Blood contains haemoglobin. Haemoglobin is an iron (Fe) containing protein that transports oxygen around the body from the lungs to where it is needed, like the brain or muscles. The structure of the haemoglobin molecule changes slightly depending on whether it is carrying oxygen or not.
In the 1930s, it was found that haemoglobin has magnetic properties that are different depending on whether it is carrying oxygen or not. When the haemoglobin is not carrying oxygen it is more sensitive or paramagnetic than oxygenated blood. If you put a drop of blood next to a magnet is there any noticeable magnetic effect?
It has only been in the last fifteen years that this difference in magnetic property has been used in magnetic resonance imaging (MRI) research. MRI uses a very strong magnetic field so this difference in the magnetic properties of oxygenated and deoxygenated haemoglobin in blood can be detected. This change is called the BOLD (blood oxygenation level dependent) signal.
A magnetic field occurs around a magnetised object. It can attract or repel other magnetic objects. You can see this field if you place iron filings around a magnet.
The earth also has a magnetic field, which is caused by electrical currents within the earth. The strength of a magnetic field is measured in teslas (T). The Earth’s magnetic field is about 50µT in New Zealand. Find out more about this in our article, fossil compass. Much higher magnetic fields are used in other magnets.
The magnetic property of blood is also part of what fuels the industry that sells magnetic items as an alternative medicinal therapy. What do you think about these products?