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In this paper we propose a simple device and a method for pH monitoring, using an organic thin-film transistor as transducer. Such organic transducers may show potential advantages for sensor technology in terms of fabrication cost and biocompatibility. To explore the applicability of organic transistors in the area of bioanalytics, we have realized a proton sensitive organic transistor and an analogue interface that takes into account the particularities of the transistor in order to illustrate the pH response. The detection principle is based on the field-enhanced conductivity of the poly(3-hexylthiophene) semiconducting polymer. The device was characterized electrically in different pH buffers. To display directly the pH response, the detector was connected to a specially developed low-noise, low-power amplifier system. The device concept, electrical characteristics, pH sensitivity and stability are discussed. [Copyright &y& Elsevier]

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]

Abstract: Neurotransmitter release is the key factor of chemical messaging in the brain. Fast, sensitive and in situ detection of single cell neurotransmitter release is essential for the investigation of synaptic transmission under physiological or pathophysiological conditions. Although various techniques have been developed for detecting neurotransmitter release both in vitro and in vivo, the sensing of such events still remains challenging. First of all, the amount of neurotransmitter released during synaptic transmission is unknown because of the limited number of molecules released and the fast diffusion and reuptake of these molecules after release. On the other hand, advances in microelectronic biosensor devices have made possible the fast detection of various analytes with high sensitivity and selectivity. Specifically, enzyme-modified field-effect (ENFET) devices are attractive for such applications due to their fast response, small dimensions and the possibility to integrate a large number of sensors on the same chip. In this paper, we present a floating-gate FET device coated with glutamate oxidase (GLOD) layer. The surface chemistry was optimized for maximal enzyme loading and long-term stability, and characterized by quartz crystal microbalance and colorimetric assays. Enzyme loading was largest on poly-l-lysin-based surfaces combined with glutaraldehyde. The surface chemistry showed excellent stability for at least one month in Tris buffers stored at 4°C. A glutamate detection limit of 10−7 M has been obtained with the GLOD-coated FET and our sensor proved to be selective to glutamate only. We show that this biosensor is a promising tool for the in vitro detection of glutamate and can be extended to other neurotransmitters. [Copyright &y& Elsevier]

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]