PDMD

Basic Operation Principle

This picoliter dispenser operates through the piezoelectric actuator's voltage-induced contraction, displacing liquid in a glass capillary by 100-250 nanometers. Most liquid exits through the nozzle, with a fraction escaping upward.

The contraction's linearity with applied voltage establishes a key parameter. Simultaneously, the voltage's temporal application, pulse width, significantly influences droplet volume and velocity. Voltage governs velocity, while pulse width regulates volume.

This intertwined control of voltage and pulse width yields a methodical and precise liquid dispensation process, enhancing precision in experiments.

Dispensing Modes

1. Stop-to-spot with Z-moves: The dispenser stops for each droplet deposition and moves up and down between consecutive positions to bypass possible obstacles. These movements cost time but can be necessary when dispensing onto specific locations of a non-planar, 3-dimensional target.
2. Stop-to-spot, no Z-moves: Without the need to move the head up between consecutive positions, dispensing is much faster. This is always the case when dispensing onto planar targets.
3. On-the-fly: The dispenser “flies” over the target and releases a droplet on defined positions during the flight. That way, up to 1000 droplets can be deposited, each at its own specific coordinates.

Digital Liquid Handling

Larger volumes are dispensed as a rapid succession of well-defined picoliter droplets, offering a key advantage by obviating the need for individual calibration. This streamlined approach enhances efficiency and temporal economy when dispensing diverse volumes within a single experiment, while preserving the vital aspects of precision and reproducibility imperative for scientific investigation.

This demonstrative video showcases the digital picoliter liquid-handling process, showing the dispensing of calibrated droplets at a frequency of 1000 Hz. The sequential deposition culminates in droplets of distinct volumes - 0.1, 0.5, 5, 10, and 100 nL - illustrating the dynamic continuum of this methodology.

Aspiration/Dispense Cycle

The aspiration/dispense cycle is a crucial aspect of picoliter dispensing, enabling efficient use of precious samples.

For example, as little as 2 µL of a sample is sufficient to dispense 10,000 picoliter-aliquots at different locations on a target. This allows for multiple experiments or the production of diagnostic chips with minimal sample usage.

To illustrate the aspiration/dispense cycle, this video showcases the process of aspirating 3 µL of a red, aqueous solution from a 5 µL droplet, followed by the dispensing of 150 pL-aliquots at different positions.

Not all aspirated sample can be dispensed without dilution towards the end. If the mixing is not enhanced by osmosis, or aspiration is too fast, then a minimum of 1 µL of the original 3 µL can be dispensed with no dilution.