Directed self-assembly of a bio-inspired peptide into ring microstructures using micro-bubbles induced in thermo-optical tweezers

Molecular self-assembly has been recognized as an important technique for organizing building blocks into ordered structures with promising applications in various fields. Spontaneous self-assembly of diphenylalanine(FF) pep- tide derivatives which have remarkable sequence similarity with Alzheimer’s Aβ peptide, give rise to micro-rods and microtubes. But, the reported structures suffer from a lack of control. Herein, we report a new technique for laser-assisted self-assembly of diphenylanaline where we obtain stable annular ring microstructures using thermo-optical tweezers. In this method, a dense aqueous dispersion of the material which has high absorption at the laser wavelength is taken in a sample holder so that some material is adsorbed on the top surface. A hot spot is created on the top surface when the adsorbed material absorbs the high intensity at the focus of the laser beam, giving rise to a water vapor bubble. Due to Gibbs Marangoni convection, self-assembly of FF peptides occurs around the bubble in the form of rings. This method of fabricating rings is fast with complete control over the spatial location, size, and thickness of the rings. Interestingly, these self-assembled ring struc- tures display wave-guiding and spectrally asymmetric Fano resonances. We demonstrate the potential of such micro-structures in sensing by changes in their Fano spectral line and wave-guiding response on binding with Congo red dye, which is commonly used to stain amyloid proteins. Such intriguing waveguiding systems may have promising applications in biological and chemical sensing, precision diagnostics of various neurodegenerative diseases and in the fabrication of multifarious micro-optical devices.