Hauer, who is a professor at the Technical University of Munich (Germany), wanted to change this. He embarked on a pan-European collaboration with researchers at the University of Copenhagen, who specialize in single molecule detection, and long-time colleagues at the Italian university Politecnico di Milano, who had already developed a compact spectrometer that perfectly suited Hauer’s research needs.
The key to Hauer’s research lies in the Italian spectrometer’s ability to generate not one, but two laser pulses, with a controlled delay in between. Hauer’s team decided on a laser that has a broad frequency range—one that mimics sunlight—to cover all visible wavelengths.
When using one laser, researchers can only excite at a single wavelength, thus the data outputted is the fluorescence spectrum at that specific wavelength. The information missing is how the molecules behave at other wavelengths. When using two lasers, the critical second pulse modulates the emission spectrum in a specific manner, which in turn provides information about the absorption spectrum. This data is then evaluated using a simple Fourier transformation.
“Two pulses allows us to encode the absorption spectrum into the emission spectrum. Thus, in one measurement, we can record both the fluorescence and absorption spectrum of a single molecule,” Hauer explained to Laboratory Equipment. "Previously, emission spectra could be routinely acquired, but absorption measurements on individual molecules were extremely expensive. We have now attained the ultimate limit of detectability."
In traditional spectroscopy, these kinds of measurements are averaged over thousands, even millions, of molecules, sacrificing important molecule-specific information. For example, the bonds in an organic molecule may arrange differently when in a large structure. While a researcher may classify a specific molecule as mediocre in terms of light-harvesting, that may only be the case since the data is averaged over a plethora of additional, useless molecules. If the molecule can be isolated as a singular entity, the researcher may discover it’s actually spectacular as light-harvesting.
“If you look at these molecules individually, you can identify the structures that do the job very well,” Hauer said. Then, it’s up to the organic chemists, material scientists and others to isolate the specific structure, mimic its functions, and eventually employ it in an applied method.
End-stage collaboration with organic chemists and material scientists is not the only teamwork propelling this research forward, however. In fact, Hauer said, the method he developed wouldn’t have been possible without the device the Italian team had already created, nor without the knowledge of single molecule detection from the Copenhagen team.
“I couldn’t ask my co-workers to just build me a single molecule setup by themselves, starting from an empty room,” Hauer said. “That would be a waste of taxpayers’ money. There is an instrument out there already in Copenhagen. You have to be willing to go out and contact other experts in other fields, and then come up with something creative together.
“You live and die by the quality of your collaborative network,” he said.
Hauer and his group want to use the new method to better understand the transfer of energy in biological systems in which photosynthesis takes place; ultimately accelerating the identification of efficient single molecules for future photovoltaic technologies.
their sights on the natural light-harvesting complex LH2.
of a novel, efficient organic solar cell.
Today’s researchers are interested in DNA for a multitude of reasons—forensic scientists, for example, analyze DNA for justice, while clinical scientists analyze it for disease biomarkers. Alternatively, some early-stage physicists and biologists analyze and manipulate “the blueprint of life” to fuel tiny components for technical applications.
In a process known as DNA origami, scientists can manipulate DNA in such a way that folding it creates 2- and 3-dimensional structures that can be used in a variety of applications. One of the most notable applications is the development of nanomachines, or nanorobots made partially or entirely of DNA that can switch between defined molecular conformations, and thus be used as sensing, computing, actuating or therapeutic devices.
“In all these systems, the mechanical properties of DNA molecules are of paramount importance,” said Remy Pawlak, a postdoc in the physics laboratory at the University of Basel (Switzerland).