Researchers say they have developed an inexpensive and faster enzyme test that can accurately detect diseases and bacterial contamination.

The test, developed by scientists at the Queen's University Belfast in the UK, can detect enzyme markers of diseases known as proteases in humans, animals and food products.

Proteases are crucial for microorganism growth and are responsible for the progression of many diseases, according to the study published in the journal Nano Research.

Levels of proteases can be highly elevated in the urine of patients with diabetic kidney disease, or at the sites of infected wounds.

Current protease detection methods are costly, time-consuming and are not always effective, researchers said.

"Not only is the test cheap to produce, but it can be used anywhere and is not reliant on laboratory conditions," said Claire McVey from the Queen's University.

"Eliminating the need to carry out tests in a laboratory setting is life-changing. As well as being cost-effective, it means faster diagnosis," McVey said.

The gold-nanoparticle based nanosensor indicates when proteases are present through a visible colour-change reaction.

Gold nanoparticles are well known for their capability in speeding up the oxidisation of a chemical called tetramethylbenzidine (TMB), visible through a vivid blue-colour formation.

When casein, a molecule present in milk, is added to gold nanoparticles, it surrounds the nanoparticles acting as a protective surface barrier.

When TMB is introduced, the casein prevents the oxidisation reaction, meaning there is no or only a slight colour change.

Where proteases are present, they 'eat' the protective casein barrier, exposing the surface of the gold nanoparticles.

In this instance, when TMB is added, the proteases have removed the casein meaning oxidisation occurs quickly causing a fast change in colour.

"When we add TMB to the casein-covered gold nanoparticles, we can tell virtually instantly if proteases are present by whether or not the solution turns blue. Normally such testing takes much longer," said Cuong Cao, lead academic on the study.

Using this approach, proteases can be detected within 90 minutes without the need for complicated or expensive laboratory equipment, researchers said.

The 'ingredients' for making the nanosensor are readily available and low cost. Gold nanoparticles can be produced in abundance, with little restriction on storage requirements, making it a durable and cheap substance.