Made from curved gold-cysteine nanosheets that all twist in the same direction, the spiky nanoparticle achieved the highest complexity measured. It absorbs UV light and emits twisted light in the visible part of the spectrum. Credit: Wenfeng Jiang, Kotov Lab, University of Michigan

University of Michigan has produced Synthetic microparticles more intricate than some of the most complicated ones found in nature.The findings pave the way for more stable fluid-and-particle mixes, such as paints, and new ways to twist light a prerequisite for holographic projectors.

If the gold-cysteine nanosheets are designed to remain flat, the result is a moderately complex design that the researchers called a “kayak” particle. Credit: Wenfeng Jiang, Kotov Lab, University of Michigan

The particles are composed of twisted spikes arranged into a ball a few microns, or millionths of a meter, across.

One of the key players in producing complexity can be chirality in this context, the tendency to follow a clockwise or counterclockwise twist. They introduced chirality by coating nanoscale gold sulfide sheets, which served as their particle building blocks, with an amino acid called cysteine. Cysteine comes in two mirror-image forms, one driving the gold sheets to stack with a clockwise twist, and the other tending toward a counterclockwise twist. In the case of the most complex particle, a spiky ball with twisted spines, each gold sheet was coated with the same form of cysteine.

The team which includes researchers at the Federal University of São Carlos and the University of São Paulo in Brazil, as well as the California Institute of Technology and the University of Pennsylvania used the new framework to demonstrate that their particles were even more complicated than coccolithophores (The most complex natural particles on the scale of the new synthetic particles are spiky coccolithophores).

From the results of the experiments and simulations, it appears that UV energy was absorbed into the hearts of the particles and transformed through quantum mechanical interactions, becoming circularly polarized visible light by the time it left through the curved spikes.

The researchers believe that the tactics they have uncovered can help scientists engineer particles that improve biosensors, electronics.

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