| AVS 65th International Symposium & Exhibition | |
| Applied Surface Science Division | Monday Sessions |
| Session AS-MoM |
| Session: | Quantitative Surface Analysis |
| Presenter: | Shin Muramoto, National Institute of Standards and Technology (NIST) |
| Authors: | S. Muramoto, National Institute of Standards and Technology (NIST) J. Bennett, National Institute of Standards and Technology (NIST) |
| Correspondent: | Click to Email |
Secondary ion mass spectrometry (SIMS) has been successfully used to detect metal nanoparticles in a wide array of organic matrices such as in biological cells, tissue, and within polymer films. However, there are also instances when the nanoparticles cannot be detected at all, presumably due to a combination of charge competition with salts, sample charging, type of primary ion source, and ion dose density. For example, 150 nm Au nanoparticles (AuNPs) embedded in soil nematodes could easily be detected and resolved in a dynamic SIMS instrument using a Cs+ ion source with a secondary ion yield of 10-12, but no signal could be generated when a ToF-SIMS instrument equipped with a Bi3+ ion source was used, even when the sample was covered with a layer of Cs to enhance signal. To test what factors influence the ionization of AuNPs and to identify the ion dose density threshold for detection, a test sample was prepared through inkjet-printing of precisely measured amount of AuNPs onto porcine skin gelatin, a surrogate for biological tissue. By systematically changing the chemistry of the AuNP solution with solutes such as salts, it is possible to see their effect on nanoparticle ionization. The test sample can also be used for the quantification of nanoparticles by changing their concentrations, and see the effects of depth profiling in quantification by changing the distribution of nanoparticles in 3-dimensional space or position inside the film. The ultimate objective of this study is to create a test sample for the spatially resolved quantification of nanoparticles in a biologically relevant environment, to be able to quantify the number of particles in a given area without resorting to high lateral resolution instruments. The effort will also develop SIMS instrumentation into a tool that can be used for determining the pharmacokinetics and biodistribution of nanoparticles in tissue. Preliminary analysis using a ToF-SIMS instrument with a Bi3+ ion source showed that the mere presence of gelatin reduced the secondary ion yield of AuNPs by an order of magnitude. In addition, increasing the concentration of Na+ from 10-6 M to 10-3 M led to a rather linear decrease in the secondary ion yield from 10-13 to 10-15, consistent with the effect of salts on analyte response in an electrospray ionization system. [1] For the dynamic SIMS, the presence of gelatin had no noticeable effect on secondary ion yield of the nanoparticles.
[1] Constantopoulos, T. L.; Jackson, G. S.; Enke, C. G. Effects of Salt Concentration on Analyte Response using Electrospray Ionization Mass Spectrometry. 1999, , 625-634.