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.