{"doi":"10.1016/j.mex.2020.100896","title":"A modified and simplified method for purification of gold nanoparticles","abstract":"2 nm gold nanoparticles (AuNPs) have promising applications within drug and protein delivery, bioimaging, and biosensing. By performing ligand place-exchange reactions, AuNPs protected with alkanethiolate ligands can be functionalized to regulate their behaviors. In this reaction, a new ligand is incorporated by mixing a thiol with the AuNPs. To remove the excess new ligand as well as the displaced thiolate, dialysis has previously been the most widely used method. However, this purification method is time-consuming and fails to remove unwanted thiols completely. In this study, we describe a fast and efficient procedure to purify AuNP aqueous solution through liquid-liquid extraction using dichloromethane.•We demonstrate a facile way to purify AuNPs after ligand place-exchange reactions through liquid-liquid extraction.•Liquid-liquid extraction is a simple, inexpensive and efficient method for AuNP purification.•This protocol enables us to completely purify AuNPs in a few hours and can be used as a much quicker and more scaleable valid alternative to dialysis. 2 nm gold nanoparticles (AuNPs) have promising applications within drug and protein delivery, bioimaging, and biosensing. By performing ligand place-exchange reactions, AuNPs protected with alkanethiolate ligands can be functionalized to regulate their behaviors. In this reaction, a new ligand is incorporated by mixing a thiol with the AuNPs. To remove the excess new ligand as well as the displaced thiolate, dialysis has previously been the most widely used method. However, this purification method is time-consuming and fails to remove unwanted thiols completely. In this study, we describe a fast and efficient procedure to purify AuNP aqueous solution through liquid-liquid extraction using dichloromethane.•We demonstrate a facile way to purify AuNPs after ligand place-exchange reactions through liquid-liquid extraction.•Liquid-liquid extraction is a simple, inexpensive and efficient method for AuNP purification.•This protocol enables us to completely purify AuNPs in a few hours and can be used as a much quicker and more scaleable valid alternative to dialysis. Specifications tableTabled 1Subject AreaChemistryMore specific subject areaGold nanoparticle synthesis and purificationMethod namePurification of gold nanoparticles from free ligand through liquid-liquid extractionName and reference of original methodEntrapment of Hydrophobic Drugs in Nanoparticle Monolayers with Efficient Release into Cancer Cells J. Am. Chem. Soc 0.200913141360–1361Resource availabilityhttps://doi.org/10.1021/ja808137c Open table in a new tab A ligand place-exchange reaction of the new thiol ligand dissolved in CH2Cl2: MeOH (1:1, 4 ml) with pentanethiolate-coated AuNPs (d= ~2 nm) was carried out for 3 days at rt (~25 °C). The final reaction mixture contained the desired AuNPs, the excess new ligand and replaced thiolate. The solvent was removed under reduced pressure and then washed with organic solvents (hexanes followed by ether). Next, the AuNPs were redissolved in water and then further purified by liquid-liquid extraction using CH2Cl2. Nuclear Magnetic Resonance (NMR) was used to check the purity. Step 1: Monolayer Exchange Reaction Materials All organic solvents were purchased from Fisher and purged through nitrogen before being used. Aqueous AuNP solutions were prepared with deionized water produced by a Millipore System. Procedure Pentanethiolate-coated AuNPs (d= ~2 nm) were synthesized using the Brust-Schiffrin gold core synthesis method [[1]Brust M. Walker M. Bethell D. Schiffrin D.J. Whyman R. Synthesis of thiol-derivatised gold nanoparticles in a two-phase Liquid–Liquid system.J. Chem. Soc. Chem. Commun. 1994; : 801-802Crossref Scopus (6546) Google Scholar]. Tetraethylene glycol trimethyl ammonium (TTMA) ligands were synthesized according to the literature (~70 ligands per particle) [[2]Kim C.K. Ghosh P. Pagliuca C. Zhu Z.-J. Menichetti S. Rotello V.M. 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