ICP-MS as a new tool for the determination of gold nanoparticles in bioanalytical applications

Abstract

Nanotechnology is of great importance and still growing interest to the analytical community. Especially gold nanoparticles have become an important tool in medical and bioanalytical applications owing to their unique physical and chemical properties [1]. These particles can be conjugated with biomolecules and serve as chemical anchors and elemental markers. Recently, the importance of gold nanoparticles as elemental tags for proteomics was outlined [2]. In these applications, functional groups in biomolecules are tagged with nanoparticles and determined quantitatively via inductively coupled plasma mass spectrometry (ICP-MS). ICP sources, especially when combined with massspectrometric detection, provide high sensitivity and robustness and are excellent tools for elemental analysis. Analyte concentrations in the sub-parts-per-trillion level can be determined by ICP-MS with a working range over 9 orders of magnitude. The signal intensities obtained are highly selective for the element observed and nearly independent of the sample matrix, which is important for bioapplications where elemental markers are embedded in complex organic matrices. Both ICP-MS and ICP optical emission spectrometry (ICP-OES) are well suited to determine the concentration of nanoparticles and nanoparticle-based elemental markers. However, ICP-MS is about 3 orders of magnitude more sensitive than ICPOES, which in turn is more rugged and can handle higher total dissolved solids contents. For applications where maximum detection power is required, ICP-MS is the method of choice. Both colloidal and ionic solutions may be analyzed with ICP spectrometry. The ICP can easily vaporize, atomize and ionize nanoparticles with radii of typically 5–25 nm in aqueous or organic solutions. However, it has been observed that gold nanoparticles show a higher adsorption behavior in sample introduction and preparation systems if they are made of materials other than quartz or borate glass. Porous plastic walls result in a high loss of particle concentration. In contrast, ionic gold shows high memory effects and analyte loss in quartz-based vessels and spray chambers. Therefore, analysts are advised to carefully select the material for the sample preparation vessels and the sample introduction system, especially if ionic and colloidal species are analyzed side by side. Overall, the ICP is a fast and reliable technique for the quantification of gold nanoparticles in solution. In the following sections, recent applications in the field of bionanotechnology are summarized, and current as well as future trends for plasma spectrometry are outlined.