When we think of invisibility cloaks, probably the first things that come to mind are Harry Potter-like contraptions that allow people or large objects to instantly disappear. Scientists from the University of Maryland and nearby Towson University, however, today announced their development of something a little different – little being the key word. They have crammed 25,000 tiny “invisibility cloaks” onto a gold sheet, which itself only measures 25 millimeters per side. While the resulting biochip array may not allow any young wizards to vanish from sight, it could allow them to identify biological materials.
The researchers began with a commercially-available microlens array, consisting of a sheet of miniature optical lenses – each individual lens is just 30 micrometers in diameter. One side of this array was coated with a gold film. The array was then placed gold-side-down onto a glass slide, which had also been cover with gold, to create a double gold layer on the bottom.
The optical qualities of the microlenses are such that when light strikes them, it is bent away from a spot in the middle of each lens – essentially, because light cannot strike it and reflect back off, this renders that middle section invisible. As the light is instead diverted around the sides of each circular lens, it is forced through the narrow gaps between the lenses. This slows it down or even stops it, and causes it to separate into its different color components.
Known as a “trapped rainbow,” this effect allows the light to have a stronger interaction with molecules placed on the array, than would be possible with light traveling at regular speed. If the array were used in a small device such as a biosensor, the identity of substances placed in that sensor could reportedly be determined based on how much light they absorb and then emit. It’s an existing process known as fluorescence spectroscopy, and it produces the most detailed results when the light is slowed down – as it would be, by the biochip array.
“In our array, light is stopped at the boundary of each of the cloaks, meaning we observe the trapped rainbow at the edge of each cloak,” said lead author of the study, Dr. Vera Smolyaninova. “The benefit of a biochip array is that you have a large number of small sensors, meaning you can perform many tests at once. For example, you could test for multiple genetic conditions in a person’s DNA in just one go.”
More details are available in the video below. A paper on the research was published today in New Journal of Physics.
Source: Institute of Physics