Small liquid droplets with volumes in the microlitre range are used in many applications today. Areas where these droplets can play a particularly important role include liquid handling in life sciences and pharmaceutical research, diagnostics and microfluidic applications. Two typical techniques for handling liquids are pipetting (a contact technique) and dispensing (a non-contact method).
A bulk dispenser can be a good option for many applications, such as dispensing buffer solutions or media for cell cultures. One method of producing microlitre-sized droplets is to use fast-switching solenoid valves. To dispense the fluid, these valves can be supplied via a fluid line, for instance from a pressurised reservoir. The image below shows an example of a simple system:
Dispensing, a non-contact method of handling liquids
Pipetting, on the other hand, can be seen as a more sophisticated method of liquid handling. In its simplest form, this type of liquid transfer device removes a volume of liquid from a container by suction after which it is positioned over a target location where it will dispense the liquid. The sample liquid is usually held in a structure called a "tip". The tips may be stationary, such as thin tubes or large metal or plastic hypodermic needles, or disposable conical pieces, also known as disposable tips. The use of disposable tips can eliminate the risk of carry-over while reducing the dead volume when handling valuable reagents compared to dosing large volumes. Many systems are equipped with multiple tips, which can speed up the transfer of liquids by simultaneously drawing in from or dispensing into multiple containers. As a rule, each work peak in a system is called a channel.
Pipetting, a contact method for handling liquids
Right now, the majority of automated liquid handling systems work with volumes in the microlitre to millilitre range. A current trend that can be observed is the increasing miniaturisation of assays; this enables laboratories to reduce reagent and sample costs while increasing throughput. An intelligent combination of pipetting and bulk dispensing can help optimise the automation of liquid handling processes.