Researchers at MIT have developed a new way of revealing the presence of specific chemicals, whether toxins, disease markers, pathogens or explosives, with a fluorescent glow.
The approach combines fluorescent molecules with an open scaffolding called a metal-organic framework (MOF). This structure provides lots of open space for target molecules to occupy, bringing them into close proximity with fluorescent molecules that react to their presence.
MOF materials were first produced about 15 years ago, but their amazing porosity has made them a very active area of research. Although they simply look like little rocks, the sponge-like structures have so much internal surface area that one gram of the material, if unfolded, would cover a football field, Dincă says.
The material’s inner pores are about one nanometer (one billionth of a meter) across, making them “about the size of a small molecule” and well suited as molecular detectors, he says.
The new material is based on the MIT team’s discovery of a way to bind a certain type of fluorescent molecules, also known as chromophores, onto the MOF’s metal atoms. While these particular chromophores cannot emit light by themselves, they become fluorescent when bunched together. When in bunches or clumps, however, target molecules cannot reach them and therefore cannot be detected. Attaching the chromophores to nodes of the MOF’s open framework keeps them from clumping, while also keeping them close to the empty pores so they can easily respond to the arrival of a target molecule.
The findings were reported in the Journal of the American Chemical Society in a paper by assistant professor of chemistry Mircea Dincă, with postdoc Natalia Shustova and undergraduate student Brian McCarthy, published online in November and to appear in a forthcoming print issue.