The ability to profile thousands of proteins in a single assay begins with exquisite specificity

See the exquisite specificity of the SomaScan® Assay

The SomaScan [Assay] also has a two-step approach to specificity that is sometimes forgotten by non-experts…between these two steps, the assay turns out to be quite highly specific.”
Peter Ganz, MD Director of the Center of Excellence in Vascular Research
Zuckerberg San Francisco General Hospital

Professor of Medicine,
University of California in San Francisco

Why modified aptamers?

The SomaScan Platform uses unique modified aptamers — short sequences of DNA — as protein affinity reagents. Our proprietary SOMAmer® (Slow Off-Rate Modified Aptamer) Reagents are chemically modified aptamers to achieve specificity and sensitivity.

Shape specificity

By using uniquely modified DNA with hydrophobic functional groups, our SOMAmer Reagents achieve a greater degree of shape matching, enabling discernment between nearly identical proteins.

Slow off-rates

SOMAmer Reagents are selected for slow off-rates when correctly bound to their intended target to ensure that correct proteins remain preferentially bound during rigorous washing.

Polyanionic competition

Polyanionic competitors are used to universally prevent rebinding of transient, non-specific interactions. There is no such universal competitor for antibodies.



X-ray crystal structure of a
SOMAmer Reagent bound

Modifications to the bases are shown in purple, and the DNA backbone and unmodified bases are in teal.

Zoom in of magnified protein

Typical dissociation
for a
SOMAmer Reagent

This graph shows the typical dissociation for a SOMAmer Reagent over time, in this case targeting C3.

Typical Dissociation for a SOMAmer Reagent chart

Thumbnail of SomaLogic Apatmers and Antibodies Comparison Sheet

How do aptamers
compare to antibodies?

Traditionally, affinity-based platforms have used antibodies as reagents. But SomaLogic pioneered the use of aptamers more than 20 years ago to address the challenges researchers face in using antibodies, including performance and natural variability in structure. Download a quick comparison here.

Primary validation and orthogonal confirmation of SOMAmer Reagent specificity

SOMAmer Reagents are protein-binding affinity reagents targeted to a specific protein.

Primary validation of all SOMAmer Reagents

  • Determination of the equilibrium binding affinity dissociation constant (KD)
  • Pulldown assay of cognate protein in buffer using the SOMAmer Reagent
  • Demonstration of buffer dose response in the SomaScan Assay
  • Estimation of endogenous signal in plasma

Orthogonal confirmation

  • At least 66% of SOMAmer Reagents have at least one additional source of orthogonal confirmation
  • Specificity of the SOMAmer Reagent for its cognate protein has been confirmed by orthogonal methods, such as mass spectroscopy and ELISA, for nearly 6,000 reagents

SOMAmer Reagent affinity and specificity
demonstrated by multiple methods

SomaLogic provides the largest number of protein measurements and the greatest number of orthogonally confirmed protein reagents in the proteomics industry.

Primary validation of all SOMAmer Reagents: 11,000 - Chart

Primary validation of 11,000
SOMAmer Reagents

  • Determination of equilibrium binding affinity dissociation constant (KD)
  • Pulldown assay of cognate protein from buffer
  • Demonstration of buffer dose response in the SomaScan Assay
  • Estimation of endogenous cognate protein signals in plasma

Over 6,000 SOMAmer Reagents have at least one additional form of orthogonal confirmation.

Approximately 3,000 SOMAmer Reagents have undergone two or more forms of orthogonal confirmation.

What evidence do we have that SOMAmer Reagents are specific?

What are the advantages of shape-specific proteomics?

How does exquisite specificity enable thousands of protein measurements?