An insight into the determination of size and number concentration of silver nanoparticles in blood using single particle ICP-MS (spICP-MS): feasibility of application to samples relevant to in vivo toxicology studies

Abstract

Toxicological studies concerning nanomaterials in complex biological matrices usually require a carefully designed workflow that involves handling, transportation and preparation of a large number of samples without affecting the nanoparticle (NP) characteristics, as well as measurement methods that enable their reliable characterisation. This work describes method development for the determination of number concentration and size of silver nanoparticles (AgNP) in blood for the purpose of application to the typical workflow of an in vivo toxicology assessment involving blood-containing AgNP and Ag(I) leached out from medical devices. A systematic comparison of single particle detection using millisecond versus microsecond dwell times in the presence of different ionic Ag [Ag(I)]-to-AgNP ratios by spICP-MS was undertaken to achieve sufficient selectivity for the determination of NP number concentration. This was achieved for the first time in a complex media such as 2.5% tetramethylammonium hydroxide (TMAH)/0.1% Triton X-100 (v/v) diluent, which was proven to preserve nanoparticle stability upon 8 days of storage following AgNP quantitative extraction from the blood matrix. The potential of microsecond dwell time for improved discrimination of AgNP (40 nm) from Ag(I) was demonstrated for ionic to nanoparticle ratios [Ag(I)/AgNP] of up to 106-fold. For NP sizing, a systematic study of the impact of matrix-matched ionic calibration on the derived particle size by spICP-MS is also described. Three different ionic calibration media including 1% HNO₃ (v/v), 1 mM trisodium citrate and 2.5% TMAH/0.1% Triton X-100 (v/v) were tested. Student t-test evidenced statistically significant differences between the slope of the calibration curve of Ag(I) in TMAH/Triton X-100 compared to HNO₃ and trisodium citrate matrices, whereas no significant differences were found between the two latter media. Moreover, a good agreement was found between the particle diameter derived from spICP-MS following ionic calibration in TMAH/Triton X-100 and the diameter obtained with transmission electron microscopy (TEM), demonstrating the importance of matrix-matched calibration for NP size determination in a complex matrix using spICP-MS. Number concentration recovery measurements on blood samples spiked with AgNP and size measurements both using spICP-MS demonstrated the feasibility of the methodology developed here for potential future application to AgNP characterisation in toxicology research.