Search Results

Now showing 1 - 10 of 115
  • Item
    Ultrasmall SnO₂ nanocrystals: hot-bubbling synthesis, encapsulation in carbon layers and applications in high capacity Li-ion storage
    ([London] : Macmillan Publishers Limited, part of Springer Nature, 2014) Ding, Liping; He, Shulian; Miao, Shiding; Jorgensen, Matthew R.; Leubner, Susanne; Yan, Chenglin; Hickey, Stephen G.; Eychmüller, Alexander; Xu, Jinzhang; Schmidt, Oliver G.
    Ultrasmall SnO2 nanocrystals as anode materials for lithium-ion batteries (LIBs) have been synthesized by bubbling an oxidizing gas into hot surfactant solutions containing Sn-oleate complexes. Annealing of the particles in N2 carbonifies the densely packed surface capping ligands resulting in carbon encapsulated SnO2 nanoparticles (SnO2/C). Carbon encapsulation can effectively buffer the volume changes during the lithiation/delithiation process. The assembled SnO2/C thus deliver extraordinarily high reversible capacity of 908 mA·h·g−1 at 0.5 C as well as excellent cycling performance in the LIBs. This method demonstrates the great potential of SnO2/C nanoparticles for the design of high power LIBs.
  • Item
    Micromotor-mediated sperm constrictions for improved swimming performance
    (Berlin ; Heidelberg : Springer, 2021) Striggow, Friedrich; Nadporozhskaia, Lidiia; Friedrich, Benjamin M.; Schmidt, Oliver G.; Medina-Sánchez, Mariana
    Sperm-driven micromotors, consisting of a single sperm cell captured in a microcap, utilize the strong propulsion generated by the flagellar beat of motile spermatozoa for locomotion. It enables the movement of such micromotors in biological media, while being steered remotely by means of an external magnetic field. The substantial decrease in swimming speed, caused by the additional hydrodynamic load of the microcap, limits the applicability of sperm-based micromotors. Therefore, to improve the performance of such micromotors, we first investigate the effects of additional cargo on the flagellar beat of spermatozoa. We designed two different kinds of microcaps, which each result in different load responses of the flagellar beat. As an additional design feature, we constrain rotational degrees of freedom of the cell’s motion by modifying the inner cavity of the cap. Particularly, cell rolling is substantially reduced by tightly locking the sperm head inside the microcap. Likewise, cell yawing is decreased by aligning the micromotors under an external static magnetic field. The observed differences in swimming speed of different micromotors are not so much a direct consequence of hydrodynamic effects, but rather stem from changes in flagellar bending waves, hence are an indirect effect. Our work serves as proof-of-principle that the optimal design of microcaps is key for the development of efficient sperm-driven micromotors.
  • Item
    A size dependent evaluation of the cytotoxicity and uptake of nanographene oxide
    (London [u.a.] : RSC, 2015) Mendes, Rafael Gregorio; Koch, Britta; Bachmatiuk, Alicja; Ma, Xing; Sanchez, Samuel; Damm, Christine; Schmidt, Oliver G.; Gemming, Thomas; Eckert, Jürgen; Rümmeli, Mark H.
    Graphene oxide (GO) has attracted great interest due to its extraordinary potential for biomedical application. Although it is clear that the naturally occurring morphology of biological structures is crucial to their precise interactions and correct functioning, the geometrical aspects of nanoparticles are often ignored in the design of nanoparticles for biological applications. A few in vitro and in vivo studies have evaluated the cytotoxicity and biodistribution of GO, however very little is known about the influence of flake size and cytotoxicity. Herein, we aim at presenting an initial cytotoxicity evaluation of different nano-sized GO flakes for two different cell lines (HeLa (Kyoto) and macrophage (J7742)) when they are exposed to samples containing different sized nanographene oxide (NGO) flakes (mean diameter of 89 and 277 nm). The obtained data suggests that the larger NGO flakes reduce cell viability as compared to smaller flakes. In addition, the viability reduction correlates with the time and the concentration of the NGO nanoparticles to which the cells are exposed. Uptake studies were also conducted and the data suggests that both cell lines internalize the GO nanoparticles during the incubation periods studied.
  • Item
    Nano-biosupercapacitors enable autarkic sensor operation in blood
    ([London] : Nature Publishing Group UK, 2021) Lee, Yeji; Bandari, Vineeth Kumar; Li, Zhe; Medina-Sánchez, Mariana; Maitz, Manfred F.; Karnaushenko, Daniil; Tsurkan, Mikhail V; Karnaushenko, Dmitriy D.; Schmidt, Oliver G.
    Today’s smallest energy storage devices for in-vivo applications are larger than 3 mm3 and lack the ability to continuously drive the complex functions of smart dust electronic and microrobotic systems. Here, we create a tubular biosupercapacitor occupying a mere volume of 1/1000 mm3 (=1 nanoliter), yet delivering up to 1.6 V in blood. The tubular geometry of this nano-biosupercapacitor provides efficient self-protection against external forces from pulsating blood or muscle contraction. Redox enzymes and living cells, naturally present in blood boost the performance of the device by 40% and help to solve the self-discharging problem persistently encountered by miniaturized supercapacitors. At full capacity, the nano-biosupercapacitors drive a complex integrated sensor system to measure the pH-value in blood. This demonstration opens up opportunities for next generation intravascular implants and microrobotic systems operating in hard-to-reach small spaces deep inside the human body.
  • Item
    Engineering interface-type resistive switching in BiFeO3 thin film switches by Ti implantation of bottom electrodes
    (London : Nature Publishing Group, 2015) You, Tiangui; Ou, Xin; Niu, Gang; Bärwolf, Florian; Li, Guodong; Du, Nan; Bürger, Danilo; Skorupa, Ilona; Jia, Qi; Yu, Wenjie; Wang, Xi; Schmidt, Oliver G.; Schmidt, Heidemarie
    BiFeO3 based MIM structures with Ti-implanted Pt bottom electrodes and Au top electrodes have been fabricated on Sapphire substrates. The resulting metal-insulator-metal (MIM) structures show bipolar resistive switching without an electroforming process. It is evidenced that during the BiFeO3 thin film growth Ti diffuses into the BiFeO3 layer. The diffused Ti effectively traps and releases oxygen vacancies and consequently stabilizes the resistive switching in BiFeO3 MIM structures. Therefore, using Ti implantation of the bottom electrode, the retention performance can be greatly improved with increasing Ti fluence. For the used raster-scanned Ti implantation the lateral Ti distribution is not homogeneous enough and endurance slightly degrades with Ti fluence. The local resistive switching investigated by current sensing atomic force microscopy suggests the capability of down-scaling the resistive switching cell to one BiFeO3 grain size by local Ti implantation of the bottom electrode.
  • Item
    High-defect hydrophilic carbon cuboids anchored with Co/CoO nanoparticles as highly efficient and ultra-stable lithium-ion battery anodes
    (Cambridge : Royal Society of Chemistry, 2016) Sun, Xiaolei; Hao, Guang-Ping; Lu, Xueyi; Xi, Lixia; Liu, Bo; Si, Wenping; Ma, Chuansheng; Liu, Qiming; Zhang, Qiang; Kaskel, Stefan; Schmidt, Oliver G.
    We propose an effective strategy to engineer a unique kind of porous carbon cuboid with tightly anchored cobalt/cobalt oxide nanoparticles (PCC–CoOx) that exhibit outstanding electrochemical performance for many key aspects of lithium-ion battery electrodes. The host carbon cuboid features an ultra-polar surface reflected by its high hydrophilicity and rich surface defects due to high heteroatom doping (N-/O-doping both higher than 10 atom%) as well as hierarchical pore systems. We loaded the porous carbon cuboid with cobalt/cobalt oxide nanoparticles through an impregnation process followed by calcination treatment. The resulting PCC–CoOx anode exhibits superior rate capability (195 mA h g−1 at 20 A g−1) and excellent cycling stability (580 mA h g−1 after 2000 cycles at 1 A g−1 with only 0.0067% capacity loss per cycle). Impressively, even after an ultra-long cycle life exceeding 10 000 cycles at 5 A g−1, the battery can recover to 1050 mA h g−1 at 0.1 A g−1, perhaps the best performance demonstrated so far for lithium storage in cobalt oxide-based electrodes. This study provides a new perspective to engineer long-life, high-power metal oxide-based electrodes for lithium-ion batteries through controlling the surface chemistry of carbon host materials.
  • Item
    Kontrolle supraleitender Wirbeldynamik in Nb rolled-up-Nanostrukturen : Laufzeit des Vorhabens: 01.04.2013-31.03.2016
    (Hannover : Technische Informationsbibliothek (TIB), 2016) Fomin, Vladimir M.; Schmidt, Oliver G.; Bürger, Danilo; Lösch, Sören; Rezaev, Roman; Levchenko, Evgenii; Dusaev, Renat
    Der Bericht enthält eine vollständige Beschreibung des wissenschaftlichen Forschungsprojekts, das durch die bilaterale BMBF-Russland-Forschungsförderung 01 DJ13009 finanziert wurde. Die Projektdauer wird in drei Perioden unterteilt, die jeweils dem Jahr der Umsetzung entsprechen. Die grundlegende Aufgabe des Projekts war es zu untersuchen, wie die Nanostrukturierung von Materialen die supraleitenden Eigenschaften ändert. Auf Basis der zeitabhängigen Ginzburg-Landau Theorie wurde das mathematische Modell der supraleitenden Phänomene in krummlinigen Nanostrukturen erstellt. Die Validierung des Modells wurde durch Vergleich mit verfügbaren experimentellen Daten für planare Strukturen durchgeführt. Weiterhin wurde das erarbeitete Modell zur Untersuchung der Wirbeldynamik in krummlinigen Nanostrukturen in einem Magnetfeld angewendet. Der Einfluss von Pinning-Zentren und die Dissipation der Energie in Abhängigkeit von den Randbedingungen wurden analysiert. Die im Rahmen des Projekts erhaltenen wissenschaftlichen Ergebnisse zeigen deutlich die Vorteile der gekrümmten supraleitenden Nanostrukturen in modernen Anwendungen der Supraleitung. Während des Projekts wurde eine innovative Software entwickelt, welche als Instrument für das virtuelle Design von Experimenten in supraleitenden gekrümmten Nano- und Mikrostrukturen genutzt werden kann.
  • Item
    Supervised discriminant analysis for droplet micro-magnetofluidics
    (Heidelberg : Springer, 2015) Lin, Gungun; Fomin, Vladimir M.; Makarov, Denys; Schmidt, Oliver G.
    We apply the technique of supervised discriminant analysis (SDA) for in-flow detection in droplet-based magnetofluidics. Based on the SDA, we successfully discriminate bivariant droplets of different volumes containing different encapsulated magnetic content produced by a GMR-based lab-on-chip platform. We demonstrate that the accuracy of discrimination is superior when the correlation of variables for data training is included to the case when the spatial distribution of variables is considered. Droplets produced with differences in ferrofluid concentration of 2.5 mg/ml and volume of 200 pl have been identified with high accuracy (98 %), indicating the significance of SDA for e.g. the discrimination in magnetic immuno-agglutination assays. Furthermore, the results open the way for the development of a unique magnetofluidic platform for future applications in multiplexed droplet-based barcoding assays and screening.
  • Item
    Human spermbots for patient-representative 3D ovarian cancer cell treatment
    (Cambridge : RSC Publ., 2020) Xu, Haifeng; Medina-Sánchez, Mariana; Zhang, Wunan; Seaton, Melanie P. H.; Brison, Daniel R.; Edmondson, Richard J.; Taylor, Stephen S.; Nelson, Louisa; Zeng, Kang; Bagley, Steven; Ribeiro, Carla; Restrepo, Lina P.; Lucena, Elkin; Schmidt, Christine K.; Schmidt, Oliver G.
    Cellular micromotors are attractive for locally delivering high concentrations of drug, and targeting hard-to-reach disease sites such as cervical cancer and early ovarian cancer lesions by non-invasive means. Spermatozoa are highly efficient micromotors perfectly adapted to traveling up the female reproductive system. Indeed, bovine sperm-based micromotors have shown potential to carry drugs toward gynecological cancers. However, due to major differences in the molecular make-up of bovine and human sperm, a key translational bottleneck for bringing this technology closer to the clinic is to transfer this concept to human material. Here, we successfully load human sperm with Doxorubicin (DOX) and perform treatment of 3D cervical cancer and patient-representative ovarian cancer cell cultures, resulting in strong anticancer cell effects. Additionally, we define the subcellular localization of the chemotherapeutic drug within human sperm, using high-resolution optical microscopy. We also assess drug effects on sperm motility and viability over time, employing sperm samples from healthy donors as well as assisted reproduction patients. Finally, we demonstrate guidance and release of human drug-loaded sperm onto cancer tissues using magnetic microcaps, and show the sperm microcap loaded with a second anticancer drug, camptothecin (CPT), which unlike DOX is not suitable for directly loading into sperm due to its hydrophobic nature. This co-drug delivery approach opens up novel targeted combinatorial drug therapies for future applications. © 2020 The Royal Society of Chemistry.
  • Item
    Integrated molecular diode as 10 MHz half-wave rectifier based on an organic nanostructure heterojunction
    ([London] : Nature Publishing Group UK, 2020) Li, Tianming; Bandari, Vineeth Kumar; Hantusch, Martin; Xin, Jianhui; Kuhrt, Robert; Ravishankar, Rachappa; Xu, Longqian; Zhang, Jidong; Knupfer, Martin; Zhu, Feng; Yan, Donghang; Schmidt, Oliver G.
    Considerable efforts have been made to realize nanoscale diodes based on single molecules or molecular ensembles for implementing the concept of molecular electronics. However, so far, functional molecular diodes have only been demonstrated in the very low alternating current frequency regime, which is partially due to their extremely low conductance and the poor degree of device integration. Here, we report about fully integrated rectifiers with microtubular soft-contacts, which are based on a molecularly thin organic heterojunction and are able to convert alternating current with a frequency of up to 10 MHz. The unidirectional current behavior of our devices originates mainly from the intrinsically different surfaces of the bottom planar and top microtubular Au electrodes while the excellent high frequency response benefits from the charge accumulation in the phthalocyanine molecular heterojunction, which not only improves the charge injection but also increases the carrier density.