Scientists have developed a method of detecting counterfeit whisky using lasers which can test samples no bigger than a teardrop.

Using a ray of light the width of a human hair, alcohol content is measured to determine whether the drink is genuine or not.

The method involves placing a tiny amount of whisky on a transparent plastic chip about the size of a credit card. Using optical fibres, the sample is illuminated by light using one fibre and collected by another.

By analysing the collection of light scattered from the whisky, the researchers at the University of St Andrews say they are able to diagnose the sample.

The key lies in the ability of the laser to detect the amount of alcohol contained in the sample, genuine whisky must contain at least 40%.

Scientists said they can use a sample the size of a teardrop to work out the brand, age and even which cask was used to create a single malt.

The research, which has been patented and is being presented to industry, was carried out by physicists Praveen Ashok, Kishan Dholakia and Bavishna Praveen.

Mrs Praveen said: "Counterfeiting is rife in the drinks industry, which is constantly searching for new, powerful and inexpensive methods for liquor analysis.

"Using the power of light, we have adapted our technology to address a problem related to an industry which is a crucial part of Scottish culture and economy."

Researchers said the method exploits both the fluorescence of whisky and the scattering of light and shift in energy when it interacts with molecules, known as its Raman signature.

Mr Ashok said: "Whisky turns out to be very interesting. We can not only gather information about the alcohol content but also (about) the colour and texture.

"These are dictated by the manufacturing process which of course influences greatly the type of whisky people enjoy."

The group originally used the chip involved in the research to detect "bioanalytes" in other studies.

Professor Dholakia added: "Light is incredible and has led to amazing advances in the last 50 years since the advent of the laser.

"It is amazing to think that the technology we are developing for biomedical analysis can also be used to help us enjoy a wee dram, and with the minimum of waste."

The study is being published by the journal Optics Express.