Microalgae on display: a microfluidic pixel-based irradiance assay for photosynthetic growth

Abstract

Microalgal biofuel is an emerging sustainable energy resource. Photosynthetic growth is heavily dependent on irradiance, therefore photobioreactor design optimization requires comprehensive screening of irradiance variables, such as intensity, time variance and spectral composition. Here we present a microfluidic irradiance assay which leverages liquid crystal display technology to provide multiplexed screening of irradiance conditions on growth. An array of 238 microreactors are operated in parallel with identical chemical environments. The approach is demonstrated by performing three irradiance assays. The first assay evaluates the effect of intensity on growth, quantifying saturating intensity. The second assay quantifies the influence of time-varied intensity and the threshold frequency for growth. Lastly, the coupled influence of red-blue spectral composition and intensity is assessed. Each multiplexed assay is completed within three days. In contrast, completing the same number of experiments using conventional incubation flasks would require several years. Not only does our approach enable more rapid screening, but the short optical path avoids self-shading issues inherent to flask based systems.

Light dilution via wavelength management for efficient high‐density photobioreactors

“…Due to their complement of pigments, cyanobacteria are known to respond poorly to shorterwavelength light (Chen et al, 2010;Graham et al, 2015;Itoh et al, 2014). Due to their complement of pigments, cyanobacteria are known to respond poorly to shorterwavelength light (Chen et al, 2010;Graham et al, 2015;Itoh et al, 2014).…”

“…In all cases, 454-nm blue light underperformed compared with other wavelengths at the same intensity. Due to their complement of pigments, cyanobacteria are known to respond poorly to shorterwavelength light (Chen et al, 2010;Graham et al, 2015;Itoh et al, 2014). In spite of the strong absorption of blue light at 454 nm, a large portion of the energy is diverted to other pathways (Bailey and Grossman, 2008).…”

Periodic harvesting of microalgae from calcium alginate hydrogels for sustained high‐density production

“…Thinner hydrogel cultures achieved greater specific growth rates (0.28 ± 0.05 day −1 for 1.0 mm hydrogels and at most 0.18 ± 0.03 day −1 among 4.0 mm hydrogels), since harvested layers of all hydrogel cultures contained 20−65% of all cells and transmitted >40 μmol m −2 s −1 to the bulk at the time of harvest (for light transmission calculations, see Supplementary Materials). This robust post‐harvest surface growth at light‐limited intensities (Graham et al, ) indicates the feasibility of periodic partial culture harvesting within rigid hydrogels for biomass production.…”

“…To evaluate the effect of light regime in harvested layers and lower layers in the hydrogel bulk, Figure shows the range of light intensities in the top two 650 μm thick layers (0−1300 μm) immediately prior to harvest iterations. Dashed lines indicate light‐replete, light‐limited, and respiratory intensities, as labeled (Graham et al, ; MacKenzie et al, ; Richardson et al, ). Calculations are based on optical density measurements and the cultivation lamp spectrum (see description in Materials and Methods, and equation 1 in Supplementary Material).…”

“…Incident light on all hydrogel cultures during experiments was 180 ± 10 μmol m −2 s −1 of photosynthetically active radiation (PAR, 400−700 nm). This intensity is in‐between growth saturation and inhibition intensities (80−500 μmol m −2 s −1 ) which ensured good photosynthetic efficiencies for this species (Graham et al, ; MacKenzie et al, ).…”