Date Published: January 24, 2018
Publisher: John Wiley and Sons Inc.
Author(s): Brian Nguyen, Percival J. Graham, Chelsea M. Rochman, David Sinton.
A platform compatible with microtiter plates to parallelize environmental treatments to test the complex impacts of multiple stressors, including parameters relevant to climate change and point source pollutants is developed. This platform leverages (1) the high rate of purely diffusive gas transport in aerogels to produce well‐defined centimeter‐scale gas concentration gradients, (2) spatial light control, and (3) established automated liquid handling. The parallel gaseous, aqueous, and light control provided by the platform is compatible with multiparameter experiments across the life sciences. The platform is applied to measure biological effects in over 700 treatments in a five‐parameter full factorial study with the microalgae Chlamydomonas reinhardtii. Further, the CO2 response of multicellular organisms, Lemna gibba and Artemia salina under surfactant and nanomaterial stress are tested with the platform.
Globally, communities are coping with warming in combination with increased CO2 levels, occurring concurrently with local environmental stressors from synthetic chemicals.1, 2, 3, 4 The challenge of predicting biological responses stems from needing to measure impacts from multiple variables at once, including changes in aqueous nutrients and toxins, gasses, light, and temperature.5, 6, 7, 8, 9 Although multiple stressors are the norm, most studies focus on effects from a single stressor.10 Microcosms and mesocosms allow both a high degree of control over parameters, and parallelization.11, 12 Unfortunately, with current microcosm‐based techniques, full factorial experiments involving multiple variables (e.g., temperature, light, gas, chemical, and a nanomaterial pollutants) are challenging and generally limits replication, making it difficult to truly measure an effect—once the number of experimental treatments reaches the 100’s—typical of multiparameter studies.5, 7
We developed a simple, but powerful platform, leveraging rapid and controlled gas diffusion through aerogels in combination with spatial light control, for parallel screening of biological responses to multiple experimental parameters in microcosms. The ability to rapidly investigate the effect of multiple parameters is a step toward overcoming the throughput barrier to performing detailed full factorial studies that capture the complexity of multiple environmental stressors.
Aerogel‐Based Gradient Generator Construction: Hydrophobic aerogel monoliths (Aerogel technologies P‐AT.A.X103, medium density, large panels) were purchased from Aerogel Technologies Inc. These aerogels had > 80% porosity55 and pores averaging ≈50 nm. The ideal aerogel for this application would have an interconnected, low tortuosity pore structure with maximum void space to maximize diffusion and small pore sizes to minimize advective mass transport. A high tortuosity porous structure was not desirable since it creates a longer effective diffusion path. The aerogel monoliths were cut to size with a fine‐toothed saw, sanded flat with 320 grit sandpaper, and thinned to a thickness of ≈6 mm. Care was taken not to contact the aerogel with solvents that would collapse the pore structure and hinder gas diffusion. The experimental apparatus consisted of a standard well plate and aerogel sandwiched between an acrylic back plate and an acrylic layer with source and sink channels 6 mm tall and 6 mm wide spaced 6.8 cm apart, center to center (6.2 cm edge to edge) (Figure S6b, Supporting Information). All acrylic components were fabricated using a CO2 laser cutter (Universal Laser Systems M‐360). Acrylic parts were bonded in a Carver hot press. The open areas of the aerogel were sealed with polyethylene terephthalate (PET) tape to ensure no‐flux conditions where desired (i.e., the source edge and the edges orthogonal to the channels). A silicon gasket was used to ensure a seal between the aerogel and the layer with the source and sink channels. While silicon is gas permeable, it did not permit advective mass transport. Clamping force was applied using ¼‐20 machine screws and wing nuts. The highest and lowest concentrations in the CO2 gradient were set by adjusting the concentration of CO2 in the gas flowing in the source and sink channel respectively. All gas inlets were maintained at constant pressure using pressure regulators.
The authors declare no conflict of interest.