(481d) AC Field-Modulated Assembly and Supramolecular Nanostructure Formation of Peptide-Polydiacetylene Conjugates

The development of techniques that can control or tune self-assembly processes involved in supramolecular structure formation with high precision can pave the way for achieving new or improved physicochemical properties of functional biomaterials. To date, self-assembled structures are often triggered via pH, temperature, or mechanical forces, which often require direct alteration of the solution formulation or distortion of the system structure. Indirect contact approaches for influencing self-assembly behavior, such as the utility of electromagnetic fields, offer the advantage of using external fields to manipulate monomer organization through changes in reaction kinetics and side chain interactions. This presentation focuses on the use of dielectrophoresis (DEP), a non-uniform electric field manipulation via an alternating current (AC) source, to control the supramolecularly assisted polymerization and chain conformations of a chromogenic model system, peptide-polydiacetylene (PDA) conjugates. PDAs are known to demonstrate biosensing capabilities based on their chromogenic responses to external stimuli, which is due to the chain conformation transitions that its polymer backbone can afford, primarily between the planar, non-fluorescent blue phase (λ_max~ 640 nm) and the non-planar, fluorescent red phase (λ_max~ 520 nm). In our work, we use a water soluble pentapeptide sequence, triaspartic acid-valine-glycine (D₃GV) conjugated to diacetylene (DA) to form the polymeric D₃GV-PDA that is negatively charged and capable of forming 1-D nanostructures under acidic to neutral pH conditions. Here, we systematically investigate how the AC fields in a quadrupole-based DEP device, as compared with DC field controls, influence the two stages of charged PDA polymerization: (i) the peptide-directed supramolecular aggregation stage, and (ii) the UV-irradiation-assisted covalent polymerization stage. Using D₃GV-DA as the model charged PDA of interest, the structural and optical response of peptide-PDA to varying DEP stimulation times (1.5, 5, 10 minutes) and varying polymerization times (10 seconds and 10 minutes) were characterized based on their resulting absorbance spectra, circular dichroism spectra, and nanostructure morphologies. By quantifying the ratio of absorbance intensities of the blue vs. red phase peaks, we observed a higher sensitivity of the conformation of D₃GV-PDA to AC field-stimulation than the aggregation process of D₃GV-DA, whereby a general preference towards the blue phase were demonstrated by the samples exposed to electric fields. The resulting nanostructures of D₃GV-PDA were further observed via TEM, showing distinct morphological effects when the DEP field was applied during the supramolecular aggregation stage (entangled network of 1D nanostructures) and after the photopolymerization stage (bundled 1D nanostructures). This presentation will also highlight how peptide-PDA structures can be manipulated in a light-induced DEP platform, offering a potential facile microfabrication approach for patterning DEP-responsive polymeric systems. In summary, this work provides insights on how AC fields can be used to control the chromogenic phases of a biomolecule-PDA conjugate and their resulting nanostructure morphologies, which have future implications for tunability, and stability of polymeric systems used for biosensing and other biomedical applications that require stimuli responsivity.