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Hendrik Reynders,1 Indra Van Zundert,1 Rui Silva,1– 3 Bram Carlier,3 Olivier Deschaume,4 Carmen Bartic,4 Susana Rocha,1 Sergey Basov,5 Margriet J Van Bael,5 Uwe Himmelreich,3 Thierry Verbiest,1 Ana Zamora1,3 1Molecular Imaging and Photonics, KU Leuven, Leuven, Belgium; 2Engineering Department, Oporto University, Porto, Portugal; 3Biomedical MRI, Department of Imaging and Pathology, KU Leuven, Leuven, Belgium; 4Laboratory for Soft Matter and Biophysics, KU Leuven, Leuven, Belgium; 5Quantum Solid State Physics, KU Leuven, Leuven, BelgiumCorrespondence: Ana Zamora Email anamaria.zamoramartinez@kuleuven.beIntroduction: The inherent fluorescence properties of iron oxide nanoparticles (IONPs) were characterized, and their applicability for multiphoton imaging in cells was tested in combination with their magnetic resonance imaging (MRI) capabilities.Methods: Superparamagnetic iron oxide nanoparticles were synthesized and subsequently coated with polyethylene glycol to make them water-dispersible. Further characterization of the particles was performed using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), dynamic light scattering (DLS), superconducting quantum interference device (SQUID) and magnetic resonance relaxivity measurements. MRI and fluorescence properties of bare IONPs were first studied in solution and subsequently in A549-labeled cells.Results: The particles, with a core size of 11.3 ± 4.5 nm, showed a good negative MRI contrast in tissue-mimicking phantoms. In vitro studies in mammalian A549 cells demonstrate that these IONPs are biocompatible and can also produce significant T2/T2* contrast enhancement in IONPs-labeled cells. Furthermore, excitation-wavelength dependent photoluminescence was observed under one- and two-photon excitation.Discussion: The obtained results indicated that IONPs could be used for fluorescence label-free bioimaging at multiple wavelengths, which was proven by multiphoton imaging of IONPs internalization in A549 cancer cells.Keywords: iron oxide nanoparticles, photoluminescence, biomedical imaging, MRI, cancer cells, multimodal imaging

Efficient functional coupling of neuronal cells and electronic sensors could result in hybrid bidirectional communication between neurons and computers (L.J. Breckenridge et al., Advantages of using microfabricated extracellular electrodes for in vitro neuronal recordings, J. Neurosci Res. 42 (1995), pp. 266-276; G. Zeck and P. Fromherz, Noninvasive neuroelectronic interfacing with synaptically connected snail neurons immobilised on a semiconductor chip, PNAS 98 (2001), pp. 10457-10462). Such systems could enable us to gain insight into the mechanisms of neuro-degenerative diseases like Parkinson's and Alzheimer's disease in vitro or could be used to improve the function and efficiency of devices used in vivo, for example in Deep Brain Stimulation devices that are already used in the treatment of Parkinson's disease. One of the major challenges for the development of reliable neuro-electronic systems is to perform extracellular recordings of action potentials with a high signal-to-noise ratio. The poor quality of these recordings is caused by the culture medium, which is present in the cleft between the cell membrane and the sensor surface (P. Fromherz, Neuroelectronic interfacing: semiconductor chips with ion channels, nerve cells and brain, in Nanoelectronics and Information Technology, R. Waser, ed., Wiley-VCH, Berlin, 2003, pp. 781-810; G. Zeck and P. Fromherz, Noninvasive neuroelectronic interfacing with synaptically connected snail neurons immobilised on a semiconductor chip, PNAS 98 (2001), pp. 10457-10462). In this article, we describe a method allowing a reduction of the distance between the membrane and the surface by combining surface chemistry and topography. We have developed a specialised surface chemistry, based on small laminin-derived peptides, which applied onto the topographical structures, triggers their engulfment by the cell membrane in a phagocytosis-like event. In the phagocytotic pit, the distance between the cell membrane and the sensor surface is believed to be minimal. We describe the surface chemistry used for the controlled immobilisation of the small peptides on the surface of the needle-like structures that are manufactured on the surface of electronic devices. PC12 neuro-blastoma cells and genetically-modified HeLa cells have been used to investigate the interaction between the cell membrane and the peptide functionalised topographical structures. The membrane-surface interaction was examined by means of electron microscopy and fluorescence microscopy. [ABSTRACT FROM AUTHOR]

In this letter, we demonstrate that organic-based transistors are able to detect charged/uncharged chemical species in aqueous media via the field effect. The chemical sensitivity of the organic transistors is illustrated for protons and glucose. The electrochemical potential developed at the solution/dielectric interface depends on the proton concentration in solution and it modifies the current flowing in the transistor according to this concentration. Glucose can also be detected if an enzymatic layer is coupled to the dielectric surface. An inorganic proton-sensitive dielectric, Ta[SUB2]O[SUB5], is used in the transistor structure in order to reduce the operational voltages. The field-effect detection of chemical species allows us to realize sensors for a variety of ions/molecules if layers with a specific functionality are added to the transistor. Organic-based sensing devices show great potential for low-cost, health-related, and environmental applications because of their very simple fabrication process, which leads to disposability. [ABSTRACT FROM AUTHOR]