Have you ever heard of a “single cell endoscopy”? Well, soon you might, thanks to an innovative research from a group of investigators from Lawrence Berkeley National Laboratory and the University of California at Berkeley. They used nanowires of potassium niobate to produce a microscopic-sized light source, “a tiny flashlight that we can potentially scan across a living cell, visualizing the cell while mechanically interacting with it,” according to Jan Liphardt, a biophysicist from Berkeley. The paper, titled ‘Tunable Nanowire Nonlinear Optical Probe’, by Peidong Yang, Jan Liphardt, et al was published in the latest Nature.
Among the many potential applications of this nano-sized light source, once the technology is refined, are single cell endoscopy and other forms of subwavelength bio-imaging, integrated circuitry for nanophotonic technology, and new advanced methods of cyber cryptography…
… the researchers describe a technique in which nanowires of potassium niobate were synthesized in a special hot water solution and separated using ultrasound. The wires were highly uniform in size, several microns long, but only about 50 nanometers in diameter. A beam from an infrared laser was used to create an optical trap that allowed individual nanowires to be grabbed and manipulated. Because of potassium niobate’s unique optical properties, this same beam of infrared laser light also served as an optical pump, causing the nanowires to emit visible light whose color could be selected. In a demonstration of the technique’s potential, these nanowire light sources were used to generate fluorescence from specially treated beads…
Central to the success of the nanowire light source are the exceptional nonlinear optical properties of potassium niobate. These nonlinear properties enable the frequencies of the incoming infrared light to be mixed or doubled, through techniques known respectively as second harmonic generation (SHG) or sum frequency generation (SFG), before being emitted as visible light. The result is light that is tunable as well as coherent, which fulfills a technological requirement that has posed a major challenge for both photo-imaging and photo-detection in subwavelength optics.
Coupled with earlier projects in which Yang and his research group created ultraviolet nanowire nanolasers, and made nanoribbon optical waveguides that can channel and direct light through circuitry, the new nanowire light source lays firm groundwork for future nanophotonic technology. Photonics, a technology in which the movement of light waves replaces the movement of electrons as information carriers, promises computers and networks that are thousands of times faster than what we have today.
Bio-imaging may be the field in which this nanowire light source technology has its biggest impact. Optical or visible light microscopy remains at the forefront of biological research because it allows scientists to study living cells and tissues. However, whereas the resolution of optical microscopy is limited by diffraction, through subwavelength techniques it becomes possible to visualize features smaller than visible light wavelengths.
Picture caption: In a demonstration of the nanowire light source’s fluorescence mode, a nanowire in the grip of an infrared beam was touched to a fluorescent bead causing the bead to fluorescence orange at the contact point. Figure a shows the experimental set up with the pair of beads on the right as control; b is a bright-field optical image of the beads, with the nanowire in contact with the leftmost bead; c is a color CCD fluorescence image showing green light emission from the nanowire and the orange emission from the bead; d is a control image of the same beads with infrared radiation but no trapped nanowire; and e is digital subtraction of d from c.
Press release: Bright Future for Nano-sized Light Source …