Immunoassay
The ultimate sensitivity of any immunoassay depends on the properties of the antibody used. Most immunoassays do not fully achieve the potential sensitivity of the antibody for two reasons. Either the readout method lacks the sensitivity to fully utilize the antibody's ability or competition is limiting the assay sensitivity. The Kinetic Exclusion Assay (KinExA) prevents competition from interfering, and the measurement sensitivity (sub pM) can take full advantage of extremely tight binding antibodies1.
In practice KinExA has been shown to be 10 to 1000 fold more sensitive than ELISA using the same reagents2. A study was conducted in Japan at the Central Research Institute of the Electric Power Industry (CRIEPI) and funded by the New Energy and Industrial Technology Development Organization (NEDO). The study compared different immunoassay systems by sending identical reagents to outside labs and analyzing the results of the most sensitive immunoassay for each set of reagents. The labs used were Biacore, for an SPR based immunoassay, Sapidyne, for a KinExA based assay, and Kyoto Electronics Manufacturing (KEM) for ELISA. For all 4 sets of reagents the KinExA assay was the most sensitive and had the widest dynamic range3. In fact, KEM has since acquired a license to use KinExA for their commercial dioxin measurement system because of the improved sensitivity, speed, and accuracy compared to ELISA.
2. Blake D.A., Jones R.M., Blake R.C., Pavlov A.R., Darwish I.A., Yu H. 2001. Antibody-based sensors for heavy metal ions. Biosens Bioelectron 16: 799-809. http://www.ncbi.nlm.nih.gov/pubmed/11679258
3. Glass T.R., Ohmura N., Saiki H. 2007. Least detectable concentration and dynamic range of three immunoassay systems using the same antibody. Anal Chem 79: 1959. Figure 4. http://www.ncbi.nlm.nih.gov/pubmed/17256970