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Isotope-labeled immunoassays without radiation waste
Publish date: Mar 14, 2000
Author: Guomin Shan, Wei Huang, Shirley J. Gee, Bruce A. Buchholz, John S. Vogel, and Bruce D. Hammock
Source: Proc Natl Acad Sci U S A. 2000 Mar 14;97(6):2445-9.

The practice of immunoassay has experienced a widespread transition from radioisotopic labeling to nonisotopic labeling over the last two decades. Radioisotope labels have drawbacks that hamper their applications: (i) perceived radiation hazards of reagents, (ii) regulatory requirements and disposal problems of working with radioactive materials, and (iii) short shelf-life of the labeled reagents. The advantage of isotopic labeling is the incorporation into analytes without altering structure or reactivity, as is often the case with ELISA or fluorescent detection systems. We developed a format for isotope label immunoassay with the long-life isotope (14)C as the label and accelerator mass spectrometer (AMS) as the detection system. AMS quantifies attomole levels of several isotopes, including (14)C. With this exquisite sensitivity, the sensitivity of an immunoassay is limited by the K(d) of the antibody and not the detection system. The detection limit of the assays for atrazine and 2,3,7,8-tetrachlorodibenzo-p-dioxin was 2.0 x 10(-10) M and 2.0 x 10(-11) M, respectively, approximately an order of magnitude below the standard enzyme immunoassay. Notably, <1 dpm (0.45 pCi) of (14)C-labeled compound was used in each assay, which is well below the limit of disposal (50 nCi per g) as nonradioactive waste. Thus, endogenous reporter ligands quantified by AMS provide the advantages of an RIA without the associated problems of radioactive waste.

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