Bank robbers are to be foiled by hot foam inspired by the chemical defences of the bombardier beetle. Scientists in Switzerland have designed a polymer foil that releases foam when ATMs or money transport cassettes are broken open; a colour agent and DNA particles are used to mark the cash and stamp them forensically.
The mm-thick foil comprises two compartments separated by a sprayed poly-acrylate clearcoat for a thin, brittle cover. The honeycomb structures between the compartments are filled by either hydrogen peroxide or manganese dioxide. Once the polymer barrier between the chemicals is smashed, the chemicals mix violently to produce oxygen and hot water vapour (J. Mater. Chem. A., doi:10.1039/C3TA15326F).
‘The chemicals produced are not dangerous, but what could be dangerous is the temperature. The foam gets up to 80 degrees,’ explains first author Jonas Halter of ETH Zurich, Switzerland. The system was inspired by the bombardier beetle, a colourful insect that defends itself by mixing reactants like hydroquinone, hydrogen peroxide and enzymes. Manganese dioxide used in the Swiss experiments is a relatively inexpensive catalyst.
Fraudsters stealing money from the ATM machine can be identified after contact with the stolen banknotes, which are forensically stamped with DNA, the researchers explained. ‘Naked DNA is not so stable so we placed it within a small sphere of glass for protection. These DNA nanoparticles work like a paternity test in that they have a certain DNA code. It is actually possible to encode every ATM machine differently, so you know which ATM it was stolen from and the robber, once in contact with the dye, will be forensically marked by the nanoparticles,’ Halter explains. Lab experiments with €5 banknotes showed that the nanoparticles mark anyone coming into contact with them.
The researchers calculate the material would cost $40/m2, or around $15 per ATM machine.
Polymer chemist Patrick Theato, at the University of Hamburg, says: ‘It is the simplicity of the approach that makes this finding so exciting. I don’t see any other big challenges to be met before such a foil could be marketed.’ He believes a number of applications are possible, including as a coating to flag up when a substrate is bent or stretched too much to avoid material failure.
The Swiss team has also thought about using the materials for protecting crops or agricultural goods from animals. ‘You could cover the goods with a foil and when the bird pecks at it, the foam is released and this would deter them,’ Halter explains.
The European ATM Security Team, based in Edinburgh, notes a rise in ATM attacks in recent years. During the first six months of 2013, more than 1000 ATM attacks took place in Europe, causing losses of around €10m. While existing protective devices can spray robbers and banknotes, these are mechanical systems, notes Wendelin Stark, research leader at ETH. ‘A small motion is set in motion when triggered by a signal from a sensor. This requires electricity, is prone to malfunctions and is expensive.’