isotopenlabeling

Isotope labeling, sometimes encountered as isotopenlabeling in non-English sources, is a set of techniques that introduce isotopes into molecules to trace their distribution, quantify components, or study reaction mechanisms. The term covers both stable isotopes, which are non-radioactive, and radioactive isotopes, which emit detectable radiation.

Stable isotope labeling uses non-radioactive isotopes such as 2H (deuterium), 13C, 15N, 18O, and 34S. Common approaches include metabolic labeling, where organisms are grown in media enriched with heavy isotopes (for example, 13C- or 15N-labeled nutrients), and chemical labeling, where inert tags containing heavy isotopes are attached to biomolecules. In proteomics, SILAC (stable isotope labeling by amino acids in cell culture) is widely used for quantitative comparisons, while AQUA peptides provide absolute quantification by spiking in isotopically labeled standards. Labeled atoms are tracked by mass spectrometry or NMR to determine fluxes, turnover rates, or molecular interactions.

Radioactive isotope labeling employs radionuclides such as 3H, 14C, 32P, 33P, 35S, 18F, and 11C. Radioisotopes are particularly valuable for in vivo imaging (PET and SPECT), tracer studies, and studies of metabolism, where emissions yield sensitive signals.

Applications span biology, chemistry, medicine, environmental science, and materials research. Advantages include specificity and compatibility with sensitive detection methods, while limitations include cost, potential isotope effects, and, for radionuclides, safety and regulatory requirements. Proper laboratory design and waste handling are essential when working with radioactive labels.