On-chip separation and detection of biological particles using dielectrophoresis and resistive pulse sensing
Since the biological reagents and particles exist in a fluidic natural environment, microfluidics-based lab-on-a-chip devices render excellent platforms for relevant biomedical manipulations and assays. This emerging field is actively approached by scientists from various disciplines and exploited for a wide range of applications. The lab-on-a-chip systems have competitive advantages over the conventional biomedical instruments because of their portability, minute sample consumption, and slashed manufacturing and operational costs. This dissertation presents an original investigation on microfluidics technology and development of lab-on-a-chip microdevices for critical on-chip manipulations of biological particles, such as separation and detection. The separation is achieved by field-flow-fractionation employing the non-linear electrokinetic phenomenon, dielectrophoresis (DEP). DEP arises from the interaction of a dielectric particle, such as a cell, and a highly non-uniform electric field which can be generated under an electric field by obstruction or hurdles made of electrically insulating materials. The DEP force acting on a particle is proportional to the particle’s volume. Thus the moving particles deviate from the streamlines and the degree of deviation is dependent on the particle size. Finally the particles of different sizes are inducted into different collection wells according to their different degrees of deviation. The detection is achieved by Coulter-type resistive pulse sensing (RPS) scheme, in which the translocation of a non-conducting particle through an electrolyte-filled small aperture leads to an increase in the resistance of the aperture. The frequency and amplitude of the resulting trans-aperture voltage modulations provide critical information about the number and size of the particles of interest. For cell detection and enumeration, the developed system integrates optical fluorescence detection with RPS enhanced by a metal oxide semiconductor field effect transistor (MOSFET). Further to improve the sensitivity, symmetric mirror channels are designed with multiple-stage differential amplifications, which significantly reduces the noise and achieves better signal-to-noise ratio. A record low volume ratio of the particle to the micron-sized sensing aperture has been recorded, which is about ten times lower than the lowest volume ratio reported in the literature.