Development of the pipetting error sensor

An air volume flow rate sensor with a resolution of nano-liter per second is developed to monitor the pipetting errors of the polymerase chain reaction (PCR) mixture dispense processes for DNA quantification experiments. Based on the CMOS and post-CMOS micromachining processes, the sensor which comprises microstructures and mixed signal processor in a die size of 2 mm square is fabricated and is set within a standard 200 μL pipette tip. The microstructures of the sensor consist of a polysilicon microheater and a thermopiles array. The centered microheater encircled by temperature sensors generates the heat plume. As the sensor is positioned against the flow, the thermal plume will be pushed towards to the temperature sensors array and the temperature difference can be converted into voltage to determine the air volume flow rate through the tip. The total volume of air movement can be correlated to liquid volumetric delivery and then the pipetting error can be tracked by the non-contact method. The DNA quantification experiments with hepatitis B virus (HBV) plasmid standard samples are performed on a real-time PCR machine as the pipetting error is monitored by the proposed sensor to reject large discrepancy in mean delivery volumes. The DNA quantification results for the serial samples with the initial template concentration ranging from 104 to 108 copies/mL give high linear standard curves, and the coefficient of variation (CV) of DNA quantification experiments for the three replicates intra-assay is less than 6%. These results indicate that accurate DNA quantification and high reproducibility of experiments can be obtained by the pipetting error sensor.