An array of gold nanoantennas laced into an artificial membrane enhances the fluorescence intensity of three different molecules when they pass through plasmonic hot spots in the array. Watch for the blue, green and red flashes. The photobleaching at the end of each fluorescence event (white flashes) is indicative of single molecule observations.
At the heart of the immune system that protects our bodies from disease and foreign invaders is a vast and complex network involving millions of cells, sending and receiving chemical signals that can mean life or death. At the heart of this vast cellular signaling network are interactions between billions of proteins and other biomolecules. These interactions, in turn, are greatly influenced by the spatial patterning of signaling and receptor molecules. The ability to observe signaling spatial patterns in the immune and other cellular systems as they evolve, and to study the impact on molecular interactions and, ultimately, cellular communication, would be a critical tool in the fight against immunological and other disorders that lead to a broad range of health problems including cancer. Such a tool is now at hand.
Researchers with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley, have developed the first practical application of optical nanoantennas in cell membrane biology. A scientific team led by chemist Jay Groves has developed a technique for lacing artificial lipid membranes with billions of gold "bowtie" nanoantennas. Through the phenomenon known as "plasmonics," these nanoantennas can boost the intensity of a fluorescent or Raman optical signal from a protein passing through a plasmonic "hot-spot" tens of thousands of times without the protein ever being touched.
"Our technique is minimally invasive since enhancement of optical signals is achieved without requiring the molecules to directly interact with the nanoantenna," Groves says. "This is an important improvement over methods that rely on adsorption of molecules directly onto antennas where their structure, orientation, and behavior can all be altered."
Groves holds joint appointments with Berkeley Lab’s Physical Biosciences Division and UC Berkeley’s Chemistry Department, and is also a Howard Hughes Medical Institute investigator.†He is the corresponding author of a paper that reports these results in the journal NanoLetters. The paper is titled "Single Molecule Tracking on Supported Membranes with Arrays of Optical Nanoantennas." Co-authoring the paper were Theo Lohmuller, Lars Iversen, Mark Schmidt, Christopher Rhodes, Hsiung-Lin Tu and Wan-Chen Lin.
Fluorescent emissions, in which biomolecules of interest are tagged with dyes that fluoresce when stimulated by light, and Raman spectroscopy, in which the scattering of light by molecular vibrations is used to identify and locate biomolecules, are work-horse optical imaging techniques whose value has been further enhanced by the emergence of plasmonics. In plasmonics, light waves are squeezed into areas with dimensions smaller than half-the-wavelength of the incident photons, making it possible to apply optical imaging techniques to nanoscale objects such as biomolecules. Nano-sized gold particles in the shape of triangles that are paired in a tip-to-tip formation, like a bow-tie, can serve as optical antennas, capturing and concentrating light waves into well-defined hot spots, where the plasmonic effect is greatly amplified. Although the concept is well-established, applying it to biomolecular studies has been a challenge because gold particle arrays must be fabricated with well-defined nanometer spacing, and molecules of interest must be delivered to plasmonic hot-spots.