Introduction
The stable isotopes of light elements such as hydrogen, carbon, nitrogen, oxygen and sulfur were widely used since the 1950s and therefore were referred as traditional stable isotope. In contrast, stable isotopes of other metals were referred as non-traditional stable isotopes and they mostly received considerable attentions since the 2000s. There are many kinds of metals elements in nature, most elements in the periodic table consist of multiple stable isotopes, only little elements consist of only one stable isotope (see Fig. 1) [1]. The stable isotope metal elements are commercially available as elemental metal, metal oxides, or metal salts. With developments in multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), applications of metal stable isotope received increasing attentions in the studies of environmental and biological applications.
Fig. 1 Periodic table with selected properties relevant with isotope.
Typical metal stable isotope
- Copper has two stable isotopes, 63Cu and 65Cu, with natural abundances of 69.17% and 30.83%, respectively. Isotopes of 63Cu and 65Cu with enrichments of up to 99% are commercially available.
- Zinc has five stable isotopes, 64Zn, 66Zn, 67Zn, 68Zn, and 70Zn, with natural abundances of 49.17%, 27.73%, 4.04%, 18.45%, and 0.61%, respectively. Isotopically enriched material is available for all five Zn isotopes with enrichment levels that can exceed 95%. Commercially available isotopically enriched Zn is usually in the form of Zn metal (sheets or filings) or micron-sized ZnO powder.
- Silver has two stable isotopes, 107Ag and 109Ag. As the two isotopes 107Ag, 109A have similar natural abundances of ~50%, 107Ag, 109A is equally applicable for labeling purposes. These two isotopes are usually available in the form of Ag metal powder.
- Titanium has five stable isotopes, namely 46Ti, 47Ti, 48Ti, 49Ti, and 50Ti. Except for 48Ti which has the highest natural abundance (73.72%), 46Ti, 47Ti, 49Ti, and 50Ti are all of low natural abundance (8.25%, 7.44%, 5.41%, and 5.18%, respectively).
- Iron has four naturally occurring stable isotopes, namely 54Fe, 56Fe, 57Fe, and 58Fe with natural abundances of 5.80%, 91.72%, 2.20%, and 0.28%.
- Calcium is one of the most-abundant elements and has five naturally stable isotopes, 40Ca, 42Ca, 43Ca, 44Ca, and 46Ca, with respective abundances of 96.941%, 0.647%, 0.135%, 2.086%, 0.004%.
Applications
Nowadays, metal stable isotope as tagging or tracers shows great potential in many applications, especially in biological and environmental fields.
Biological fields
Metal stable isotope tagging is an effective tool in biological field and opened a post-fluorescence era of cytometry. Specially, the metal stable isotope tagging is used in following two fields: (1) multiplex analysis of biomolecule and (2) absolute quantification of biomolecule.
Fig. 2 Historical timeline of analytical strategies in biological fields using metal stable isotope tagging.
(1) Multiplexed assays of biomolecule. In principle, more than 100 metal stable isotopes can be simultaneously and selectively detected without spectral overlap. Therefore, after the research efforts on tagging strategies, multiplex analysis of biomolecules with metal stable isotope tags has been successfully constructed in recent years such as multiplex analysis of protein quantification, enzyme activity, cell interrogation and nucleic acid assays. Thereinto, Liu's group [2] developed the first multiplex nucleic acid assays based on the metal stable isotope labeling strategy without the fabrication of complicated DNA chips. Fifteen clinical disease (cancer, heredopathia, and virus) associated DNA targets were simultaneously detected in homogeneous solution by tagging with Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu stable isotope ions (see Fig. 3a, b).
Fig. 3 Nucleic acid assays based on the metal stable isotope tagging strategy: (a) tagging DNA with lanthanide stable isotope tags; (b) multiplex nucleic acid assay procedures.
(2) Absolute quantification of biomolecules. Absolute quantification of biomolecules is easy to achieve based on metal stable isotope tagging. Absolute quantification of biomolecules provides the data validation and traceability in clinical, environmental, and drug development laboratories, which is feasible by isotope dilution strategy. Today, the absolute quantification of many biomolecules such as nucleic acid, proteins and peptides has been realized by using this strategy.
Environmental fields
Metal-containing engineered nanoparticles (MENPs) have been extensively produced and applied in many sectors. Nevertheless, during the production, transport, use, disposal, and recycling of MENPs, the release of MENPs into the environment is inevitable. Thus, as a class of emerging contaminants, MENPs have drawn considerable attention with regard to their environmental behavior in recent years. Intrinsic labeling of MENPs with stable isotopes metal is a useful tool for the analysis of MENPs environmental behaviors, which has recently become a research focus. For example, the environmental fates of MENPs including dissolution, interaction with natural organic matter, deposition, and adsorption on the sediment have been probed and studied by metal stable isotopes. The uptake, accumulation, distribution, and clearance by organisms and toxicity to organisms of MENPs were also can be evaluated by in vitro and in vivo experiments using stable isotope tracers. Metal stable isotope tracers provide great opportunities to further elucidate the behavior of MENPs in environmental systems [3].
Fig. 4 Schematic diagram of metal stable isotope tracers in analysis of MENPs environmental behaviors (Take zinc stable isotopes as example).
What can we offer?
As a professional supplier of stable isotope-labeled compounds, Alfa Chemistry has always shown great interest in the latest developments in metal stable isotope. Alfa Chemistry has excellent R&D staffs with rich experience who aim to provide high quality and cost-effective metal stable isotope timely. We can offer you with all kinds of metal stable isotopes such as Li, Mg, Ca, Ti, V, Cr, Fe, Ni, Cu, Zn, Ge, Se, Br, Sr, Mo, Ag, Cd, Sn, Sb, Te, Ba, W, Pt, Tl, etc. You can click on our product list for a detailed view. If you do not find the product you want, we also provide you with custom synthesis service. Please contact us, if you are in need of assistance.
References
- Wiederhold, J. G. Metal stable isotope signatures as tracers in environmental geochemistry[J]. Environmental science & technology, 2015, 49(5): 2606-2624.
- Liu, R., et al. Metal stable isotope tagging: renaissance of radioimmunoassay for multiplex and absolute quantification of biomolecules[J]. Accounts of chemical research, 2016, 49(5): 775-783.
- Yin, Y., et al. Isotope tracers to study the environmental fate and bioaccumulation of metal-containing engineered nanoparticles: techniques and applications[J]. Chemical reviews, 2017, 117(5): 4462-4487.
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