Imperial College London

Colourful carbon monoxide sensor could help save lives

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Orange to white colour gradient

Scientists have designed a new carbon monoxide sensor that uses a strip which changes from orange to white when it senses the poisonous gas.

The sensor is very sensitive and can detect even low levels of carbon monoxide (CO). Under an ultraviolet lamp, the strip also fluoresces allowing even lower levels of CO to be detected. 

The new design is unaffected by steam, smoke or common solvents found in domestic cleaning products, which can, over time, lead to false and inaccurate readings in some existing detectors.

Carbon monoxide is often referred to as the silent killer and according to the UK Government it kills 50 people each year and many more are critically poisoned. Even though you can’t smell it and you can’t see it, with our new design we can help you detect it

– Dr James Wilton-Ely

Department of Chemistry

CO is a toxic gas that prevents blood from transferring oxygen around the body. CO poisoning can cause dizziness and loss of consciousness; it can also induce comas and cause death. As it has no odour, colour or taste, it can be difficult to detect. It is produced by burning fuels, such as petrol, gas and wood, in unventilated conditions where there is not enough oxygen for the carbon to form carbon dioxide.

The scientists suggest that the strip, which can be manufactured for just one penny, could be attached to the sleeve of scientists working with CO in a laboratory or mechanics working in a garage who may be vulnerable to indoor toxic fumes. 

The strips have already been tried in a simple prototype device suitable for use in the home, which converts the colour change into a numerical reading and sounds an alarm if levels become dangerous.

The findings of the study are published in the Journal of the American Chemical Society.

Lead researcher Dr James Wilton-Ely, from the Department of Chemistry at Imperial College London said: “Carbon monoxide is often referred to as the silent killer and according to the UK Government it kills 50 people each year and many more are critically poisoned. Even though you can’t smell it and you can’t see it, with our new design we can help you detect it. Our device can even sense amounts of the poisonous gas that are below the toxic level for humans, alerting you to the fact that your boiler is starting to develop problems and allowing it be serviced straight away and prevent dangerous CO levels building up”.

Household devices that detect, monitor and alert CO leakages have been on the market since the early 1980s. However, smoke or steam from bathrooms often gave false alarms causing people to turn off their detector in annoyance. While modern devices have improved this situation markedly, the researchers believe that there is room for improvement.

As an alternative, the scientists created a chemical probe that is unaffected by steam and smoke. Its dramatic colour change can be easily seen by the naked eye.

Colour changes on reaction with CO happen with many compounds in the liquid state, but this is difficult to incorporate into a viable sensor that detects CO present in air.

In the new study, scientists found that a solid containing the metal ruthenium can also indicate the presence of CO in air by binding to it strongly, which produces the colour change and switches on the fluorescence, causing it to ‘glow’. The scientists coated a strip of cellulose paper with the metal compound, making it portable and easy to use. When even small quantities of the poisonous gas are present, CO displaces a molecule attached to the metal, which creates a colour change and turns on the fluorescence.

Under an ultraviolet lamp, the strip literally glows in the presence of CO as the compound absorbs the ultraviolet energy and makes it appear blue. Without CO, there is no colour change and no fluorescence.

The scientists are now working towards improving their design to make sure that the sensor keeps its colour long-term, remains stable in light conditions, and is safe for the public to handle in their home.

Anita Toscani, who is currently working towards her PhD in the College’s Department of Chemistry said: “The sensitivity and selectivity of the ruthenium compound offers huge advantages over current methods of CO sensing. It’s also cheap, robust and very reliable. This compound opens up new research frontiers in CO sensing.”

The system described in the article is part of an academic research study and is not currently available to the public. The researchers recommend that everyone with gas appliances or a fireplace should fit the currently available (EN 50291 certified) detectors in their homes.

This research was carried out in collaboration with the Polytechnic University of Valencia, Spain and was funded by the Spanish regional government and The Leverhulme Trust.

The article was amended on 18/09/14 to clarify the performance of past and current CO detectors and to encourage readers to fit CO alarms.

REFERENCE: María E. Moragues, et al. ‘A chromo-fluorogenic synthetic “canary” for CO detection based on a pyrenylvinyl ruthenium(II) complex’. Journal of the American Chemical Society, 2014, 136, 11930.

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Gail Wilson

Gail Wilson
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