Abstract
Amphiphilic block copolymers with weak polyelectrolyte blocks can assemble stimulus-responsive nanostructures and interfaces. Applications of these materials in drug delivery, biomimetics, and sensing largely rely on the well-understood swelling of polyelectrolyte chains upon deprotonation, often induced by changes in pH or ionic strength. This deprotonation can also tune interfacial interactions between the polyelectrolyte blocks and surrounding solution, an effect which is less studied than morphological swelling of polyelectrolytes but can be just as critical for intended function. Here, we investigate whether the pH-driven morphological response of polyelectrolyte-bearing nanostructures also affects the interactions of these nanostructures with molecules in solution, using micelles of a short-chain polybutadiene-block-poly(acrylic acid) (pBd-pAA) as a model system. We introduce a Förster resonance energy transfer (FRET) approach to probe interactions between micelles and fluorescent molecular solutes as a function of solution pH. As expected, the pAA corona of these pBd-pAA micelles increases in thickness monotonically as a function of pH. However, FRET efficiency, which provides a metric of the spatial proximity of fluorescently labeled micelles and freely diffusing fluorophores, exhibits complex nonmonotonic behavior as a function of pH, indicating that the average separation of micelles and acceptor fluorophores is not strictly correlated with micelle swelling. Dialysis experiments quantify the affinity of fluorophores for micelles as a function of pH, confirming that changes in FRET are driven almost entirely by the pH-dependent affinity of the pAA block for the investigated molecular fluorophores, not simply by a shape change of the pAA corona. This study provides key insights into the interfacial interactions between weak-polyelectrolyte-bearing nanostructures and molecular solutes, of importance for the development of their stimulus-responsive applications.
| Original language | English |
|---|---|
| Pages (from-to) | 2038-2045 |
| Number of pages | 8 |
| Journal | Langmuir |
| Volume | 38 |
| Issue number | 6 |
| DOIs | |
| State | Published - Feb 15 2022 |
Funding
The authors acknowledge financial support by the Laboratory Directed Research and Development (LDRD) program and the use of the MIRA! core facilities at Northern Arizona University supported in part by ECCS-2025490. S.M.C. acknowledges support for materials costs from a University of California President’s Postdoctoral Fellowship and a L’Oreal USA for Women in Science Fellowship. Bio-SANS is supported by ORNL’s Center for Structural Molecular Biology funded by the DOE Office of Biological and Environmental Research. This research used resources at the High Flux Isotope Reactor and Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory. This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Los Alamos National Laboratory (Contract No. 89233218CNA000001) and Sandia National Laboratories (Contract No. DE-NA-0003525).
| Funders | Funder number |
|---|---|
| U.S. Department of Energy | |
| University of California | |
| Office of Science | |
| Biological and Environmental Research | |
| Oak Ridge National Laboratory | |
| Sandia National Laboratories | DE-NA-0003525 |
| Laboratory Directed Research and Development | ECCS-2025490 |
| Los Alamos National Laboratory | 89233218CNA000001 |