This dissertation deals with two researches of optoelectronic tweezers (OET) using a liquid crystal display (LCD). The OET is an optical image-driven dielectrophoretic technique that permits high resolution and high throughput at the same time for manipulating single particles or biological cells. First research is developing a new portable microfluidic platform, “lab-on-a-display,” that microparticles are manipulated by OET on an LCD. Without lens or optical alignments, the LCD image directly forms virtual electrodes on the photoconductive layer for dielectrophoretic manipulation. Due to the portability and compatibility for disposable applications, this new platform has potential for programmable particle manipulation or chip-based bioprocessing including cell separation and bead-based analysis. Second research is about a grayscale OET which allows adjustment of the electric field strength at each position of OET. A grayscale light image was used to pattern vertical electric field strength on an OET. As an electric field depends on the brightness at each point, the brighter light patterns generate the stronger electric field in the OET. Its feasibility for application to cell manipulation was demonstrated by aligning highly motile protozoan cells in vertical direction. Depending on the brightness of each pixel, the behaviors of aligned cells varied due to the different electric field strength to each cell.