Spiky hedgehog particles can be self-assembled from twisted ribbons formed by gold-copper-cysteine complexes.1 Furthermore, the chirality of these twisted ribbons can be controlled by the cysteine amino acid and their arrangement into supraparticles is dictated by the ratio of L- vs D-form during the initial stages of self-assembly. Here we report that the seemingly spherically symmetric arrangement of twisted ribbons displays a Maltese cross diffraction pattern typical of spherulites and liquid crystals under cross-polarizers.2 This optical effect is observed at the single particle level3 with tunable diameters of 1-10 um. We investigate the optical effects in chiral hedgehog particles using single particle methodology and find that the emergence of Maltese cross pattern is dependent on the sphericity of the supraparticle and the spacing between individual spikes. The interaction of light with hierarchically self-assembled structures was modeled by finite-element electromagnetic simulations and reconstructed the distribution of electromagnetic fields around the hedgehog particles in three dimensions. These multiscale nanostructured colloids are omnidispersible in a variety of solvents, which offsets the limitations of commonly observed organic molecules and particles based spherulitic arrangement for biomolecular sensing under harsh environments.4

1. Jiang, W. et al. Emergence of complexity in hierarchically organized chiral particles. Science (1979) 368, 642–648 (2020).
2. Shtukenberg, A. G., Punin, Y. O., Gunn, E. & Kahr, B. Spherulites. Chemical Reviews 112, 1805–1838 (2011).
3. Bahng, J. H. et al. Mie Resonance Engineering in Meta-Shell Supraparticles for Nanoscale Nonlinear Optics. ACS Nano 14, 17203–17212 (2020).
4. Sivakumar, S., Wark, K. L., Gupta, J. K., Abbott, N. L. & Caruso, F. Liquid crystal emulsions as the basis of biological sensors for the optical detection of bacteria and viruses. Advanced Functional Materials 19, 2260–2265 (2009).

Daniel Katz

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