A self-adjusted precise liquid handling system

In biomedical areas, such as protein crystallization, drug discovery and medical diagnostics, thousands of reagents with different viscosities need to be transferred or dispensed in submicroliter range. Most of the commercial automated liquid dispensing systems need to be calibrated through experiment to accurately dispense liquids when the reagents viscosities change, which is time consuming and less accurate. In this paper, an intelligent precise liquid handling system was developed, in which a high speed MEMS flow sensor was used. Benefiting from the feedback of sensor information, the system can self-adjust the open time of the solenoid vale to accurately dispensing desired reagent volume without pre-calibration. Firstly, the system construction was introduced in detail. Secondly, a novel closed-loop control strategy was proposed to calculate valve open-time for each dispensing cycle, which makes the system immune to liquid viscosity, pressure fluctuation and some other disturbances. Finally, experiments results are presented with different dispensing volumes, coefficient of variance (CV) has been shown to be below 3% at 1ldquol and approach 4% at 100 nl.