Highly stable noble metal nanoparticles dispersible in biocompatible solvents: synthesis of cationic phosphonium gold nanoparticles in water and DMSO

Abstract

In this work, we report the synthesis of novel cationic phosphonium gold nanoparticles dispersible in water and dimethyl sulfoxide (DMSO) for their potential use in biomedical applications. All the cationic-functionalising ligands currently reported in the literature are ammonium-based species. Here, the synthesis and characterisation of an alternative system, based on phosphonioalkylthiosulfate zwitterions and phosphonioalkylthioacetate were carried out. We have also demonstrated that our phosphonioalkylthiosulfate zwitterions readily disproportionate into phosphonioalkylthiolates in situ during the synthesis of gold nanoparticles produced by the borohydride reduction of gold(III) salts. The synthesis of the cationic gold nanoparticles using these phosphonium ligands was carried out in water and DMSO. UV-visible spectroscopic and TEM studies have shown that the phosphonioalkylthiolates bind to the surface of gold nanoparticles which are typically around 10 nm in diameter. The resulting cationic-functionalised gold nanoparticles are dispersible in aqueous media and in DMSO, which is the only organic solvent approved by the U.S. Food and Drug Administration (FDA) for drug carrier tests. This indicates their potential future use in biological applications. This work shows the synthesis of a new family of phosphonium-based ligands, which behave as cationic masked thiolate ligands in the functionalisation of gold nanoparticles. These highly stable colloidal cationic phosphonium gold nanoparticles dispersed in water and DMSO can offer a great opportunity for the design of novel biorecognition and drug delivery systems.

Methoxy-phenyl groups reduce the cytotoxicity and increase the aqueous solubility of phosphonium zwitterions and salts

“…Our own work has focused on the synthesis and biological properties of alkylthiosulfate zwitterions [3][4][5][6], and alkylthioacetate salts [3,7], conjugated with triphenylphosphine and other trialkyl-and triaryl-phosphines [3][4][5][6][7], and also arsines [8], which can be used as precursors for the formation of phosphonium-or arsoniumfunctionalized gold nanoparticles [4,8], potentially useful species in mitochondriatargeted pharmaceutical nanotechnology. Other groups have developed and applied our methodology [9,10]. Although triphenylphosphonium-functionalized nanoparticles are soluble in water and biological media [4,10] and are taken-up by cells [4,9] the parent triphenylphosphonioalkylthiosulfate zwitterions are insoluble in aqueous media [3,10].…”

Comparison of Chemical and Biological Properties of Metal Nanoparticles (Au, Ag), with Metal Oxide Nanoparticles (ZnO-NPs) and their Applications

“…Nanoparticles surface functionalisation plays a significant role in cellular uptake and producing cellular responses [33]. It is known that NPs have ability to form stable bonds with ligands contain sulphur atoms such as sulphides and thiols [34,35].…”

“…The ability of modified NPs, such as gold NPs with various organic thiolate ligands make them versatile systems and open variety of possibilities for their use as drug delivery systems, and bio-applications [33]. Capping agents used with strong affinity for NP are a common approach, which cause the preparation of NPs with good size dispersion in water.…”

“…For instance, the dodecane-thiolate ligand used for stabilizing the AuNPs ( Figure 4), where AuCl4 − is transferred from aqueous phase to organic phase (toluene) and using tetraoctylammonium bromide as a phasetransfer reagent and then reduced by NaBH4, yielded AuNPs having average range of 2-8 nm. The size of the resulting AuNPs can be decreased by increasing the thiol/HAuCl4 ratio [28][29][30][31][32][33]. These monolayer-protected AuNPs are repeatedly isolated and redissolved in common organic solvents such as toluene, dichloromethane, and hexane without aggregation or fusion.…”

“…The alkanethiolate monolayer-protected NPs are insoluble in aqueous solution, so it was important to find alternative solvent to water as mentioned in the literature [33], and it was dimethyl sulfoxide (DMSO). So, according to the FDA, DMSO is only organic solvent approved by USA Food and Drug Administration (FDA) for drug carrier tests, which indicates its potential future use in biomedical applications [33].…”