The Development Of Surface Tension Induced Control And Manipulation Inside Microchannels

Microfluidic has been widely used in biochemical analysis and clinical diagnosis, due to the capability of high throughput, low consumption and fast detection. In this thesis, we focused on the developments of new approaches to simplify the fabrication and utility of microfluidics to perform the microfluidic application for on-site analysis. On the basis of surface tension inside microchannels, we have developed five new methods to realize the control and manipulation inside microchannels.A new method for the measurement of surface tension inside microchannels was developed. This method offered the multiple measurements with 15μL sample within 1 min. The measurement was also performed at different temperatures. Seven organic solvents were tested with relative high accuracy (0.4-6.4%) and reproducibility (RSD<2%, n=9).A new approach to generate uniform-sized (RSD<0.56%, n=70) nanoliter droplets (74-576nL) inside microchannel was developed by using a circular groove to break off the liquid induced by surface tension. Carrier solution was not necessary, and the influence of flow rate on droplets formation was eliminated. Controlled coalescence of two droplets inside microchannel was realized to enhance the chaotic mixing inside droplets. Reagents could mix completely in 1 second by using two approaches to control their motions.A method based on the self-assembly of polystyrene beads was developed to generate masters for soft lithography. The masters were used to fabricate microarrays for single cells analysis. The time consuming of master fabrication was less than 10 min, and the feature sizes of master could be easily adjusted for different kinds of cells which were used in single cells analysis.A photolithography approach was developed to generate hydrogel microstructures inside microchannels to immobilize biomolecules and cells. Based on the sample introduction driven by surface tension, bioanalysis was performed inside microchannels, the detect limit of sample DNA was as low as 1 pM. Fluorescence microscope was used to control the UV illumination to selectively trap single cells for single cells analysis, requiring only five seconds for each single cell immobilization.A paper based microfluidic technique was developed and successfully utilized for ambient ionization of mass spectrometry. A wide range of samples could be directly detected with the detect limit of ppb level, including small molecules, peptides and proteins. The paper based microfluidic offered sample pre-preparation for complex samples. The detections of drugs in blood and urine samples were performed with low sample consumptions (<1μL), short detection time (<1 min) and good accuracy. The sample preseparation and on-line derivatization were also demonstrated.