Fig. 1

Examples of flow-based microfluidic devices. A Multi-mixing, serpentine channel network microfluidic device. A stable concentration gradient was established across the observation channel after multi-stage split recombination in the serpentine channels. (Reprinted with permission from [23]. Copyright (2013) American Chemical Society.); B the converging–diverging microchannel to generate desired gradient in a short mixing length based on the enhanced diffusion in the channel. Reprinted from Ref. [29], Copyright (2005), with permission from Elsevier. C the microfluidic device with a pressure balance zone unit for stabling the flows from different source inlet wells to generate concentration gradients in the gradient channel. (Figure reproduced from Ref. [25]); D the planner microfluidic networks device to establish concentration gradients with any given monotonic function shape. Republished from Ref. [24], copyright 2007, with permission of Royal Society of Chemistry; permission conveyed through Copyright Clearance Center, Inc