Pulsed-temperature metal oxide gas sensors for microwatt power consumption

Metal Oxide (MOX) gas sensors rely on chemical reactions that occur efficiently at high temperatures, resulting in too-demanding power requirements for certain applications. Operating the sensor under a Pulsed-Temperature Operation (PTO), by which the sensor heater is switched ON and OFF periodically, is a common practice to reduce the power consumption. However, the sensor performance is degraded as the OFF periods become larger. Other research works studied, generally, PTO schemes applying waveforms to the heater with time periods of seconds and duty cycles above 20%. Here, instead, we explore the behaviour of PTO sensors working under aggressive schemes, reaching power savings of 99% and beyond with respect to continuous heater stimulation. Using sensor sensitivity and the limit of detection, we evaluated four Ultra Low Power (ULP) sensors under different PTO schemes exposed to ammonia, ethylene, and acetaldehyde. Results show that it is possible to operate the sensors with total power consumption in the range of microwatts. Despite the aggressive power reduction, sensor sensitivity suffers only a moderate decline and the limit of detection may degrade up to a factor five. This is, however, gas-dependent and should be explored on a case-by-case basis since, for example, the same degradation has not been observed for ammonia. Finally, the run-in time, i.e., the time required to get a stable response immediately after switching on the sensor, increases when reducing the power consumption, from 10 minutes to values in the range of 10-20 hours for power consumptions smaller than 200 microwatts

Nanostructure ITO and get more of it. Better performance at lower cost

In this paper, we investigated how different growth conditions (i.e., temperature, growth time, and composition) allows for trading off cost (i.e., In content) and performance of nanostructured indium tin oxide (ITO) for biosensing applications. Next, we compared the behavior of these functionalized nanostructured surfaces obtained in different growth conditions between each other and with a standard thin film as a reference, observing improvements in effective detection area up to two orders of magnitude. This enhanced the biosensor's sensitivity, with higher detection level, better accuracy and higher reproducibility. Results show that below 150 °C, the growth of ITO over the substrate forms a homogenous layer without any kind of nanostructuration. In contrast, at temperatures higher than 150 °C, a two-phase temperature-dependent growth was observed. We concluded that (i) nanowire length grows exponentially with temperature (activation energy 356 meV) and leads to optimal conditions in terms of both electroactive surface area and sensitivity at around 300 °C, (ii) longer times of growth than 30 min lead to larger active areas and (iii) the In content in a nanostructured film can be reduced by 10%, obtaining performances equivalent to those found in commercial flat-film ITO electrodes. In summary, this work shows how to produce appropriate materials with optimized cost and performances for different applications in biosensing

Portable flow multiplexing device for continuous, in situ biodetection of environmental contaminants

A compact, low-cost and low-powered device was developed and arranged for multiplexed biodetection of sea water contaminants from continuous flow mode. Electronics, mechanics and fluidics were designed to guarantee identical functional liquid flow through eight parallel sensor microchambers during a predetermined time period providing 8 values at the same time. The accuracy and repeatability of the device was tested in-lab, achieving a deviation of less than 10% when measuring the same analyte in all the chambers. The experimental results obtained with our device were finally compared with those measured in continuous flux by a commercial potentiostat SP150 (Bio-Logic Science Instruments), obtaining identical results, which validated the proposed device

Development of an ImmunoFET for Analysis of Tumour Necrosis Factor- (alfa) in Artificial Saliva: Application for Heart Failure Monitoring

Assessing tumour necrosis factor-(alfa) (TNF-(alfa)) levels in the human body has become an essential tool to recognize heart failure (HF). In this work, label-free, rapid, easy to use ImmunoFET based on an ion-sensitive field effect transistor (ISFET) was developed for the detection of TNF-(alfa) protein. Monoclonal anti-TNF-(alfa) antibodies (anti-TNF-(alfa) mAb) were immobilized on an ISFET gate made of silicon nitride (Si3N4) after salinization with 11-(triethoxysilyl) undecanal (TESUD). The obtained ISFET functionalized with the mAbs (ImmunoFET) was used to detect TNF-(alfa) protein in both phosphate buffer saline (PBS) and artificial saliva (AS). The change in the threshold voltage of the gate (DVT) showed approximately linear dependency on the concentration of the antigens in the range 5-20 pg/mL for both matrixes. The cross-selectivity study showed that the developed ImmunoFET demonstrated to be selective towards TNF-(alfa), when compared to other HF biomarkers such as N-terminal pro-brain natriuretic peptide (NT-proBNP), interleukin-10 (IL-10), and cortisol, even if further experiments have to be carried out for decreasing possible unspecific absorption phenomena. To the best of our knowledge, this is the first ImmunoFET that has been developed based on Si3N4 for TNF-(alfa) detection in AS by electrical measurement

Readout electronics for LGAD sensors

In this paper, an ASIC fabricated in 180 nm CMOS technology from AMS with the very front-end electronics used to readout LGAD sensors is presented as well as its experimental results. The front-end has the typical architecture for Si-strip readout, i.e., preamplification stage with a Charge Sensitive Amplifier (CSA) followed by a CR-RC shaper. Both amplifiers are based on a folded cascode structure with a PMOS input transistor and the shaper only uses passive elements for the feedback stage. The CSA has programmable gain and a configurable input stage in order to adapt to the different input capacitance of the LGAD sensors (pixelated, short and long strips) and to the different input signal (depending on the gain of the LGAD). The fabricated prototype has an area of 0.865 mm × 0.965 mm and includes the biasing circuit for the CSA and the shaper, 4 analog channels (CSA+shaper) and programmable charge injection circuits included for testing purposes. Noise and power analysis performed during simulation fixed the size of the input transistor to W/L = 860 μm/0.2 μm. The shaping time is fixed by design at 1 us and, in this ASIC version, the feedback elements of the shaper are passive, which means that the area of the shaper can be reduced using active elements in future versions. Finally, the different gains of the CSA have been selected to maintain an ENC below 400 electrons for a detector capacitor of 20 pF, with a power consumption of 150 μ W per channel

Prediction of neonatal respiratory morbidity by quantitative ultrasound lung texture analysis: a multicenter study.

BACKGROUND: Prediction of neonatal respiratory morbidity may be useful to plan delivery in complicated pregnancies. The limited predictive performance of the current diagnostic tests together with the risks of an invasive procedure restricts the use of fetal lung maturity assessment. OBJECTIVE: The objective of the study was to evaluate the performance of quantitative ultrasound texture analysis of the fetal lung (quantusFLM) to predict neonatal respiratory morbidity in preterm and early-term (<39.0 weeks) deliveries. STUDY DESIGN: This was a prospective multicenter study conducted in 20 centers worldwide. Fetal lung ultrasound images were obtained at 25.0-38.6 weeks of gestation within 48 hours of delivery, stored in Digital Imaging and Communication in Medicine format, and analyzed with quantusFLM. Physicians were blinded to the analysis. At delivery, perinatal outcomes and the occurrence of neonatal respiratory morbidity, defined as either respiratory distress syndrome or transient tachypnea of the newborn, were registered. The performance of the ultrasound texture analysis test to predict neonatal respiratory morbidity was evaluated. RESULTS: A total of 883 images were collected, but 17.3% were discarded because of poor image quality or exclusion criteria, leaving 730 observations for the final analysis. The prevalence of neonatal respiratory morbidity was 13.8% (101 of 730). The quantusFLM predicted neonatal respiratory morbidity with a sensitivity, specificity, positive and negative predictive values of 74.3% (75 of 101), 88.6% (557 of 629), 51.0% (75 of 147), and 95.5% (557 of 583), respectively. Accuracy was 86.5% (632 of 730) and positive and negative likelihood ratios were 6.5 and 0.3, respectively. CONCLUSION: The quantusFLM predicted neonatal respiratory morbidity with an accuracy similar to that previously reported for other tests with the advantage of being a noninvasive technique

Desarrollo de una tarjeta RFID flexible con capacidades sensoras para aplicaciones en logística de alimentación

[spa] En el momento de la realización de esta tesis doctoral, sobre el año 2004, la tecnología RFID empezaba a crecer, básicamente, gracias a la mejora en el control de stocks de los almacenes que implicaba posibilidad de realizar un inventario sin la necesidad de leer los códigos de barras de los productos. Esta tecnología se basa, en resumen, en la interactuación de dos dispositivos, un lector que envía energía y datos a la vez y una etiqueta que se alimenta mediante la energía enviada por el lector y responde a los datos recibidos. Para el funcionamiento de esta tecnología es necesario que la etiqueta requiera de muy bajo consumo para funcionar. En esta tesis doctoral se pretende utilizar tecnología RFID para la monitorización en la cadena logística de distribución de productos perecederos, en concreto productos de alimentación, dentro del proyecto europeo “Food Safety and Quality Monitoring with Microsystems, GoodFood. El principal objetivo es asegurar la calidad de los productos en aquellas partes de la cadena logística donde no se tiene control de dicha calidad. En la fabricas procesadoras, en los grandes almacenes o en los mercados se realizan controles que aseguran la calidad. Pero una de las partes donde el control no se realiza, o se realiza de forma deficiente, es la fase de transporte, donde es más difícil implementar dichos controles debido a la movilidad de los elementos que la componen. Para una mejora en el control de calidad en la cadena logística de productos perecederos se desarrolla una tarjeta RFID con sensores integrados, que permite la monitorización de los productos perecederos en la fase de transporte. Para poder realizar este tipo de tarjeta es necesario implementar una pequeña batería para poder funcionar sin la presencia del lector, además reducir su consumo, reducir su tamaño e implementarla en un formato flexible para una mayor versatilidad. A lo largo del manuscrito de esta tesis se describe como se ha diseñado la tarjeta físicamente, teniendo en cuenta los requerimientos previos y las especificaciones del estándar ISO/IEC 15693. También se describen las técnicas de reducción de consumo implementadas en la programación de la tarjeta. A su vez, se describe como se ha realizado el diseño de lectores, los cuales han de comunicarse con la tarjeta para configurarla o recoger sus datos. Una vez descrito el diseño, se exponen todos los resultados obtenidos en los experimentos, donde se compara la tarjeta RFID junto a otros dispositivos comerciales, tanto en los test de laboratorio como en las pruebas de campo dentro de la cadena logística de distribución de pescado fresco. Los resultados demuestran la viabilidad y el buen funcionamiento de la tarjeta en comparación con los dispositivos comerciales. Posteriormente se describe la implementación de sensores químicos en la tarjeta RFID. Se explican los métodos de encendido y apagado de estos sensores para una disminución drástica de su consumo energético y se analiza cómo afecta a la dinámica de los sensores este tipo de reducción de consumo. Se demuestra la viabilidad de la implementación de este tipo de sensores en tarjetas RFID de muy bajo consumo se analiza el método adecuado en función del tipo de transporte. Para finalizar se describen las conclusiones, donde se analizan todas las mejoras aportadas por la tarjeta RFID con capacidades sensoras dentro de la cadena logística de distribución de los productos perecederos en la industria agroalimentaria.[eng] Food Logistics require new information technology tools for traceability and advanced monitoring. Industries do not only want to introduce more data concerning food products, but also require having maximum information about environment data during transport and storage, as well as any additional data, that may be essential to the product lifetime. Typical variables of interest may be temperature, humidity, light and chemicals. This doctoral thesis consists in the development of a semi-active tag with sensing capabilities. The tag features power feed from a 13.56 MHz field, plus a battery for sensing purposes. This tag allows interfacing a variety of sensors, as well as data logging for the full duration of the transport. The tag is ISO/IEC 15693 compliant. The developed tag features a credit card form factor and it has been integrated onto a flexible substrate using commercial components. Along this manuscript is described all the tag development, the application description and the specifications of the tag, all the design, from de conceptual to the detailed. It is explained all the hardware and software/firmware implemented in all the components involved in the ISO/IEC 15693 standard. It also described the design of the two readers used with the tags. After the description of the tag development it is reported all the results obtained from the functionality tests and field test where the tag was compared with another commercial data loggers. And finally it is described a gas sensor implementation. It have been used an array of ultra low power MOX sensors in order to detect specific volatile compounds related with the fresh food fruits. As the tag as a very small battery, has been used a save energy method that consist in switch on and off the heather of the MOX sensor, allowing this implementation. It is also described the MOX sensor behavior working in such conditions, how the limit of detection increases, how the sensitivity decreases, how the stabilization time increases and how the sensor base line and noise change in relation of the power consumption saves

Towards nanostructured ITO-based electrochemical sensors: Fabrication, characterization and functionalization

The need for miniaturized, low-cost and ultrasensitive electrochemical sensors has motivated the search and study of new nanostructured materials. We propose nanostructured indium tin oxide (ITO) electrodes as a promising platform due to their good electrical conductivity, transparency to visible wavelengths and high surface-to-volume ratio. The nanostructured electrodes were fabricated by electron beam evaporation, and electrochemical techniques were used to quantify more than a 40% increase in electrochemical surface area compared to thin ITO films. The electrodes were derivatized with organosilanes and coated with a molecule providing redox activity. Indeed, an increase in detectability of more than 400% was observed with respect to thin films, indicating the potential viability of nanostructured ITO-based electrochemical biosensors

Low-cost impedance measurements for lab-on-a-chip architectures: Towards potentiostat miniaturization

The development of miniaturized potentiostats capable of measuring in a wide range of conditions and with full characteristics (e.g., wide bandwidth and capacitive/inductive contribution to sensor's impedance) is still an unresolved challenge in bioelectronics. We present a simple analogue design coupled to a digital filter based on a lock-in amplifier as an alternative to complex architectures reported hitherto. A low-cost, miniaturized and fully integrated acquisition electronic system was developed, tested for a fully integrated three-lead electrochemical biosensor and benchmarked against a commercial potentiostat. The portable potentiostat was coupled to an array of miniaturized gold working electrodes to perform complex impedance analyses for tumor necrosis factor α (TNF-α) cytokine detection. This wearable potentiostat is very promising for the development of low-cost point-of-care (POC) with low power consumption

Devices and methods for multiplexing liquid in biosensor micro-chambers

A biosensors device for simultaneous multiple-analyte analysis by a plurality of biosensors dipped in single biosensor micro-chamber flooded with a functional liquid flowing to the biosensor micro-chambers from a fluidic circuit with no symmetry prerequisite comprises micro-valves operably associated to biosensor micro-chambers for selectively allowing the crossing of a functional liquid to the biosensor micro-chambers, a biosensor micro-chamber at a time, according to a pulsating flow mode so that the total flow rate can be greatly reduced and a predetermined amount of a pressured functional liquid is multiplexed to biosensor micro-chambers. Companion methods are defined for such a biosensors device.Dispositivo de biosensores para análisis simultáneo de múltiples analitos por una pluralidad de biosensores sumergidos en una microcámara biosensora inundada con un líquido funcional que fluye a las microcámaras biosensoras a partir de un circuito fluídico sin ningún prerequisito de simetría que comprende microválvulas asociadas operativamente a las microcámaras biosensoras para permitir selectivamente el cruce de un líquido funcional a las microcámaras biosensoras, una microcámara biosensora cada vez, de acuerdo con un modo de flujo pulsante, de manera que el caudal total puede ser reducido en gran medida y una cantidad predeterminada de un líquido funcional presurizado es multiplexado hacia las microcámaras biosensoras. Se definen métodos asociados para dicho dispositivo de biosensores