Cell biologists use microelectrodes to study the real-time biochemistry of cell-to-cell signaling, factor secretion, and other extracellular events. But when it comes to the kinetics of intracellular biochemistry, much smaller electrodes are needed. So Michael Mirkin of the City University of New York, Queens College and colleagues at Université Pierre et Marie Curie have reduced them to nanoscale sizes.
Specifically, they have made nanoelectrodes that are coated with platinum black—a high-surface-area version of platinum used on larger-size electrodes for detecting reactive oxygen and nitrogen species.
Downsizing microelectrodes might sound straightforward, but it is far from simple, says Adrian Michael of the University of Pittsburgh, who was not involved in the study. “What the paper shows is that to do it well you have to do it very carefully and incorporate things like the atomic force microscope so you can watch what you’re doing,” he says.
Mirkin used the microscope to monitor the platinum coating process. “We need to produce an electrode with good geometry”—a smooth shape—“otherwise it will destroy the cell when we punch a hole in the membrane,” he explains.
Electrodes that passed inspection were used to analyze reactive oxygen and nitrogen species inside macrophages, which use these chemicals to kill bacteria and other microbes. The team resolved a long-standing debate about whether these potent chemicals ever leak from their storage vacuoles into the cell itself, and if so, how the cell survives. Apparently leakage does occur, but is cleared up in scant seconds, thus minimizing toxicity.
Besides macrophage biology, says Michael, the electrodes could be used to study any number of situations involving oxidative stress, which is “a matter of great significance in a number of disease states.” (PNAS, 109:11534-39, 2012.) .
|COMPARING METHODS:||DIAMETER OF GLASS NEEDLE AND CONDUCTIVE ELEMENT||APPLICATIONS||DISADVANTAGES|
|Microelectrodes||~100 µm, ~10 µm||Real-time extracellular electrochemistry, or static intracellular electrochemistry if cells are lysed||No real-time intracellular analysis|
|Nanoelectrodes||~0.5 µm, ~10–100 nm||Real-time intracellular electrochemistry||Characterization of the electrode tip is difficult. Electrodes must be checked before each use because performance may deteriorate with time.|