Colin Kelsey

Continuous In-Flight Synthesis for On-Demand Delivery of Ligand-Free Colloidal Gold Nanoparticles

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.

Chemistry and new applications of plasmas created in conducting liquids

Summary form only given. There are many current and potential applications for plasmas created in conducting liquids and particularly in isotonic saline solution1. As a result there is interest in the physics of the plasma production, how it is sustained, the type of plasmas produced, their parameters and the subsequent plasma produced chemistry. There have been a number of studies of various topics in this list2 however the full characterisation of the plasma has been hampered since the plasma formation process is not reproducible and many conventional plasma diagnostic techniques cannot, as yet, be applied in the liquid environment.

Characterisation of plasmas created in conducting liquids

Summary form only given. There are many current and potential applications for plasmas created in conducting liquids and particularly in isotonic saline solution1. As a result there is interest in the physics of the plasma production, how it is sustained, the type of plasmas produced, their parameters and the subsequent plasma produced chemistry. There have been a number of studies of various topics in this list2 however the full characterisation of the plasma has been hampered since the plasma formation process is not reproducible and many conventional plasma diagnostic techniques cannot, as yet, be applied in the liquid environment.