Tiny crystals give a plain fish twinkling, colorful dots under light
Puzzling fish twinkles from wide-banded hardyhead silversides might lead to ultra-tiny sensors. As light shines steadily on a silver slip of a fish, minuscule dots on the fish start flashing: blue, yellow, blue, yellow. Instead of making their own light, it turns out that remarkable little photonic crystals in fish spots reflect certain wavelengths of light, alternating between blues and more greenish-yellows.
Tiny crystals give a plain fish twinkling, colorful dots under light
Lots of biological materials have evolved tricks manipulating light. The iconic morpho blue butterfly doesn’t have a flake of blue pigment. It creates its dream-perfect sky blue with stacks of microscopic light-manipulating plates. So do blue-leaved begonias. Those fish reflectors are doing something similar in wide-banded hardyhead silversides (Atherinomorus lacunosus). Inside the reflective flash spots lie little platelets of the compound guanine that have grown in such a way that they can reflect colorful light depending on the angle.
Tiny crystals give a plain fish twinkling, colorful dots under light
Guanine may sound familiar. It’s one of the four major coding units that pair up in storing DNA’s genetic information. What gives the fish guanine platelets particular abilities though remains a puzzle. Inside a spot, platelets move in ways that change their apparent color and dazzle power. The blue-yellow light pulses only in living silversides. Dead fish just reflect white-white.
Tiny crystals give a plain fish twinkling, colorful dots under light
Versions of little sparkling fish lights could fit into the world of micro-electromechanical systems (MEMS) to monitor conditions inside living tissues, responding to light or flashing themselves.
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