High Precision Bead Dispensing using the Nanodrop™
Introduction
Reliability and robustness are critical issues in bead dispensing. Beads have the potential to become lodged in moving parts, thus reducing the lifetime and increasing the downtime of many traditional liquid handlers. Innovadyne’s scientists have established a reliable instrument configuration and protocols for low volume bead dispensing for a variety of microscopic bead types. Here we test the reliability of the Innovadyne Nanodrop™ II instrument dispensing two typical types of beads at various dispense volumes and concentrations. To test the feasibility of performing low volume bead applications that have to date been constrained by the inability to dispense small bead volumes at high bead concentrations, we will also attempt to dispense 100 nL of beads at a concentration of 80 mg/mL.
Methods and Materials
In order to test the reliability of the Nanodrop II instrument for dispensing beads, a total of thirteen 384-well plates were dispensed at various dispense volumes (9 plates at 1 µL, 3 at 500 nL, and 1 at 100 nL) with 10 µm fluorescent polystyrene beads suspended in de-ionized water at concentrations of 5, 20 and 80 mg/mL (Duke Scientific, Palo Alto, CA). The dispensing precision was determined by reading the plates in a fluorescence plate reader (see Figure 1). Additionally, nine plates were dispensed with yttrium oxide beads to test for tip/harness clogging.
Results and Discussion
The data shows successful dispensing of fluorescent polystyrene and yttrium oxide SPA beads at concentrations of 5 mg/mL to 80 mg/mL. We were able to demonstrate precise and accurate low volume dispensing of polystyrene beads at a range of volumes down to 100 nL, and variously dispensed polystyrene and yttrium oxide beads to a total of 27 plates (384-well) in succession without tip clogging or degradation of system performance. Dispensing precision for all plates was well within acceptable limits for all the bead concentration and volume ranges (Table 1). At volumes less than 1 µL and with bead concentrations in the 10-50 mg/mL range, detection signal is often too weak to be useful. Here we have shown that it is possible to dispense volumes of 100 nL at concentrations of 80mg/mL demonstrating the ability to miniaturize bead assays.
| Bead Concentration | Dispensed volume 1000 nL | Dispensed volume 500 nL | Dispensed volume 100 nL |
| 5 mg/mL | 5.5, 4.9, 5.3 | 8.8, 8.2, 9.0 | |
| 20 mg/mL | 4.8, 5.1, 8.1 | ||
| 80 mg/mL | 4.9, 4.2, 3.8 | 6.9 |
Table 1: Dispensing precision achieved for fluorescent polystyrene beads expressed in % coefficient of variance (Cv)
Figure 1 (below) shows the dispensing profile obtained for a typical plate when dispensing 1 µL of fluorescent polystyrene beads at a concentration of 80 mg/mL. Each curve shows the dispensing performance of one of the tips to 48 wells. Plates are not centrifuged prior to plate read.
| RFU % of Plate Mean for a Typical 384-Well Plate |
|
Figure 1: RFU % of Plate Mean for 48 Wells x 8 Tips (1000 nL Dispense, 80 mg/mL Concentration)
Applications