Sandra C. Kuhn

LC-MS/MS method development for quantitative analysis of acetaminophen uptake by the aquatic fungus Mucor hiemalis.

Acetaminophen is a pharmaceutical, frequently found in surface water as a contaminant. Bioremediation, in particular, mycoremediation of acetaminophen is a method to remove this compound from waters. Owing to the lack of quantitative analytical method for acetaminophen in aquatic organisms, the present study aimed to develop a method for the determination of acetaminophen using LC-MS/MS in the aquatic fungus Mucor hiemalis. The method was then applied to evaluate the uptake of acetaminophen by M. hiemalis, cultured in pellet morphology. The method was robust, sensitive and reproducible with a lower limit of quantification of 5 pg acetaminophen on column. It was found that M. hiemalis internalize the pharmaceutical, and bioaccumulate it with time. Therefore, M. hiemalis was deemed a suitable candidate for further studies to elucidate its pharmaceutical tolerance and the longevity in mycoremediation applications.

Oxidative stress responses in the animal model, Daphnia pulex exposed to a natural bloom extract versus artificial cyanotoxin mixtures

In the natural environment, Daphnia spp. are constantly exposed to a complex matrix of biomolecules, especially during cyanobacterial bloom events. When cyanobacterial cells decay, not only are toxic secondary metabolites known as cyanotoxins released, but also multiple other secondary metabolites, some of which act as enzyme inhibitors. The present study examined the effects of such a natural toxin matrix (crude extract from a bloom) versus artificial toxin mixtures in terms of oxidative stress in Daphnia pulex. The results indicate that there is no significant effect on the survival of D. pulex. However, exposure to the bloom extract resulted in increased lipid peroxidation over a shorter exposure period and reduced antioxidative enzyme activities when compared to the artificial mixtures. The daphnids also needed a longer recovery time to reduce the increased cellular hydrogen peroxide concentration associated with the exposure to the crude extract than with the artificial mixtures. The results indicate a significant difference between the bloom crude extract and the two synthetic mixtures for all stress markers tested, indicating enhanced toxicity of the bloom extract.

Development and validation of an in‐house quantitative analysis method for cylindrospermopsin using hydrophilic interaction liquid chromatography–tandem mass spectrometry: Quantification demonstrated in 4 aquatic organisms

The cyanobacterial toxin cylindrospermopsin (CYN) is of great concern in aquatic environments because of its incidence, multiple toxicity endpoints, and, therefore, the severity of health implications. It may bioaccumulate in aquatic food webs, resulting in high exposure concentrations to higher-order trophic levels, particularly humans. Because of accumulation at primary levels resulting from exposure to trace amounts of toxin, a sensitive analytical technique with proven aquatic applications is required. In the present study, a hydrophilic interaction liquid chromatographic-tandem mass spectrometric method with a lower limit of detection of 200 fg on column (signal-to-noise ratio = 3, n = 9) and a lower limit of quantification of 1 pg on column (signal-to-noise ratio = 11, n = 9) with demonstrated application in 4 aquatic organisms is described. The analytical method was optimized and validated with a linear range (r(2) = 0.999) from 0.1 ng mL(-1) to 100 ng mL(-1) CYN. Mean recovery of the extraction method was 98 ± 2%. Application of the method was demonstrated by quantifying CYN uptake in Scenedesmus subspicatus (green algae), Egeria densa (Brazilian waterweed), Daphnia magna (water flea), and Lumbriculus variegatus (blackworm) after 24 h of static exposure to 50 μg L(-1) CYN. Uptake ranged from 0.05% to 0.11% of the nominal CYN exposure amount. This constitutes a sensitive and reproducible method for extraction and quantification of unconjugated CYN with demonstrated application in 4 aquatic organisms, which can be used in further aquatic toxicological investigations.

Physiological responses of Cladophora glomerata to cyanotoxins: a potential new phytoremediation species for the Green Liver Systems

Due to increased pollution of potable water sources as a consequence of eutrophication and anthropogenic xenobiotics, sustainable water purification is an essential concern. Therefore, the Green Liver System, a natural, economic and sustainable water purification system employing the biotransformation capabilities of aquatic plants, was developed. To expand the capacities and applications of this system, new aquatic plants are continually evaluated for their potential to remediate various aquatic pollutants. In this study, the potential of Cladophora glomerata to internalize cyanotoxins, microcystins (MCs) and anatoxin-a, and consequently its ability to cope with the subsequent oxidative stress associated with toxin-uptake were investigated. C. glomerata was able to take up all three of the tested MC congeners as well as anatoxin-a, similarly to previous toxin internalizations reported for aquatic plants such as Ceratophyllum demersum, Myriophyllum spicatum and Hydrilla versiculata. The antioxidative stress defense of C. glomerata proved to efficiently endure the toxin-uptake with no adverse effects. Subsequently, the uptake potential of C. glomerata was investigated at lab-scale by exposure to the three MC congeners and anatoxin-a collectively. After a period of seven days, 95–97% of the MCs and 100% of anatoxin-a were removed from the exposure media. C. glomerata therefore, is a suitable candidate to be incorporated in future Green Liver Systems.

Cavity assisted emission of single, paired and heralded photons from a single quantum dot device.

The photon emission into different spatial directions of a quantum dot in a micropillar cavity is theoretically analyzed. We propose two types of photon emission statistics from a single quantum light device: (i) single photon emission into the axial, strong coupling direction and a two-photon emission into the lateral, weak coupling direction, as well as (ii) the simultaneous use of both emission directions for the temporally ordered generation of two photons within a defined time-bin constituting a heralded single photon source. Our results open up exciting perspectives for solid state based quantum light sources, which can be generalized to any quantum emitter-microcavity system featuring spatially distinct emission channels between the resonator and unconfined modes.

Theory of phonon-assisted intraband transitions in semiconductor quantum dots

The investigation of the intersubband dynamics occurring in the conduction band of doped semiconductor quantum dots (QDs) has emerged as a powerful tool to probe their electronic structure and properties. Here, the temperature, the dephasing and the relaxation dynamics are of interest, both from a fundamental point of view but also regarding the performance of QD-based optoelectronic devices. Whereas the lineshape of QD interband transitions is well described by the independent boson model treating a diagonal electron-phonon coupling. For intraband transitions both diagonal and non-diagonal electron-phonon coupling are relevant. Typically, such problems involving diagonal and non-diagonal coupling are treated within approximate or perturbative approaches. Here, we present a fully quantized theory to calculate the coupled electron-phonon dynamics based on a non-perturbative equation of motion approach reproducing also correct results for limits of known exactly solvable models.

Excitonic effects in quantum dot intraband spectroscopy indicating the formation of bound continuum excitons

We present a theoretical analysis of Coulomb induced effects on intraband transitions between bound quantum dot and unbound continuum states of the host material. The intraband adsorption spectra show characteristic spectral signatures. In particular, the numerical results confirms the existence of bound excitons consisting of a localized carrier inside the quantum dot and a delocalized carrier of the continuum, which are spatially delocalized in the vicinity of the quantum dot.

Efficient numerical method for calculating Coulomb coupling elements and its application to two-dimensional spectroscopy

Typically, to calculate the two-particle Coulomb interaction between nanostructures, a six dimensional spatial integral need to be evaluated. For increasing size or complexity of the system, the calculation of the Coulomb coupling elements presents a significant limiting factor for simulations. The number of integrals in real space can be reduced by using a Greens function representation of the solution of a generalized Poisson equation. Without the restriction to specific symmetries, this efficient numerical method allows the inclusion of an arbitrary dielectric function. The Coulomb interaction between two colloidal quantum dots (QDs) is calculated without specifying the Greens function to an explicit analytic form. Nevertheless, the monopole-monopole interaction and the Förster induced excitation transfer are calculated separately. The Coulomb coupling between semiconductor QDs depends on the center-to-center distance between the nanostructures as well as on their relative dipole orientation to each other. To identify the effects of the spatially dependent Coulomb coupling on single excitons and biexcitons, a multidimensional coherent spectroscopy is used. The characteristic two dimensional optical signatures of different spatial arranged colloidal QDs are calculated with respect to the arrangement dependent Coulomb coupling between the nanostructures.