Meso Scale Discovery (MSD) is a well-regarded technique used with Ligand Binding Assays (LBA). An interesting aspect of this technique is that it uses electrochemiluminescence (ECL) as a detection technique. By comparison, the popular ELISA technique makes use of colorimetric reactions for detection.
How Meso Scale Discovery Detection Works
Meso Scale Discovery Electrochemiluminescence uses a combination of electric current and SULFO-TAG labels to represent the presence of an analyte. High binding carbon electrodes are present at the bottom of the plates. These electrodes have ten times the binding capacity for attachment of reagents, as compared to the commonly used polystyrene bases.
SULFO-TAG labels are electrochemiluminescent and conjugated for easier detection of antibodies. The application of electricity on the electrodes causes a light emission by SULFO-TAG labels. The intensity of light emission is analyzed to quantify the presence of analytes.
Sulfo-tag makes use of amine-reactive label Ruthenium (II) tris-bipyridine, N-hydroxysuccinimide. If exposed to primary proteins, the N-hydroxysuccinimide esters form a stable bond. This bonding results in the presence of electrochemiluminescent ruthenium (Ru) metal ions in the label.
A greater presence of analytes in the MSD assay results in a larger availability of Ru ions. This, in turn, causes a higher intensity of light emission. The light intensity is detected by the use of a CCD camera.
Multiplexing To Go Faster
MSD assays can be multiplexed to analyze multiple analytes in the sample matrix. Available plates for MSD-ECL have configurations that allow the use of one, four, seven, or ten analytes. For example, the single-spot plate allows the detection of one analyte, while the seven-spot plate enables multiplexing for seven analytes.
As compared to conventional methods, MSD-ECL can accomplish in one plate, which would require 10 ELISA plates. This assumes a 10-spot multiplex but the advantage that multiplexing brings is clear. Plates for the MSD assay are available in the conventional 96-well and 384-well configuration.
To make things easier, pre-made kits are available for MSD. Several variants are available, like the pre-validated V-plex, non-multiplexed R-plex, S-plex for ultra-sensitive assays, and U-plex for customized multiplexing.
Dynamic Range and Assay Sensitivity
Meso Scale Discovery Electrochemiluminescence is also superior to conventional ELISA systems in dynamic range and sensitivity. It has a higher dynamic range than conventional ELISA as well as high-sensitivity ELISA. The dynamic range for MSD-ELC is 3–4+ logs with reduced matrix interference.
To offer low background noise and higher sensitivity, the system decouples electricity from the signal. In this setup, only labels that are close to the electrode surface are detected. In a sandwich assay, the capture antibody is at the bottom of the well, which is also the electrode. As the second antibody binds the antigen, the Ru metal-ion produces electroluminescence.
Overall, this results in signal amplification, increased throughput, and low background noise. The read times can be very fast, with up to 960 results in three minutes.
An additional advantage of the Meso Scale Discovery technique is that it requires relatively low sample volume. While a conventional ELISA requires anything from 50-100 μL of sample per analyte, MSD can work with 10-25 μL. This is especially helpful for cases where the sample is in short supply like the earlier stages of drug development.