Matthew D. Ooms

Photon management for augmented photosynthesis

Microalgae and cyanobacteria are some of natures finest examples of solar energy conversion systems, effortlessly transforming inorganic carbon into complex molecules through photosynthesis. The efficiency of energy-dense hydrocarbon production by photosynthetic organisms is determined in part by the light collected by the microorganisms. Therefore, optical engineering has the potential to increase the productivity of algae cultivation systems used for industrial-scale biofuel synthesis. Herein, we explore and report emerging and promising material science and engineering innovations for augmenting microalgal photosynthesis.

Culturing photosynthetic bacteria through surface plasmon resonance

In this work, cultivation of photosynthetic microbes in surface plasmon enhanced evanescent fields is demonstrated. Proliferation of Synechococcus elongatus was obtained on gold surfaces excited with surface plasmons. Excitation over three days resulted in 10 μm thick biofilms with maximum cell volume density of 20% vol/vol (2% more total accumulation than control experiments with direct light). Collectively, these results indicate the ability to (1) excite surface-bound cells using plasmonic light fields, and (2) subsequently grow thick biofilms by coupling light from the surface. Plasmonic light delivery presents opportunities for high-density optofluidic photobioreactors for microalgal analysis and solar fuel production.

A photosynthetic-plasmonic-voltaic cell: Excitation of photosynthetic bacteria and current collection through a plasmonic substrate

Excitation of photosynthetic biofilms using surface-confined evanescent light fields enables energy dense photobioreactors, while electrode-adhered biofilms can provide electricity directly. Here, we demonstrate concurrent light delivery and electron transport through a plasmonically excited metal film. Biofilms of cyanobacterium Synechococcus bacillaris on 50-nm gold films are excited via the Kretschmann configuration at λ = 670 nm. Cells show light/dark response to plasmonic excitation and grow denser biofilms, closer to the electrode surface, as compared to the direct irradiated case. Directly irradiated biofilms produced average electrical powers of 5.7 μW/m2 and plasmonically excited biofilms produced average electrical powers of 5.8 μW/m2, with individual biofilms producing as much as 12 μW/m2.

Wavelength-selective plasmonics for enhanced cultivation of microalgae

Optimal photon management is a key challenge for photobioreactor design, since light gradients and varying spectral sensitivities between organisms result in uneven illumination and unused photons. This paper demonstrates wavelength specific scattering from plasmonic nano-patterned surfaces as a means of addressing the challenge of photon management in photobioreactors. Modular photobioreactors were constructed with different reflective substrates including arrays of plasmonic nanodisks, broadband reflectors, and untreated glass. It was found that the growth rate of cyanobacterium S. elongatus in photobioreactors equipped with a plasmonic substrate (R623 nm ∼ 35%) was enhanced by 6.5% compared to photobioreactors equipped with untreated glass. Furthermore, plasmonic reflectors showed a normalized power efficiency improvement of 52% over broadband reflectors. Wavelength-specific reflection from plasmonic reflectors increases the flux of useful light to cultures without sacrificing the full spectrum.

Light dilution via wavelength management for efficient high-density photobioreactors

The spectral distribution of light influences microalgae productivity; however, development of photobioreactors has proceeded largely without regard to spectral optimization. Here, we use monochromatic light to quantify the joint influence of path length, culture density, light intensity, and wavelength on productivity and efficiency in Synechococcus elongatus. The productivity of green light was ∼4× that of red at the highest levels of culture density, depth, and light intensity. This performance is attributed to the combination of increased dilution and penetration of this weakly absorbed wavelength over a larger volume fraction of the reactor. In contrast, red light outperformed other wavelengths in low‐density cultures with low light intensities. Low‐density cultures also adapted more rapidly to reduce absorption of longer wavelengths, allowing for prolonged cultivation. Taken together, these results indicate that, particularly for artificially lit photobioreactors, wavelength needs to be included as a critical operational parameter to maintain optimal performance. Biotechnol. Bioeng. 2017;114: 1160–1169.

Disposable Plasmonics: Rapid and Inexpensive Large Area Patterning of Plasmonic Structures with CO2 Laser Annealing

We present a method of direct patterning of plasmonic nanofeatures on glass that is fast, scalable, tunable, and accessible to a wide range of users-a unique combination in the context of current nanofabrication options for plasmonic devices. These benefits are made possible by the localized heating and subsequent annealing of thin metal films using infrared light from a commercial CO2 laser system. This approach results in patterning times of 30 mm(2)/min with an average cost of

Hydrothermal disruption of algae cells for astaxanthin extraction

0.10/mm(2). Colloidal Au nanoparticles with diameters between 15 and 40 nm can be formed on glass surfaces with x-y patterning resolutions of ∼180 μm. While the higher resolution provided by lithography is essential in many applications, in cases where the spatial patterning resolution threshold is lower, commercial CO2 laser processing can be 30-fold faster and 400-fold less expensive.

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

We demonstrate a hydrothermal method of astaxanthin extraction from wet biomass using a high temperature and high pressure microfluidic platform. Haematococcus pluvialis cysts are trapped within the device and visualized in situ during the cell wall disruption and astaxanthin extraction processes. The device provides a highly controlled environment and enables direct comparison of chemical vs. hydrothermal processes at the cellular level. Hydrothermal disruption at a temperature of 200 °C was shown to be highly effective, resulting in near-complete astaxanthin extraction from wet biomass – a significant improvement over traditional methods.

A scalable evanescent light-based photobioreactor

High‐density biomass production is currently only realized in biofilm‐based photobioreactors. Harvest yields of whole biofilms are self‐limited by daughter‐upon‐parent cell growth that hinders light and leads to respiratory biomass losses. In this work, we demonstrate a sustainable multi‐harvest approach for prolonged generation of high‐density biomass. Calcium‐alginate hydrogel cultures loaded with Synechococcus elongatus PCC 7942 achieved production densities comparable to that of biofilms (109 cells/mL) and optimal total productivity in harvest periods of 2 or 3 days that allowed high‐density surface growth without self‐limiting cell buildup or surface death. Cross‐linking calcium concentration had a strong influence on surface growth and harvest yields, especially in the first harvests. Subsequent harvests achieved more uniform biomass yields and distributions, unaffected by bulk respiration or light penetration. Collectively, these results demonstrate the feasibility of sustained, high‐density biomass production by periodic harvesting within microalgal hydrogel cultures. Biotechnol. Bioeng. 2017;114: 2023–2031.

Plasmonic gold islands enhanced photobioreactors

The evanescent growth of photosynthetic cyanobacteria on an LED-lit PMMA waveguide is demonstrated as modularly scalable photobioreactor architecture.