Blood Typing Made Simple

For anyone who has ever wondered what their blood type is, a new paper-based device will literally write the answer, providing an inexpensive and unambiguous way to determine blood type (Angew. Chem. Int. Ed., DOI: 10.1002/anie.201201822).

The presence or absence of certain antigens on red blood cells determines a person’s blood type. Specific antibodies will react with these antigens and make the red blood cells clump. Researchers led by Wei Shen, of Australia’s Monash University, use an ink-jet printer to apply these antibodies in the shapes of letters A, B, and X as well as a vertical line onto postage-stamp-sized pieces of paper towel. O and rhesus-negative blood types don’t have antigens that react with these antibodies, so the researchers preprint an O in the same spot as the X and a horizontal line intersecting the vertical line on the paper in red waterproof ink.

Place a few drops of blood on the paper, wash it with saline, and in under a minute,the blood type appears in text. For example, if the blood type is A-positive, antigens will react with printed A antibody to produce a clump of red blood cells in the shape of the letter A and with antibody in the vertical line to form a + sign. The antigens will also cause a red X to form over the preprinted O. For O-negative blood, no reaction with the antibodies would occur, and the preprinted paper would simply read O above a – sign.

Shen got the idea after seeing the film adaptation of J. K. Rowling’s book “Harry Potter and the Chamber of Secrets,” in which the characters query a diary that responds in writing. Shen realized technology he had previously helped develop could be modified to respond in writing to the question: What’s my blood type?

“The ability to form letters that directly report blood type makes it possible for nonexperts to interpret the results rapidly, which is of particular importance in rapid-response scenarios,” comments John D. Brennan, an expert in bioanalytical chemistry at McMaster University in Ontario. “This method also shows the advantage of implementing simple ink-jet printers to produce paper assays rather than conventional lateral flow printers, which produce only lines.”