Three-in-one sensor detects multiple chemical warfare agents

A new sensor can detect three different chemical warfare agents simultaneously, revealing the presence of sarin, cyanide and sulfur mustard via a smartphone app.

There are five main types of chemical warfare agents: blister, nerve, blood, choking and incapacitating. Sulfur mustard – or mustard gas – is a blister agent that has been used with devastating effect. Sarin and cyanide are nerve and blood agents, respectively, and these agents are described as the only type of lethal agents capable of causing mass casualties, even at low concentrations. The use of such chemicals in warfare is prohibited under the Chemical Weapons Convention, which every country on Earth – with the exception of five – has ratified.

Led by scientists at the Naval Medical University in Shanghai, the system detects the three agents through coumarin-based fluorescent sensors. Both sarin and sulfur mustard are recognised by an imidazole group attached to the coumarin, which on reacting causes the quenching of fluorescence. This shows up as a colour change from yellow to red, in 10 seconds for sarin and 60 seconds for sulfur mustard. Cyanide acts differently. It reacts with the coumarin-based molecule instead, where an electron-withdrawing ketone neighbour enables the nucleophilic attack of cyanide ions. The yellow compound fades to colourless in 90 seconds to indicate the presence of cyanide.

Test strips are loaded with the coumarin-based molecule and tested for the three agents using a smartphone-based colorimetric analysis program.

With sarin and sulfur mustard causing the same colour change at the same wavelength a further distinguishing step is needed. The team introduced an internal reference probe to determine one from the other. Comparative analysis between the sensor and reference via the smartphone app results in individual detection limits for sulfur mustard, sarin and cyanide of 0.05ppm, 0.01ppm and 5ppm respectively. However, the presence of each agent, even at these levels, is still cause for concern.

The team also tested the probe on each chemical agent in living cells, successfully detecting all three chemical weapons in live cells and mouse models before they were poisoned.

The sensor has similar sensitivity and response times to other products, yet few, if any, manage to detect three separate chemical warfare agents at once. On-site analysis via a smartphone is an added benefit, although it has not yet been tested in the field.