Rapid and efficient microwave-assisted extraction of Caesalpinia sappan Linn. heartwood and subsequent synthesis of gold nanoparticles

Abstract Since microwave (MW)-assisted synthesis of gold nanoparticles (AuNPs) using Caesalpinia sappan (CS) extract as both a reducing and stabilizing agent is currently unavailable, a MW-based synthesis protocol was investigated and presented for the first time in this work. In addition, to rapidly prepare the reactant for this purpose, the MW-assisted extraction of CS heartwood was studied. From the optimization experiments, it was found that the extraction using the MW irradiation at 300 W for 3 min produced the extract with high and reproducible brazilin content which could be readily used for the synthesis of AuNPs. Under the optimal synthesis conditions, roughly spherical CS-AuNPs with an average diameter size of 49.6 nm and acceptable 28-day stability were obtained within only 1 min. The resulting CS-AuNPs were capable of selective binding to Fe2+, Fe3+, and Al3+, leading to particle aggregation as well as noticeable change of color and shift of UV-Vis absorption maxima. From these results, CS-AuNPs could be fabricated via this fast, green, and efficient route. Furthermore, their potential application for colorimetric sensing of certain metal ions was preliminarily explored and proposed in this work.