Determination of metallic nanoparticles in biological samples by single particle ICP-MS: a systematic review from sample collection to analysis

Abstract

A systematic review of the use of single particle ICP-MS to analyse engineered nanomaterials (ENMs) in biological samples (plants, animals, body fluids) has highlighted that efforts have focused on a select few types of ENMs (e.g., Ag and TiO₂) and there is a lack of information for some important tissues (e.g., reproductive organs, skin and fatty endocrine organs). The importance of sample storage is often overlooked but plays a critical role. Careful consideration of the ENM and matrix composition is required to select an appropriate protocol to liberate ENMs from a tissue whilst not promoting the transformation of them, or genesis of new particulates. A 'one size fits all' protocol, applicable to all possible types of ENM and biological matrices, does not seem practical. However, alkaline-based extractions would appear to show greater promise for wide applicability to animal tissues, although enzymatic approaches have a role, especially for plant tissues. There is a lack of consistency in metrics reported and how they are determined (e.g. size limit of detection, and proportions of recovery), making comparison between some studies more difficult. In order to establish standardised protocols for regulatory use, effort is needed to: develop certified reference materials, achieve international agree on nomenclature and the use of control samples, and to create a decision tree to help select the best sample preparation for the type of tissue matrix.

Fig. 1. Publication trend showing the number of papers published each year where ENMs were extracted from a biological matrix and analysed by spICP-MS. Bars outlined in solid, dashed and dotted lines indicate studies that looked at animal organs and tissues, plant tissues and biofluids respectively.

Fig. 2. Overview of systematic review process. Web of science was used to identify all peer-reviewed papers associated with the indicated topics published since 2010. The search was conducted January 2021. The numbers show how many papers were identified with each criterion.

Fig. 3. A summary of the sample preparation approaches used in the literature and the biological matrices and ENM combinations to which they have been applied. Boxes with multiple symbols indicate combinations where different approaches have been used in different studies, full details can be seen in Tables 1–3.

Fig. 4. A comparison of spICP-MS LOD_size determined theoretically by Lee et al. to those reported in the literature cited in Tables 1–3.

Fig. 5. Example time scans of Ag extracted from the mucosa of the mid intestine of rainbow trout following exposure to no added Ag (control, A), 1 mg L⁻¹ AgNO₃ (B) or 1 mg L⁻¹ Ag ENMs (C). Note, the Ag from the AgNO₃ treatment remains dissolved, and the Ag extracted from the Ag ENM treatment remains particulate. Also note the control sample (A) is on a different scale. The extraction was performed according to Clark et al., using 20% TMAH + 5 mM CaCl₂. Note the absence of particles in (B) indicates the Ag has remained in the dissolved form.

Fig. 6. Summary of key findings and recommendations.