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Photonic crystals aid Raman signals

03 Feb 2005

Patterned substrates that enable fast and accurate detection of Raman signals go on sale.

Mesophotonics, UK, has unveiled a patterned substrate which it says enhances the signal produced by surface enhanced Raman spectroscopy (SERS) by a factor of a million. The extra sensitivity opens the door to applications ranging from medical diagnostics and drug discovery to environmental monitoring and forensics.

"SERS has never had broad ranging applications because the technique is difficult to use and inconsistent," John Lincoln of Mesophotonics told Optics.org. "We believe we can make it highly reproducible so that it works every time."

The key behind these bold statements is the firm's semiconductor background and understanding of photonic crystals. Using its knowledge, Mesophotonics has found a way to tightly control the Raman amplification process and consistently produce enhanced Raman signals.

Launched at last month's Photonics West, the initial Klarite product consists of a 5x5 mm piece of silica wafer mounted on a standard 3 inch glass slide. The silica is patterned with a series of holes using a lithography process before it is covered with a thin layer of gold. Initial products are available for Raman excitation wavelengths of 633 nm and 785 nm.

"We have released the initial product on 3 inch glass slides so that it is entirely compatible with existing Raman microscopes," said Lincoln. "But you don't have to place them on a glass slide. You could cover a whole 4 inch silicon wafer with these devices. They can be as big as you want."

An excitation power of 5 mW is sufficient for a 10 second signal acquisition. Acording to Lincoln, this means that measurements can now be carried out in real time and are far more sensitive than before.

These benefits are attractive to a range of applications. "For example, cell-level and medical diagnostics to distinguish between bacterial and viral infections," explained Lincoln. "You can also use it for forensics. This could be anything from finding counterfeit whiskey or cocaine. There is a lot of work going on to use Raman to detect illegal drugs and here sensitivity is key."

He adds that the technique could also be used for drug discovery to aid amino assay studies and environmental applications such as checking for water impurities.

Jacqueline Hewett is technology editor on Optics.org and Opto & Laser Europe magazine.

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