FIGURE 3: Microfluidic devices for bacterial chemotaxis (flow-conditions). (A) A microfluidic chip with three inlets (one for chemo effectors, other for buffer and middle for bacterial culture), the main channel and terminated by outlets of 22 microchannels. Reproduced from [32]. (B) Schematic diagram of ‘μFlow’ – multiple chemo-gradient generators. The chip consists of a gradient generator and a chemotaxis chamber. Single or mixture of chemo effectors was introduced from one of the inlets. When the chemo effectors were passed through the microstructure, single or multiple chemical gradients were formed across the chemotaxis chamber. In the presence of high chemorepellents concentration (grey) at the lower end of the chemotaxis chamber, chemotactic bacteria tend to concentrate at the upper end. Reproduced from [33]. (C) Chemotaxis-based automatic sorter. Chemo effectors and buffer were injected from the two side-inlets to create chemical gradients, whereas bacterial sample was subjected from the middle inlet (Part I). Chemotactic motile bacteria were sorted as they swam towards the outlet by chemotaxis Eventually, each sorted bacterium was encapsulated as a single cell inside a droplet and collected in Teflon tubing (Part II) and imaged for analysis and cultivated in soft agar plates to test the cell viability. Reproduced from [18]. (D) A chemical gradient was generated across the middle channel (injected with bacterial culture) by connecting the source of chemoattractant and buffer with numerous micron-sized channels. Reproduced from [36].

18. Dong L, Chen D-W, Liu S-J, and Du W (2016). Automated Chemotactic Sorting and Single-cell Cultivation of Microbes using Droplet Microfluidics. Sci Rep 6(1): 24192. doi: 10.1038/srep24192

32. Mao H, Cremer PS, and Manson MD (2003). A sensitive, versatile microfluidic assay for bacterial chemotaxis. Proc Natl Acad Sci 100(9): 5449–5454. doi: 10.1073/pnas.0931258100

33. Englert DL, Manson MD, and Jayaraman A (2009). Flow-Based Microfluidic Device for Quantifying Bacterial Chemotaxis in Stable, Competing Gradients. Appl Environ Microbiol 75(13): 4557–4564. doi: 10.1128/AEM.02952-08

36. Roggo C, Picioreanu C, Richard X, Mazza C, van Lintel H, and van der Meer JR (2018). Quantitative chemical biosensing by bacterial chemotaxis in microfluidic chips. Environ Microbiol 20(1): 241–258. doi: 10.1111/1462-2920.13982