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Colour-changing sensor detects eye damage

Washington: Scientists, including those of Indian origin, have developed a colour-changing contact lens that can detect a key marker of eye injury in minutes -- a time frame crucial to treating eye trauma.

The researchers from University of Illinois in the US used the sensor, called OjoGel, to measure ascorbic acid levels in artificial tears and in clinical samples of fluid from patients' eyes.

The gel laden with gold nanoparticles changes colour when it reacts with a teardrop containing ascorbic acid, released from a wound to the eye, according to the study published in the journal Biosensors and Bioelectronics.

"We expect a significant potential impact of this biosensor for evaluating the eye in post-surgical patients as well as trauma patients," said Dipanjan Pan, a professor at the University of Illinois. Ascorbic acid, also known as vitamin C, is found in high concentrations in the fluid inside the eye, called aqueous humour, but normally has very low concentration in tears.

"Deep damage to the cornea from trauma or incisional surgery releases aqueous humour into the tear film, which increases the concentration of ascorbic acid in tears to a measurably higher level than that found in normal eyes," said Pan.

"OjoGel offers a unique biosensing technique that provides an effective and simple method for testing ascorbic acid in a point-of-care delivery system," he said.

A tiny teardrop is all that is needed to cause a color-change reaction in the OjoGel. The extent of the colour change correlates to the concentration of ascorbic acid in the tear sample, shifting from pale yellow to a dark reddish-brown as the concentration increases.

The researchers, including visiting scholar Ketan Dighe, did extensive testing to determine the concentrations associated with each degree of colour change. They developed a colour key and guidelines for using a mobile phone app, Pixel Picker, to precisely measure the concentration indicated by a reacted gel sample. 

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