Tip-enhanced Raman Spectroscopy reveals hierarchical self-assembly of block copolymer conjugates

In fifteen words or less, explain the significance of this contribution (Novel Aspect).: TERS / AFM study correlates peptide linker induced morphological and structural changes in potential drug-carriers

Abstract Text: The structural and morphological investigation of surfaces is possible down to a nanometer lateral resolution through the use of two techniques: tip-enhanced Raman scattering (TERS) and atomic force microscopy. Consequently, physical properties such as elasticity, contour, and persistence length can be directly correlated with the structure. The present study will investigate polymer-based micellar structures that form core-shell structures intended for drug delivery. The following investigation will demonstrate the effects of inserting a tetrapeptide linker between the hydrophobic and hydrophilic parts of a block copolymer on the appearance of self-assembled micelles. More specifically, the focus will be on alterations in height, length, bending rigidity, and Young's modulus.
In order to comprehend the structural alterations underlying such variations, TERS studies were conducted on elongated micelles (filomicelles). As anticipated, the Raman signals of the hydrophobic core were found to be significantly weaker in comparison to those of the hydrophobic shell (PEO), despite the thickness of the micelles being less than 10 nm. It was surprising to find that, given a polymer to tetrapeptide mass ratio of 40:1, the signals of the tetrapeptide were often well distinguishable, indicating a location at or very close to the surface. The pattern of the amide bands permitted the determination of the secondary structure of the peptides. As was the case in previous investigations, approximately 80% of the spectra indicate a β-structure, which is consistent with prior findings. This short-range order extends up to 10 nanometers and aligns well with the six-fold increase in average contour length and the augmented persistence length.
In summary, the present study demonstrates the efficacy of nanoscale investigations of structure and morphology in facilitating comprehension of structure-property relations. This is achieved through the alignment of lateral scales, extending down to the single unit range of the respective polymers.