Silicon nanoparticles and cells can now be printed with lasers
An article in SPIE Newsroom (Boris Chichkov et al., DOI: 10.1117/2.1201503.005750, March 30, 2015) describes how Laser Zentrum Hannover (Hannover, Germany) researchers are printing biological cells and silicon nanoparticles using lasers. The technique prints spherical silicon (Si) nanoparticles onto a specific position of a receiver glass substrate. The printed nanoparticles have a predefined size and are characterized by unique optical properties. With sizes of 100-200 nm in diameter, they exhibit pronounced electric and magnetic dipole resonances within the visible spectral range. Due to these resonances, they appear colorful in a dark-field microscopic image.
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For the printing process, we focused single 50fs laser pulses at a wavelength of 780nm through a receiver glass substrate and onto a silicon-on-insulator (SOI) substrate. This substrate consists of a 50 nm crystalline silicon layer on a 200 nm silicon dioxide layer with an underlying Si wafer substrate. Each laser pulse induces strongly localized melting in the Si layer. Due to surface tension, the melted volume contracts into a sphere, which is ejected back toward the receiver glass substrate.
The generated Si nanoparticles are initially in an amorphous phase and can be recrystallized by a second femtosecond laser pulse with a square-shaped flat top intensity distribution to get a homogenous intensity distribution, and thus a homogenous crystallization. After this step, the optical response of the Si nanoparticles is much stronger and their color is different, indicating they are crystallized.
The forward transfer setup used for cell printing consists of a glass slide or transparent ribbon that is coated with a layer of a laser-absorbing material and a second layer of a biomaterial to be printed. Typically, this biomaterial layer is a hydrogel with embedded cells. The coated glass slide is mounted upside-down and focused laser pulses pass through the slide into the absorption layer, which evaporates in the focal spot. The subjacent biomaterial is then propelled down (in the forward direction) by the vapor pressure and deposited as a droplet onto a surface located under the glass slide. By moving the glass slide and the laser beam focus, any desired 2D and 3D patterns can be printed layer-by-layer. In this printing setup, the group applied a laser with a 10 ns pulse duration at a wavelength of 1064 nm.
In a series of publications, the researchers proved that cells are not harmed by this printing process. Future research will focus on printing bacteria and microorganisms.
SOURCE: SPIE Newsroom; http://spie.org/x113128.xml?WT.mc_id=KNRBIOMEDE
Gail Overton | Senior Editor (2004-2020)
Gail has more than 30 years of engineering, marketing, product management, and editorial experience in the photonics and optical communications industry. Before joining the staff at Laser Focus World in 2004, she held many product management and product marketing roles in the fiber-optics industry, most notably at Hughes (El Segundo, CA), GTE Labs (Waltham, MA), Corning (Corning, NY), Photon Kinetics (Beaverton, OR), and Newport Corporation (Irvine, CA). During her marketing career, Gail published articles in WDM Solutions and Sensors magazine and traveled internationally to conduct product and sales training. Gail received her BS degree in physics, with an emphasis in optics, from San Diego State University in San Diego, CA in May 1986.