Piezoelectric mechanical pump with nanoliter per minute pulse-free flow delivery for pressure pumping in micro-channels

Abstract

A novel computer-controlled mechanical syringe pump is described which uses a piezoelectric actuator and a pivoted lever for amplification of the linear displacement of the piezo-actuator to deliver solvents free from pump pulsations at volumetric flow rates approaching 1 nl min^–1 even at high loading levels (high output pressures). The flow patterns can be programmed by controlling the voltage waveform to the piezo-actuator to produce a linear displacement of 72 µm. By using the pivoted lever, a ninefold amplification of the piezo-expansion was achieved producing a total linear displacement of 648 µm. When a gas-tight glass syringe of 1.0 mm diameter was interfaced to the piezo-pump, the total volume delivered in a single pump stroke was 511 nl. Whereas the pumping profile was governed by the expansion behavior of the piezoelectric actuator, the flow rate was also slightly affected by the loading pressure on the pump as well. The piezo-pump was found to deliver adequately a stable flow of solutions with loading pressures as high as 3.79 × 10⁵ Pa (actual loading pressure at the piezo-actuator = 3.41 × 10⁶ Pa). Monitoring the flow stability using fluorescence indicated that the volume flow was fairly noise free at pumping rates from 4 to 150 nl min^–1. Below a volume flow rate of 4 nl min^–1, the pump exhibited extensive noise characteristics due to the step resolution of the DAC driving the piezo-actuator. A diffuser–nozzle system was fabricated which allowed automatic refilling of the syringe pump and was micromachined into Plexiglas (PMMA) using X-ray lithography. The diffuser–nozzle system contained channels that were 50 µm in depth and tapered from 300 to 30 µm. The diffuser–nozzle system was interfaced to the syringe pump by connecting conventional capillary tubes to the PMMA-based diffuser–nozzle, the piezo-pump and the chemical analysis system.