Research On AFM Based Measurement Of Microdroplet And Performance Improvement

Micro fluidic controlling and detecting have attracted a great deal of interest, and the technique controlling discrete microdroplet has many applications in microfluidic chip, microarray, microinjection, ink jet, microdroplet jetting forming, organism manufacturing in recent years. The fluid volume control with high precision plays important roles in the analytical chemistry and biomedical fields which require accurate liquid dispensing in the nanoliter and picoliter ranges. At the same time, controlling is related closely to volumes detection what the correct analysis of micro liquid handling results depend upon. The technologies for measuring the volume of microdroplet and micro mass encounter a serious problem, since they are limited by some factors. So how to achieve effective and reliable measurement of small volumes is of great importance in droplet based microfluidic system.In this paper, a novel method is presented for measuring the volumes of microinjected droplet, which is based on AFM system, and the detected result is not influenced by the properties of liquid. The principle of the method is: the polyester cantilever is bent mechanically while the droplet injected onto the cantilever .the deflection of it is detected by approaching AFM tip to the cantilever and so the gravity of droplet is translated into voltage increment of AFM scanner. A micropipette puller and pressure injector have been designed to obtain the detecting object. The driving of micropipette in vertical direction is modified experimentally. The injecting and detecting site are optimized based on mathematical and experimental analysis.Such sensitive detection system is disturbed easily by the external microvibration. Experiments and investigations have been done for analyzing the influencing factors during measurements and the corresponding strategies are employed. Liquid paraffin was used as droplet receiving pool and sand box was modified to restrain higher frequencies disturbance. It reveals that there exists a low frequency disturbance from responsive swing of the detecting system, which gives measurements much influence. A damping structure is designed for depressing such disturbance, which promotes the performance of small volume detection system. Experiment about microinjection detection has been done and injected volumes are calculated based on elastic modulus and size of cantilever.