In the book “Harry Potter and the Chamber of Secrets” by J. K. Rowling, Harry writes a question in Tom Riddle’s diary—and a written answer appears.
Australian researchers were inspired by the idea of paper that writes on itself. In the journal Angewandte Chemie, they have introduced a blood test that indicates blood type in plain text.
Rapid tests made of paper are a simple and inexpensive alternative for diagnostic tests, particularly for use in developing nations. However, they are not completely uncomplicated, and a lack of expertise can lead to fatal misinterpretations. For example, if the wrong supply is used for a blood transfusion, it could result in death. A team led by Wei Shen at Monash University has now developed a “responsive” paper that indicates blood type as unambiguous text.
Currently, blood types are classified with the ABO system, in which designations of A, B, AB, and O are possible.
The letter indicates which antigens are present on the red blood cells. Individuals with type A blood have type A antigens, those with type B have type B antigens; individuals with blood type AB have both types of antigens, those in the O group have no antigens. The system is also used to indicate whether the blood cells have rhesus factor D (RhD positive) or not (RhD negative).
So how does the paper “write” the blood type? For types A, B, and AB it is easy: Two of the windows are shaped like the letters A and B, and are filled with the antigens A and B, respectively. Type A results in a red tint in the A-shaped window, type B in the B-shaped window, and type AB in both. However, type O doesn’t respond to any antibody, so the researchers had to get creative. They made the third window in the shape of an X, included antibodies against A and B, and printed on a red letter “O”, which was printed with a waterproof ink. Blood types A, B, or AB turn the X red, telling the user that the sample is not O type by “crossing out” the O. If the sample is type O, the X becomes white after saline washing, leaving only the red letter O.
The researchers were equally clever in their approach to indicating whether the blood is RhD positive or negative: The fourth window is shaped like a vertical line and contains antibodies against rhesus factor D. A red horizontal line is printed on the paper with the water-proof ink. If the blood is RhD positive, it tints the vertical line red. In combination with the printed water-proof horizontal line, this forms a plus sign. If the blood is RhD negative, the vertical line becomes white after saline washing and the paper shows only a minus sign.About the Author
Angewandte Chemie International Edition, Permalink to the article: http://dx.doi.org/10.1002/anie.201201822
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