S-PLEX: TrueSensitivity, Simple Execution

DISCOVER True Sensitivity

S-PLEX logo  

S-PLEX is MSD’s ultra-sensitive assay platform. It can dramatically improve the sensitivity of immunoassays, reducing the lower limit of detection (LLOD) by 10- to 1000-fold over other assay methods. Detection limits in the low femtogram/mL range are common. These low detection limits enable the measurement of analytes at lower concentrations, reduce sample volume required, and reduce the amount of critical reagents used. The S-PLEX assay format builds on MSD consumables and instruments and leverages MSD’s assay development expertise by using a procedure that is similar to other MSD assay methods.

For Research Use Only. Not for use in diagnostic procedures.




S-PLEX Performance

Explore S-PLEX sensitivity with up to 1,000-fold improvement over existing ELISAs.

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S-PLEX Technology

Learn how S-PLEX assays build on existing MSD consumables and instruments.

How It Works
S-PLEX Sample Testing Services

Learn how S-PLEX assays can be developed and run in our sample-testing lab.

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Available S-PLEX Assays

Each S-PLEX assay comes with specific components to run an ultrasensitive assay in a single-analyte format. Click on an analyte listed in the table below for more detailed information.


View our recent poster on the S-PLEX Platform

Development and Implementation of the S-PLEX® Platform for Converting Standard Immunoassays to High-Sensitivity Assays


S-PLEX Performance

The increased sensitivity of the S-PLEX platform allows shifts in the dynamic range of assays, resulting in low detection limits. This enables detection of analytes in samples that are not readily detected by other assay formats. Additional information on S-PLEX assay performance, sensitivity, and sample detection is provided in each product insert.


Human TNF-alpha sensitivity ranges
TNF-alpha calibration curves
TSLP native samples

Figure 1: (A) Comparison of sensitivity ranges for different human TNF-α assay types shows the unique sensitivity of the S-PLEX assay format. Increasingly, studies have shown that many biomarker levels are actually lower than previously thought (red dotted box). (B) Calibration curves for multiple TNF-α assay formats compare sensitivity. (C) Data from TSLP measured in a set of native samples using three assay platform reveal how samples on the S-PLEX format fall easily within detection limits. Each sample tested is represented by a closed circle, upward triangle, or downward triangle. The solid line indicates the LLOD, and dashed lines indicate the estimated lower limit of quantitation (LLOQ) and upper limit of quantitation (ULOQ) for each assay format.

To evaluate the performance advantages of the S-PLEX platform, assays that were developed on either U-PLEX and S-PLEX or V-PLEX and S-PLEX platforms using the same antibodies were compared. More than 50% of assays improved sensitivity 10X or more in the S-PLEX platform

LLOD comparison
LLOQ comparison

Figure 2: Improvement of U-PLEX (A) and V-PLEX (B) assays when converted to S-PLEX format. The S-PLEX platform offers many advantages over alternative immunoassay formats as shown in the table below. Note that S-PLEX assays offer a significant conservation of precious samples and antibodies with gains in sensitivity, and large dynamic range.


Table 1. Comparison of S-PLEX, ELISA, and bead-based immunoassays

Feature S-PLEX ELISA
Bead-based
Sample volume
25 µL 50–100 µL 50 µL
Antibody amount ~0.1 µg/mL ~1 µg/mL ~1 µg/mL
Dynamic range 3–4 logs 1–2 logs 2–3 logs
Assay Sensitivity fg/mL pg/mL-ng/mL pg/mL-ng/mL
Multiplex enabled No No Yes
Protocol Simple Simple Bead Separation
Matrix effects Assay Dependent Interference with Enzymatic Reagents Yes (bead aggregation)
Read time 1 min 5 min 60 min
Instrument maintenance None Monthly calibration Fluidic maintenance

S-PLEX Technology

The improved sensitivity is, in part, a result of TURBO-TAG label that, when combined with an antibody conjugated with TURBO-BOOST label, results in larger signals generated when compared to using SULFO-TAG as the detection label. The S-PLEX procedure is a simple modification to standard MSD assay protocols, with high sensitivity and specificity achieved through three easy steps. A graphical representation of the protocol is show in Figure 3.

Assemble the immunoassay

Enhance with TURBO-BOOST and TURBO-TAG

Read assay on an MSD instrument


The first step of an S-PLEX assay is to ASSEMBLE the immunoassay with a TURBO-BOOST label on the detection antibody and additional S-PLEX reagents to reduce non-specific signals.









Signal generation is achieved, in part, through an ENHANCE step which includes enhancement of the TURBO-BOOST and addition of TURBO-TAG molecule. TURBO-TAG is an electrochemiluminescent label that binds to the enhanced TURBO-BOOST label during the ENHANCE step.







The READ step of the assay is the addition of MSD GOLD Read Buffer and reading of the assay on an MSD instrument where voltage applied to the plate electrodes causes the captured TURBO-TAG labels to emit light.