What is the Goal of Your Research?

Water is absolutely necessary for all the living creatures. Recently, however, usable water is becoming scarce and its quality is declining all over the world. This is because of rapid population and economic growth. The water shortage or the decline in water quality threatens the lives of humans, animals and plants. To solve these problems, it is important to frequently measure the quality of drinking, agricultural and natural waters, in as many places as possible, in order to constantly ensure the safety of water. One of the solutions for water shortage is recycling sewage water or wastewater. In this case as well, the safety of the recycled water must always be guaranteed. As seen above, measuring water quality is extremely important. However, the measurement apparatuses for water quality that are available now are large and expensive, and unfortunately, they are specialized machines that often cannot be used unless the user has specific, professional knowledge.

This is why we are working on the development of sensors that anyone in the world can measure water quality in a cheap and quick way. Right now, we are specifically developing sensors for pathogenic microorganisms and sensors for heavy metals. Heavy metals, as you learned in school, are quite hazardous to your health even in small amounts, causing Minamata (mercury poisoning) and itai-itai (cadmium poisoning) diseases. To measure the concentrations of the heavy metals dissolved in water easily and instantaneously, we decided to make molecules that change fluorescent color when they react with heavy metals. We use a technique where molecules are combined sequentially one by one just like making an arbitrary-shaped structure when putting together Lego blocks. This is called organic synthesis. I specialize in environmental engineering, which usually deals with large-scale (scale: kilometers) subjects or topics, such as the entire globe, oceans, rivers and lakes. One of the unique aspects of our research is that we have combined environmental engineering with nanotechnology, which deals with molecules (scale: nanometers). One of the major goals of my research group is to try new types of research projects and educate students through an interdisciplinary education.

 

What Kind of Experiments are You Conducting?

Fig. 1 Organic Synthesis

Our research starts from making molecules using organic synthesis. Fig. 1 shows how we perform the organic synthesis. Molecules, being extremely small, cannot be assembled by hand. We conduct many experiments over and over using various types of molecules dissolved in liquids. The temperatures are adjusted, the reaction time is made longer or shorter and various catalysts are tested. You might think it’s cool to be able to create molecules freely on your own, however, conducting the actual experiments is rather unpretentious work. The procedure of putting powder in solutions and controlling the temperature is just like cooking. If you like cooking, you might enjoy this research.

Once created, the molecules are put into a solution to examine whether it contains heavy metals or not. Fig. 2 shows a photograph of fluorescence emitted by a solution that contains one kind of heavy metal, and it is taken right after the molecules are added. Three types of molecules were tested. The end column on the left (none) shows the fluorescence emitted by only the molecule. For example, molecule 1 itself shows a green color, which turns yellow when a harmful heavy metal Zn (zinc), Cd (cadmium), or Hg (mercury) is present in the solution. The color change is completed around ten seconds (Reference (1)). Each molecular “hand” (called a ligand or chelate) which captures the heavy metal ion corresponds to a specific type of heavy metal. The fluorescent color changes when Cr (chromium), Fe (iron), Zn, Cd, or Hg exists in the solution for molecule 2, and Cr or Hg for molecule 3. In this way, adding a molecule (actually in powder form) to the water allows the user to assess right away whether the water is contaminated by a heavy metal or not. Expensive measurement apparatuses or advanced technologies are not necessary. Hopefully, the technology will enable people all over the world to use water safely.

Fig. 2

 

 

What Will be Your Next Goal?

Right now, the molecule is not reusable because it is added in water. We are trying to develop a sensor with the molecule attached to the tip of an optical fiber using covalent bonding. The sensor enables us to measure the concentration of heavy metals by simply immersing the fiber into water. This method can prevent the loss of the molecules because they are attached onto the glass surface, even after many repeated measurements. I am also going to develop sensors for pathogenic microorganisms.

 

References

(1) http://www.youtube.com/watch?v=yxpF7ZlrvrM