Under the microscope

"It is already very difficult to capture an image of a covalent bond using the current microscopy techniques, not to say a hydrogen bond, which is much weaker than a covalent bond," Liu says.

Hydrogen bonds are decisive for the structure of some of the most essential substances in our life, like water, DNA and protein. "If scientists want to understand the reason why a snowflake has a delicate six-pointed shape, why DNA has a double-heli structure, and why protein folds into its optimum shape, we explain it by hydrogen bonds, though no one had ever seen it," Liu says.

"Now that we can see the image of hydrogen bonds directly, it will be a great help for future research of life science."

International debates over the nature of hydrogen bonds, however, did not cease until the recent publication of the real-space images published by the Chinese scientists, contributing this decisive evidence.

In 2011, the International Union of Pure and Applied Chemistry published a seven-page draft redefinition on hydrogen bonds after extensive research into evidence found over the past 40 years questioned the nature of this form of bond.

"Qiu Xiaohui and his team's real-space identification of hydrogen bonding has indeed been very, very important in my opinion, as I have seen chemists arguing endlessly about 'bonding' without solid experimental evidence," Elangannan Arunan says. Arunan is the chemistry professor of the Indian Institute of Science who led IUPAC's committee to redefine hydrogen bonds.

Flemming Besenbacher, founder and director of the Interdisciplinary Nanoscience Center located at Aarhus University, Denmark, says the work of Qiu's team "allows us to 'see' something invisible bonding".

"The intermolecular bonding is like an invisible glue linking molecules together to assemble molecules from DNA, protein to build up you and me," he says.

"Qiu used - in a very elegant way - the Atomic Force Microscope to image hydrogen bonds between DNA bases.