**2.6. Solenoid-based devices**

Solenoid-based devices are non-contact dispensers that use a positive displacement mecha‐ nism (Bateman et al. 1999). The flow of pressurized liquid is occluded by a solenoid valve, which is actuated by electric current to allow for liquid to pass through the valve. The dis‐ pensed volume is regulated by the fluid pressure, duration of the valve in the open position, solution properties and orifice diameter (Bateman et al. 1999; Niles and Coassin 2005). De‐ pending on the time the valve stays in the open position, the device can eject droplets or a continuous stream (Niles and Coassin 2005).

Microplate washers can be categorized into two types: strip washers, which wash a single column or row of a plate at a time, and full plate washers (Rudnicki and Johnston 2009). The availability of 8-/12-/16-channel manifolds for strip washers provides both single strip wash‐ ing and full-plate washing capability in the same device, but at the cost of increased wash time for full plates. On the other hand, full plate washers with either a 96- or 384-channel manifold may be preferred for time-efficient wash operations (from a few seconds to a few

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The combination of plate washing and bulk dispensing features within the same device may be favored for a space-efficient solution. They are designed to dispense reliably low volumes and reduce prime volume (Rudnicki and Johnston 2009). A major advantage of the washerdispenser combination comes into play with assay protocols that require the direct addition of fluid after or between the washing steps, such as cell fixation or microplate surface coat‐

Assessment of instrument performance has become important in order to minimize falsepositive and false-negative rates in high-throughput screening (Taylor et al. 2002). One of the most important figures of merit in evaluating the performance of liquid handlers is accu‐

*VT*

where *VM* is the measured volume and *VT*is the theoretical volume (desired). %bias repre‐ sents the deviation from the desired volume, with a value of 0% indicating no deviation

The precision, a measure of reproducibility, is calculated from the mean and standard devia‐ tion (SD) of a set of measurements, and it is reported as percent coefficient of variation (%CV) or relative standard deviation (RSD), as shown in Eq. 2. For most cases, it is adequate

There have been several approaches for volume verification, which typically consist of gravimetric or photometric methods. Gravimetric measurements utilize the mass and the density (ρ) of the dispensed solution to determine the volume. It has been used extensively to calibrate and verify the accuracy of liquid dispensers (Bergsdorf et al. 2006; Rhode et al. 2004; Taylor et al. 2002). Typically, the solution is dispensed across a pre-weighed microtiter

) (1)

mean (2)

%*bias* =100 <sup>×</sup> ( *<sup>V</sup> <sup>M</sup>* - *VT*

%CV=100 × SD

minutes), but lack the flexibility of the 8-/12-/16-channel units.

**3. Considerations for using liquid handling devices**

**3.1. Determination of quality assessment descriptors**

racy, which is commonly reported as %bias (Rose 1999):

to have a bias value below 5% and a CV below 10% (Rose 1999).

ing reagents.

from the true value.
