Invisibility cloak promises spectroscopy on a chip (video)

WHILE the general media are agitated by the far-fetched possibilities of Harry Potteresque camouflage from today’s announcement of a so-called invisibility cloak, here at the LabHomepage we’re much more excited about the prospects for massively-multiplexed spectroscopy on a single chip that the research presents.

A team of scientists at Towson University and the University of Maryland led by Vera Smolyaninova have published a paper today in the New Journal of Physics, describing their work using commercially-available microlens arrays and the potential they hold for fluorescence spectroscopy.

A thin film of gold was applied to the microlens array, which contained about 25,000 individual lenses and is of a type commercially available for use in CCD cameras and multi-channel sensors. The coated array was mounted on a glass slide which was also gold-coated, and the space between the two gold surfaces became an effective waveguide.

This is, say the researchers, the first experimental realisation of an array of broadband invisibility cloaks of the type suggested recently by Farhat et al, operating in the visible spectum. This work, published in 2011 and widely reported, suggested that such microlens arrays of could be useful in low-interference communication, non-invasive probing, and in sensing and communication networks.

As reported in the groups’s published paper, each individual lens in the array creates within itself a tiny ‘cloaked’ area that effectively shields its contents from scrutiny. As these lenses are so tiny, each cloaked area is just 30 micrometres in diameter and is separated from its neighbouring cloaked areas by an uncloaked gap of about 120 micrometres.

Because of the different refractive properties of different wavelengths, the effect of each invisibility cloak is to create and trap a spectrum – the so-called ‘trapped rainbow’. These spectra, the researchers speculate, could be used in an advanced biochip sensor exploiting fluorescence spectroscopy.

Lead author Dr Vera Smolyaninova explained: “With the biochip array you have a large number of small sensors, so you can perform many tests at once. You could test for multiple genetic conditions in a person’s DNA in just one run. 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. Therefore we could do ‘spectroscopy-on-a-chip’ and examine fluorescence at thousands of points at once”.

Ref: Experimental demonstration of a broadband array of invisibility cloaks in the visible frequency range, by Smolyaninova V N et al, 2012 New J. Phys. 14 053029

The paper can be viewed here:

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