The recipient of the biochemistry award of the Royal Irish Academy produces tailor-made antibodies that can detect anything from illegal drugs to dangerous bacteria, writes Dick Ahlstrom
Researchers at Dublin City University are working on new types of sensor that instantly warn of dangerous bacteria in foods. The same technology is being used in equipment that responds to the presence of illegal drugs. These are just two of the many applications opening up to the advanced sensors being developed at DCU's National Centre for Sensor Research. The centre involves the efforts of 130 academic and student researchers across a wide range of disciplines, from biochemistry to microchip technology.
Prof Richard O'Kennedy, the leader of a team using biochemistry as a tool in this work, was this week awarded the Royal Irish Academy's award in biochemistry for 2001. The prize acknowledges his significant contribution to the use of antibodies in "biosensors" that can measure just about any substance.
O'Kennedy, who is professor of biological science at DCU, leads a team that includes two postdoctoral researchers, 10 postgraduates, five other students and visiting academic researchers. The effort has attracted funding from the EU, Enterprise Ireland and the Government's Programme for Research in Third Level Institutions, administered by the Higher Education Authority.
The focus of Prof O'Kennedy's work is antibodies, essential proteins produced by our immune systems that protect us against disease. "We have been working on antibodies for the best part of 20 years," he says.
Antibodies are extremely useful in sensors, because they can be customised. "We can tailor-make the antibody, using either conventional or genetic approaches, to interact with any material we wish to measure," he says.
The body produces antibodies to defend against bacterial or viral invaders. When the immune system identifies something that is not "self", it raises antibodies against it. These attach to the organism, in many cases inactivating it immediately but also acting like a flag that calls other parts of the immune system to seek and destroy.
Antibodies are also produced against other substances, such as chemicals and foreign proteins, collectively known as antigens; the immune system produces a unique antibody for any antigen it encounters.
One of the most important aspects of the antibody response is immune memory, a characteristic that enables vaccines to work. Once an antibody is produced, the immune system remembers the antigen and can launch an immediate response the next time it detects it.
Antigens make ideal detectors, because each one responds only to the antigen it was created to recognise. This means antibodies can be raised against a drug of abuse, a harmful food bacteria such as listeria or highly dangerous aflatoxins, produced by a fungus that grows on improperly stored grain.
"We are working with a company that wants to develop a device that could be placed in a police car," says Prof O'Kennedy. It would be used to give an instant read-out on the presence of illegal drugs.
The conventional method for raising an antibody is to inoculate an animal with a target substance, then harvest the antibody produced against it. A more advanced technique involves using a "library" of genes capable of producing many millions of distinct antibodies.
The library is challenged using the target antigen, and the resultant antibody is detected and harvested. It can be made smaller or extra elements can be added; an enzyme or fluorescent substance can be attached, for example, to make activation of the antibody easier to read. "The reason we tend to make the antibody is we can modify it as we want."
The antibody alone would not be enough to make a sensor; it has to be built into a system, so both the presence of a substance and its amount can be read.
"A sensor has three components: an interrogation unit, a transducer, which converts that to a signal, and an output," says Prof O'Kennedy. "The antibody is the interrogation unit we use."
The general approach is to produce the antibody for a target, then attach this to a detector. The antibody will bind only to its target, but there are many ways to read whether the antibody has connected.
One is the "surface plasmon response", where the light reflected from the detector's surface changes if the antibody has bound to its target. Another is to attach a fluorescent substance or an enzyme to the antibody before it is placed on the detector. A change in colour or fluorescence shows that the antibody has attached to its target.