Search Results
Self-propelled micromotors for cleaning polluted water
2013, Soler, L., Magdanz, V., Fomin, V.M., Sanchez, S., Schmidt, O.G.
We describe the use of catalytically self-propelled microjets (dubbed micromotors) for degrading organic pollutants in water via the Fenton oxidation process. The tubular micromotors are composed of rolled-up functional nanomembranes consisting of Fe/Pt bilayers. The micromotors contain double functionality within their architecture, i.e., the inner Pt for the self-propulsion and the outer Fe for the in situ generation of ferrous ions boosting the remediation of contaminated water.The degradation of organic pollutants takes place in the presence of hydrogen peroxide, which acts as a reagent for the Fenton reaction and as main fuel to propel the micromotors. Factors influencing the efficiency of the Fenton oxidation process, including thickness of the Fe layer, pH, and concentration of hydrogen peroxide, are investigated. The ability of these catalytically self-propelled micromotors to improve intermixing in liquids results in the removal of organic pollutants ca. 12 times faster than when the Fenton oxidation process is carried out without catalytically active micromotors. The enhanced reaction-diffusion provided by micromotors has been theoretically modeled. The synergy between the internal and external functionalities of the micromotors, without the need of further functionalization, results into an enhanced degradation of nonbiodegradable and dangerous organic pollutants at small-scale environments and holds considerable promise for the remediation of contaminated water.
Magnetic Micromotors for Multiple Motile Sperm Cells Capture, Transport, and Enzymatic Release
2020, Xu, H., Medina-Sánchez, M., Schmidt, O.G.
An integrated system combining a magnetically-driven micromotor and a synthetized protein-based hyaluronic acid (HA) microflake is presented for the in situ selection and transport of multiple motile sperm cells (ca. 50). The system appeals for targeted sperm delivery in the reproductive system to assist fertilization or to deliver drugs. The binding mechanism between the HA microflake and sperm relies on the interactions between HA and the corresponding sperm HA receptors. Once sperm are captured within the HA microflake, the assembly is trapped and transported by a magnetically-driven helical microcarrier. The trapping of the sperm-microflake occurs by a local vortex induced by the microcarrier during rotation-translation under a rotating magnetic field. After transport, the microflake is enzymatically hydrolyzed by local proteases, allowing sperm to escape and finally reach the target location. This cargo-delivery system represents a new concept to transport not only multiple motile sperm but also other actively moving biological cargoes.
Imaging of buried 3D magnetic rolled-up nanomembranes
2014, Streubel, R., Han, L., Kronast, F., Ünal, A.A., Schmidt, O.G., Makarov, D.
Increasing performance and enabling novel functionalities of microelectronic devices, such as three-dimensional (3D) on-chip architectures in optics, electronics, and magnetics, calls for new approaches in both fabrication and characterization. Up to now, 3D magnetic architectures had mainly been studied by integral means without providing insight into local magnetic microstructures that determine the device performance. We prove a concept that allows for imaging magnetic domain patterns in buried 3D objects, for example, magnetic tubular architectures with multiple windings. The approach is based on utilizing the shadow contrast in transmission X-ray magnetic circular dichroism (XMCD) photoemission electron microscopy and correlating the observed 2D projection of the 3D magnetic domains with simulated XMCD patterns. That way, we are not only able to assess magnetic states but also monitor the field-driven evolution of the magnetic domain patterns in individual windings of buried magnetic rolled-up nanomembranes.
Photoactive rolled-up TiO2 microtubes: Fabrication, characterization and applications
2014, Giudicatti, S., Marz, S.M., Soler, L., Madani, A., Jorgensen, M.R., Sanchez, S., Schmidt, O.G.
Because of its unique properties, titania (TiO2) represents a promising candidate in a wide variety of research fields. In this paper, some of the properties and potential applications of titania within rolled-up nanotechnology are explored. It is shown how the structural and optical properties of rolled titania microtubes can be controlled by properly tuning the microfabrication parameters. The rolling up of titania films on different sacrificial layers and containing different shapes, achieving a control on the diameter of the fabricated titania microtubes, is presented. In order to obtain the more photoactive crystalline form of titania, one during-fabrication and two post-fabrication methods are demonstrated. Interesting applications in the fields of photocatalysis and photonics are suggested: the use of titania rolled-up microtubes as micromotors and optical microresonators is presented.
Resistive switching in polycrystalline YMnO3 thin films
2014, Bogusz, A., Müller, A.D., Blaschke, D., Skorupa, I., Bürger, D., Scholz, A., Schmidt, O.G., Schmidt, H.
We report a unipolar, nonvolatile resistive switching in polycrystalline YMnO3 thin films grown by pulsed laser deposition and sandwiched between Au top and Ti/Pt bottom electrodes. The ratio of the resistance in the OFF and ON state is larger than 103. The observed phenomena can be attributed to the formation and rupture of conductive filaments within the multiferroic YMnO3 film. The generation of conductive paths under applied electric field is discussed in terms of the presence of grain boundaries and charged domain walls inherently formed in hexagonal YMnO3. Our findings suggest that engineering of the ferroelectric domains might be a promising route for designing and fabrication of novel resistive switching devices.
Tuning emission energy and fine structure splitting in quantum dots emitting in the telecom O-band
2019, Höfer, B., Olbrich, F., Kettler, J., Paul, M., Höschele, J., Jetter, M., Portalupi, S.L., Ding, F., Michler, P., Schmidt, O.G.
We report on optical investigations of MOVPE-grown InGaAs/GaAs quantum dots emitting at the telecom O-band that were integrated onto uniaxial piezoelectric actuators. This promising technique, which does not degrade the emission brightness of the quantum emitters, enables us to tune the quantum dot emission wavelengths and their fine-structure splitting. By spectrally analyzing the emitted light with respect to its polarization, we are able to demonstrate the cancelation of the fine structure splitting within the experimental resolution limit. This work represents an important step towards the high-yield generation of entangled photon pairs at telecommunication wavelength, together with the capability to precisely tune the emission to target wavelengths.
Ultracompact three-dimensional tubular conductivity microsensors for ionic and biosensing applications
2014, Martinez-Cisneros, C.S., Sanchez, S., Xi, W., Schmidt, O.G.
We present ultracompact three-dimensional tubular structures integrating Au-based electrodes as impedimetric microsensors for the in-flow determination of mono- and divalent ionic species and HeLa cells. The microsensors show an improved performance of 2 orders of magnitude (limit of detection = 0.1 nM for KCl) compared to conventional planar conductivity detection systems integrated in microfluidic platforms and the capability to detect single HeLa cells in flowing phosphate buffered saline. These highly integrated conductivity tubular sensors thus open new possibilities for lab-in-a-tube devices for bioapplications such as biosensing and bioelectronics.
Self-Assembled Flexible and Integratable 3D Microtubular Asymmetric Supercapacitors
2019, Li, F., Wang, J., Liu, L., Qu, J., Li, Y., Bandari, V.K., Karnaushenko, D., Becker, C., Faghih, M., Kang, T., Baunack, S., Zhu, M., Zhu, F., Schmidt, O.G.
The rapid development of microelectronics has equally rapidly increased the demand for miniaturized energy storage devices. On-chip microsupercapacitors (MSCs), as promising power candidates, possess great potential to complement or replace electrolytic capacitors and microbatteries in various applications. However, the areal capacities and energy densities of the planar MSCs are commonly limited by the low voltage window, the thin layer of the electrode materials and complex fabrication processes. Here, a new-type three-dimensional (3D) tubular asymmetric MSC with small footprint area, high potential window, ultrahigh areal energy density, and long-term cycling stability is fabricated with shapeable materials and photolithographic technologies, which are compatible with modern microelectronic fabrication procedures widely used in industry. Benefiting from the novel architecture, the 3D asymmetric MSC displays an ultrahigh areal capacitance of 88.6 mF cm−2 and areal energy density of 28.69 mW h cm−2, superior to most reported interdigitated MSCs. Furthermore, the 3D tubular MSCs demonstrate remarkable cycling stability and the capacitance retention is up to 91.8% over 12 000 cycles. It is believed that the efficient fabrication methodology can be used to construct various integratable microscale tubular energy storage devices with small footprint area and high performance for miniaturized electronics.
Artificial micro-cinderella based on self-propelled micromagnets for the active separation of paramagnetic particles
2013, Zhao, G., Wang, H., Sanchez, S., Schmidt, O.G., Pumera, M.
In this work, we will show that ferromagnetic microjets can pick-up paramagnetic beads while not showing any interaction with diamagnetic silica microparticles for the active separation of microparticles in solution.
A highly flexible and compact magnetoresistive analytic device
2014, Lin, G., Makarov, D., Melzer, M., Si, W., Yan, C., Schmidt, O.G.
A grand vision of realization of smart and compact multifunctional microfluidic devices for wearable health monitoring, environment sensing and point-of-care tests emerged with the fast development of flexible electronics. As a vital component towards this vision, magnetic functionality in flexible fluidics is still missing although demanded by the broad utility of magnetic nanoparticles in medicine and biology. Here, we demonstrate the first flexible microfluidic analytic device with integrated high-performance giant magnetoresistive (GMR) sensors. This device can be bent to a radius of 2 mm while still retaining its full performance. Various dimensions of magnetic emulsion droplets can be probed with high precision using a limit of detection of 0.5 pl, providing broad applicability in high-throughput droplet screening, flow cytometry and drug development. The flexible feature of this analytic device holds great promise in the realization of wearable, implantable multifunctional platforms for biomedical, pharmaceutical and chemical applications.