Plasma-Assisted and Solvent-Free Ultra-Fast Synthesis of Gold and Gold Oxide Ultra-Small Nanoparticles and its use as Multi-Sensing Platforms.

In this work, a plasma-assisted and solvent-free synthesis of gold (Au) and gold oxide (Au2O3) nanoparticles (NPs) is explored. Accordingly, only the precursor (i.e., HAuCl4 powder) is exposed to the N2:O2 plasma gas mixtures, selected to promote its reduction to Au (HAuCl4-to-Au0) and/or favor its further oxidation to Au2O3. As a result, the production of highly crystalline spherical Au ultra-small NPs (USNPs) of 2.7 ± 0.7 nm and Au2O3 edged pyramidal-like NPs of 18 ± 5 nm is obtained in very short times (i.e., 10 s-1 min), showing excellent stability without the need to add any ligands. To investigate the potential features of the synthesized particles, they are loaded into alginate hydrogels and tested as multi-detection sensor platforms of H2O2 and NADH in front of several interferents. Although both samples present excellent electrochemical sensing activity (as compared to Au NPs synthesized through the Turkevich method), Au2O3 NPs stand out for its high analytical sensibility toward H2O2 (153.1 and 16.8 µA mm-1 cm-2 for single and multiplexing detection, simultaneously); and capacity to measure NADH in real human urine and low detection limits produced by Escherichia coli (7.5 × 103 CFU mL-1). Herein, a green, easy, and fast method is proposed to produce stable Au USNPs and Au2O3 NPs, showing great potential for the catalytic and biomedical fields.