Plenty of warning signs also preceded Nigerian Umar Farouq Abdulmutallab's attempt to blow up Northwest flight 253 over Detroit on Christmas Day 2009 with an underwear bomb made with PETN, a plastic explosive that was not detected by airport security.

CNN: Agencies often miss warning signs of attacks

Using a thin film of polyfluorene, a light-emitting plastic, they have created a laser which reacts with explosive vapour.

BBC: Plastic lasers shed light on hidden explosives