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Pen-like sensor ‘shines’ when exposed to toxic gases

Image credit: Jevgenikurnikov/Dreamstime

Researchers based in China have developed a pen-like sensor that changes colour when exposed to harmful gases.

Exposure to some odourless, colourless and tasteless gases, such as nerve agents, can be toxic or even lethal. Having the ability to detect other types of vapours could save people from eating spoiled or rotten food. Easy-to-use portable devices could, therefore, go a long way toward protecting the health of the public, experts have said.

Humans cannot detect many toxic fumes, such as toxic neurotransmitters or powerful amines released from spoiled foods, so experts believe a sensor that can detect these high gas levels will be useful. Fluorescence-based sensors are a possible solution because they are inexpensive and can reveal a number of compounds.

However, some electromagnetic compounds combine as soon as they come in contact with gas, reduce their volume and may require complex manufacturing processes. Meanwhile, some fluorophores emit a greater brightness when they are combined with a compound caused by greenhouse gases (AIEgens).

Most current detection methods using AIEgens are liquid; require gas to be dissolved in the solution before analysis, and are not easily taken. The Chinese research team - Zhe Jiao, Pengfei Zhang, Haitao Feng, Ben Zhong Tang - adjusted the AIEgens to be connected to thin needle fibres, creating a handheld device with a tip that “ignites” in the presence of certain gases.

The researchers developed two AIEgen-based pens: one for identifying the diethyl chlorophosphite (DCP) neurotransmitter and the other for amines produced by perishable food.

The handy pen's tip changes colour when exposed to harmful gases.

The tip of the flexible pen changes colour when exposed to harmful gases.

Image credit: Adapted from ACS Materials Letters 2021, DOI: 10.1021/acsmaterialslett.0c00516

To create the pen, they first coated silicon dioxide polymer fibres with a thin layer of sol-gel to prevent AIEgens. Next, they added AIEgen, which changes colour when it faces DCP on one set of fibres, and AIEgen which reacts and assumes in another set. 

Covered fibres were then placed at the end of the device as a pen with a UV light source inside. The tip of the DCP sensor changed from a yellow to blue light within 30 minutes of being disclosed by DCP, according to the researchers.

The team also observed that the tip of the amine sensors was previously a gray colour, but produced a yellowish light within five minutes when exposed to volatile amine vapour. Both sensors returned to their original colour when exposed to steam reduction, indicating that they could be replaced.

Furthermore, the team used a suitable pen to respond positively to distinguish between salmon samples that had been correctly stored in the refrigerator and salmon that had been left at room temperature for 48 hours.

The researcher concluded that this could provide an effective solution for detecting seafood damage. It could also be used for food security, environmental monitoring, and public safety use.

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