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Tham khảo tài liệu 'atomic force microscopy in cell biology episode 2 part 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 226 Kindt et al. not available for some systems and where available is often problematic leaks limited scan size high load on scanner . The ideal fluid-exchange system runs different solutions continuously and in small controlled portions at a given rate and low noise. In addition it can remove the fluid at exactly the same rate from an open fluid cell therefore maintaining the fluid level in an open low-volume cavity. This versatility is ideal for use with a variety of probe microscopes many of which have only open fluid cells. We have constructed a system with the potential to combine all these properties using four high-precision computer-controlled syringe pumps Fig. 4 . Unlike other pumps these pump modules have proven to be very quiet. These pumps show minimal or no disturbance in nanometer-scale images of DNA plasmids on a mica surface while continuously running a buffer solution at flow rates up to 15 L s. The long-term stability of the flowrate was shown to be better than 200 nL min resulting in volume changes inside the fluid cell of less than 6 ijL in 1 2 h. A. Principle of Operation Two syringe pumps inject fluid into the AFM fluid cell in an alternating manner providing continuous in-flow. The modules are equipped with computer-controlled valves that can connect the syringe to one of multiple ports. While one module is running fluid into the fluid cell the other module switches over to a different port and refills at a suction rate that is higher than that in the flow rate into the cell. Then it switches back to the port connected to the fluid cell and waits for the module currently running to complete its stroke. When that happens the now refilled module takes over and starts running. This changeover needs to be well synchronized to avoid glitches in the continuous flow and hence in the AFM image. The in-flow modules have eight ports to choose from so that the fluid to be injected into the AFM can be selected from various sources and the source can be
