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In this work, we provided a strategy for high-throughput monitoring of temporal and spatial gradients of electrons/protons in electrogenic bacterial biofilms by utilizing 3D multi-laminate structures of paper as a scaffold to support bacterial biofilms and/or media. Assembly of a 3D paper stack can be modular and allows us to control the thickness of the overall biofilm construct and diffusion of nutrients/redox mediators through the stack and the shapes of gradients in the stacks can be modulated by changing the composition of each layer. By measuring the current generated from different stack configurations, the electron/proton fluxes through biofilms were quantitatively investigated.

In this work, we provided a new technique to monitor the flow of bacterial cells in paper. This was based on real-time measuring of the electricity generated from bacterial metabolism. Despite recent efforts to monitor liquid flow in paper, there is not yet a technique that provides detailed flow information of particles in paper microfluidics. Our device contained three hydrophilic spots linked by a hydrophilic channel on paper. Each spot came into contact with an anode that was electrically connected to a cathode through an external load. When bacterial cells were transported to each spot by capillary force, the current generated from the bacteria was monitored and bacterial cells' transportation through the channel was quantitatively investigated according to the pore size of the paper.