A minor lipid component of soy lecithin causes growth of triangular prismatic gold nanoparticles

Abstract

Reduction of bromoauric acid by ascorbic acid in the presence of crude soybean lecithin produced a mixture of spherical and triangular prismatic nanoparticles while higher purity phosphatidylcholine (PC) produced only spherical nanoparticles. The triangular prismatic nanoparticles made with lecithin had an average edge length of 90 nm and a localized surface plasmon resonance between 700 and 1050 nm, depending on the synthetic conditions used. Although crude soy lecithin is composed of 75% PC and phosphatidylethanolamine, additional lipids and other small molecules are present. Preparatory gel electrophoresis was used to separate the different nanoparticle shapes and phosphatidic acid (PA) was identified as bound to the triangular prismatic nanoparticles by mass spectrometry of the gel-purified nanoprisms. Furthermore, PA proved essential to the asymmetric growth. When bromoauric acid was reduced by ascorbic acid using a mixture of pure PA and pure PC, triangular prismatic gold nanoparticles also resulted, confirming the role of PA and providing a second route to these near infrared active nanoparticles. Nanoparticles prepared in soy lecithin or PA-PC mixtures exhibited extended stability with no aggregation after months of storage, in contrast to nanoparticles prepared in pure PC. These nanoparticles were prepared without the use of the alkyl ammonium salts that have limited in vivo applications with other asymmetric gold nanoparticles. This is a versatile synthetic method providing stable, shape-controlled gold nanoparticles using a mild reducing agent and soy lecithin as an environmentally benign ligand source. Nano impactPlant-derived lipids have the potential to function as versatile, environmentally benign ligands for nanoparticle synthesis, although the complex chemistry of the lipids must be understood in order to use them effectively. This work adds to the growing list of nanoparticle syntheses performed using renewable, plant-derived ligands in place of fossil fuel derived chemicals. This synthetic route provides control over the shape and the optical properties of the gold nanoparticles, making the resultant materials useful for biomedical, catalytic, and photonic applications. One critical impact of this work comes from the identification of a specific molecular component in soy lecithin that is responsible for causing asymmetric growth. Through this molecular level understanding it becomes possible to optimize the nanoparticle synthesis both from the perspective of the desired application of the nanoparticles and from the perspective of the environmental impact of their synthesis.

Polymer mediated layer-by-layer assembly of different shaped gold nanoparticles

“…Citrate-capped spheres were prepared from the Turkevich method 39 and had an average diameter of 20 nm (not shown). The PC-coated sphere (Figure 1A) and PC-coated prism (Figure 1C) method 40 was developed in our laboratory and lead to an average diameter of 20 nm and average edge length of 90 nm, respectively. We optimized the purification of large scale PC-coated prism synthesis using a simple, quick, and inexpensive sucrose density method via centrifugation for 2 h, which is much less than other reports taking 12 h using more expensive surfactants.…”

“…40 PC 30 (200 mg, 80 µmol) was dissolved in a minimal amount (1–2 mL) of cyclohexane. This solution was dried by rotary evaporation or under a stream of nitrogen followed by drying under vacuum to yield a thin film.…”

Simultaneous extraction of phosphatidylcholine and phosphatidylethanolamine from soybean lecithin

“…By using this eluent condition, pure PC and PE could be obtained in 35 and 16% yields, respectively. The purity of the compounds was confirmed by 1 H and 13 C NMR , FTIR and UV/vis spectroscopies , and elemental analysis . 31 P NMR spectra of extracted lecithin, purified PC and PE are also recorded in order to further confirm the purity (Fig.…”

Papaya latex mediated synthesis of prism shaped proteolytic gold nanozymes

“…The spherical nanoparticles can easily be synthesized by reduction of the metal salt as spheres possess lowest energy 17 . However, the synthesis of anisotropic nanoparticles is challenging and requires efficient protocol 18 – 20 . Anisotropic nanopartcles can be synthesized by controlling the reaction parameters such as concentration of metal ion, reducing agent, stabilizing agent and reaction time though the exact working mechanism of these parameters is yet to be understood 8 , 20 .…”

“…However, the synthesis of anisotropic nanoparticles is challenging and requires efficient protocol 18 – 20 . Anisotropic nanopartcles can be synthesized by controlling the reaction parameters such as concentration of metal ion, reducing agent, stabilizing agent and reaction time though the exact working mechanism of these parameters is yet to be understood 8 , 20 . The nanoprisms are considered as one of the recent members in the list of anisotropic nanomaterials 21 .…”