Nanoparticles - a target for speciation analysis

Background:
Chemical species are defined by the International Union of Pure and Applied Chemistry (IUPAC) as “specific form of an element defined as to isotopic composition, electronic or oxidation state, and/or complex or molecular structure”. The speciation of elements is mandatory for understanding their mobility in the environment, their uptake by organisms, their biological activities and toxicity. Nanoparticles (NPs) are discrete solid pieces of material with at least one dimension in the size range of 1 to 100 nm. Inorganic NPs can be considered a distinct chemical species of elements themselves, and their analysis can therefore be discussed as part of speciation analysis.  

In this sense the most simple analytical task is the differentiation of the particular species from the dissolved species. However, more specific characterization is needed to understand the bahavior of NPs in different environmental compartments or organisms.

Nanoparticle size: The size of nanoparticles is critically important in various fields and applications due to the profound impact it has on their properties, behaviors, and performance. Here are some key reasons why nanoparticle size is important:

• Surface Area-to-Volume Ratio: As nanoparticles get smaller, their surface area relative to their volume increases significantly. This high surface area is advantageous for various applications, including catalysis, sensors, and drug delivery, as it provides more active sites for interactions with other substances.
• Optical Properties: Nanoparticle size can strongly influence their optical properties, such as absorption, scattering, and emission of light. This is crucial in fields like nanophotonics, plasmonics, and the development of nanoscale optical materials.
• Electromagnetic Properties: In nanoelectronics and nanomaterials, the size of nanoparticles can affect their electrical and magnetic properties, making them suitable for specific electronic or magnetic applications.
• Catalysis: Smaller nanoparticles often exhibit higher catalytic activity due to their increased surface area, making them valuable in catalytic reactions.
• Drug Delivery: The size of nanoparticles is critical in drug delivery systems, as it affects their ability to cross biological barriers, target specific cells or tissues, and release drugs in a controlled manner.
• Toxicity and Biocompatibility: In the field of nanotoxicology and nanomedicine, nanoparticle size can significantly influence their toxicity and biocompatibility. Smaller nanoparticles may have different interactions with biological systems compared to larger ones.
• Stability and Aggregation: Nanoparticle size can impact their stability in colloidal solutions. Smaller nanoparticles are often more prone to aggregation due to increased Brownian motion, which can affect their performance and applications.
• Drug Solubility and Bioavailability: In pharmaceuticals, the size of nanoparticles can improve the solubility of poorly water-soluble drugs, increasing their bioavailability.
• Imaging: Nanoparticle size is crucial in biomedical imaging techniques like magnetic resonance imaging (MRI) and computed tomography (CT) scanning, as it affects the contrast and distribution of imaging agents.
• Mechanical Properties: In nanomaterials and nanocomposites, nanoparticle size can influence the mechanical properties of the materials, such as strength, stiffness, and toughness.
• Transport and Diffusion: The size of nanoparticles affects their transport and diffusion properties, which is important in applications like filtration, membrane technologies, and drug transport through biological barriers.
• Environmental and Ecological Impact: In environmental science, understanding the size distribution of nanoparticles is critical for assessing their transport, behavior, and potential ecological impact in natural systems.

In summary, the size of nanoparticles is a fundamental parameter that influences their performance and behavior in various applications, making it a critical factor to consider when designing, characterizing, and utilizing nanoparticles in science and technology.


Engineered nanomaterials are nowadays widely integrated into consumer and industrial products. Besides cosmetic and cleaning products, food is a major source of exposure of consumers to NPs through ingestion. Also nanomaterials released to the environment can be taken up by organisms and re-enter the food web. Even further, NPs can be formed naturally in the environment or in-vivo by the organisms themselves. In order to characterize and quantify NPs in products and in the environment, several analytical techniques have been developed or adapted.

Among these techniques are single-particle ICP-MS and ICP-MS coupled to separation techniques like field flow fractionation (FFF), capillary electrophoresis (CE), hydrodynamic chromatography (HDC) and reversed phase HPLC. Bio-imaging techniques such as laser ablation ICP-MS, nanoscale secondary ion mass spectrometry (nano-SIMS) and X-ray fluorescence support the qualitative analysis of NPs, whereas electron microscopy is typically considered the gold standard when it comes to determination of particle sizes. Electron microscopy provides additional information on particle shape, crystal structure and if
combined with Energy Dispersive X-ray Spectroscopy (EDS), chemical composition can be determined.

Especially challenging is the sample preparation as NPs can agglomerate, aggregate, dissolve or change their crystalline structure or chemical composition. They interact with matrix components and surfaces and might undergo changes.