Microfluidics as an Emerging Platform for Exploring Soil Environmental Processes: A Critical Review

Abstract

Investigating environmental processes, especially those occurring in soils, calls for innovative and multidisciplinary technologies that can provide insights at the microscale. The heterogeneity, opacity, and dynamics make the soil a “black box” where interactions and processes are elusive. Recently, microfluidics has emerged as a powerful research platform and experimental tool which can create artificial soil micromodels, enabling exploring soil processes on a chip. Micro/nanofabricated microfluidic devices can mimic some of the key features of soil with highly controlled physical and chemical microenvironments at the scale of pores, aggregates, and microbes. The combination of various techniques makes microfluidics an integrated approach for observation, reaction, analysis, and characterization. In this review, we systematically summarize the emerging applications of microfluidic soil platforms, from investigating soil interfacial processes and soil microbial processes to soil analysis and high-throughput screening. We highlight how innovative microfluidic devices are used to provide new insights into soil processes, mechanisms, and effects at the microscale, which contribute to an integrated interrogation of the soil systems across different scales. Critical discussions of the practical limitations of microfluidic soil platforms and perspectives of future research directions are summarized. We envisage that microfluidics will represent the technological advances toward microscopic, controllable, and in situ soil research.

Spatiotemporal Mineral Phase Evolution and Arsenic Retention in Microfluidic Models of Zerovalent Iron-Based Water Treatment

“… 4 − 9 Although microchannels may not replicate the entire complexity of natural or engineered systems, their specifically reduced complexity allows us to disentangle the coupling between processes such as fluid–fluid and fluid–solid reactions under single and multiphase flow conditions. 4 , 7 , 10 , 11 Microchannels are therefore well-suited for pore-scale investigations into phase formation and transformation in porous media.…”

“…To date, however, spatially resolved studies have mostly focused on embedded samples and did not observe temporal evolution. Experiments in microfluidic flow channels (microchannels), coupled with optical microscopy and synchrotron X-ray spectroscopy, may allow us to bridge the gap between spatially and temporally resolved process-oriented geochemical studies in complex porous media. − Although microchannels may not replicate the entire complexity of natural or engineered systems, their specifically reduced complexity allows us to disentangle the coupling between processes such as fluid–fluid and fluid–solid reactions under single and multiphase flow conditions. ,,, Microchannels are therefore well-suited for pore-scale investigations into phase formation and transformation in porous media.…”

Pore-Scale Mechanisms of Solid Phase Emergence During DNAPL Remediation by Chemical Oxidation

“…First, our work has elucidated the mechanisms of solid phase emergence and has explored the effects of oxidant concentration and injection rate on the remediation efficiency, which can be combined with additional optimization of reaction conditions (e.g., selection of oxidants and stabilization chemicals) to further elevate DNAPL remediation efficiency and to facilitate the development of other treatment technologies with similar working principles. Second, since the rapidly evolving microfluidic and imaging technologies permit the 3D observations of dynamics of multiphase flow and reactive transport in porous and fractured media, 56 we emphasize the necessity of well-controlled pore-scale investigations of the fundamental processes involved in groundwater remediation as flow, mass transfer and chemical reaction ultimately occur at the pore scale. Lastly, the pore-scale mechanisms of solid phase emergence and their effect on remediation efficiency can be also of theoretical and practical significance in other natural or engineered systems where the complex dynamics and interactions resulting from multiple physical and chemical processes are involved during various processes in the environment such as groundwater and soil remediation.…”

Low-cost microfluidics: Towards affordable environmental monitoring and assessment

“…Despite many successful applications in the air and soil monitoring areas, as evidenced in research publications, low-cost devices have yet to be widely commercially available in the market due to complexity of air and soil samples (Jokerst et al, 2012;Schulze et al, 2017). Samples are normally filtered and washed, which is time consuming (especially for air samples, which have to be captured in open space) hindering the use of low-cost technologies by the general public (Sun et al, 2018;Zhu et al, 2022). Though microfluidic devices have been widely used for environmental applications, not all devices can be considered user-friendly and low-cost (Tomazelli Coltro et al, 2014;Faustino et al, 2016).…”