Transport, retention and fluorescent measurement of single biological cells studied in microfluidic chips

Cellular manipulation and fluorescent measurement were performed on two types of biological cells. First, transport and retention of yeast cells were demonstrated on a glass microfluidic chip, which consists of special U-shaped microstructures. These microstructures have the openings parallel to the liquid flow and weirs perpendicular to the flow. These allow the retention of yeast cells in the U-shaped pocket and drainage of liquid over the weirs. Thereafter, the same chip was used to carry out real-time fluorescent measurement for the cellular changes in single Jurkat T cells. In this case, the Jurkat cells were localized inside the straight portion of a microchannel. Fluorescent imaging on the same, single suspension cell was carried out to study two cellular processes occurring in viable cells, (1) the intracellular conversion of fluorescein diacetate (FDA) to fluorescein; (2) the degradation of an inhibitory protein, IκB, as involved in the NF-κB signalling pathway. In the former, the increase in fluorescent intensity of single Jurkat T cells (due to fluorescein formation) was measured; whereas in the latter, the decrease in the fluorescent intensity of a single transfected Jurkat cell (due to the degradation of the IκB-EGFP fusion protein) was monitored. In addition, we employed a Jurkat cell expressed with IκB-EGFP to probe any possible action of an herbal compound, isoliquiritigenin (IQ), on the degradation of IκB-EGFP. These examples have demonstrated that Jurkat cells remain viable within microfluidic channels for cellular studies and that the microfluidic chip can facilitate monitoring of cellular changes of biological cells at the single cell level and in the same cell.