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. 2019 Jul 24;5:12. doi: 10.1186/s40842-019-0086-7

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© The Author(s). 2019

Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

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Fig. 2 — Illustration of non-competitive “sandwich” immunoassay. a In non-competitive “sandwich” immunoassay, capture antibodies are anchored to a solid phase in the testing tube. Then, the sample containing the studied hormone as well as the signal antibodies are added. b The hormone binds to the capture antibody from one end and to the signal antibody from the other end, forming antibody-hormone-antibody “sandwich”. The unbound signal antibodies is then washed out and the signal from the remaining “sandwiches” is measured. The higher the concentration of the hormone (illustrated in green), the more “sandwiches” will be formed, and thus, the higher signal will be measured. In other words, the stronger the signal, the more of the endogenous hormone is present in the sample and vice versa (i.e. the signal is directly proportional to the hormone concentration)