Developing new Nanogold-based Test Strip for Environmental and Bio-Monitoring of Mercury (HG) Traces - NANOTEHG -
Final Report Abstract
The excessive use of mercury in small-scale gold mining and increasing emissions from coal-fired power plants still results in high Hg discharges to our environment. Because of its high neurotoxicity at low-levels mercury is still one of the most critical environmental pollutants that need to be monitored globally. Since consumption of contaminated fish is nowadays the main source for general human Hg exposure, monitoring of the hydrosphere is mandatory. Standard analytical methods available for Hg trace determination in waters, however, have several disadvantages, like consumption of highly toxic reagents, time-consuming sample preparation, and bulky instrumentation. Simplified procedures for rapid monitoring of Hg traces in real-world samples are therefore to be developed. Therefore, the aim of this project was the provision of a robust and valid analytical method for determination of Hg traces in aqueous samples that at the same time offers a high selectivity and sensitivity, benefits from reagent-free procedure, and allows ease of handling and minimisation of time-effort. The envisaged procedure was established on basis of a nanogold test-strip that is dipped for a few minutes or less into the sample, accumulates Hg traces in a highly efficient way and can be read-out for Hg quantification afterwards. Quantification was achieved after thermal desorption of mercury from the stick in a specially designed and constructed heating chamber which was connected inline to an atomic fluorescence spectrometer. Hence, completely reagent-free procedure including sorption, desorption and detection was achieved. In the course of the project two individual test strip were prepared on silicon wafers carrying gold nanoparticles (AuNPs) and a mesoporous protective layer. Both sticks were characterised in detail and tested for their application to Hg trace determination in water samples. The top layer of the sticks was either made of silica (SiO2) or titania (TiO2) providing different analytical features. The AuNPs@TiO2 dipstick clearly showed a superior performance with regard to sensitivity due to higher accumulation rate. In addition, Hg trace analysis in natural waters that contain dissolved organic carbon (DOC) using the silica-based test strip suffered from significantly lower accumulation probably due to the formation of stabile Hg-DOC complexes. This problem was solved using the photoactive TiO2 layer instead of silica and treating the sample by UV irradiation during accumulation. Quantitative recovery of mercury in DOC-containing water was possible, which was confirmed also by investigation of real river water. For both sticks all analytical figures of merit were determined, including most importantly trueness and precision. With recovery rates from 92 to 118% and a precision ≤ 3.5 % the developed NanoDip-based method is perfectly feasible of Hg trace analysis in waters. Finally, the achieved analytical performance was compared to other nanomaterial-based approaches recently reported in literature. Particularly, the extremely low detection limit of 0.137 ng L-1 achieved for an accumulation time of only 5 min is remarkable. In this context, it is important to mention that the proposed procedure is adjustable to the Hg concentration range of the sample by adaption of either the active area of the used sticks or even more simple, by adjusting the dipping time. The later can be reduced to a few seconds for samples with elevated Hg concentration. A unique feature of the nanogold-based method is the reagent-free procedure. This ensures low blank values, which is one of the reasons for the high sensitivity and good reproducibility of the method. Another aspect is clearly the sustainability of this approach which does not produce any chemical waste. In addition, the sticks are re-useable for at least 60 cycles.
Publications
- 2016. Environmental monitoring of mercury and its species, International Conference Series on Environmental and Food Monitoring, Hamburg, Germany
Leopold K.
- 2018. New nanogold-modified dipsticks for reagent-free mercury detection in aqueous solution, 5. Interdisziplinäre Doktorandenseminar des Deutschen Arbeitskreises für Analytische Spektroskopie (DAAS), Geestacht, Germany
Stock, V., Mutschler, A., Lindén, M., Leopold, K.
- 2019. Development of mesoporous silica-gold films for trace-level monitoring of mercury in water, 14th International Conference on Mercury as a Global Pollutant, Krakow, Poland
Stock, V., Mutschler, A., Lindén, M., Leopold, K.
- 2019. Mesoporous silica-gold films for trace level monitoring of mercury in water, ANAKON 2019, Münster, Germany
Stock, V., Mutschler, A., Lindén, M., Leopold, K.
- 2019. Mesoporous Silicagold Films for Straightforward, Highly Reproducible Monitoring of Mercury Traces in Water. Nanomaterials 9:35, 1
Mutschler, A., Stock, V., Ebert, L., Björk, E., Leopold, K., Lindén, M.
(See online at https://doi.org/10.3390/nano9010035) - 2019. Sustainable and reagent-free mercury trace determination in natural waters using nanogold dipsticks. Microchemical Journal 147, 253
Schlathauer, M., Friedland, J., Lindén, M., Leopold, K.
(See online at https://doi.org/10.1016/j.microc.2019.03.032) - 2021. Photoactive Titanium Dioxide Films with Embedded Gold Nanoparticles for Quantitative Determination of Mercury Traces in Humic Matter- Containing Freshwaters. Nanomaterials 11:2, 512
Stock, V., Mutschler, A., Lindén, M., Leopold, K.
(See online at https://doi.org/10.3390/nano11020512)
