A versatile one-pot room temperature approach for the synthesis of gold nanoparticles with multiple sizes and shapes

Simplifying the synthetic methods to produce metallic gold nanoparticles (AuNPs) is a key point to increment their applicability in multiple fields. In this work, we present a new, simple and fast method that ensures the one-pot production of AuNPs in less than two minutes, at room temperature. The proposed methodology is based on the use of a mixture of two usual reductants (ascorbic acid – H₂Asc – and sodium citrate) and polyvinylpyrrolidone as stabilizing agent. The particles were obtained by adequately controlling the reductants concentrations and the mixture pH (using citric/citrate-based buffers). Interestingly, two different results were observed, depending on the initial buffer solution. At citric-rich conditions, both buffer and [H₂Asc] did not significantly affect the synthesis outcome and spherical AuNPs of around 25 nm were obtained in all cases. However, at citrate-rich conditions, varying the ascorbic acid concentration provoked marked changes in the size and shape of the AuNPs ranging from spherical (at low [H₂Asc]) to spiked ones (at high [H₂Asc]). Finally, and as a proof of concept, we show that both kinds of AuNPs could be useful for different applications. The small spherical ones can be used as stable seeds for the overgrowth of anisotropic AuNPs, whose characteristics depend on the chosen growth solution. On the other hand, the spiked ones can be employed for both refractive index or Raman spectroscopy-based sensing, with interesting prospects.