Quantification of hydroxyl radicals and solvated electrons produced by irradiated gold nanoparticles suggests a crucial role of interfacial water.

The potential benefit of gold nanoparticles (GNP) to radiotherapy has been demonstrated in a range of cell lines and radiation sources as well as in rodent models, sometimes with contradictory results. Few experimental studies have explored the involved deleterious species, hydroxyl radical being so far the most cited, whereas theoretical studies have usually focused on secondary electrons emitted from GNP, making comparison between these two approaches difficult. Here we focus on the physico-chemical step (i.e. radical production) and report the first experimental determination of both hydroxyl radicals and solvated electrons yields of formation in the presence of GNP. We also compare these yields between X- and γ-rays under different atmospheres. Our main finding is a massive and equivalent production of both species under X- and more surprisingly γ-rays. For concentration as low as 1 nM (0.02% wt of gold), both radiations lead to 3 to 4 times more radicals than water radiolysis without GNP. This is in contradiction with a physical prediction of dose enhancement. Supported by our whole set of experiments the key role of water molecules at the nanoparticle interface in the radical production emerges. This leads us to propose the paramount importance of the physico-chemical step compared to the physical one. Classical approaches based on energy-absorption coefficients and electron ejections should therefore be revisited.

A novel experimental approach to investigate radiolysis processes in liquid samples using collimated radiation sources.

Here is detailed a novel and low-cost experimental method for high-throughput automated fluid sample irradiation. The sample is delivered via syringe pump to a nozzle, where it is expressed in the form of a hanging droplet into the path of a beam of ionising radiation. The dose delivery is controlled by an upstream lead shutter, which allows the beam to reach the droplet for a user defined period of time. The droplet is then further expressed after irradiation until it falls into one well of a standard microplate. The entire system is automated and can be operated remotely using software designed in-house, allowing for use in environments deemed unsafe for the user (synchrotron beamlines, for example). Depending on the number of wells in the microplate, several droplets can be irradiated before any human interaction is necessary, and the user may choose up to 10 samples per microplate using an array of identical syringe pumps, the design of which is described here. The nozzles consistently produce droplets of 25.1 ± 0.5 µl.

Gold nanoparticles functionalization notably decreases radiosensitization through hydroxyl radical production under ionizing radiation.

The purpose of this work was to study the influence of gold nanoparticles (GNP) coating on hydroxyl radical (HO) production under ionizing radiation. Though radiosensitizing mechanisms are still unknown, radical oxygen species are likely to be involved, especially HO. We synthesized six different types of GNP, choosing relevant ligands such as polyethylene glycol or human serum albumin. A great attention was paid to characterize these GNP in terms of size, charge and number of atoms in the coating. Our results show that functionalization dramatically decreases HO production, which is correlated to reduced plasmidic DNA damages. These findings are of high importance as GNP translation from fundamental research to applied medicine requires their functionalization to increase blood circulation time and specific cancerous cells addressing. We suggest that to keep GNP efficient for radiotherapy, a wispy coating is required.

How protein structure affects redox reactivity: example of Human centrin 2.

Electron transfer inside proteins plays a central role in their reactivity and biological functions. Herein, we developed a combined approach by gamma radiolysis and electrochemistry which allowed a deep insight into the reactivity of Human centrin 2, a protein very sensitive to oxidative stress and involved in several key biological processes. This protein bears a single terminal tyrosine and was observed to be extremely sensitive to ionizing radiation sources, leading to a tyrosine dimer. By cyclic voltammetry in the 100-1000 V s(-1) range, its redox potential and dimerization rate could be evaluated. Accordingly, reaction in solution with a redox mediator revealed an efficient catalysis. Finally, protein denaturation by a progressive increase in temperature was proportional to a decrease of dimerization radiolytic yield. Our results thus demonstrated that the protein structure plays a major role in oxidation sensitivity. This leads to meaningful results to understand protein redox reactivity.

A new mechanism for hydroxyl radical production in irradiated nanoparticle solutions.

The absolute yield of hydroxyl radicals per unit of deposited X-ray energy is determined for the first time for irradiated aqueous solutions containing metal nanoparticles based on a "reference" protocol. Measurements are made as a function of dose rate and nanoparticle concentration. Possible mechanisms for hydroxyl radical production are considered in turn: energy deposition in the nanoparticles followed by its transport into the surrounding environment is unable to account for observed yield whereas energy deposition in the water followed by a catalytic-like reaction at the water-nanoparticle interface can account for the total yield and its dependence on dose rate and nanoparticle concentration. This finding is important because current models used to account for nanoparticle enhancement to radiobiological damage only consider the primary interaction with the nanoparticle, not with the surrounding media. Nothing about the new mechanism appears to be specific to gold, the main requirements being the formation of a structured water layer in the vicinity of the nanoparticle possibly through the interaction of its charge and the water dipoles. The massive hydroxyl radical production is relevant to a number of application fields, particularly nanomedicine since the hydroxyl radical is responsible for the majority of radiation-induced DNA damage.