Scientists Seeking to Develop Biosensors to Fight Illness

With their superb sense of smell, dogs have long been utilized for such purposes as the detection of illegal drugs and helping with criminal investigations. A growing number of research projects are attempting to use such "biosensors," which can identify the presence and quantity of various chemicals, employing the special abilities that living organisms possess.

There are hopes this research will lead to the development of technologies that can, among other things, be used for the early detection of cancer and replace drug-sniffing dogs.

Mold enzymes
The first biosensor to have been introduced is believed to be a device used to measure the blood glucose levels of diabetes patients. Developed in the 1960s, it utilizes an enzyme known as glucose oxidase found in a type of mold.

Currently, popular measuring devices for individuals use a needle prick to the fingertip to take a minute amount of blood and see how it reacts with enzymes. The devices detect the electrons and hydrogen peroxide that is produced when enzymes break down glucose and display a numerical value, such as 86 or 105, that indicates how many milligrams of glucose are present in each deciliter of blood.

"These devices were roughly the size of a lunch box not that long ago, but now they're pocket-sized. They can take measurements with as little as 0.8 microliters of blood," said Takayuki Sugiyama, who is in charge of such devices' development at Terumo Corp. in Tokyo. One micro means one-millionth.

Diabetes patients typically measure their blood-glucose levels several times a day. If patients can constantly keep track of changes, they can more closely and safely manage their health.

Professor Koji Mitsubayashi at Tokyo Medical and Dental University is currently developing technology that continually measures the glucose found in tears and saliva by embedding enzymes and electrodes into contact lenses and mouthpieces.

The technology could eliminate the need to draw blood each time a reading is taken. Mitsubayashi said the goal is to create a practical application in five years.

Detecting cancer
There is also research attempting to utilize live organisms themselves as sensors for early cancer detection.

Last year, Assistant Professor Takaaki Hirotsu at Kyushu University discovered that a species of nematodes roughly 1 millimeter in length is capable of differentiating cancer patients from non-cancer patients by the smell of their urine. When a drop of urine is placed on a petri dish containing nematodes, they are drawn toward urine from cancer patients and avoid non-cancer samples.

When nematodes were used to examine urine samples from 242 people, including 24 cancer patients, nematodes detected 23 of the 24 cancer samples, resulting in a detection rate of over 95 percent. Moreover, the nematodes shied away from 207 of the 218 non-cancer samples, which was a 95 percent accuracy rate.

"The material cost required for one test is roughly 100 yen (about $0.96), which should make it possible to get cancer screenings cheaply and easily," Hirotsu said. He founded a venture company in October last year, and aims to turn his discovery into a practical application in three years. Although this method is not yet capable of distinguishing what types of cancer it is, it may eventually become possible to do so.

Meanwhile, Professor Shoji Takeuchi from University of Tokyo is attempting to directly utilize receptors, proteins that sense smell and taste, among other things, as sensors. He focuses on a type of receptor that opens the gates connecting the interior and exterior of cells when it binds to a specific substance.

"When one molecule sticks to this receptor, 10 million ions flow into the cell per second. Because the signal is amplified 10 million times, this can be used as a highly sensitive sensor," Takeuchi said.

He said research is now being conducted to determine whether this technology can be used to detect narcotics and such hazardous materials as explosives.

Tokyo University of Technology President Isao Karube, who is well versed in biosensors, said: "This is an exciting area of research where new ideas are constantly being generated. Although its applications are now geared mainly toward the medical field, we can also expect to see it being used for a broader range of purposes."

DNA: Material of interest
In recent years, DNA - referred to as "the blueprint of life" - has been attracting interest as a material for a new type of biosensor. By rearranging the order of the four chemical substances that make up the long, string-like strands, it can be made to bind to specific molecules. Emphasizing the technology's advantages, Professor Kazunori Ikebukuro at Tokyo University of Agriculture and Technology, said, "Because DNA can be artificially synthesized, it is relatively easy to create a sensor that binds to the desired substance."