The Nucleic Acid (NA) probe assays typically include PCR to amplify the number of copies of DNA to a detectable level. The PCR technique requires a relatively pure DNA sample in aqueous solution, free of inhibitors during the PCR process. Therefore, the extraction and purification of nucleic acids from biological samples are the critical steps that should be carefully handled in the NA assays. In this work we have proposed a new microfluidic chip to address this sample preparation process for NA probe assays.

The proposed microfluidic system is composed of three parts: microfilter, micromixer and DNA purification chip. In the microfilter, red blood cells are separated from whole blood sample. In the mixer, the plasma blood sample is mixed with lysis reagents to release the DNA into the solution and the lysed solution is mixed with chaotropic salt. In the DNA purification chip, the DNA’s in the solution will bind to the exposed SiO2 surface at a high concentration of chaotropic salt. After DNA has been adequately extracted in the binding process, wash solutions flow through the microchannel of the chip to wash away the remaining sample fluid. Finally, the DNA can be eluted from the chip by flowing through appropriate chemical buffer solutions. Figure 1. Schematic diagram of the proposed microfluidic system for sample preparation of Nucelic acid probe assay.

- Microfilter using metallic microsieves
- Passive micromixer in three dimensional microchannels
- DNA purification chip on photosensitive glass

Microfilter using Metallic Microseives

MEMS microfilter improvement is driven by the need to perform absolute separation of micro-sized particles from micro-scale fluid volumes. Filtration is an essential step in many biological and medical applications. For example, routine blood tests require separating blood plasma from whole blood. By using microfabrication techniques it has recently become possible to create integrated miniaturized fluid handling devices. Promising applications include miniaturized systems for the filtration, fractionation, and manipulation of biological cells and nucleic acids.

In this work, we have designed the microfilter to separate red blood cells from whole blood. When designing filters to effect blood cell separation, it is known that the deformability of the cells plays a major role in the separation efficiency. The reported sizes of blood cells are often based on morphological studies of the stained cells. However, filtration of the spherical and discoid white and red blood cells is influenced by the cell concentration, applied pressure, viscosity of the medium, and the size of the filter port. Red blood cells with relatively stable discoid architecture cannot pass through a gap smaller than 3mm. The proposed microfilter has a metallic microsieve.