Interferometric Volume Measurement in Microplates

Low-coherence interferometry is presented as a method for nondestructive, noncontact, and high-resolution measurement of liquid volumes and fill heights in microplates. A Meniscense (Bolton, MA) prototype system captures both fill height and meniscus shape and combines them into a volume measurement, allowing for the measurement of a wide range of liquids with different meniscus shapes. The system has a liquid fill height resolution of 0.7 µm, corresponding to a volume resolution of 0.02 µL in a typical 96-well plate, demonstrated in an ideal model system. Initial data on the gravimetric verification of volume measurements on aliquots of distilled water between 50 and 350 µL in a 96-well plate suggest an inaccuracy of volume measurement of <2%. The Meniscense system offers accuracy comparable to ratiometric photometry, the only commercially available high-resolution volume measurement system. Its fill height resolution is substantially better than that of ultrasonic ranging, the only other noncontact, nondestructive method for fill height measurement.