Kenjiro Hanaoka: Immersed in the Development of Fluorescent Probes

2024/04/18

When you hear the word "fluorescence," what comes to mind? The first thing you might think of is a highlighter pen. I remember when I was a university student, Professor Tetsuo Nagano of the Graduate School of Pharmaceutical Sciences at the University of Tokyo mentioned in a lecture (though the lecture itself was on drug metabolism...) that the green color of Bathclin bath salts is a fluorescent dye called fluorescein. Because of things like this, I simply had the impression that fluorescence equals bright, sparkling colors.

In that sense, although I would go on to study fluorescence in graduate school, I might not have properly understood it until partway through my undergraduate years. For example, you cannot observe bright fluorescence simply by dissolving fluorescent dye powder in water and leaving it in the dark (I didn't properly understand this either). Fluorescence is only emitted when a fluorescent dye is irradiated with light of a wavelength it absorbs. I think the way a shirt glows bluish-white when exposed to blacklights at amusement parks or aquarium attractions is fluorescence. Currently, our group is developing fluorescent dyes (called fluorescent probes) that have the function of capturing specific biomolecules and switching fluorescence from "off" to "on." Twenty years ago, the mainstream approach was gritty trial and error—making something and then evaluating it—but today, sophisticated design of fluorescent probes has become possible, allowing for the rational development of various probes.

In life science research today, the most valuable application of fluorescence is "fluorescence imaging." Fluorescence imaging is a method for observing biological phenomena occurring within living cells in real time by, for example, introducing fluorescent probes into living cells and observing them with a fluorescence microscope. These technologies have made it possible to observe not only the inside of cells but also the conditions within animal organs. The importance of fluorescence imaging in enabling such in vivo observations is evident from the fact that Nobel Prizes in Chemistry were awarded in 2008 for the "discovery and development of the green fluorescent protein (GFP)," in 2014 for the "development of super-resolved fluorescence microscopy," and in 2023 for the "discovery and synthesis of quantum dots." In research to develop new fluorescent probes, the ability to see previously unseen, unknown biological phenomena with one's own eyes is what makes it exciting and represents the true thrill of research.