Life sciences research labs rely heavily on the processing and evaluation of a variety of liquid solutions. Handling these liquids accurately and efficiently is a key facet in the overall productivity of the laboratory. The tools and processes used for liquid handling have evolved significantly over time, consistently improving accuracy and throughput with each innovation.
A variety of devices for volumetric analysis of liquids have been in use since the 1700s. The 1960s saw the introduction of micropipettes, tools used to hold, and dispense liquids in an accurate and repeatable fashion. The first effective micropipettes were developed by Dr Heinrich Schnitger of Germany. Handheld pipettes are available in fixed volume and adjustable volume configurations. In some cases, the ability to adjust the size of the volume can affect accuracy.
Standard Micropipette Configurations
The most common micropipettes are air displacement micropipettes, which rely on piston-driven air displacement to dispense liquid. The benefit of the air displacement micropipette is that the piston does not come into contact with the dispensed liquid, which is contained within a disposable tip. This helps to prevent cross-contamination and easily allow researchers to switch between solutions.
Positive displacement micropipettes include a plunger that contacts the liquid being handled. They contain a disposable syringe and are most often used when cross-contamination has to be completely avoided, such as when handling DNA samples, or when handling volatile or viscous liquids. Volumetric pipettes are designed for a high level of accuracy, and are used when the volumetric accuracy of the liquid transfer is critical. Like many laboratory components, a variety of specialty pipette designs have also been created to address very specific needs.
Non-Contact Liquid Handling
For applications that require the transfer of very small volumes, a variety of non-contact liquid handling methods have been created. These include valve dispensing technologies, inkjet technologies, glass capillary dispensers, and ultrasonic droplet generation. These types of systems dispense volumes in the nanoliter to picoliter range, and must overcome the Weber number of the liquid to create these small droplets while maintaining accuracy of droplet size. Some of these technologies were developed originally for the printing industry, but they have become an important part of microarrays and “lab on a chip” systems in the life sciences arena.
Automated Liquid Handling Now the Norm
Today, automated systems are used to control liquid handling in the life sciences laboratory. Microfluidic systems are commonly used to precisely control very fine tipped pipettes and allow for multiple solutions to be used on demand. These systems can also support concentration control and solution pulsing. Multichannel pipette systems are integrated with microplate handling systems to rapidly process sample arrays. These automated systems have evolved into a complex array of storage, movement, manipulation, and evaluation components, software control systems, and operational rules. Despite their complexity, automated liquid handling processes result in higher accuracy and throughput of liquid handling tasks, resulting in higher overall laboratory efficiency.
 J. Comley, Drug Discovery World, vol. summer 2004, pp. 1-8, July 2004.