Paper discs that can pick up hydrogen peroxide

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Researchers at the Indian Institute of Science (IISc) have developed a paper-based sensor to detect even tiny volumes of hydrogen peroxide. This chemical is widely used in household and healthcare products like hand sanitizer as a disinfectant, in rocket fuel as a propellant, and is also found in biological cells.

The technique they used involves preparing a gel from a solution containing a specially designed molecule, treated with a liquid containing hydrogen peroxide, and air-drying them on a disc of thin paper. ‘about 0.45 cm in diameter. The paper disc emits green light when placed under a UV lamp, only in the presence of hydrogen peroxide. The intensity of the light was found to be directly proportional to the concentration of hydrogen peroxide.

“You can actually visualize this green emission (photoluminescence) with the naked eye. You don’t need fancy instruments. All you need is a simple source of UV light,” says Arnab Dutta, a PhD student in the Department of Organic Chemistry and first author of the study published in ACS sensors.

Because the paper disk is inexpensive, biodegradable, and easy to use, it could serve as a powerful tool in low-resource settings, even for testing biological fluids like blood. Effectively detecting hydrogen peroxide is also crucial in other areas; peroxide-based explosives, for example, can be traced using hydrogen peroxide which is sometimes used as a raw material.

When the researchers used their technique to randomly test five different brands of hand sanitizer, they found that only three of them contained the level of hydrogen peroxide prescribed by the World Health Organization – 0.125% . A fourth seemed to have much less than 0.125% and one had almost zero hydrogen peroxide.

“Hydrogen peroxide can be detected on a larger scale using titration and other experiments, but these are cumbersome and require training. This method is easy due to its simplicity,” says Uday Maitra, Professor in the Department of Organic Chemistry and lead author of the study.

Maitra’s lab has been working on the development of several “sensitizer” molecules that activate the photoluminescence of elements called lanthanides in the presence of specific chemicals or compounds. They previously developed paper-based sensors to detect specific antioxidants in green tea – and thus test its quality – as well as sensors for various enzymes.

The sensitizer molecule they designed in this study causes a metal called terbium to emit green light under a UV lamp. When the sensitizer is combined with a masking agent, the green light disappears. When hydrogen peroxide is added to this combination, it unmasks the sensitizing molecule, causing it to glow green again. “The way we designed the mask is where the thought process comes in,” says Maitra. “The molecule we designed is very specifically unmasked by hydrogen peroxide.”

Currently, the team is working to reduce the reaction time; it takes a little longer if the concentration of hydrogen peroxide is lower. Maitra adds that they are also working on developing a small, handheld device where detection can be done in a more automated way. “We are in contact with a start-up in Chennai. We have some prototypes made with UV LEDs and a camera, to generate the emission, take a photo and use an image processing application to quantify the amount of hydrogen peroxide.

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