A comprehensive review of the current state of microfluidic bioanalytical research applied to bacterial biofilms.

The anchoring biofilm layer is expected to exhibit a different response to environmental stresses than for portions in the bulk, due to the protection from other strata and the proximity to the attachment surface. The effect of hydrodynamic stress on surface-adhered biofilm layers was tested using a specially designed microfluidic bio flow cell with an embedded three-electrode detection system. In situ electrochemical impedance spectroscopy (EIS) measurements of biocapacitance and bioresistance of Pseudomonas sp. biofilms were conducted during the growth phase and under different shear flow conditions with verification by other surface sensitive techniques. Distinct, but reversible changes to the amount of biofilm and its structure at the attachment surface were observed during the application of elevated shear stress. In contrast, regular microscopy revealed permanent distortion to the biofilm bulk, in the form of streamers and ripples. Following the application of extreme shear stresses, complete removal of significant portions of biofilm outer layers occurred, but this did not change the measured quantity of biofilm at the electrode attachment surface. The structure of the remaining biofilm, however, appeared to be modified and susceptible to further changes following application of shear stress directly to the unprotected biofilm layers at the attachment surface.

Strong control over experimental conditions in microfluidic channels provides a unique opportunity to study and optimize membraneless microbial fuel cells (MFCs), particularly with respect to the role of flow. However, improved performance and transferability of results to the wider MFC community require improvements to device stability under all applied operational conditions. To address these challenges, we present an easy-to-fabricate membraneless MFC that combines i) O 2 protection via a gas diffusion barrier, ii) integrated graphite electrodes, and iii) optimized electrode placement to avoid cross-contamination under all applied flow rates. Attention to all of these design features in the same platform resulted in the operation of a MFC with a pure-culture anaerobic Geobacter sulfurreducens biofilm for half a year, that is, six times longer than previously reported, without the use of an oxygen scavenger. As a result of higher device stability under high flow rates, power densities were four times higher than reported previously for microfluidic MFCs with the same biofilm.

Biofilms from Geobacter sulfurreducens are promising materials for new bioelectrochemical systems. To improve the performance of such systems, limitations related to biofilm acidification should be addressed. This work examines a long‐held assumption that liquid flow can deacidify biofilm pH by enhancing molecular mass transport in the biofilm subdomain. A microfluidic electrochemical system was used to measure changes to biofilm pH in situ while accurately modulating hydrodynamic conditions under turnover, nutrient‐limited and starvation conditions. We discovered that increased flow rates could indeed mitigate biofilm acidification, but not under turnover concentrations, which are the predominant conditions used in research studies. This effect is demonstrated with the observation that relative increases to bio‐current under increased flow rates were stronger for experiments conducted under nutrient‐limited concentrations compared to turnover concentrations. This can open the way for a solution to poor performance of some bioelectrochemical systems at low concentrations.