Assessing the Fate of Superparamagnetic Iron Oxide Nanoparticles Carrying Usnic Acid as Chemical Cargo on the Soil Microbial Community

In the present study we evaluate the effect of superparamagnetic iron oxide nanoparticles (SPIONs) carrying usnic acid (UA) as chemical cargo on the soil microbial community in a dystrophic red latosol (oxysol). Herein, 500 ppm UA or SPIONs-framework carrying UA were diluted in sterile ultrapure deionized water and applied by hand sprayer on the top of the soil. The experiment was conducted in a growth chamber at 25 °C, with a relative humidity of 80% and a 16 h/8 h light-dark cycle (600 lx light intensity) for 30 days. Sterile ultrapure deionized water was used as the negative control; uncapped and oleic acid (OA) capped SPIONs were also tested to assess their potential effects. Magnetic nanostructures were synthesized by a coprecipitation method and characterized by scanning and transmission electron microscopy (SEM and TEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), zeta potential, hydrodynamic diameter, magnetic measurements, and release kinetics of chemical cargo. Uncapped and OA-capped SPIONs did not significantly affect soil microbial community. Our results showed an impairment in the soil microbial community exposed to free UA, leading to a general decrease in negative effects on soil-based parameters when bioactive was loaded into the nanoscale magnetic carrier. Besides, compared to control, the free UA caused a significant decrease in microbial biomass C (39%), on the activity of acid protease (59%), and acid phosphatase (23%) enzymes, respectively. Free UA also reduced eukaryotic 18S rRNA gene abundance, suggesting a major impact on fungi. Our findings indicate that SPIONs as bioherbicide nanocarriers can reduce the negative impacts on soil. Therefore, nanoenabled biocides may improve agricultural productivity, which is important for food security due to the need of increasing food production.

Underivatized amino acids detection by anion-exchange chromatography coupled to a nanostructured detector

This work reports the development of a fast and reliable amperometric sensor for the detection of amino acids. The detector was constructed using copper nanoparticles (CuNPs) supported on reduced graphene oxide (RGO) modified glassy carbon electrode (CuNPs-RGO/GCE) and based on the application of high performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD). Under optimized isocratic HPAEC-PAD conditions (using 40 mmol L^-1 NaOH as mobile phase, flow rate of 0.30 mL min^-1 and detection potential of 0.45 V vs. Pd/PdO), the linear dynamic ranges of the concentration of amino acids obtained were 0.50-50 µmol L^-1 for lysine, 1.0-100 µmol L^-1 for alanine, glycine and serine, and 5.0-100 µmol L^-1 for leucine. The limits of detection (S/N = 3) obtained ranged from 0.10 (for lysine and leucine) to 0.50 µmol L^-1 (for alanine, glycine and serine) and sensitivity varied from 6.1 (for leucine) to 21.5 nA µmol^-1 L (for serine). The average recovery percentages ranged from 97% (for glycine) to 102% (for leucine and serine). The results obtained showed that the CuNPs-RGO/GCE has good long-term stability, repeatability and reproducibility; this makes the device suitable for application as an electrochemical detector. The successful application of the proposed method for the analysis of sugarcane vinasse demonstrates its suitability for separation and determination of amino acids in complex matrices.