• New optical tweezers put on the pressure

    From ScienceDaily@1:317/3 to All on Mon Feb 28 21:30:40 2022
    New optical tweezers put on the pressure to change color

    Date:
    February 28, 2022
    Source:
    Osaka City University
    Summary:
    Scientists demonstrate an optical trapping technique using
    nanotextured black silicon that can efficiently trap polymer
    chains. By adjusting the laser intensity, these 'optical tweezers'
    can control the florescence color emitted through a local
    concentration of a perylene-modified polymer solution. From a low
    intensity blue to high intensity orange, this reversible and fully
    remote technology can almost reach the entire RGB spectrum.



    FULL STORY ==========================================================================
    One big stumbling block in the field of photonics is that of color
    control.

    Until now, to control color, i.e. the wavelength of light emission,
    researchers would have to alter the chemical structure of the emitter or
    the concentration of the solvent -- all of which require direct contact, greatly limiting their application.


    ========================================================================== "Such conditions make it impossible to change color quickly, use it as
    a light source in microscopic spaces like a cell, or in closed systems
    where exchange is not an option," says Yasuyuki Tsuboi and professor
    of the Department of Chemistry, Osaka City University. With "optical
    tweezers," a technology he developed in previous research, Prof. Tsuboi
    led a team of researchers to show it possible to control the luminescence
    color remotely, using only the effect of light pressure.

    Their findings were recently published online in the German international journal Angewandte Chemie Intl.

    For years, Professor Tsuboi and his colleagues have been conducting
    research on a technology that can capture and manipulate nano- and micrometer-sized materials with a laser. In exploring this "optical
    tweezers" technology, they found that when a silicon crystal with
    a special needle-shaped nanostructure, called black silicon, was
    submerged in a sample solution, the optical field enhancement effect
    of the nanostructure trapped a perylene-modified polymer, causing a
    local concentration of the solution to increase and form an aggregate
    of polymers.

    "When the concentration of the perylene increases, it forms a
    dimeric excited complex called an excimer," explains lead author Ryota
    Takao. These excimers emit fluorescence that changes color depending on
    the degree of concentration.

    This is what the research team investigated in prior trapping experiments
    that did not employ a trapping laser. Here they found that as the laser
    beam intensity increased, light pressure did as well, which caused the concentration of the polymer aggregate on the black silicon to become
    denser -- and vice versa.

    "We observed the color of the fluorescence emitted by the polymer
    aggregate change in response to this," explains Prof, Tsuboi, "with low intensities producing blue, and then changing to green, yellow, green
    yellow, to orange as the intensity increases." As the laser intensity
    is what is being controlled, the color change is fully reversible and
    able to be done remotely.

    While the research is still in its infancy, it relies on excited complexes
    and excitation energy transfer, which means potential applications
    in ultraviolet and near-infrared regions, in addition to the visible
    realm. The research team is currently promoting further research in the direction of encapsulating the perylene-modified polymer solution to
    be used as a light source in micromachine components and intracellular bioimaging.

    ========================================================================== Story Source: Materials provided by Osaka_City_University. Note: Content
    may be edited for style and length.


    ========================================================================== Related Multimedia:
    * Optical_trapping_technique_traps_polymer_chains ========================================================================== Journal Reference:
    1. Ryota Takao, Kenta Ushiro, Hazuki Kusano, Ken‐ichi Yuyama,
    Tatsuya
    Shoji, Denver P. Linklater, Elena Ivanova, Saulius
    Juodkazis, Yasuyuki Tsuboi. Fluorescence Colour Control in
    Perylene‐Labeled Polymer Chains Trapped by Nanotextured
    Silicon. Angewandte Chemie International Edition, 2022; 61 (11)
    DOI: 10.1002/anie.202117227 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/02/220228172049.htm

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