- The Simoa (Single Molecule Array) technique is a highly sensitive digital immunoassay technology that allows for the detection of extremely low concentrations of proteins and other biomolecules, reaching the femtomolar (fM) to attomolar (aM) range.
- It is particularly useful in fields like neurology, oncology, immunology, and infectious disease research, where detecting minute quantities of biomarkers is critical for early diagnosis, monitoring, and understanding disease progression.
- Simoa is conceptually similar to a traditional ELISA but incorporates digital readout and single-molecule detection. It uses paramagnetic beads coated with capture antibodies that specifically bind to the target analyte. These beads are then incubated with a detection antibody conjugated to an enzyme, forming a “sandwich” immunocomplex on the bead if the analyte is present. The beads are then dispersed into a microarray containing thousands of microwells—each designed to hold a single bead. A fluorogenic substrate is introduced, and any enzymatic activity from the bound complex converts the substrate into a fluorescent signal.
- The key innovation in Simoa lies in its digital counting approach. After loading, each well is imaged to detect fluorescence. Wells that contain beads with bound enzyme-labeled complexes emit a fluorescent signal, which is interpreted as a “yes” or “no” response—indicating whether a single molecule of the target was present. This binary readout eliminates much of the background noise associated with analog measurements and allows for extremely precise quantification of low-abundance proteins.
- One of the major advantages of Simoa is its unparalleled sensitivity, making it ideal for detecting biomarkers in bodily fluids where concentrations are too low for conventional assays to measure reliably. For example, it enables the detection of neurological biomarkers like neurofilament light (NfL), amyloid-beta, and tau proteins in blood—previously only measurable in cerebrospinal fluid. In immunology and infectious diseases, Simoa can detect cytokines such as IL-6 or viral proteins at very early stages of infection, even before symptoms appear.
- Commercially, the most widely used Simoa platforms are produced by Quanterix, including the Simoa HD-X and SR-X systems. These platforms are increasingly being integrated into both clinical research and diagnostics due to their high sensitivity, specificity, and ability to work with very small sample volumes.
