McDonald's is rolling out a state-of-the art security system across Australia that douses fleeing robbers with an invisible, synthetic DNA spray in attempt to stop criminals seeing their fast food restaurants as a soft target.

The move comes as police ramp up their patrols of local McDonald's restaurants after a spate of robberies across Sydney during the Christmas and New Year period.

The solution contains a UV tracer and a unique DNA code, linking the robber irrefutably to the crime scene.

A McDonald's spokeswoman said the company will increase the use of 'SelectaDNA' in stores all over the country after a successful trial in their six busiest Sydney restaurants was launched in January last year.

According to the SelectaDNA website, spray heads are fitted at the entry points of premises which, on activation, emit a burst of solution onto the offenders. The solution contains a UV tracer which is invisible to the naked eye but will show up under UV light. It also has a unique DNA code, linking the thieves to the specific crime scene in question.