A scene from a Harry Potter film has inspired a new user-friendly device that literally spells out what blood type you are.

Engineer Associate Professor Wei Shen, from Monash University, and colleagues, report their findings in the journal Angewandte Chemie.

"We have tested 99 samples and so far we have found it has the same accuracy as the mainstream blood typing tests," Professor Shen said.

Sensors that can diagnose blood type cheaply and rapidly are important, especially in emergency situations, including humanitarian disasters.

But Professor Shen says existing sensors are not as user-friendly as they could be.

Blood type can be determined by mixing different blood antigens and antibodies on a glass slide and looking to see which react.

For example, if a blood sample coagulates when it is mixed with antibody A, that tells you it is blood type A.

But Professor Shen points out that using a sensor like this requires interpretation of the results and a certain level of scientific knowledge.

Harry Potter inspiration

One day while watching the film Harry Potter and the Chamber of Secrets, Professor Shen came up with an idea for making a more user-friendly sensor.

In the story, Harry Potter writes a question in Tom Riddle's Diary: "Do you know anything about the Chamber of Secrets?". The paper responds with a 'Yes' in writing.

Professor Shen says this made him think about developing a sensor that reported a blood type result in writing.

"The movie shows that you can have a text result, and that's where the idea comes from," he says.

Written in blood

The prototype sensor developed by Professor Shen and his colleagues consists of a 2.5-centimetre-square piece of paper towel.

The paper is printed with a water-repellent coating, except for in four areas on the surface, which are in different shapes relevant to blood type.

For example there is an area in the shape of the letter A, and another in the shape of the letter B.

These water-loving areas are filled with antibodies that interact with blood antigens on red blood cells to spell out the blood type.

So, for example, when blood of type A is put on the 'A' area, with antibody A, coagulation occurs.

"Agglutinated [coagulation] blood has many cells clumped together and these stick or get caught in between the fibres," Professor Shen said.

When the sensor is rinsed, the coagulation remains, spelling out the answer - literally - in blood.

The sensor can tell whether the blood sample is A, B, AB or O, and whether it is Rhesus positive or negative.

Professor Shen says the sensor was funded by the ARC and a commercial partner, and will need to undergo extensive tests for two to five years before it can be used for everyday medicine.

He adds the device could also be used as a basis for pregnancy and other tests.