Optimization of Pulsed Laser Ablation and Radio-Frequency Sputtering Tandem System for Synthesis of 2D/3D Al2O3-ZnO Nanostructures: A Hybrid Approach to Synthesis of Nanostructures for Gas Sensing Applications

In this paper, a unique hybrid approach to design and synthesize 2D/3D Al₂O₃-ZnO nanostructures by simultaneous deposition is presented. Pulsed laser deposition (PLD) and RF magnetron sputtering (RFMS) methods are redeveloped into a single tandem system to create a mixed-species plasma to grow ZnO nanostructures for gas sensing applications. In this set-up, the parameters of PLD have been optimized and explored with RFMS parameters to design 2D/3D Al₂O₃-ZnO nanostructures, including nanoneedles/nanospikes, nanowalls, and nanorods, among others. The RF power of magnetron system with Al₂O₃ target is explored from 10 to 50 W, while the ZnO-loaded PLD's laser fluence and background gases are optimized to simultaneously grow ZnO and Al₂O₃-ZnO nanostructures. The nanostructures are either grown via 2-step template approach, or by direct growth on Si (111) and MgO<0001> substrates. In this approach, a thin ZnO template/film was initially grown on the substrate by PLD at ~300 °C under ~10 milliTorr (1.3 Pa) O₂ background pressure, followed by growth of either ZnO or Al₂O₃-ZnO, using PLD and RFMS simultaneously under 0.1-0.5 Torr (13-67 Pa), and Ar or Ar/O₂ background in the substrate temperate range of 550-700 °C. Growth mechanisms are then proposed to explain the formation of Al₂O₃-ZnO nanostructures. The optimized parameters from PLD-RFMS are then used to grow nanostructures on Au-patterned Al₂O₃-based gas sensor to test its response to CO gas from 200 to 400 °C, and a good response is observed at ~350 °C. The grown ZnO and Al₂O₃-ZnO nanostructures are quite exceptional and remarkable and have potential applications in optoelectronics, such in bio/gas sensors.

The Role of Different Lanthanoid and Transition Metals in Perovskite Gas Sensors

Beginning with LaFeO₃, a prominent perovskite-structured material used in the field of gas sensing, various perovskite-structured materials were prepared using sol–gel technique. The composition was systematically modified by replacing La with Sm and Gd, or Fe with Cr, Mn, Co, and Ni. The materials synthesized are comparable in grain size and morphology. DC resistance measurements performed on gas sensors reveal Fe-based compounds solely demonstrated effective sensing performance of acetylene and ethylene. Operando diffuse reflectance infrared Fourier transform spectroscopy shows the sensing mechanism is dependent on semiconductor properties of such materials, and that surface reactivity plays a key role in the sensing response. The replacement of A-site with various lanthanoid elements conserves surface reactivity of AFeO₃, while changes at the B-site of LaBO₃ lead to alterations in sensor surface chemistry.

Rapid Room-Temperature Synthesis of Mesoporous TiO2 Sub-Microspheres and Their Enhanced Light Harvesting in Dye-Sensitized Solar Cells

Submicron sized mesoporous spheres of TiO₂ have been a potential alternative to overcome the light scattering limitations of TiO₂ nanoparticles in dye-sensitized solar cells (DSSCs). Currently available methods for the growth of mesoporous TiO₂ sub-microspheres involve long and relatively high temperature multi-stage protocols. In this work, TiO₂ mesoporous sub-microspheres composed of ~5 nm anatase nanocrystallites were successfully synthesized using a rapid one-pot room-temperature CTAB-based solvothermal synthesis. X-Ray Diffraction (XRD) showed that the grown structures have pure anatase phase. Transmission electron microscopy (TEM) revealed that by reducing the surfactant/precursor concentration ratio, the morphology could be tuned from monodispersed nanoparticles into sub-micron sized mesoporous beads with controllable sizes (50–200 nm) and with good monodispersity as well. The growth mechanism is explained in terms of the competition between homogeneous nucleation/growth events versus surface energy induced agglomeration in a non-micelle CTAB-based soft templating environment. Further, dye-sensitized solar cells (DSSCs) were fabricated using the synthesized samples and characterized for their current-voltage characteristics. Interestingly, the DSSC prepared with 200 nm TiO₂ sub-microspheres, with reduced surface area, has shown close efficiency (5.65%) to that of DSSC based on monodispersed 20 nm nanoparticles (5.79%). The results show that light scattering caused by the agglomerated sub-micron spheres could compensate for the larger surface areas provided by monodispersed nanoparticles.

PO-48 - Assessment of the procoagulant potential state of tumour-MP in cancer patients

INTRODUCTION

The venous thromboembolism is considered one of the highest risk factor in cancer patients for instance ovarian and pancreas. This hypercoagulability state is believed to be caused by tumour cells that can produce a variety of procaogulant factors including tissue factor (TF) bearing microparticles (MP). Chemotherapy is an independent risk factor for venous thromboembolism (VTE) in patients and it can leads to coagulation activation and may increase microparticles that can increase risk of thrombosis.

AIM

Therefore, our current hypothesis is that this increased risk of VTE is due to release of tumour MP into the blood. To further investigate this mechanism an ex-vivo microfluidic model system was developed wherein tumour spheroids were grown and transferred onto a microfluidic chip and assessed, under flow conditions, for procoagulant activity (PCA).

MATERIALS AND METHODS

Tumour spheroids from pancreatic cancer cell line AsPC1 and human glioblastoma cell line U87 were generated using the liquid overlay method in a 96-well plate, then transferred to a microfluidic chip, designed with a trap within the device to immobilise the spheroid. The procoagulant potential of cell-free supernatant was measured using a prothrombin time clotting assay. Procoagulant activity was assessed under flow rate of 3.0 μL min-1 for 6 hours.

RESULTS

Several tumour cell lines (A2780, SKOV3, MIA Paca2, AsPC1 and U87) were assessed for PCA of media (MP associated) and then subsequently assessed for spheroid formation. Prothrombin time of cell-free media was A2780: 794s, SKOV3: 203.4s, MIA Paca2: 412s, AsPC1: 69s and U87: 50.3s. The pancreatic cell line AsPC-1 and glioblastoma cell line U87 were selected for further study on the basis of relatively high PCA and ability to form stable spheroids. When transferred to a microfluidic chip, AsPC1 tumour spheroids showed a slowing of PCA of media over a 6-hour period from 36.6 to 309s. U87 tumour spheroids showed a reduction in PCA of media over a 6-hour period from 51.3 to 108.9s.

CONCLUSIONS

This is the first report of tumour spheroids maintained in a microfluidic device and then subsequently assessed for PCA. Tumour spheroids of AsPC1 were shown to produce continuous procaogulant activity and this is presumably due to tumour microparticle release. This new model system offers a way to assess tumour associated PCA under flow conditions.