Little Drop Goes a Long Way in Studying Microbial and Atmospheric Reactions

When you look at a snapshot of an event, all you know is what you see at that moment. You don't know what happened next. Scientists struggle with this challenge when studying aerosols and living cells. Electron microscopes and other tools take a snapshot and can damage the sample in the process.

The answer? A simple drop of liquid and a complex scientific instrument that's providing new answers.

Led by Julia and Alexander Laskin at Pacific Northwest National Laboratory (PNNL), scientists created a technology that uses a tiny drop of liquid to release molecules from the sample. Scientists begin with a sample on any surface that fits in the instrument's holder, whether that's a petri dish or a dollar bill. No time-consuming preparation is needed. No freezing or fussing with the sample. A tiny drop of liquid is delivered to the sample. The drop picks up molecules from the surface. The sample-laden liquid is then drawn off and injected into a mass spectrometer. The mass spectrometer provides detailed analysis of the molecules.

The technique is called Nanospray Desorption Electrospray Ionization, or nano-DESI for short. Invented in 2009, nano-DESI Mass Spectrometry is both fast and minimally invasive. Using it, scientists can repeatedly remove and analyze molecules from living bacterial colonies without harming the colony as a whole. Scientists can thus follow – over the course of hours, days, and weeks – the creation and distribution of metabolites, peptides and lipids secreted by a colony.

Recently, a team used nano-DESI to determine the neighborliness of blue-green bacterial colonies. After the colonies have grown for a few days, clusters of the microbe Shewanella grow nearby. Why? By continually sampling the blue-green colonies, the scientists learned that the colony steadily secretes two molecules. The team hypothesizes that these molecules feed the Shewanella.

Understanding when the molecules are secreted and how far they travel will help scientists interpret and manipulate microbial communities for sustainable energy and environmental remediation. But, the technology has broader applications.

Scientists are using nano-DESI to determine the concentrations of hundreds of molecules in a complex aerosol mixture without knowing much about the molecules in advance, other than the fact that they possessed a carbonyl group. This group is a carbon atom double bonded to an oxygen atom, and it reacts strongly with Girard's reagent T. The team added that reagent to the nano-DESI drop. It reacted, and the scientists detected the desired molecules at ~0.5-picogram level. To put this weight in perspective, it is 1,000,000,000,000 times smaller than the weight of one sip of coffee.

Nano-DESI is available for other scientists to use through a competitive proposal process at EMSL, a Department of Energy national scientific user facility located at PNNL.

By using a tiny drop of liquid, scientists are answering some big questions, proving that a humble drop goes a long way for science.

Kristin Manke is a Communications Specialist at Pacific Northwest National Laboratory in Richland, Wash.

The Department’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information please visit For more information about PNNL, please go to