Performance Assessment of a Liquid Handling Robot

Fluorescence-Based Volume Verification Method

 

A premade fluorochrome solution, such as Fluorescein, was pipetted into a microtiter plate by a liquid handling system. A microplate reader is implemented to measure the fluorescence intensity in each well. The fluorescence intensity F is determined by:

 

F=GCJ

 

where J is the characteristic factor of fluorochrome, G is characteristic factor of the incident power of the light beam emitted by the microplate reader and C is the concentration of the fluorochrome.

 

According to this equation, the fluorescence intensity is proportional to the concentration, which corresponds to the volume of liquid dispensed into each well. Because of the variations of liquid transfer in different channels, there are deviations of the fluorescence intensities in each well. With multiple fluorescence measurements, the mean values of each channel are calculated, and the standard deviation of each channel can be determined. Therefore, the precision from well to well can be evaluated from the coefficient of variation.

 

To determine the accuracy of liquid delivery, it is necessary to generate a standard curve (Bradshaw and Albert, 2010). A serial column of fluorochrome solution in different desired target volumes is dispensed into a microtiter plate. The measured fluorescence intensity is plotted against the requested volume of pipetting. Accordingly, a linear regression curve is generated over the volume range of interest, which can be subsequently applied to determine the unknown volume of fluorochrome solution dispensed into each well. Then, the readouts of each well are substituted into the linear equation to estimate the dispensed volume. In this way, the accuracy can be determined with estimated volumes.