title: Continuous In-Flight Synthesis for On-Demand Delivery of Ligand-Free Colloidal Gold Nanoparticles.
abstract: We demonstrate an entirely new method of nanoparticle chemical synthesis based on liquid droplet irradiation with ultralow (<0.1 eV) energy electrons. While nanoparticle formation via high energy radiolysis or transmission electron microscopy-based electron bombardment is well-understood, we have developed a source of electrons with energies close to thermal which leads to a number of important and unique benefits. The charged species, including the growing nanoparticles, are held in an ultrathin surface reaction zone which enables extremely rapid precursor reduction. In a proof-of-principle demonstration, we obtain small-diameter Au nanoparticles (∼4 nm) with tight control of polydispersity, in under 150 μs. The precursor was almost completely reduced in this period, and the resultant nanoparticles were water-soluble and free of surfactant or additional ligand chemistry. Nanoparticle synthesis rates within the droplets were many orders of magnitude greater than equivalent rates reported for radiolysis, electron beam irradiation, or colloidal chemical synthesis where reaction times vary from seconds to hours. In our device, a stream of precursor loaded microdroplets, ∼15 μm in diameter, were transported rapidly through a cold atmospheric pressure plasma with a high charge concentration. A high electron flux, electron and nanoparticle confinement at the surface of the droplet, and the picoliter reactor volume are thought to be responsible for the remarkable enhancement in nanoparticle synthesis rates. While this approach exhibits considerable potential for scale-up of synthesis rates, it also offers the more immediate prospect of continuous on-demand delivery of high-quality nanomaterials directly to their point of use by avoiding the necessity of collection, recovery, and purification. A range of new applications can be envisaged, from theranostics and biomedical imaging in tissue to inline catalyst production for pollution remediation in automobiles.
authors.affiliation: NIBEC, University of Ulster , Belfast, BT37 0QB, Northern Ireland.
authors.forename: Paul
authors.identifier: 0000-0002-2725-4647
authors.initials: P
authors.lastname: Maguire
authors.affiliation: NIBEC, University of Ulster , Belfast, BT37 0QB, Northern Ireland.
authors.forename: David
authors.initials: D
authors.lastname: Rutherford
authors.affiliation: NIBEC, University of Ulster , Belfast, BT37 0QB, Northern Ireland.
authors.forename: Manuel
authors.identifier: 0000-0002-5508-928X
authors.initials: M
authors.lastname: Macias-Montero
authors.affiliation: NIBEC, University of Ulster , Belfast, BT37 0QB, Northern Ireland.
authors.forename: Charles
authors.initials: C
authors.lastname: Mahony
authors.affiliation: NIBEC, University of Ulster , Belfast, BT37 0QB, Northern Ireland.
authors.forename: Colin
authors.initials: C
authors.lastname: Kelsey
authors.affiliation: NIBEC, University of Ulster , Belfast, BT37 0QB, Northern Ireland.
authors.forename: Mark
authors.initials: M
authors.lastname: Tweedie
authors.affiliation: NIBEC, University of Ulster , Belfast, BT37 0QB, Northern Ireland.
authors.forename: Fátima
authors.initials: F
authors.lastname: Pérez-Martin
authors.affiliation: NIBEC, University of Ulster , Belfast, BT37 0QB, Northern Ireland.
authors.forename: Harold
authors.initials: H
authors.lastname: McQuaid
authors.affiliation: SUPA, School of Physics and Astronomy, University of Glasgow , Glasgow G12 8QQ, United Kingdom.
authors.forename: Declan
authors.initials: D
authors.lastname: Diver
authors.affiliation: NIBEC, University of Ulster , Belfast, BT37 0QB, Northern Ireland.
authors.forename: Davide
authors.initials: D
authors.lastname: Mariotti
keywords: Colloidal nanoparticles; droplet microreactors; plasmas; segmented flow; solvated electron