SEISMIC ISOLATION OF LEAD-COOLED REACTORS: THE EUROPEAN PROJECT SILER

SILER (Seismic-Initiated event risk mitigation in LEad-cooled Reactors) is a Collaborative Project, partially funded by the European Commission in the 7th Framework Programme, aimed at studying the risk associated to seismic-initiated events in Generation IV Heavy Liquid Metal reactors, and developing adequate protection measures. The project started in October 2011, and will run for a duration of three years. The attention of SILER is focused on the evaluation of the effects of earthquakes, with particular regards to beyond-design seismic events, and to the identification of mitigation strategies, acting both on structures and components design. Special efforts are devoted to the development of seismic isolation devices and related interface components. Two reference designs, at the state of development available at the beginning of the project and coming from the 6th Framework Programme, have been considered: ELSY (European Lead Fast Reactor) for the Lead Fast Reactors (LFR), and MYRRHA (Multi-purpose hYbrid Research Reactor for High-tech Applications) for the Accelerator-Driven Systems (ADS). This paper describes the main activities and results obtained so far, paying particular attention to the development of seismic isolators, and the interface components which must be installed between the isolated reactor building and the nonisolated parts of the plant, such as the pipe expansion joints and the joint-cover of the seismic gap

Amorphous silicon photosensors integrated in microfluidic structures as a technological demonstrator of a "true" Lab-on-Chip system

In this paper we present a compact technological demonstrator including on the same glass substrate an electrowetting-on-dielectrics (EWOD) system, a linear array of amorphous silicon photosensor and a capillary-driven microfluidic channel. The proposed system comprises also a compact modular electronics controlling the digital microfluidics through the USB interface of a computer. The system provides therefore both on-chip detection and microfluidic handling needed for the realization of a 'true' Lab-on-Chip. The geometry of the photosensors has been designed to maximize the radiation impinging on the photosensor and to minimize the inter-site crosstalk, while the fabrication process has been optimized taking into account the compatibility of all the technological steps for the fabrication of the EWOD system, the photosensor array and the microfluidics channels. As a proof of the successful integration of the different technological steps we demonstrated the ability of the a-Si:H photosensors to detect the presence of a droplet over an EWOD electrode and the effective coupling between the digital and the continuous microfluidics, that can allow for functionalization, immobilization and recognition of biomolecules without external optical devices or microfluidic interconnections

Technologies for autonomous integrated lab-on-chip systems for space missions

Lab-on-chip devices are ideal candidates for use in space missions where experiment automation, system compactness, limited weight and low sample and reagent consumption are required. Currently, however, most microfluidic systems require external desktop instrumentation to operate and interrogate the chip, thus strongly limiting their use as stand-alone systems. In order to overcome the above-mentioned limitations our research group is currently working on the design and fabrication of “true” lab-on-chip systems that integrate in a single device all the analytical steps from the sample preparation to the detection without the need for bulky external components such as pumps, syringes, radiation sources or optical detection systems. Three critical points can be identified to achieve ‘true’ lab-on-chip devices: sample handling, analytical detection and signal transduction. For each critical point, feasible solutions are presented and evaluated. Proposed microfluidic actuation and control is based on electrowetting on dielectrics, autonomous capillary networks and active valves. Analytical detection based on highly specific chemiluminescent reactions is used to avoid external radiation sources. Finally, the integration on the same chip of thin film sensors based on hydrogenated amorphous silicon is discussed showing practical results achieved in different sensing task

Amorphous silicon photosensors for on-chip detection in digital microfluidic system

In this paper we present the integration, on a single glass substrate, of amorphous silicon photodiodes with an electrowetting-on-dielectric (EWOD) system as a technological demonstrator for achieving a compact, stand alone Lab-on-Chip (LoC) system. The EWOD system comprises a thin film of indium tin oxide (ITO) acting as actuation electrodes and a 1 μm-thick polydimethylsiloxane (PDMS) layer acting as both insulation and hydrophobic layer. The a-Si:H photosensors are ITO/p-type/intrinsic/n-type/metal stacked structures, aligned with the transparent EWOD electrodes, to detect optical signals generated inside (or modulated by) the liquid droplets handled by the digital microfluidic system. The fabrication process has been designed and performed taking into account the compatibility of all the technological steps of the photosensor and EWOD structures fabrication. The successful integration has been demonstrated checking the correct geometry of EWOD electrodes and measuring the optoelectronic performances of the a-Si:H photosensors at the end of the system fabrication. The correct operation and potentiality of the presented device has been assessed monitoring a photodiode current when a water droplet is moved forward and backward over the EWOD electrodes aligned with the photosensors. © 2014 Published by Elsevier B.V

a-Si:H temperature sensor integrated in a thin film heater

In this work we present an hydrogenated amorphous silicon (a-Si:H) temperature sensor integrated in a thin film heater to perform biomolecular treatments. The system is fabricated on a microscope glass slide and includes a PolyDiMethylSiloxane (PDMS) chamber to confine the solution containing the sample and to avoid its evaporation. The heater is a 200 nm-thick titanium/tungsten sputtered film with a serpentine shaped geometry that has been designed by a finite element simulator in order to obtain a spatial-uniform temperature distribution. A uniformity better than 3% has been achieved over the surface of the structure. The temperature sensor is a n-type/intrinsic/p-type a-Si:El stacked structure deposited by plasma enhanced chemical vapor deposition. The top and bottom contacts of the diode are made by the same metal utilized to fabricate the heater. The characterization of the sensor response has been performed both under forward and reverse bias condition. In reverse bias condition, at fixed voltage, the current temperature curve exhibits an exponential behavior. In forward bias condition, at constant bias current, the voltage across the diode is linearly dependent on the temperature in the range 30-90 degrees C. In particular, using a constant bias current of 10 nA, a sensitivity around -3.3 mV/degrees C has been achieved. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Amorphous silicon balanced photodiode for microuidic applications

In this paper, we present the first integration of an amorphous silicon balanced photosensor with a microfluidic network to perform on-chip detection for biomedical applications, where rejection of large background light intensity is needed. This solution allows to achieve high resolution readout without the need of high dynamic range electronics. The balanced photodiode is constituted by two-series-connected a-Si:H/a-SiC:H n-i-p stacked junctions, deposited on a glass substrate. The structure is a three terminal device where two electrodes bias the two diodes in reverse conditions while the third electrode (i.e., the connection point of the two diodes) provides the output signal given by the differential current. The microfluidic network is composed of two channels made in PolyDimetilSiloxane (PDMS) positioned over the glass substrate on the photodiode-side aligning each channel with a diode. This configuration guarantees an optimal optical coupling between luminescence events occurring in the channels and the photosensors. The experiments have been carried out measuring the differential current in identical and different conditions for the two channels. We have found that: the measurement dynamic range can be increased by at least an order of magnitude with respect to conventional photodiodes; the balanced photodiode is able to detect the presence or absence of water in the channel; the presence of fluorescent molecules in the channel can be successful detected by our device without any need of optical filter for the excitation light. These preliminary results demonstrate the successful integration of a microfluidic network with a-Si:H photosensor for on-chip detection in biomedical applications

Amorphous silicon balanced photodiode for application in biomolecular analysis

In this work we present an amorphous silicon/amorphous silicon carbide balanced photodiode structure suitable for differential photocurrent measurements in the ultraviolet (UV) and visible range. The device is a three-terminal structure constituted by two series-connected amorphous silicon p-i-n photodiodes. The structure takes advantage of the differential measurement to reveal very small variations of photocurrent in a large background current signal. Application of the device in detection of biomolecules based on the use of photosensors, can allow the increase of both the dynamic range and the sensitivity ofthe measurement. Several balanced structures with different geometries have been fabricated utilizing a four mask-step process . The devices have been characterized by measuring the common mode rejection ratio as a function of radiation intensity and wavelength and ofbias voltage. Experimental results demonstrated that in dark condition differential currents three orders of magnitude lower than the current of each sensor are detected, while under ultraviolet illumination CMRR values around 40 dB have been achieved independent on the bias voltage. These performances are comparable with those obtained by crystalline differential photodiode structures

Thin film device for background photocurrent rejection in biomolecular analysis systems

In this paper we report on the integration, on a glass substrate, of a microfluidic network with a balanced photodiode constituted by two series-connected amorphous silicon/silicon carbide n-i-p stacked junctions. The photosensor is suitable for detection of small variations of photocurrent in biomedical application. The experiments have been carried out measuring the differential current under a large background light intensity to reproduce realistic operating conditions for a point-of-care analysis system. We have found that the proposed device is able to detect the presence or absence of water flow in the channel. © 2014 Springer International Publishing Switzerland

Two-Color Sensor for Biomolecule Detection

In this paper we report on biomolecule detection based on a two-color amorphous silicon photosensor. The revealed biomolecules are DNA strands labeled with two fluorochromes (Alexa Fluor 350 or Cy5) with different spectral properties and the device is a p-i-n-i-p amorphous silicon/amorphous silicon carbide stacked structure, that is able to detect different spectral regions depending on the voltage applied to its electrodes. The device design has been optimized in order to maximize the spectral match between the sensor responses and the emission spectra of the fluorochromes. This optimization process has been carried out by means of a numerical device simulator, taking into account the optical and the electrical properties of the amorphous silicon materials. We found that the detection limit of DNA molecules labeled with Alexa Fluor 350 is 3 nmol/l, while a detection limit around 400 nmol/l has been measured for the Cy5 dye