We investigated the effect of increasing the optical penetration length, inside polydimethylsiloxane (PDMS)-based photobioreactors (PBRs), upon the photosynthetic cell growth of cyanobacteria. A thin layer of Teflon amorphous fluoropolymer (Teflon AF) was applied inside the PDMS-based PBRs to prevent light loss at the solid–liquid interface. The Teflon AF layer, with a refractive index ( n _(Teflon) = 1.31) lower than PDMS ( n _(PDMS) = 1.442) and higher than the culture medium ( n _(medium) = 1.332), constructed the light waveguide in the PBRs via the total internal reflection. Such a combination of refractive indices led to the prevention of light loss at the interface. The cell growth rate and the optical cell density were measured periodically for 5 days under different light power and Teflon AF-coating conditions. The local or global auto-fluorescence signal and the optical density at 450 nm wavelength (OD _(450) ) were measured in parallel by a fluorescence microscope and a micro plate reader, respectively. The optofluidic waveguide-based PBR improved the photosynthetic cell growth up to ～9% compared to a regular PBR.
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