Automated pipetting system

An automated pipetting system is GeneRally a device which performs programmed transfers of liquid between preselected groups of containers.

The word "pipetting" is referring to the laboratory manual tool called pipette, which is the commonly used in molecular biology, analytical chemistry, and medical tests, to transport a measured volume of liquid. Moreover its performances are regulated by the International Standard ISO8655-1:2002.

Automated pipetting systems are also commonly known as Liquid Handling Robots; nevertheless the latter definition is preferred whenever add-on modules are present (e.g. laboratory shaker), while the former typically focuses on liquid transfer property. One of main advantages of these devices is the ability to enhance the reproducibility and the throughput of laboratory experiments.

Components

The vast majority of automated pipetting systems have the following 'structural' components:

• pipetting head
• user interface
• working area
• waste

Pipetting head

Pipetting head is the mechanical component which has been designed for liquid transfer. The majority of pipetting head are based on peristaltic pump system, while some anthropomorphic systems directly uses manual pipette. Pipetting head basically can be multi-channel or single-channel : while the former has higher throughput, the latter has greater flexibility and reproducibility. For an accurate placement into the source and destination containers, the pipetting head is placed on an automated axis system, typically based on servo motors or stepper motors.

User interface

User interface allows the communication between the user and the system via PC or touchscreen. The most advance user interface gives the possibility to the user to design its own experiment which has to be executed on the system.

Working area

Working area is the zone where liquid dispensing takes place and it is the area where the pipetting head can move. It is composed of holders which have on one side the functionality of hosting the containers in liquids are stored, on the other side they allow the recognition of the position of the source and destination containers. The recognition of their position can be made 'statically' (off-line calibration of the position) or 'dynamically' (e.g. vision-controlled spatial localization).

Waste

Waste is a special container which stores the disposable tips used by the system. It could be used also to throw away excess of liquid or washing buffer

Functionality

An automated pipetting system obtains a volume of liquid from a source by creating suction, described as aspirating, and dispensing this liquid over the destination container. This is achieved by the pipetting head installed on the system.

Anyway liquids are not in direct contact with the pipetting head, but they are held by structure called tips. Tips can be permanent structure or disposable conical pieces. Disposable tips, in general made from injection molded plastic (typically polypropylene), have the advantage of being discarded between liquid transfers thus removing any chance of cross contamination. The choice of the most suitable tip mainly depends on the dispensing volume set on the pipetting head.

Critical parameters

There are some critical parameters which affect liquid transfer in automated pipetting system; the most common are listed below :

• accuracy or systematic error, difference between the dispensed volume and the selected volume.
• repeatibility or random error, scatter of the dispensed volumes around the mean of the dispensed volumes.
• CV (coefficient of variation), which is a normalized measure of dispersion of a probability distribution.
• speed of the system, in performing liquid transfer.
• volume range, currently the majority of devices operate in the microliter to milliliter range.

Curiosity

The first manual pipette was patented in 1950's by G.S. Riggs and the first automated analyzing apparatus less than ten years after.

See also

• Liquid Handling Robot
• Pipette

fr:Système de pipettage automatisé it:Sistema di pipettaggio automatizzato