MALDI-MS Applications Overview


1) Proteomics Work Flow: 2D gels, spot excision, in gel tryptic digestion, extract the peptides with ACN/H2O/TFA, evaporate the solvent, redissolve in small volume and prepare them for MALDI-MS and -MS/MS.

The MS comes from companies like Bruker, the other equipment (gels, spot exciser etc.) from companies like GE Healthcare.

Our instrument does the following:
The samples are provided in 96 or 384-well MTPs as dried lyophilisates. The robot dispenses a small volume (a few uL) of the the solvent of choice as a series of small droplets to assist and ensure dissolving of the peptides. This solution it will then aspirate and dispense onto the MALDI target. In addition, the instrument aspirates MALDI matrix solution (CHCA in ACN/H2O/TFA) as well as a solution of two known peptides for optional internal calibration and dispense them to the MALDI target before, or after transfer of the redissolved peptide solutions. This solutions are provided in 0.5 mL Sarstedt or Eppendorf tubes. Of course, the instrument could dispense other solutions as well and the samples must not be provided in a dried state etc.

2)Work Flow: Off-line nano- or micro-LC-MALDI-MS and -MS/MS
This application is to perform proteomics research and to identify and characterize complex peptide mixtures (shot gun proteomics work flow).

The instrument is used as a non-contact fraction collector that starts doing this on demand controlled by a TTL or shortcut signal send by the LC software. The fraction collection works the following: The effluent of the LC is combined with a dispensing solution and jointly send off as a series of little droplets (on-demand, timely controlled) down to the MALDI target. Each droplet can be dispensed to a different position on that target (one droplet, one fraction) or several (user's choice) can be collected on the same position to enhance the detection sensitivity and maintain the chromatographic resolution. In this case it is a fused silica capillary with an outer diameter of 90 um and an ID of 20 um coming from a for example Dionex nano-HPLC in a special T-connector it enters our dispensing tip with a dispense orifice (channel) with an ID of 200 um. That tip is filled with dispensing solution (e.g. 20% ACN/80% H2O). Each time, when a droplet of the dispensing solution with a typical volume of 50 nL (or larger, e.g., 100, 200, 500 nL...), is send off that amount passes the end of the capillary and takes along the eluted peptides which have accumulated in form of a tiny droplet. The accumulation time is set by the user, e.g. 1, 2, 3, 10 or 20 seconds. The time frame depends on the LC flow. The small size of the droplets ensures that the sample is not too much diluted. The non-contact operation is what separates our instruments from our competitors. It minimizes sample carry over, excludes contamination of the tip by target contacts (dust particles etc.) and damage of the capillary or failure to deposit a fraction caused by variations in height (non-perfectly planar targets).

Other tasks with the same instrument are dispensing of the matrix solution with or without internal standards or a acidic water (pH < 2) for washing/conditioning of thin-layer sample preparations. To make this possible, the instrument also provides a sucking nozzel (capillary) that works much like a vacuum cleaner. It sucks the washing solution (sitting droplet of 1-3 uL) away without touching the target (non-contact removal).

All in all that instrument provides 2 dispense channels (LC effluent + one other solution) and one liquid removal channel, which can be combined in any way.

More information on this including video sequences showing the different applications you find here: LINK

3) MALDI-MS imaging of biological or medical tissue sections

Workflow: MALDI-MS imaging => image analysis => selection of spots or regions of interest => using our robot for the following tasks:
Load image, recognize reference markers, align with our head mounted camera, mark positions and dispense tiny amounts of buffered trypsin solution to these spots (individual droplets or a defined array of droplets). During this operation, the target can be heated up to 37 or 40 C° to assist protein digestion. After this part fresh acidic matrix solution is dispensed to these spots enabling their subsequent analysis in a second MALDI-MS and -MS/MS run to identify proteins within these spots.

All instrument setups described above come with options, among which the most popular is a head mounted digital camera with high quality magnification optics.
This can be used for instance for manual operation (e.g., mark and hit meaning you mark positions you see in the image of that camera and afterwards the robot will send one or a series of droplets thereto). It can be used during a run to automatically record and store a sharp image of each prepared sample (e.g. fraction of the LC run) in order to always have the possibility to go back and see whether that sample was alright etc. It can be used to recored an image of each sample after a first MALDI-MS or MALDI-MS/MS analysis to judge how much sample is left for a second analysis or addition of another reagent (e.g. internal standard to selected spots).