Exploring the potential of high-resolution continuum source graphite furnace atomic absorption spectrometry for the analysis of gold nanoparticles in the single-digit size range

Gold nanoparticles (AuNPs) exhibit unique properties due to their high surface-to-volume ratio, opening a wide range of innovative applications and requiring fast, sensitive and robust analytical techniques for their monitoring. In recent years, high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS-GFAAS) has proven to be useful for this task. In this study, its applicability to detect and size very small AuNPs in the single-digit size range is shown. This is of particular interest, given that alternative techniques often lack sufficiently low size detection limits. The time of first inflection point (t ip ) was introduced as a new sizing parameter in GFAAS, particularly sensitive within the tested size range of 2.2 nm to 10.1 nm regardless the coating of the AuNPs and moreover not significantly affected by the presences of Au(III) ions. Experimentally, a minimum distinguishable size difference of 1.6 nm could be demonstrated, and we predict a theoretical value of 0.4 nm. As a reference method to determine the size of the very small AuNPs, high-resolution transmission electron microscopy (HRTEM) was used. Additionally, the mass proportions of bimodal mixtures of AuNP suspensions were recovered by deconvolution of the transient absorbance signals. For total gold quantification, a mass quantification limit of 0.8 pg was achieved, equivalent to 20 ng L −1 in liquid samples and independent of the introduced gold species. In summary, the proposed method has demonstrated its significant potential as a screening tool for the simultaneous speciation, quantification and sizing of very small AuNPs with minimal sample preparation requirements.