts in improving the sensibility of the technique. Improvements, such as double-pulsed LIBS (DP-LIBS), femtosecond LIBS (fs-LIBS), or the use of metallic nanoparticles (NELIBS), have been studied for optimizing, among other parameters, the limit of detection (LOD). The use of metallic nanoparticles, in particular, associated to LIBS (NELIBS) has shown relevant results for the enhancement of the technique. While most of the work in the literature has been focused on metallic, vitreous or ceramics, samples, this work is focused on the use (or incorporation) of metallic nanoparticles, as well as thin metallic films, in grain samples (coffee, corn, sorghum, soy) for the analytic enhancement of LIBS. The best results were achieved using thin gold (Au) films deposited on the surface of the grain samples. Expressive gains in intensity of the atomic lines were observed, in the order of 200% for coffee, 600% for corn, 1500% for sorghum, 600% for soy in selected atomic lines of iron (Fe). This work aims to measure the gain in intensity of the most relevant atomic lines present in the spectrum, and to analyze the possible mechanism that led to this phenomenon, through the investigation of the plasma’s temperature and electron density. The results show an indicative increase in both temperature and plasma density for the samples with deposited nanoparticles, as well as, the ones coated with thin films.