Radioactive tracer
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A radioactive tracer, also called a radioactive label, is a substance containing a radioisotope that is used to measure the speed of chemical processes and to track the movement of a substance through a natural system such as a cell or tissue.[1] A number of different radioactive forms of hydrogen, carbon, phosphorus, sulfur, and iodine are commonly used in applications including biochemical assays, metabolism studies, and medical diagnostics.
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[edit] History
Radioactive tracing was developed by George de Hevesy, who won the 1943 Nobel Prize for Chemistry for his pioneering work using radioactive tracers to study metabolic processes in plants and animals.
[edit] Methodology
Radioactive tracers are compounds that contain one or more radioactive atoms that allows for easy detection and measurement. Tracers are frequently used to track the localization of a specific compound or to trace the path of a compound through a series of chemical reactions. A radioactive tracer is identical in chemical composition to the compound of interest and is administered in minute amounts that do not perturb the experimental system. The tracer behaves in exactly the same way as an unlabeled molecule, but the tracer molecule continually gives off radiation that can be detected with a Geiger counter, scintillation counter or other type of radiation detection instrument.
[edit] Tracer isotopes
A number of different radioisotopes are used as radioactive tracers depending on the application.
[edit] Hydrogen
Tritium (3H) is a radioactive form of hydrogen that contains one proton and two neutrons in its nucleus. Tritium decays into helium-3 by emission of a low energy beta particle. The low energy of the emitted particle causes tritium to have low detection efficiency by scintillation counting. However, due to the abundance of hydrogen in organic compounds, tritium is frequently used as a tracer in biochemical studies.
[edit] Carbon
Carbon-11 is a radioactive form of carbon that contains five neutrons and six protons in its nucleus. Carbon-11 decays into boron-11 by positron emission. Carbon-11 is frequently used as a tracer in positron emission tomography, an imaging technique that allows for three-dimensional imaging of functional processes in the human body.
Carbon-14 is a radioactive form of carbon that contains eight neutrons and six protons in its nucleus. Carbon-14 decays into nitrogen-14 by emission of a beta particle. Carbon-14 has been used as a tracer in both medical and scientific tests. Carbon-14 is frequently used to trace carbons through metabolic pathways.
[edit] Phosphorus
Phosphorus-32 is a radioactive form of phosphorus that contains 17 neutrons and 15 protons in its nucleus. Phosphorus-32 decays into sulfur-32 by emission of a beta particle. Phosphorus-32 is frequently used to label amino acids and phosphoproteins and is commonly used to study protein phosphorylation by kinases in biochemistry. Phosphorus-32 emits a relatively high energy beta particle, and a number of safety precautions are needed when working with it.
Phosphorus-33 is a radioactive form of phosphorus that contains 18 neutrons and 15 protons in its nucleus. Phosphorus-33 decays into sulfur-33 by emission of a beta particle. Phosphorus-33 is used similarly to phosphorus-32, except that it emits less energetic beta particles, allowing for higher resolution assays and requiring less usage of safety equipment. Phosphorus-33 is less common and more expensive to produce than phosphorus-32.
[edit] Sulfur
Sulfur-35 is a radioactive form of sulfur that contains 18 neutrons and 16 protons in its nucleus. Sulfur-35 decays into chlorine-35 by emission of a beta particle. Sulfur-35 is frequently used as a tracer in biochemical experiments, where it is used to label amino acids and nucleic acids containing sulfur. Alternatively, a labeled sulfur can replace an oxygen in a phosphate group on a given nucleotide to create a thiophosphate which has very similar biochemical properties to the original phosphate group.
[edit] Iodine
Iodine-123 is a radioactive form of iodine that contains 70 neutrons and 53 protons in its nucleus. Iodine-123 decays into tellurium-123 by electron capture, producing gamma rays. Iodine-123 is used in nuclear medicine imaging, specifically to study thyroid function. Because of its short half-life, Iodine-123 is the most frequently used isotope in thyroid function studies.
Iodine-125 is a radioactive form of iodine that contains 72 neutrons and 53 protons in its nucleus. Iodine-125 decays into tellurium-125 by electron capture, producing gamma rays. Iodine-125 is frequently used in radioimmunoassays because of its relatively long half-life and ability to be detected with high sensitivity by gamma counters.[2]
[edit] Applications
[edit] Industry and research
[edit] Metabolic Research
In metabolism research, radioactive tracers are frequently used in glucose clamps to measure rates of glucose uptake, fatty acid synthesis, and other metabolic processes. Tritium and carbon-14-labeled water and glucose are commonly used tracers for metabolic clamp studies.[3] While radioactive tracers are sometimes still used in human studies, stable isotope tracers such as carbon-13 are more commonly used in current human clamp studies. Radioactive tracers are also used to study lipoprotein metabolism in humans and experimental animals.[4]
[edit] Medical applications
[edit] Diagnostics
In medicine, tracers are applied in a number of tests, such as technetium-99 in autoradiography and nuclear medicine, including single photon emission computed tomography (SPECT), positron emission tomography (PET) and scintigraphy. The urea breath test for helicobacter pylori commonly used a dose of carbon-14 labeled urea to detect h. pylori infection. If the labeled urea was metabolized by h. pylori in the stomach, the patient's breath would contain labeled carbon dioxide. In recent years, the use of the stable isotope carbon-13 has become the preferred method to minimize patient exposure to radiation.[5]
[edit] See also
[edit] References
- ^ Rennie M (1999). "An introduction to the use of tracers in nutrition and metabolism". Proc Nutr Soc 58 (4): 935–44. doi:10.1017/S002966519900124X. PMID 10817161.
- ^ Gilby, ED; Jeffcoate, Edwards (July 1973). "125-Iodine tracers for steroid radioimmunoassay.". Journal of Endocrinology 58 (1): xx. PMID 4578967.
- ^ Kraegen, EW; Jenkins, Storlien, Chisholm (1990). "Tracer studies of in vivo insulin action and glucose metabolism in individual peripheral tissues.". Horm Metab Res Suppl. 24: 41–8. PMID 2272625.
- ^ Magkos, F; Sidossis (September 2004). "Measuring very low density lipoprotein-triglyceride kinetics in man in vivo: how different the various methods really are.". Curr Opin Clin Nutr Metab Care 7 (5): 547–55. doi:10.1097/00075197-200409000-00007. PMID 15295275.
- ^ Peeters, M (1998). "Urea breath test: a diagnostic tool in the management of Helicobacter pylori-related gastrointestinal diseases". Acta Gastroenterol Belg 61 (3): 332–5. PMID 9795467.
[edit] Bibliography
http://www.scienceclarified.com/Qu-Ro/Radioactive-Tracers.html#ixzz0yOctPz00
[edit] External links
- National Isotope Development Center U.S. Government resources for radioisotopes - production, distribution, and information
- Isotope Development & Production for Research and Applications (IDPRA) U.S. Department of Energy program sponsoring isotope production and production research and development
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