A New Mechanism for Hydroxyl Radical Production in Irradiated Nanoparticle Solutions

Abstract

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.

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

“…An example of the device's use can be found in SicardRoselli et al 5 , which details an experiment to investigate the radiolysis mechanisms which take place during the irradiation of a water and colloid gold solution; in particular, the influence the gold's presence has on the production of the hydroxyl radical. This is valuable information to the field of nanoparticle-based cancer therapeutics, as metallic nanoparticles have been shown to increase conventional radiotherapy efficacy.…”

“…1. Schematic diagram of the apparatus with the main components detailed: [1] Stage Datum Laser Gate, [2] Multiwell Microplate, [3] Nozzle Carousel, [4] Droplet Detector, [5] Waste Arm, [6] Carousel Datum. a) Electronic mail: cpolin01@qub.ac.uk ber of applications including cancer radiotherapy 1 , civil nuclear power 2 , and the semiconductor industry 3 .…”

“…A 'C'-section support beam [3] holds the actuator above the driver syringe [4]. The secondary 'reservoir' syringe [5] is also shown, attached to a 3-way stopcock [6]. The sample is then delivered along a PTFE tube [7].…”

Improving proton therapy by metal-containing nanoparticles: nanoscale insights

“…31,32 In this context, it is important to note that the dose rate used in our work (30 Gy/min) is higher than the dose rates commonly used in therapy (typically 3-7 Gy/min). However, even at 30 Gy/min, effects such as hydroxyl radical recombination are still low and oxidative stress processes most likely remain unaffected (as opposed to, eg, flash irradiation).…”

A Simple Model to Quantify Radiolytic Production following Electron Emission from Heavy-Atom Nanoparticles Irradiated in Liquid Suspensions

“…Pathway B corresponds to water radiolysis and is part of conventional radiotherapy. The X rays interact with the water, resulting in HO via a complex network of reactions (not shown) (17 The existence of pathway C was detected by subtracting an upper bound for the yield of pathway A and a literature value for the yield of pathway B from the measured yield (13). Thus, a better determination of the yield of pathway A, replacing the upper bound used by Sicard-Roselli et al (13), will facilitate a better estimate of the yield due to pathway C.…”