In-line micro-spectrometer with a structural color polymer filter for the color and concentration monitoring system

Monitoring systems for color and concentration of liquids have an important role in improving the fabrication process stably, not only in pipelines but also in microchannels. Our suggested in-line micro-spectrometer with an elastic structural color filter has detectability for color and concentration changes with a 40-mm size. The sequence of our device is the following: (1) the elastic structural color filter splits the white light from an LED, (2) the split light transmits the sample liquid, and (3) a photodiode receives the transmitted light. The structural color polymer is mechanically compressed inside the micro-spectrometer, leading to fixing the optical path even though the light wavelength is changed continuously. We fabricated the elastic structural color polymer with 200 nm silica nanoparticles and PEGPEA (poly- (ethylene glycol) phenyl ether acrylate). The prototype of the in-line micro-spectrometer with a red (λ = 596 nm) filter showed the detectability of the difference between yellow and green dyes. Moreover, the micro-spectrometer successfully distinguished the concentration of green-dyed water. This proposed in-line micro-spectrometer would contribute to developing in-line microfluidic color monitoring systems for biochemical analyses and material production.