Manja Vogel

Lanthanides and actinides are emerging contaminants, but little is known about their uptake and distribution by plants and their interactions in the rhizosphere. To better understand the fate of these metals in plants, the bioassociation of 2, 20 and 200 µM Eu(III) by five hydroponically grown crops endemic to Europe was assessed. The metal’s concentration and its speciation were monitored by inductively coupled plasma mass spectrometry and laser spectroscopy, whereas root exudation was investigated by chromatographic methods. It has been shown, that Eu(III) bioassociation is a two-stage process, involving rapid biosorption followed by accumulation in root tissue and distribution to the stem and leaves. Within 96 h of exposure time, the plant induces a change of Eu(III) speciation in the liquid medium, from a predominant Eu(III)aquo species, as calculated by thermodynamic modelling, to a species with longer luminescence lifetime. Root exudates such as citric, malic, and fumaric acid were identified in the cultivation medium and affect Eu(III) speciation in solution, as was shown by a change in the thermodynamic model. These results contribute to a comprehensive understanding of the fate of lanthanides in the biosphere and provide a basis for further investigations with the chemical analogues Cm(III) and Am(III).

Lanthanides and actinides are emerging contaminants, but little is known about their uptake and distribution by plants and their interactions in the rhizosphere. To better understand the fate of these metals in plants, we assessed the bioassociation of 2, 20 and 200 µM Eu(III) by five hydroponically grown crops endemic to Europe. The metal’s concentration and its speciation was monitored by inductively coupled plasma mass spectrometry and laser spectroscopy, whereas root exudation was investigated by chromatographic methods. It has been shown, that Eu(III) bioassociation is a two-stage process, involving rapid biosorption followed by accumulation in root tissue and distribution to the stem and leaves. Within 96 h of exposure time, the plant induces a change of Eu(III) speciation in the liquid medium, from a predominant Eu(III) aquo species, as calculated by thermodynamic modelling, to a species with longer luminescence lifetime. Root exudates such as citric, malic, and fumaric acid were identified in the cultivation medium and affect Eu(III) speciation in solution, as was shown by a change in the thermodynamic model. These results contribute to a comprehensive understanding of the fate of lanthanides in the biosphere and provide a basis for further investigations with the chemical analogues Cm(III) and Am(III).

The extensive use of lanthanides in science, industry and high-technology products is accompanied by an anthropogenic input of rare earth elements into the environment. Knowledge of a metal's environmental fate is essential for reasonable risk assessment and remediation approaches. In the present study, Eu(III) was representatively used as a luminescent probe to study the chemical environment and to elucidate the molecular interactions of lanthanides with a suspension cell culture of Nicotiana tabacum BY-2. Biochemical methods were combined with luminescence spectroscopy, two-dimensional microspectroscopic mappings, and data deconvolution methods to resolve the bioassociation behavior and spatial distribution of Eu(III) in plant cells. BY-2 cells were found to gradually take up the metal after exposure to 100 μM Eu(III) without significant loss of viability. Time-resolved luminescence measurements were used to specify the occurrence of Eu(III) species as a function of time, revealing the transformation of an initial Eu(III) species into another after 24 h exposure. Chemical microscopy and subsequent iterative factor analysis reveal the presence of four distinct Eu(III) species located at different cellular compartments, e.g., the cell nucleus, nucleolus and cell walls, which could be assigned to intracellular binding motifs. In addition, a special type of bioaccumulation occurs through the formation of a Eu(III)-containing oxalate biomineral, which is already formed within the first 24 hours after metal exposure. Oxalate crystals were also obtained in analogous experiments with Gd and Sm. These results indicate that tobacco BY-2 cells induce the precipitation of metal oxalate biominerals for detoxification of lanthanides, although they also bind to other cellular ligands at the same time.

Chemical microscopy provides spatial discrimination of individual europium(iii) species – proteinaceous europium(iii) complexes (orange) and an extracellular europium(iii)-eDNA complex (purple) – in the Shewanella-calcite-europium(iii) system.

Using two different types of impedance biochips (PS5 and BS5) with ring top electrodes, a distinct change of measured impedance has been detected after adding 1–5 µL (with dead or live Gram-positive Lysinibacillus sphaericus JG-A12 cells to 20 µL DI water inside the ring top electrode. We relate observed change of measured impedance to change of membrane potential of L. sphaericus JG-A12 cells. In contrast to impedance measurements, optical density (OD) measurements cannot be used to distinguish between dead and live cells. Dead L. sphaericus JG-A12 cells have been obtained by adding 0.02 mg/mL of the antibiotics tetracycline and 0.1 mg/mL chloramphenicol to a batch with OD0.5 and by incubation for 24 h, 30 °C, 120 rpm in the dark. For impedance measurements, we have used batches with a cell density of 25.5 × 10⁸ cells/mL (OD8.5) and 270.0 × 10⁸ cells/mL (OD90.0). The impedance biochip PS5 can be used to detect the more resistive and less capacitive live L. sphaericus JG-A12 cells. Also, the impedance biochip BS5 can be used to detect the less resistive and more capacitive dead L. sphaericus JG-A12 cells. An outlook on the application of the impedance biochips for high-throughput drug screening, e.g., against multi-drug-resistant Gram-positive bacteria, is given.

Deionized water and glucose without yeast and with yeast (Saccharomyces cerevisiae) of optical density OD₆₀₀ that ranges from 4 to 16 has been put in the ring electrode region of six different types of impedance biochips and impedance has been measured in dependence on the added volume (20, 21, 22, 23, 24, 25 µL). The measured impedance of two out of the six types of biochips is strongly sensitive to the addition of both liquid without yeast and liquid with yeast and modelled impedance reveals a linear relationship between the impedance model parameters and yeast concentration. The presented biochips allow for continuous impedance measurements without interrupting the cultivation of the yeast. A multiparameter fit of the impedance model parameters allows for determining the concentration of yeast (c_y) in the range from c_y = 3.3 × 10⁷ to c_y = 17 × 10⁷ cells/mL. This work shows that independent on the liquid, i.e., DI water or glucose, the impedance model parameters of the two most sensitive types of biochips with liquid without yeast and with liquid with yeast are clearly distinguishable for the two most sensitive types of biochips.

In this work, we report on the impedance of p-n junction-based Si biochips with gold ring top electrodes and unstructured platinum bottom electrodes which allows for counting target biomaterial in a liquid-filled ring top electrode region. The systematic experiments on p-n junction-based Si biochips fabricated by two different sets of implantation parameters (i.e. biochips PS5 and BS5) are studied, and the comparable significant change of impedance characteristics in the biochips in dependence on the number of bacteria suspension, i.e., Lysinibacillus sphaericus JG-A12, in Deionized water with an optical density at 600 nm from OD₆₀₀ = 4–16 in the electrode ring region is demonstrated. Furthermore, with the help of the newly developed two-phase electrode structure, the modeled capacitance and resistance parameters of the electrical equivalent circuit describing the p-n junction-based biochips depend linearly on the number of bacteria in the ring top electrode region, which successfully proves the potential performance of p-n junction-based Si biochips in observing the bacterial suspension. The proposed p-n junction-based biochips reveal perspective applications in medicine and biology for diagnosis, monitoring, management, and treatment of diseases.