Table 1.
Summary of the immunomagnetic reduction and single molecule array technologies
| Assay characteristics | IMRa | SIMOAa |
|---|---|---|
| Assay principles | The IMR assay measures the change in magnetic susceptibility over time caused by the association of antigen with antibody-coated paramagnetic nanobeads | Digital ELISA counts antibody coated paramagnetic microbeads that have undergone a procedure similar to conventional ELISA techniques |
| Diameter of magnetic beads | 50–60 nm | 2.7 μm |
| Capture antibodies |
Tau: Anti-tau (Sigma, St. Louis, MO; T9450) Aβ42: Anti-β amyloid 37–42 (ABCAM, Cambridge, UK; ab34376) Aβ40: Anti-β amyloid (Sigma; A3981) [61] |
Tau: Tau5 targeting a linear epitope in the mid-region of all tau isoforms Aβ42/Aβ40: Antibodies targeting N-terminus of Aβ |
| Detection antibodies | None |
Tau: HT7 and BT2 targeting linear epitopes in the N-terminal region of T-tau Aβ42/Aβ40: biotinylated C-terminal-specific antibodies |
| Washing steps | None | Two 3-step washes, and one 8-step wash with 5× phosphate buffered saline + 0.1% Tween-20 |
| Type of signals for detection | Magnetic susceptibility detected by SQUID magnetometer | Digital counting of enzyme-labeled and unlabeled microbeads via presence and absence of fluorescent substrate |
| Equipment capacity | 36 Wells (XacPro-S) |
96-well plate (four 24-array discs) (Simoa HD-1) [63] |
| Low limit of detection |
Tau: 0.002 pg/ml Aβ42: 7.53 pg/ml Aβ40: 4.91 pg/ml |
Tau: 0.019 pg/ml Aβ42: 0.044 pg/ml Aβ40: 0.522 pg/ml |
| Low limit of quantification | Information not available |
Tau: 0.061 pg/ml Aβ42: 0.137 pg/ml Aβ40: 1.23 pg/ml |
| Assay range |
Tau: 0.002–2500 pg/ml Aβ42: 7.53–50,000 pg/ml Aβ40: 4.91–500 pg/ml |
Tau: 0–360 pg/ml Aβ42: 0–400 pg/ml Aβ40: 0–800 pg/ml |
| Sample volume (plasma) |
Tau: 40 μl Aβ42: 60 μl Aβ40: 40 μl |
Tau: 45.5 μl Aβ42: 32.5 μl Aβ40: 32.5 μl |
| Dilution factor (plasma) |
Tau: threefold dilution Aβ42: twofold dilution Aβ40: threefold dilution |
Fourfold dilution for all analytes in an automatic procedure |
IMR, Immunomagnetic reduction assay; SIMOA, single molecule array assay; SQUID, superconducting quantum interference device; ELISA, enzyme-linked immunosorbent assay; T-tau, total tau
aInformation in this table was obtained from the websites www.magqu.com and www.quanterix.com, and in the published studies which used these technologies, as shown in the table