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Novel LEDs Could Eliminate Bacteria

Photonics Spectra
Jul 1999
Laurel M. Sheppard

A new resonant cavity light-emitting diode (LED) could help to eradicate antibiotic-resistant bacteria, emitting the necessary light (670 to 680 nm) to activate special bug-killing chemicals.

Conventional LEDs are already used in photodynamic therapy, but they need a lot of power and extra cooling systems to produce light bright enough to trigger photosensitive drugs. The new devices -- developed at the Centre for Electronic Materials and Devices at Imperial College, London University -- are 10 times more efficient, can be fabricated as arrays on the substrate, need no packaging to improve their directionality, are cooler and have a narrower spectrum.

Using very short optical cavities, researchers have developed resonant cavity LEDs that emit red light, perfect for killing bacteria with photodynamic therapy.

Although resonant cavity LEDs that emit IR and near-IR light exist, the difficulty with red light is confining enough electrons within the microcavities long enough to produce light. The key to the success at Imperial College is the ability to make strained quantum wells with very short optical cavities that confine the electrons.

The achievement is good news for hospitals, where contamination by the staphylococcus aureus superbug, which cannot be killed by ordinary antibiotics, is a serious threat. The bacterium is "causing major concerns in hospitals, particularly as many patients have depressed immune systems already," said professor David Phillips, head of chemistry at the college.

The resonant cavity LED could make sterilizing an operating theater as easy as shining a flashlight. Once a light-sensitive chemical has been sprayed around the room, a wave of the glowing wand could eradicate bugs before they get to work. A nurse could sterilize wounds in the same way, stopping infection with a red light stick.

Combined with a laser, the device could also make photodynamic therapy for stomach ulcers complete. "Laser light is already used to fry stomach ulcers and stop them bleeding, but it doesn't eradicate the bacterium, h. pylori, that causes the ulcers in the first place, so they reoccur," Phillips said. "Now, if the patient was to take a light-sensitive drug before the operation, once the laser has done its job the new LEDs could bathe the area in strong, pure red light to activate the chemicals that wipe out the bacteria."

The new LEDs could also be cost-competitive. They require less packaging than standard LEDs, arrays can be made on a single chip, and their surface emittance allows testing on the wafer -- factors that contribute to lower production costs.

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