Substrate-free self-assembly of peptides nano-particles through acoustic levitation

Abstract

Peptides self-assembled into nano-structures such as nano-tubes have shown to have great potential in different biomedical applications. However, when it comes to interacting with biological environment, the need for substrate (e.g. glass, silicone, and gold) during the self-assembling process, can have potential impeding effects, both on the resultant nanostructures as well as the very diligent biological subparts such as cells. This work, for the first time, shows the possibility of a substrate-fee peptide self-assembling process, through acoustic levitation. A pair of transducers was used to create standing acoustic waves at a high frequency of 40KHz to levitate water-based droplets. Two independent control variables of the self-assembling process were considered, namely the peptide concentration level and the velocity amplitude of the acoustic wave, to understand their effects on controlling the morphology, alignment and dimensional properties of the resultant nano-structures. The results showed that, at low concentration level of 1 mg/ml and independent of the velocity amplitude, no clear nano-structure was developed under the levitation conditions. However, at the concentration levels above 1.5 mg/ml, self-assembly of the peptide nano-particles do happen while the velocity amplitude can significantly affect the resultant nano-structures, in terms of fiber morphology, fiber dimension and fiber alignment. We also found that under levitation conditions, there is a preferred length for the resultant nano-fibers which is independent of the control variables, while the number of nano-fibers with that dominant size depends on the concentration level.