Some targets employ a highly polished plate and therefore possess a “hydrophobic” surface. In this situation, the distribution of small droplets can be difficult to control when the distance between the probe and target is very small. However, the superb precision of the SunCollect system ensures that there is no contamination between neighboring spots, even when difficult targets are employed (Fig. 2).
Figure 2a-c: Spotting precision for difficult targets with 100 (a) and 192 spots (b) respectively. Even 5625 spots of 4 nl each (c) on only 5 x 5 cm (2×2 inch) area are feasible with SunCollect (40x magnification).
In addition, it allows the user to shorten the measuring time, since the time required searching for „hot spots“ by the laser of the MALDI-MS is minimized. Several studies have clearly shown that the shape of the drop is optimized when:
- The needle does not touch the surface
- The droplets can be formed in a symmetrical shape by the tip of the probe
- Small droplets are deposited by the probe onto the plate
- Past adjustments to the system are kept in memory so that similar droplets can be treated in a common manner
- Sufficient time is provided for the deposition of the sample so that the liquid film can drain from the probe tip and minimized carryover.
Figure 3: SunCollect’s patented fused silica spotting needle (20x magnification).
An additional benefit is the extremely fast changeover from spot to spot (less than 1 sec) that allows fractionation even at high flow rates (e.g. with Micro-HPLC).As an example, the spots in Figure 2a were collected with a fraction time of 1 sec. The probe needle is made of 360 µm OD quartz to ensure very small and precise spots.