How Real-Time Monitoring of Pipetting Processes Works

Problem: Automation solutions offer a great alternative to laborintensive manual processes. Liquid handling automation eliminates human errors and process inconsistencies over extended periods of time, resulting in an increased robustness compared to manual processes. It is important, however, to use the appropriate controls to monitor the accurate and reliable implementation of a robotic process. A key component of success in automation is the use of samples that have been well qualified. Robotics can only run a process consistently when the appropriate samples and volumes are fed into the system. For example, if there is a missing sample or there is insufficient sample in a well, the robot may still perform its function but cannot deliver volumes into the source plate as expected. Often times, this poses a challenge to the end user. How does the user know whether the robot is aspirating and dispensing volumes accurately? How does he know if there are wells with insufficient volumes, or if a tip gets clogged?

Solution: Hamilton Robotics addresses these problems with a unique solution that uses TADM (Total Aspiration and Dispense Monitoring) technology described below. It offers real-time monitoring of aspiration and dispensing, allowing customers to have a record profile of all the pipetting steps in each of the wells.

TADM increases the accuracy and robustness of the pipetting process. A pressure sensor inside each individual pipetting channel constantly records the pressure in the system during aspiration and dispensing. The software generates a pressure-over-time curve (Figure 1) that is different for each liquid class and each volume pipetted.

The values obtained by the pressure sensor during a pipetting step (aspiration or dispense) can be compared to user-defined values, thereby enabling realtime monitoring of the pipetting process.

The TADM feature would not be feasible if the pressure curves obtained were instrument-, weather- and altitude-dependent. Therefore, the reference point of the pressure curve is zeroed automatically by the software before pipetting commands are executed. Because the pressure value is not re-zeroed between consecutive aspiration steps, TADM curves from the different aspiration cycles will be shifted. In other words, the reference point for the start of an aspiration curve will always be the pressure value obtained before the tip was picked up. Since the pressure value is rezeroed between consecutive dispensing steps, curves will be obtained, where the curves from all consecutive dispense cycles are not shifted.

By examining the TADM curves of many aspiration or dispense steps, it becomes apparent that curves obtained from a normal, errorfree pipetting step are distinctively different from curves from erroneous pipetting steps. These differences are quite obvious and can be used to distinguish between correct and erroneous pipetting steps. Some of the common pipetting errors during aspiration and dispense cycles and the corresponding pressure curve behaviors are listed in Table 1.

For more information, go to www.hamiltonrobotics.com