Enhancing and Mitigating Radiolytic Damage to Soft Matter in Aqueous Phase Liquid-Cell Transmission Electron Microscopy in the Presence of Gold Nanoparticle Sensitizers or Isopropanol Scavengers

Abstract

In this work, we describe the radiolytic environment experienced by a polymer in water during liquid-cell transmission electron microscopy (LCTEM). We examined the radiolytic environment of aqueous solutions of poly(ethylene glycol) (PEG, 2400 g/mol) in the presence of sensitizing gold nanoparticles (GNPs, 100 nm) or radical scavenging isopropanol (IPA). To quantify polymer damage, we employed post-mortem analysis via matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS). This approach confirms IPA (1− 10% w/v) can significantly mitigate radiolysis-induced damage to polymers in water, while GNPs significantly enhance damage. We couple LCTEM experiments with simulations to provide a generalizable strategy for assessing radiolysis mitigation or enhancement. This study highlights the caution required for LCTEM experiments on inorganic nanoparticles where solution phase properties of surrounding organic materials or the solvent itself are under investigation. Furthermore, we anticipate an increased use of scavengers for LCTEM studies of all kinds.

Visualizing Electron Beam-Capping Ligand Reactions for Controlled Nanoparticle Imaging with Liquid Phase Transmission Electron Microscopy

“…The results emphasize the magnifying effect of high atomic number nanoparticles on local radiation damage, in agreement with a recent report, 50 and the effectiveness of radical scavengers in mitigating electron beam damage. We expect this method can be applied to other nanoparticle surface ligands as well as biomolecules by drawing from the extensive library of conjugation reactions developed for conjugating fluorophores to biomolecules.…”

“…Prior works have established that alcohols, such as isopropanol and tert-butanol, and other organic molecules can act as hydroxyl radical scavengers to mitigate radiation damage to organic molecules during LP-TEM imaging. 50,[56][57][58][59] We added 1 M tert-butanol in DI water as a radical scavenger to test its impact on electron beam damage of BPEI in the presence of silver nanoparticles (Figure 6). Similar to the experiment without any nanoparticles, there was no visible change in fluorescence intensity in the image regions exposed for 30 seconds and 1 minute at a dose rate of 0.274 MGy/s.…”

“…Korpanty et al found that gold nanoparticles accelerated the radiation crosslinking of polyethylene glycol and found through modeling that nanoparticles enhanced the yields of hydroxyl and polymer radicals. 50 Prior numerical radiolysis simulations predicted that the local yield of radicals was several times higher near a metalwater interface compared to bulk liquid due higher yield of secondary and backscattered electrons from metals when irradiated. 68 In the field of radiation processing of bulk polymers, empirical evidence shows that crosslinking predominates at low cumulative dose while chain scission dominates at larger cumulative doses.…”

“…Electron beam induced reactions during LP-TEM are only perceptible if visible changes occur in the material being imaging, e.g., growth/etching of nanoparticles, [41][42][43][44][45][46] dissolution of metal organic frameworks, 47 pitting of carbon nanotubes, 48 shrinkage of bacterial cells, 49 or formation of visible polymeric nanoparticles. 50 Nanoparticle surface ligands are not observed during LP-TEM due to their small size (typically < 2 nm ligand layer thickness) and low image contrast compared to inorganic nanoparticles. Even if ligands can be visualized with state-of-the-art aberration corrected or graphene liquid cell TEM, LP-TEM images provide no information about the chemical structure of the ligands.…”

Beam-induced heating at low electron fluxes during liquid phase transmission electron microscopy

“…Especially when investigating heavy metal structures such as gold nanoparticles, secondary electrons increase the effective dose locally (Gupta et al, 2018;Korpanty et al, 2021). This is particularly significant, because gold nanostructures are one of the most frequently analysed material systems in LPTEM.…”