Katja Toensing

Bio: Katja Toensing is an academic researcher from Bielefeld University. The author has contributed to research in topics: Magnetic tweezers & Force spectroscopy. The author has an hindex of 7, co-authored 13 publications receiving 299 citations.

Binding mechanism of anti-cancer chemotherapeutic drug mitoxantrone to DNA characterized by magnetic tweezers

Abstract: Chemotherapeutic agents (anti-cancer drugs) are small cytostatic or cytotoxic molecules that often bind to double-stranded DNA (dsDNA) resulting in modifications of their structural and nanomechanical properties and thus interfering with the cell proliferation process. We investigated the anthraquinone compound mitoxantrone that is used for treating certain cancer types like leukemia and lymphoma with magnetic tweezers as a single molecule nanosensor. In order to study the association of mitoxantrone with dsDNA, we conducted force-extension and mechanical overwinding experiments with a sensitivity of 10−14 N. Using this method, we were able to estimate an equilibrium constant of association Ka ≈ 1 × 105 M−1 as well as a binding site size of n ≈ 2.5 base pairs for mitoxantrone. An unwinding angle of mitoxantrone-intercalation of ϑ ≈ 16° was determined. Moreover, we observed a complex concentration-dependent bimodal binding behavior, where mitoxantrone associates to dsDNA as an intercalator and groove binder simultaneously at low concentrations and as a mere intercalator at high concentrations.

Compact microscope-based optical tweezers system for molecular manipulation

Abstract: A compact single beam optical tweezers system for force measurements and manipulation of individual double-stranded deoxyribonucleic acid (DNA) molecules was integrated into a commercial inverted optical microscope. A maximal force of 150 pN combined with a force sensitivity of less than 0.5 pN allows measurements of elastic properties of single molecules which complements and overlaps the force regime accessible with atomic force microscopy (AFM). The manipulation and measurement performance of this system was tested with individual λ-DNA molecules and renders new aspects of dynamic forces phenomena with higher precision in contrast to AFM studies. An integrated liquid handling system with a fluid cell allows investigation of the force response of individual DNA molecules in the presence of DNA binding agents. Comparison of YOYO-1-, ethidium bromide intercalated DNA, and distamycin-A complexed DNA revealed accurate and reproducible differences in the force response to an external load. This opens the possibility to use it as a single molecule biosensor to investigate DNA binding agents and even to identify molecular binding mechanisms.

An Oil-Based Lubrication System Based on Nanoparticular TiO2 with Superior Friction and Wear Properties

Abstract: We evaluated the performance of five different commercially available nanoparticle classes as additives for an oil-based lubrication system. While the silicon dioxide particles Aerosil® 300, RY300, and R972V tended to increase wear and friction in our 100Cr6 versus cast iron disc–disc contact, Aeroxide® P 25 and especially T 805 TiO2 nanoparticles showed superior anti-wear and anti-friction properties. The underlying tribological mechanism was investigated with optical microscopy, helium ion microscopy, and X-ray photoelectron spectroscopy. Subsequently, we formulated a stable lubrication system based on the best performing T 805 particles. Here, the base oil is a highly purified paraffin oil which was supplemented with 1 wt% T 805 TiO2 particles, 1 wt% Estisol® 242 or 1 wt% oleic acid, 0.15 wt% oleylamine, and 0.15 wt% Pluronic® RPE 2520. Superior lubrication and anti-wear properties of this formulation were demonstrated in 4-h test runs with a normal force of F N = 2.5 kN and a sliding velocity of 0.15 m/s in our disc–disc contact. Wear was significantly reduced along with a nearly 12-fold reduction in the friction coefficient, compared to the base oil $$(\mu_{\text{base}}^{\text{fto}} = 0.155\;\;{\text{vs}} .\;\;\mu_{\text{T805}}^{\text{fto}} \approx 0.01)$$ . Using 100Cr6 disc–ball contacts, we additionally analyzed the properties of our lubrication system in the border friction regime under higher loads (F N = 0.5 kN) in 2-h runs. In particular, on the discs with lower engagement ratio, chemo-tribological protective layers were built, which protected the parts very well against wear.

Fluorescent Proteins and Their Applications in Imaging Living Cells and Tissues

Abstract: Green fluorescent protein (GFP) from the jellyfish Aequorea victoria and its homologs from diverse marine animals are widely used as universal genetically encoded fluorescent labels. Many laboratories have focused their efforts on identification and development of fluorescent proteins with novel characteristics and enhanced properties, resulting in a powerful toolkit for visualization of structural organization and dynamic processes in living cells and organisms. The diversity of currently available fluorescent proteins covers nearly the entire visible spectrum, providing numerous alternative possibilities for multicolor labeling and studies of protein interactions. Photoactivatable fluorescent proteins enable tracking of photolabeled molecules and cells in space and time and can also be used for super-resolution imaging. Genetically encoded sensors make it possible to monitor the activity of enzymes and the concentrations of various analytes. Fast-maturing fluorescent proteins, cell clocks, and timers further expand the options for real time studies in living tissues. Here we focus on the structure, evolution, and function of GFP-like proteins and their numerous applications for in vivo imaging, with particular attention to recent techniques.

Future lab-on-a-chip technologies for interrogating individual molecules

Abstract: Advances in technology have allowed chemical sampling with high spatial resolution and the manipulation and measurement of individual molecules. Adaptation of these approaches to lab-on-a-chip formats is providing a new class of research tools for the investigation of biochemistry and life processes.

Advances in multiphoton microscopy technology

Abstract: The ability to dynamically image features deep within living organisms, permitting real-time analysis of cellular structure and function, is important for biological science. This Review article discusses multiphoton microscopy capable of such analysis, along with technologies that are pushing the limits of phenomena that can be quantitatively imaged.