spICP-MS was recently adopted as a means to detect NPs at ultra low concentration as its detection limit is in the ng/L range. However, spICP-MS fails to differentiate between engineered ENMs composed of high-abundance elements (such as titanium) and their natural counterparts. To ensure that only engineered TiO₂ ENMs are identified in complex media and the environmental compartments of interest to NanoFASE, Ho core–TiO₂ shell (NaHoF4@TiO₂) ENMs were synthesized with the low-abundance element Holmium used as a chemical marker.   

The core–shell design was proposed to achieve a high dopant concentration for better detection while retaining the structural integrity of the ENMs being investigated via the shell. The resulting ENMs consisted of a 60 nm NaHoF₄ core and a 5 nm anatase TiO₂ shell, as determined by TEM, STEM-EDX mapping, and spICP-MS.

NanoFASE partner University of Birmingham demonstrated that these core–shell NaHoF₄@TiO₂ ENMs remain detectable by spICP-MS in the presence of a high background of Ti despite the ENMs being present at an extremely low concentration. The NPs exhibited excellent detectability by spICP-MS at concentrations down to 1 × 10^-3 ng/L even in complex natural environments with high Ti background, such as river water from Birmingham.

The figure presents spICP-MS results relative to NaHoF₄@TiO₂ core-shell ENM dispersions in ultrapure (UP) water and river water. (A) Real-time Ho signal from NaHoF₄@TiO₂ suspension in river water; (B) real-time Ti signal from NaHoF₄@TiO₂ suspension in river water; (C) real-time Ho signal from NaHoF₄@TiO₂ suspension in ultrapure water; (D) real-time Ti signal from NaHoF₄@TiO₂ suspension in ultrapure water; (E) size distribution of NaHoF₄ component detected by spICP-MS; and (F) size distribution of TiO₂ component detected by spICP-MS. Stock suspensions of ENMs were diluted 100 million times with ultrapure water and river water, respectively, from ca. 1.5 mg/mL to ca. 15 ng/L for spICP-MS measurements. River water was collected from the Worcester and Birmingham Canal, near the University of Birmingham, and was used without filtration. From: Cui et al., 2019.

Read more

Cui X, Fryer B, Zhou D, Lodge R, Khlobystov A, Valsami-Jones E, Lynch I (2019) Core-shell NaHoF4@TiO2 NPs: A labelling method to trace engineered nanomaterials of ubiquitous elements in the environment. ACS Applied Materials & Interfaces, 2019, 11, 19452-19461. https://pubs.acs.org/doi/10.1021/acsami.9b03062

Contact

Xianjin Cui

 

 

 

 

Benjamin Fryer

University of Birmingham

 

 

 

 

Iseult Lynch

University of Birmingham

i.lynch@bham.ac.uk