On-Chip Pretreatment of Whole Blood by Using MEMS Technology

The development of micro-total analysis systems targeting blood sample detections requests the availability of microfluidic devices for whole blood sample pretreatment including blood cell and plasma separation, white blood cell lysis and DNA purification, to name a few. In this chapter, background introduction of whole blood samples is conducted followed by a summary of key features and historical development of microfluidics. The marriage of microfluidics and whole blood pretreatment is highlighted with advantages and potential concerns discussed in detail.

Since most conventional clinical assays are performed on cell-free serum or plasma, plasma isolation is a necessary step in the processing of whole blood sample pretreatment. Traditional technologies for plasma isolation are based on centrifugation or membrane filtration, which are time and cost intensive processes. Microfluidic chips for whole blood plasma isolation are attractive alternatives, which lead to more gentle, fast, and consistent manipulation of the whole blood samples, and therefore more accurate and better quality of plasma isolation. In this chapter, a variety of microfluidic devices for blood plasma separation are reviewed and compared. Two specific examples of plasma isolation leveraging MEMS technologies are included for further concept demonstration in which design, fabrication and testing of these microfluidic devices are covered in detail. These plasma isolation microfluidic devices can be easily connected with other microfluidic components to form micro total analysis systems for blood testing with the advantages of continuous and real time separation of plasma from whole blood samples.

Various methods have been demonstrated in literature for blood cell sorting and separation as one essential step of blood sample pretreatment in both the macro and micro scale. In this chapter, the latest development of the cell/particle separation using microfluidic devices is first reviewed. Furthermore, two specific microfluidic chips developed in our group targeting blood cell separation are discussed in detail as case studies. In these two examples, pillar-type and weir-type filtration structures were designed and fabricated by microelectromechanical system (MEMS) technologies, aimed to remove Red Blood Cells (RBCs) from White Blood Cells (WBCs) based on their size differences. In these two microfluidic chips, the effects of relevant parameters (e.g., cell concentration variations and the dimensions of separation channels) on cell separation efficiency were investigated. Under the optimal condition, more than 95% RBC can be removed from the initial whole blood, while 27.4% WBC can be obtained.

Cell lysis is an essential step in whole blood sample preparation, which can pave road for intracellular proteomic analysis or genomic analysis and therefore cell membrane rupture is requested for protein and gene release. In this chapter, we firstly introduce reported microfluidic devices for cell lysis. And then an example using the chemical cell lysis method in microfluidic chip is put forward in which a sandwich microfluidic chip was designed, fabricated and tested to disrupt blood cell membranes.

Nucleic acid extraction is an important element of sample preparation for genomic analysis which requires extracting DNA or RNA and removing other proteins or impurities. In this chapter, we firstly review traditional large-scale methods for DNA extraction and purification, followed by corresponding microfluidics based approaches. And then an example of DNA extraction from whole blood and culture cells in a microfluidic chip is provided in which the device design, fabrication and testing, based on the principle of solid phase extract (SPE) are covered in detail. In this specific example, various solid phase matrixes have been prepared, characterized and tested.

Integrated on-chip whole blood sample pretreatment includes blood cell separation, cell lysis and DNA extraction. Compared to macro-counterparts, whole blood sample pretreatment using integrated microfluidic devices has the advantages of low sample consumption, short time-scale measurement and high portability. In this chapter, reported integrated microfluidic devices for blood sample preparation are briefly summarized and compared. And then a specific microfluidic chip with the function of cell separation, cell lysis and DNA extraction is proposed for detailed discussion. The integrated microfluidic device is capable of pre-treating whole blood samples, paving ways for the eventual integration of sample preparation, PCR, and electrophoresis on a single chip in the field of point-of-care genetic analysis, environmental testing, and biological warfare agent detection.