SEM Image of the Opal's Surface (image) The Optical Society Caption This is a closeup of the surface of the opal, taken with a scanning electron microscope. The ethanol-responsive gel used in the device would fill the spaces between the rows of regularly spaced nanoparticles that comprise the opal. Credit Riccardo Pernice, Università degli Studi di Palermo Usage Restrictions Must include caption & credit. Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.