Optimal design of a microfabricated diffusion-based extraction device

The miniaturization of micro-fluidic chemical assays of fluid mixtures containing particles such as biological molecules and cells is a technically and commercially significant objective. Successful automation of chemical analysis of small samples requires seamless integration of several subsystems that perform tasks routinely carried out by a skilled technician. In this paper is presented a methodology for the optimal design of a novel micro-flow diffusion-based constituent extraction device based on parallel fluid flow through a microchannel. The streamwise distance required for the constituent being extracted to achieve an average concentration across the micro-channel that is a fixed percentage of the equilibrium concentration is defined as the equilibration length. The constituent concentration within the micro-channel is calculated using a 1-D analytical diffusion model. The equilibration length is used to construct a family of process space design curves specific to the extracted constituent. An optimization objective function is specified to identify the design that maximizes the volume flow rate of product stream. The methodology is applied to the design of a device for the extraction of albumin (a protein present in blood) from a carrier sample stream with viscosity approximately that of water. The device is specified for a length sufficient for the mean albumin concentration in the product stream to reach a value that is 99% of the equilibrium concentration of albumin for an infinite length device. This process sensitivity information provides design requirements for upstream and downstream fluidic components, and is essential for integration of the device into a “lab on a chip” chemical analysis system. NOMENCLATURE