The photostability of two donor polymers, DPP-TT-T and PTB7, is compared in neat films and blend films with PC(71)BM. In both neat and blend films, PTB7 is shown to be relatively unstable. This observation is shown to correlate with transient optical studies of long lived polymer triplets and with molecular probe studies of singlet oxygen yields.
One of the key challenges facing liquid-phase transmission electron microscopy (TEM) of biological specimens has been the damaging effects of electron beam irradiation. The strongly ionizing electron beam is known to induce radiolysis of surrounding water molecules, leading to the formation of reactive radical species. In this study, we employ DNA-assembled Au nanoparticle superlattices (DNA-AuNP superlattices) as a model system to demonstrate that graphene and its derivatives can be used to mitigate electron beam-induced damage. We can image DNA-AuNP superlattices in their native saline environment when the liquid cell window material is graphene, but not when it is silicon nitride. In the latter case, initial dissociation of assembled AuNPs was followed by their random aggregation and etching. Using graphene-coated silicon nitride windows, we were able to replicate the observation of stable DNA-AuNP superlattices achieved with graphene liquid cells. We then carried out a correlative Raman spectroscopy and TEM study to compare the effect of electron beam irradiation on graphene with and without the presence of water and found that graphene reacts with the products of water radiolysis. We attribute the protective effect of graphene to its ability to efficiently scavenge reactive radical species, especially the hydroxyl radicals which are known to cause DNA strand breaks. We confirmed this by showing that stable DNA-AuNP assemblies can be imaged in silicon nitride liquid cells when graphene oxide and graphene quantum dots, which have also recently been reported as efficient radical scavengers, are added directly to the solution. We anticipate that our study will open up more opportunities for studying biological specimens using liquid-phase TEM with the use of graphene and its derivatives as biocompatible radical scavengers to alleviate the effects of radiation damage.
We demonstrate a generalizable strategy
to use the relative trajectories
of pairs and groups of nanocrystals, and potentially other nanoscale
objects, moving in solution which can now be obtained by in
situ liquid phase transmission electron microscopy (TEM)
to determine the interaction potentials between nanocrystals. Such
nanoscale interactions are crucial for collective behaviors and applications
of synthetic nanocrystals and natural biomolecules, but have been
very challenging to measure in situ at nanometer
or sub-nanometer resolution. Here we use liquid phase TEM to extract
the mathematical form of interaction potential between nanocrystals
from their sampled trajectories. We show the power of this approach
to reveal unanticipated features of nanocrystal–nanocrystal
interactions by examining the anisotropic interaction potential between
charged rod-shaped Au nanocrystals (Au nanorods); these Au nanorods
assemble, in a tip-to-tip fashion in the liquid phase, in contrast
to the well-known side-by-side arrangements commonly observed for
drying-mediated assembly. These observations can be explained by a
long-range and highly anisotropic electrostatic repulsion that leads
to the tip-selective attachment. As a result, Au nanorods stay unassembled
at a lower ionic strength, as the electrostatic repulsion is even
longer-ranged. Our study not only provides a mechanistic understanding
of the process by which metallic nanocrystals assemble but also demonstrates
a method that can potentially quantify and elucidate a broad range
of nanoscale interactions relevant to nanotechnology and biophysics.
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