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Đây là một bài báo khoa học về dây nano silic trong lĩnh vực nghiên cứu công nghệ nano dành cho những người nghiên cứu sâu về vật lý và khoa học vật liệu.Tài liệu có thể dùng tham khảo cho sinh viên các nghành vật lý và công nghệ có đam mê về khoa học
Please cite this article in press as: X.T. Vu, et al., Fabrication and application of silicon nanowire transistor arrays for biomolecular detection, Sens. Actuators B: Chem. (2009), doi:10.1016/j.snb.2008.11.048 ARTICLE IN PRESS G Model SNB-11150; No. of Pages 7 Sensors and Actuators B xxx (2009) xxx–xxx Contents lists available at ScienceDirect Sensors and Actuators B: Chemical journal homepage: www.elsevier.com/locate/snb Fabrication and application of silicon nanowire transistor arrays for biomolecular detection X.T. Vu, R. GhoshMoulick, J.F. Eschermann , R. Stockmann, A. Offenhäusser, S. Ingebrandt ∗ Institute of Bio- and Nanosystems and CNI – Centre of Nanoelectronic Systems for Information Technology, Forschungszentrum Jülich GmbH, Leo-Brandt-Str., D-52428 Jülich, Germany article info Article history: Available online xxx Keywords: Biosensor Silicon nanowire transistor arrays Field-effect sensors Nanoimprint lithography abstract We present a novel approach for large-scale silicon nanowire (SiNW) array fabrication for bioelectronic applications. Nanoimprint lithography was combined with standard CMOS processing on 4in. SOI wafers in order to produce highly integrated arrays of siliconnanowire field-effect transistors (SiNW-FET). Witha very smooth surface due to wet anisotropic etching, SiNW-FET arrays show a good electronic performance with a subthreshold slope of about 85 mV/decade. When applying a front-gate control of the wires via an electrochemical reference electrode, reliable electronic performance inside an electrolyte solution can be achieved. Our SiNW-FET sensors exhibit almost no electronic hysteresis on forward and backward bias sweeps. In this article the fabrication process, electronic and electrochemical characterizations and first biomolecular detection experiments are presented. For biodetection experiments we used a differential readout between molecule-free wires and wires carrying covalently attached biomolecules such as short, single-stranded DNA or biotin. With our SiNW-FET arrays a reliable detection of biomolecular layers can be achieved. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Nano-scale bioelectronic devices have the potential to achieve exquisite sensitivity for the direct detection of biomolecular inter- actions at surfaces. Because of their high surface-to-volume ratio, fast response time and reliability of the electronic readout, sil- icon nanowire field-effect transistor (SiNW-FET) arrays promise ultra high sensitivity for various, label-free biosensing applications. These device types will have a high impact for analyses in biomed- ical diagnosis and early warning of bioterrorism attacks. In the past few years, the number of reports about SiNW-biosensors, which were either fabricated by “top-down” or “bottom-up” methods, is steadily increasing. The biosensors were used for glucose detec- tion [1], protein binding orDNA hybridization detection [2–4], virus detection [5], and even for extracellular recording from electrogenic cells [6]. For real biosensor applications, the reliability of the devices and the reduction of the fabrication cost are the major issues. In our project, we developed a wafer-scale approach to fabri- cate the SiNW-FET biosensors. We employ a novel method in ∗ Corresponding author. Present address: University of Applied Sciences Kaiser- slautern - Campus Zweibrücken, Department of Informatics & Microsystem Technology, Amerikastr.1, D-66482 Zweibrücken, Germany. Tel.: +49 6332 914 413; fax: +49 6332 914 313. E-mail address: sven.ingebrandt@fh-kl.de (S. Ingebrandt). nanofabrication, the nanoimprint lithography [7], in combina- tion with anisotropic wet etching with tetramethylammonium hydroxide (TMAH) [8,9]. In addition, our process includes stan- dard CMOS processes like wet, dry etching and conventional photolithography techniques. We improved the device perfor- mance by boron doping on the conducting lines to reduce the serial resistance, while retaining the high charge mobility inside the SiNW-FETs. Chips were passivated by a layer of low pres- sure chemical vapor deposited (LPCVD) SiO 2 . As gate oxide of the SiNW-FETs, a thin thermal SiO 2 (6–8 nm) was chosen, which serves as input dielectric. Main advantage of our process flow is that mass production with reproducible devices can be achieved. We developed a portable electronic readout system for the use of the SiNW-FET arrays in biosensing experiments [10,11]. With this system, the simultaneous readout of all 16-channels can be achieved. We describe in this article the electrical and electrochemical characterization of the SiNW transistors. The devices can be oper- ated by applying a back gate voltage through theburied oxide (BOX) layer as well asto the front-gatethrough anelectrolyte solution con- tacted by a liquid-junction Ag/AgCl reference electrode. The wires showed good pH sensitivity with little hysteresis. As a first proof- of-principle experiments for biomolecular detection we covalently immobilized short DNA molecules or biotin molecules at the wire surfaces. The biomolecules were site-selectively attached at the array surface using a micro-spotter system. A reliable detection of the biomolecules can be done by using a differential read- 0925-4005/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2008.11.048 Please cite this article in press as: X.T. Vu, et al., Fabrication and application of silicon nanowire transistor arrays for biomolecular detection, Sens. Actuators B: Chem. (2009), doi:10.1016/j.snb.2008.11.048 ARTICLE IN PRESS G Model SNB-11150; No. of Pages 7 2 X.T. Vu et al. / Sensors and Actuators B xxx (2009) xxx–xxx out between molecule-free wires and wires having biomolecules attached. 2. Experimental methods The fabrication process for our SiNW-FET arrays was recently described in detail [12]. Here we summarize the process and men- tion the main steps. 2.1. Imprint-mold fabrication We used the electron-beam writer of the IBN clean room facil- ities to fabricate the imprint-mold for the thermal nanoimprint process in house. The mold was etched on a 4 in. silicon wafer from a 200 nm thick, thermal oxide. Structures included templates for wet etching of nanowires and feed lines to the individual sensor spots. Fabrication of the structures was done by direct electron-beam lithography with a poly(methyl methacrylate) (PMMA) e-beam resist. Structures were transferred into the SiO 2 layer by reactive ion etching (RIE) with CHF 3 gas. To improve release of the mold after imprinting and to increase the aspect ratio of the small struc- tures (down to 100 nm), we used a monolayer of fluorsilane as anti-adhesion layer on the mold surface. 2.2. Si-nanowire process For fabrication of the devices we used 4 in. silicon-on-insulator (SOI) wafers (SOITEC, France) with a BOX thickness of 40 0 nm and a top Si layer of 360 nm thickness (Si 100 , boron doped 14–22 cm). The wafer carried three different layouts of nanowire arrays (4 × 4-common source, 16 × 16 and 32 × 32-cross contacts). The length of the wires was 3 m in all three designs. For investi- gation of possible size effects we varied the widths of the starting structures for wet etching by 100 nm, 200 nm, 500 nm, and 1 m (mask measures), respectively. In Fig. 1a the layout of the 32 × 32 SiNW array and a scanning electron micrograph of a sensor spot including six wires are shown (Fig. 1b). A schematic of the process flow is shown in Fig. 2. Firstly the top silicon layer of the SOI wafer was thinned out down to about 60 nm (Fig. 2, steps 1 and 2). Then the starting structures were trans- ferred from the mold to the 4 in. SOI wafers by thermal nanoimprint (Nanonex NX-2000, USA) (Fig. 2, step 3). After imprinting, RIE was used to etch the residual resist layer and to etch off the SiO 2 layer between the contact lines (Fig. 2, step 4). Then the device struc- tures were transferred to the top Si layer by anisotropic wet etching with TMAH (25%, 90 ◦ C) [8,9]. Due to the large etch rate difference between Si and SiO 2 , the Si was etched off in the regions which were not covered by the oxide. The etch rate ratio between the Si 100 and the Si 111 directions was about 12:1 in our process. Under the oxide mask, when the wet etching process reached the 111 surface of the Si layer, the etching process was slowed down. Fur- ther etching slowly reduced the width of the wires under the oxide mask (Fig. 2, step 5). To maintain the surface quality of the SiNWs after TMAH etching, wire structures were protected by a 100 nm LPCVD silicon oxide. This layer was further structured by optical lithography to act as protection mask for the feed line implanta- tion. Boron ions (1 × 10 14 cm −2 ) were implanted on the conducting lines with an energy of 7 keV and subsequently annealed at 900 ◦ C for 30 min in a nitrogen atmosphere (Fig. 2, step 6). After annealing, 270 nm of LPCVD silicon oxide was deposited for passivation of the contact lines against the electrolyte solution (Fig. 2, step 7). The gate areas and the bond pads were re-opened and a contact to the bulk Si was realized as back gate contact. A high quality thermal silicon gate oxide (8 nm thickness) was grown on the wires surfaces. At this stage the 16-channel devices were finalized by deposition of a metal stack consisting of Al 150 nm, Ti 10 nm and Au 150 nm at the bond Fig. 1. (a) Differential interference contrast microscopy of the 32 × 32 silicon nanowire array. (b) SEM image of one sensor spot with six nanowires. The open- ing of the passivation layers on top of the nanowire area can be seen. (c) Scanning electron micrograph of a single silicon wire (<100 nm). One can see the Si 100 and Si 111 surfaces of the trapezoid wire structure. pads (Fig. 2, step 8). For the 16 × 16 and 32 × 32 arrays this metal layer served as second contact line inside the grid array (Fig. 1a). To enable operation of these devices in an electrolyte solution, a nitride-oxide stack was deposited by plasma enhanced chemical vapor deposition (PECVD) (at the clean room facilities of the Uni- versity of Applied Sciences Kaiserslautern - Campus Zweibrücken, Germany) and the bond pads were re-opened. 2.3. Electronic readout and detection methods For measurements in a liquid environment, devices were wire bonded on 68-pin LCC carriers (LCC0850, Spectrum, USA) and encapsulated using glass rings and a biocompatible epoxy glue Please cite this article in press as: X.T. Vu, et al., Fabrication and application of silicon nanowire transistor arrays for biomolecular detection, Sens. Actuators B: Chem. (2009), doi:10.1016/j.snb.2008.11.048 ARTICLE IN PRESS G Model SNB-11150; No. of Pages 7 X.T. Vu et al. / Sensors and Actuators B xxx (2009) xxx–xxx 3 Fig. 2. Main process steps for the fabrication of the SiNW-FET arrays. Our wafer-scale process for SOI wafers is combining nanoimprint lithography with wet etching using TMAH. Contact lines are p-doped for reliable operation of the devices. The finalized structure in step 8 shows back gate contact, bond pad, contact line and open wire (from left to right). (U300 8OZ, Epo-TEK, USA) (Fig. 3b). Recording was done on a wafer probe station or with our previously described 16-channel FET amplifier system for dc and for ac readout [10–13] (Fig. 3a). To record the small currents of the SiNW-FETs in their respective working points (about 1–10 A), we used a 250 k feedback resistor in the Fig. 3. (a) Portable, 16-channel amplifier system for SiNW-FETs. The electrochemical Ag/AgCl reference electrode is fixed on top of the encapsulated chip. (b) Photograph of a fully encapsulated, 16-channel SiNW chip. (c) Schematic principle of the readout circuit. By applying a sinusoidal reference signal to the SiNW-FET array, the transfer function of the system reference electrode/electrolyte solution/biomolecules/SiNW- FET/first amplifier stage can be recorded using the lock-in electronics of the amplifier system. first amplifier stage (Fig. 3c). For operation in a liquid environment, the gate voltage was applied via a small, liquid-junction Ag/AgCl electrode (Super Dry-Ref (SDR2), WPI, Germany) and the position of this electrode with respect to the SiNW-FET array was fixed on top of the amplifier (see Fig. 3a). Generally, signals from biomolecular reactions at surfaces (such as DNA hybridization or protein interaction) can be obtained either by potentiometric dc [14–17] or impedimetric ac [10,18–21] read- out. It is generally accepted that for dc readout, the biomolecules are detected based on their intrinsic charge [14,15,22–26] or based on a re-distribution of ions near the liquid–solid interface [27]. When SiNW-FETs are functionalized with biomolecular receptors, specific binding of charged target molecules results in deple- tion or accumulation of charge carriers inside the SiNWs and hence in a change of the transistor’s drain–source current. This is because the resulting change in the surface charge density is shifting the flat band voltage of the transistor b efore and after the biomolecular adsorption process. These effects were monitored in the present article by recording the transfer characteristics of the SiNW-FETs before and after biomolecule attachment and by a direct comparison of channels with biomolecules to channels without biomolecules. As a second effect, the biomolecular layer on the surface of the SiNWs is acting as an additional, passive RC element inside Please cite this article in press as: X.T. Vu, et al., Fabrication and application of silicon nanowire transistor arrays for biomolecular detection, Sens. Actuators B: Chem. (2009), doi:10.1016/j.snb.2008.11.048 ARTICLE IN PRESS G Model SNB-11150; No. of Pages 7 4 X.T. Vu et al. / Sensors and Actuators B xxx (2009) xxx–xxx the readout circuit (resistance R mem and capacitance C mem of the biomembrane in Fig. 3c). The DNA hybridization reaction or the protein binding is leading to a change of the input impe dance of the device. This change can be accessed by using an impedimetric readout method utilizing the transistor transfer function (TTF) prin- ciple [10,11,18,20,21]. For this detection method the combination of sensor, its first amplification circuit with feedback resistor R FB , the reference electrode resistance R RE , the liquid solution resistance R sol , the contact line capacitance C CL , the gate oxide capacitance C ox , and the resistance R mem and capacitance C mem of an attached biomolecular membrane are regarded as an electronic circuit of passive elements. Such a circuit can be well described by a transfer function H. It is defined by the ratio of the output v out to the input voltage v in of the amplifier H = v out /v in (Fig. 3c). The parameter H is dimensionless and simply describes the attenuation of the system at a specific frequency. 2.4. Covalent attachment of biomolecules on SiNW-FETs For covalent immobilization of DNA molecules, the chips were cleaned and activated in a protocol including both wet chemical and plasma cleaning. Firstly the chips were immersed for 20 min in 2% Hellmanex (Hellma, Germany) followed by rinsing with ultra pure water (Milli-Q, Gradient A10 18.2 M, Millipore Inc., Germany) and drying with Argon. The final activation of the silicon oxide surface was done in oxygen plasma (100E Plasma System from Techniques Plasma GmbH, 1.4 mbar, 200 W, and 1 min). For biofunctionaliza- tion of the wire surfaces, we used a vapor phase silanization protocol with 3-glycidoxypropyltrimethoxysilane (GPTES) [28,29]. The chips were placed in a desiccator containing a few drops of silane (300 l). The desiccator was sealed, heated and the reac- tion was allowed for 1 h. The complete silanization procedure was performed inside a glove box containing a water- and oxygen-free argon atmosphere. The silanization procedure was finalized by rins- ing several times with ultra pure water in order to remove unbound silane molecules. Finally all samples were dried with argon. For micro-spotting with our single-nozzle system with aiming option [13], the amino-modified 20 base-pair (bp) DNA probes (MWG- Biotech AG, Germany) were prepared in a concentration of 1 Min a 0.1 M phosphate buffer of pH 8.5. After micro-spotting, the immo- bilization process was performed by overnight incubation at 37 ◦ C in a humid atmosphere. For covalent immobilization of biotin to the SiNW-FETs, the chip surface was functionalized with 3-aminopropyl-triethoxysilane (APTES) [30–32]. Chips were wet-chemically cleaned in three steps including ethanol for 2 min, HCl (2%, v/v) for 2 min, and piranha solution for 2 min. The chip surfaces were then activated by H 2 SO 4 (20% (v/v), 80 ◦ C for 10 min). After each step, the chips were carefully rinsed with ultra pure water and dried with argon. For silaniza- tion the chips were transferred to the glove box containing an argon atmosphere. Silanization with APTES was performe d for 1 h inside a desiccator, too. A drop of pure APTES (300 l) was placed inside the desiccator and the whole system was evacuated. The pressure of the desiccator was controlled at p = 5 mbar residual argon gas. After silanization the chips were firstly rinsed with 1% acetic acid and then rinsed with ultra pure water and dried with argon [30]. The EZ-Link Sulfo-NHS-LC-Biotin (sulfosuccinimidyl- 6-(biotinamido)hexanoate; Pierce Biotechnology, Inc., USA) with a concentration of 1 M (1 mg/1.5 ml) was dissolved in sodium phos- phate buffer (2.5 mM, pH 8.2). This biotin solution was spotted on the SiNW areas using our micro-spotter [13,33]. Then the chips were incubated for 1 h at 37 ◦ C in a humid environment. After that the chips were rinsed with ultra pure water in order to remove unbound biotin. This protocol binds the biotin molecules covalently to the silicon oxide surfaces. 3. Results and discussion 3.1. Process characterization During the fabrication process of the SiNW arrays imaging ellip- sometry, scanning electron microscopy, and optical microscopy were used for process control. By the use of thermal nanoimprint in combination with the TMAH wet etching, the nanowire structures were reliably transferred to the full area of the 4 in. SOI wafers. The imprint process was reproducible with a high aspect ratio of the structures. The imprint-mold was very stable and was re-used many times. However, due to the complexity of the structures, the residual resist layer after nanoimprint was not homogenous. There- fore the RIE etching of this residual layer was strictly controlled to maintain the high aspect ratio of the structures. The anisotropic TMAH etching created a trapezoidal SiNWs structure having Si 111 sidewalls in an angle of 54.7 ◦ with 100 top and bottom surfaces (Fig. 1c). By further etching, the size of the top and bottom 100 planes will be slowly reduced under the top oxide mask. The etching rate for the Si 111 direction was about 20 nm/min for our process. Using this process SiNWs with very smooth surfaces were achieved (Fig. 1c). Since the contact lines of our chips were passivated by a high quality LPCVD oxide, a reliable performance in electrolyte solution was achieved. Addi- tionally, our chips can be re-used for many experiments by the use of a standard cleaning protocol [30,31,33]. Fig. 4. When the contact lines of the SiNW-FET array are additionally implanted by boron, a reliable p-FET operation of the wires can be achieved. (a) Transfer charac- teristics of a SiNW-FET with p-doped contact lines. (b) Subthreshold characteristics of a SiNW-FET. Please cite this article in press as: X.T. Vu, et al., Fabrication and application of silicon nanowire transistor arrays for biomolecular detection, Sens. Actuators B: Chem. (2009), doi:10.1016/j.snb.2008.11.048 ARTICLE IN PRESS G Model SNB-11150; No. of Pages 7 X.T. Vu et al. / Sensors and Actuators B xxx (2009) xxx–xxx 5 Fig. 5. Characterization of the pH sensitivity of the SiNW-FETs (six wires of 400 nm width per sensor spot). (a) When the silicon contact lines of the wires are not implanted by boron, an n-FET behavior is achieved. The usage of different pH buffer solutions is shifting the threshold voltage of the transistors as indicated in the graphs. (b) When we use an implantation of the contact lines, exclusively a p-FET behavior is achieved. With different pH buffer solutions the threshold voltage shifts are accord- ingly. Note that in the graphs both, forward and backward bias sweeps are shown indication almost no electronic hysteresis. Fig. 6. Transfer function characteristics of the SiNW-FETs with different NaCl con- centrations of the electrolyte buffer. The behavior is quite similar to what we usually achieve with our standard, micro-sized FET arrays. 3.2. Electrical and electrochemical characterization We previously described that the performance of our SiNW-FETs inside an electrolyte solution with front-gate operation is depen- dent on the implantation status of the silicon contact lines. In Fig. 4 the electronic performance of a SiNW-FET with implanted contact lines is shown. Fig. 4a shows the transfer characteris- tics and Fig. 4b the subthreshold characteristics of the device. The wires can clearly be operated as p-type transistors and the subthreshold slope was as small as 85 mV/decade for the best devices. In Fig. 5a comparison of a device with and without implanted contact lines is shown. We characterized the pH sensitivity of both device types using titrisol buffer solutions between pH 2 and 10. The gate voltage was applied via the front-gate using the liquid-junction Ag/AgCl reference electrode. In Fig. 5a the n-FET characteristics of a device with non-implanted contact lines is shown. Note that in both graphs of Fig. 5 the data for forward and backward bias sweeps are shown. Both device types show almost no electronic hysteresis indicating a small density of trapped charges inside the structure. In previous version of these chips, when we used RIE etching in contrast to the TMAH etching, the wire surfaces were much rougher resulting in a strong electronic hysteresis (data not Fig. 7. Detection of immobilized DNA on the SiNW-FETs. Transfer characteristics before (solid lines) and after DNA immobilization (dashed lines) are shown. DNA was site-selectively immobilized on some channels out of the same array using a micro-spotter. (a) One channel out of the same array having no DNA attached. (b) Another channel out of the same array having 20-bp DNA attached with a high grafting density. For the DNA-modified sensor a shift of 250 mV of the flat band voltage was recorded. Please cite this article in press as: X.T. Vu, et al., Fabrication and application of silicon nanowire transistor arrays for biomolecular detection, Sens. Actuators B: Chem. (2009), doi:10.1016/j.snb.2008.11.048 ARTICLE IN PRESS G Model SNB-11150; No. of Pages 7 6 X.T. Vu et al. / Sensors and Actuators B xxx (2009) xxx–xxx shown). For our current device types the transfer characteristics was shifting to the left side for smaller pH values and to the right side for larger pH values independent if p-type or n-type devices were used. The sensitivity in both cases was measured to 38–41 mV/pH, which is a typical value for silicon oxide sur- faces. With our lock-in based amplifier system the SiNW-FET devices can also be used as impedimetric sensors like recently reported with our standard, micro-sized FETs [10,11].InFig. 6 the trans- fer characteristics of a SiNW-FET in buf fer solutions with different concentrations of NaCl (pH 7) is shown. Similar to what we previ- ously reported for our micro-sized FETs, the transfer characteristics is shifting, because the solution resistance R sol in the electronic cir- cuit is changing. The time constant for this low pass is build out of solution resistance R sol plus reference electrode resistance R RE in combination with the contact line capacitance C CL (Fig. 3c). In future we will elaborate, if the previously describe d TTF method for detection of DNA [10] and of cellular adhesion [11] can also be used with our new SiNW-FET devices. 3.3. Electronic detection of biomolecules In Fig. 7 the potentiometric detection of a covalently immo- bilized DNA layer on top of the SiNWs is shown. In Fig. 7aan exemplary molecule-free channel is shown, whereas the attach- ment of the dense DNA layer was shifting the flat band voltage of the SiNW-FET channel (six wires with 160 nm wire width in this Fig. 8. Detection of covalently immobilized biotin with the SiNW-FET arrays. Trans- fer characteristics before (solid lines) and after biotin functionalization (dashed lines) are shown. Biotin was site-selectively immobilized on some channels out of the same array using a micro-spotter. (a) SiNW-FET channel having no biotin attached. (b) SiNW-FET channel of the same sensor array having biotin attached. In this case a flat band voltage shift of 33 mV was recorded. exemplary recording) by 250 mV. This behavior was confirmed with several devices and many channels showed a similar shift. The flat band voltage shift was very large compared to what we previously reported for the micro-sized FET devices [14,31,33]. For this mea- surement a sodium phosphate buffer (5 mM, pH 7) was used as electrolyte solution. In Fig. 8a similar experiment for detection of biotin with the SiNW-FET arrays is shown. In the biomolecular-free channels a minor shift was recorded, whereas in the channels spotted with biotin a shift of 33 mV was recorded (Fig. 8b). For this measurement a sodium phosphate buffer (2.5 mM, pH 8.2) was used as electrolyte solution. Again with several chips containing many channels a sim- ilar, reliable behavior was observed. 4. Conclusions We present a robust, wafer-scale fabrication process for SiNW transistor arrays. With a combination of nanoimprint and TMAH wet anisotropic etching, we produced smooth surfaces for the SiNW transistors. We achieved a wire width down to 20 nm on top and 100 nm at the bottom of the trapezoid nanowire structure having a height of about 60 nm. In future designs the width of the wire could be even reduced using longer etching times or a thinner start layer. The devices were successfully operated in a liquid environ- ment in different kinds of electrolyte solutions. SiNW-FETs with their silicon oxide surface had a linear pH response with a typi- cal sensitivity of about 40 mV/pH. The electronic performance was stable and forward and backward bias sweeps of the transfer char- acteristics revealed almost no hysteresis. When applying the TTF method, we showed that the devices are sensitive to different ionic strengths of the buffer electrolyte similarly to what we previously reported for our micro-sized FET arrays. For biomolecular experi- ments the devices were silanized with either APTES or GPTES using our standard protocols. We present first biomolecular detection experiments with the SiNW-FET arrays, where we site-selectively and covalently attached single-stranded DNA molecules and biotin molecules at the wire surfaces. In the case of DNA we recorded a very large shift of the flat band voltage of 250 mV. For biotin a smaller, but still large shift of 33 mV was measured. With this device platform and this protocol for biofunctionaliza- tion of the wire surfaces we are now ready for real bioassays such as DNA hybridization or protein binding. 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Interf. Anal. 38 (4) (2006) 176–181. [32] R. GhoshMoulick, X.T. Vu, S. Gilles, D. Mayer, A. Offenhäusser, S. Ingebrandt, Impedimetric detection of covalently attached biomolecules on field-effect transistors. Phys. Status Solidi A: Appl. Mater., in press. [33] S. Ingebrandt, A. Offenhäusser, Label-free detection of DNA using field-effect transistors, Phys. Status Solidi A: Appl. Mater. 203 (14) (2006) 3399–3411. Biographies Xuan Thang Vu was born in Thaibinh, Vietnam, in 1979. He graduated from the College of Science, Vietnam National University, Hanoi, in 2001 with a B.Sc. degree in Materials Science. In 2003 he received a M.Sc. degree in Materials Science at the International Training Institute for Materials Science (ITIMS), Hanoi University of Technology (HUT), Vietnam. From 2003 to 2006 he was working as research assistant at ITIMS. Since 2006 he is working as Ph.D. student at the RWTH-Aachen Univer- sity, Aachen, Germany and at the Institute of Bio- and Nanosystems (IBN), Institute 2: Bioelectronics, at the Forschungszentrum Jülich, Germany. His current research interests are SiNW transistor array design and fabrication for biosensor applications and for electronic detection of biomolecules. Ranjita Ghosh Moulick was born in India, near Kolkata, in 1976. She studied Chem- istry and Biochemistry for her Bachelor and Master Degree, respectively. In 2007 she received her Ph.D. in Biochemistry from the Calcutta University on the topic ‘Fold- ing and aggregation pattern of glycosylated hemoglobin’. Currently she is working as a postdoctoral fellow in the Institute of Bio- and Nanosystems (IBN), Institute 2: Bioelectronics, at the Forschungszentrum Jülich, Germany. Her current research topics are covalent immobilization of biomolecules on oxidic sensor surfaces and electronic detection of biomolecules with field-effect devices. Jan Felix Eschermann was born in Friedrichshafen, Germany, in 1980. He graduated in electrical engineering at the Technical University Munich, Germany in 2006. Dur- ing his master thesis he was working as a visiting scholar at the Beckman Institute in Urbana-Champaign, IL, USA. Since 2006 he is working as Ph.D. student at the RWTH- Aachen University, Aachen, Germany and at the Institute of Bio- and Nanosystems (IBN), Institute 2: Bioelectronics, at the Forschungszentrum Jülich, Germany. His cur- rent research interests are SiNW transistor array design, fabrication and simulation for bioelectronic applications and extracellular recording from electrogenic cells. Regina Stockmann was born in Aachen, Germany, in 1969. She graduated in Applied Chemistry at the Aachen University of Applied Sciences in 1996. After years of experience in clean room processing she joined in 2002 the Institute of Bio- and Nanosystems (IBN), Institute 2: Bioelectronics, at the Forschungszentrum Jülich, Germany. From then on her main focus was on optimizing semiconductor chips to achieve better sensors for bioelectronic measurements. Her current interests are silicon nanowire design, fabrication and optimization for biosensor applications. Andreas Offenhäusser was born in Heidenheim, Germany in 1959. He graduated in physics (Diplom) from the University of Ulm in 1985 and completed a Ph.D. at the University of Ulm in 1989. From 1990 to 1992 he worked as an engineer at Robert Bosch GmbH, Reutlingen. From 1992 to 1994 he joined the Frontier Research Program, RIKEN, Japan. From 1994 to 2001 he worked at the Max Planck Institute for Polymer Research, Mainz, as a group leader. In 2000 he received his “habilitation”. He moved to the Forschungszentrum Jülich in 2001 where he is presently director of the Institute of Bio- and Nanosystems (IBN), Institute 2: Bioelectronics. He is a professor for experimental physics at the RWTH-Aachen University, Germany. The focus of his work is the functional coupling of sensory cells and neurons with microelectronic devices, signal processing in biological neuronal networks, electronic DNA-Chip, and biophysics of lipid bilayers and membrane receptors. Sven Ingebrandt was born in Alzey, Germany, in 1971. He graduated in physics (Diplom) in 1998 at the Johannes Gutenberg University Mainz, Germany. From 1998 to 2001 he was working as Ph.D. student at the Max Planck Institute for Polymer Research in Mainz, Germany. He received his Ph.D. degree in physical chemistry in 2001 from the Johannes Gutenberg University Mainz, Germany. In 2001 and 2002 he was working as postdoctoral researcher at the Frontier Research Program, RIKEN, Japan. From 2002 to 2008 he was working as group leader in the Institute of Bio- and Nanosystems (IBN), Institute 2: Bioelectronics, at the Forschungszentrum Jülich, Germany. Recently he moved to the Kaiserslautern University of Applied Sciences as a professor of Biomedical Engineering. Currently he is still leading a research group in Jülich elaborating topics such as cell–sensor coupling, whole-cell biosensors and electronic field-effect based sensors for biomolecular detection. His main interests are micro- and nanochip design and fabrication for bioelectronic applications and bioelectronic signal recording and interpretation. . article in press as: X.T. Vu, et al., Fabrication and application of silicon nanowire transistor arrays for biomolecular detection, Sens. Actuators B: Chem homepage: www.elsevier.com/locate/snb Fabrication and application of silicon nanowire transistor arrays for biomolecular detection X.T. Vu, R. GhoshMoulick,