Colloidal Crystals For Precision Sensors

Scientists have developed a method to create colloidal crystals that crystallize into the diamond lattice. This photonic technique could lead to cheap, reliable, and scalable fabrication of 3D photonic crystals for optical circuits and light filters.

Colloidal crystals, made up of spheres hundreds of times smaller than the diameter of a human hair, can be arranged in different crystalline shapes depending on how the spheres are linked to one another. Each colloid attaches to another using strands of DNA glued to surfaces of the colloids that function as a kind of molecular Velcro. When colloids collide with each other in a liquid bath, the DNA snags and the colloids are linked. Depending on where the DNA is attached to the colloid, they can be programmed to spontaneously create complex structures.

This process has been used in the past to create strings of colloids and even close-packed cubic colloidal crystals, but not the diamond structure–which displays an optical band gap for visible light. Much as a semiconductor filters out electrons in a circuit, an optical band gap completely rejects certain wavelengths of light. Filtering light in this way is practical only if the colloids are arranged in a diamond formation, a process previously deemed too difficult and expensive to perform at commercial scale.

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