How?
Basic Principles, Procedures and Challenges
We offer three distinct dispensers:
PDMD read more
PinDMD read more
M2MD read more
Non-contact Microdispener
The sample solution is transferred through the air towards the target as a small individual droplet, a series thereof, or as a liquid jet. The main advantage of non-contact dispensing is that the properties of the target surface do not affect the deposited volume. The surface is not touched by the dispenser: no damage, no contamination. Another benefit is that no down and up movement is required for sample transfer, which saves valuable time.
The wet area on the target (spot size) is determined by the surface tension of both the liquid and the target surface. If a moderate number of samples need to be dispensed onto many targets, non-contact microarray spotting is clearly the best method.
Contact-based Microdispener
The sample solution is transferred from a pin or capillary to the target surface via short contact. The main advantage of contact-based microdispensing is the ease of parallel sample transfer, enabling high sample throughput. If many samples are to be printed onto a moderate number of targets, contact-based microdispensing using many pins is the method of choice.
Low-volume Dispensing Procedure:
- Aspirate an aliquot of the sample solution.
- Pre-dispense some droplets in order to get the dispenser running and prevent initial effects.
- Move to the desired target and start dispensing.
- Move to the wash station and clean the inside and outside of the dispenser tip.
- Proceed with the next sample.
If only one solution must be dispensed, it can be advantageous to feed it from a reservoir attached to the dispenser, instead of aspirating it. Our so-called Bulk Dispenser does exactly that. The solution to be dispensed is filled into a 20 mL glass vial and transported from there through a connection capillary into the dispenser.
When a larger volume of solution needs to be dispensed than can be aspirated, bulk dispensing often becomes an appealing option. This choice saves time and space, while also protecting the sample solution from solvent loss due to evaporation.
Challenges During Dispensing:
Evaporation
Exposure to ambient air can increase solvent loss through evaporation, leading to intensified solution concentration. Elevating humidity over aqueous solutions effectively curtails solvent evaporation, as does lowering the temperature.
Nevertheless, caution is needed to avoid going below the dew point, as this could lead to condensation and, therefore, the dilution of samples. Hence, maintaining the dew-point temperature strikes a balance between evaporation and condensation.
Our Microdispensing Instruments can be equipped with an accurate dew-point control.
Dust/Dirt
Dust is a common source of contamination and it can cause problems during sample aspiration, like the clogging of the dispenser tip. Therefore, a clean environment is highly recommended. Our instruments are well sealed to accurately enable internal climate control (temperature and humidity) and prevent dust ingress. In addition, the production machines can optionally be equipped with a HEPA-filter module.
Electrostatic Charging
Electrostatic charges residing on non-conductive surfaces can generate strong electrical fields. As droplets ejected by microdispensers are charged, they can be deflected by such fields. This is a common problem when dispensing onto plastic targets, e.g. the bottom of a 96-well MTP or a channel of a lab-on-a-chip device. The smaller and lighter the droplets, the more severe the effects.
For that reason, it is necessary to eliminate all charges on plastic target surfaces before microdispensing. For that task, our Instruments can optionally be equipped with de-ionizers. These devices quickly and efficiently neutralise all electrical charges residing on the surfaces.