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There are numerous commercial and industrial applications of nanoparticles in use today. However, despite their infinitesimally small size, these particles can pose significant risks to humans and other animals, plant life, ecosystems, and industrial processes. Close analysis of the elemental composition of these particles is therefore required to ensure safe and sustainable development of nanotechnology applications.
A team of researchers from the Dutch food safety institute RIKILT, based in Wageningen University & Research in the Netherlands, TOFWERK, a Swiss headquartered time-of-flight mass spectrometry firm, and Fluidigm Corp, an American biological research equipment manufacturer, and supplier, has tested methods for this crucial analysis of nanoparticles’ elemental composition.
What is a nanoparticle?
There is currently considerable scientific and industrial interest in nanoparticles, as they effectively bridge atomic or molecular structures to bulk materials. This makes them able to impart properties onto the bulk materials.
Nanoparticles measure between one and one hundred nanometers (nm) in at least one dimension, and in nanotechnology, the term is used to describe discrete objects that act as one unit in transport and with the same properties. The definition of a nanoparticle includes the interfacial layer that surrounds the particle itself, which usually consists of ions, inorganic molecules, and organic molecules referred to as stabilizers, capping, and surface ligands, or passivating agents.
Nanoparticles are incredibly small. “Nano-” means one-billionth, and 1 nm is 10-9 m (one billionth of a meter). One sheet of paper is approximately 100,000 nm thick, and a strand of human hair is about 80,000 nm thick. Comparatively, if a marble was 1 nm in diameter, then our planet would only be one meter thick.
Nanoparticles are commonly added to consumer products for a variety of reasons in a variety of industries. A few examples include silver nanoparticles included in sports textiles for better fabric performance against odor, zinc oxide nanoparticles added to sun cream for its superior ultraviolet (UV) light protection, and titanium dioxide nanoparticles included in various materials to create the so-called self-cleaning effect.
The best method for analyzing the elemental composition of nanoparticles
The best ways to analyze the elemental composition of nanoparticles are found in the family of techniques known as mass spectrometry. Mass spectrometry (MS) measures the mass-to-charge ratio of ions in the interfacial layer and is used to identify atoms or molecules in the sample.
MS methods use various techniques to ionize the sample, causing its molecules to charge and fragment. These molecules are then subjected to one of a few methods for mass selection, which separates them according to their mass-to-charge ratio. The now separate groups of molecules can be analyzed to provide information about the elemental composition of the specimen.
In last year’s study, researchers tested two methods of single-particle inductively coupled plasma mass spectrometry (spICP-MS). ICP refers to the means for creating ions to interact with the material and involves the generation of electrically neutral plasma from argon gas. The researchers tested this method using time-of-flight (TOF) and quadrupole (Q) analyzers.
TOF analyzers measure the time taken by particles to reach the detector after an electric field has accelerated them. Q analyzers, however, create a radio frequency quadrupole (one sequence of electrical current) field between four rods set parallel to each other which effectively filters different elements through the instrument.
The team found that both methods of mass spectrometry were effective at analyzing the elemental composition of single nanoparticles. However, the TOF method was able to detect smaller particles than the Q method, with 29 nm titanium, 14 nm molybdenum and 7 nm gold identified in the spICP-TOFMS analysis. They concluded that spICP-TOFMS is: “The first choice for multi-element detection of unknown nanoparticle.”
- Bustos, A.R.M., and Winchester, M.R. (2016).Single-particle-ICP-MS advances. Analytical and Bioanalytical Chemistry, 408(19), pp.5051–5052.
- Naasz, S., Weigel, S., Borovinskaya, O., Serva, A., Cascio, C., Undas, A.K., Simeone, F.C., Marvin, H.J.P., and Peters, R.J.B. (2018). Multi-element analysis of single nanoparticles by ICP-MS using quadrupole and time-of-flight technologies. Journal of Analytical Atomic Spectrometry, 33(5), pp.835–845.