Roser Mas

Application of ion sensitive field effect transistor based sensors to soil analysis

Abstract Standard methods to measure nutrient levels in soil are complex and time consuming due to the extraction and pre-treatment processes involved. Besides, the instrumentation used for these measurements is also expensive. Therefore, the use of chemical sensors warrants investigation since they can be placed directly in the soil and results can be provided in real or quasi-real time at a moderate cost. The control of nutrients with sensors will permit an optimisation of irrigation and fertilisation management systems and thus will be useful for reducing the environmental impact caused by the runoff of nutrients into surface and ground waters. In this work, the use of chemical sensors based on ion sensitive field effect transistors (ISFETs) for soil analysis is proposed. These devices are fabricated with microelectronic technology – providing some important advantages such as robustness, small size, low output impedance and mass production. Fabrication of pH, Ca2+, K+ and NO3− ISFETs with photocurable polymeric membranes and their evaluation in aqueous solutions is reported. Studies of their response in horticulture soils and comparison with standard methods have been performed. The results confirm the feasibility of ISFET based sensors for in-soil monitoring and the promising future applications they have.

Electrochemical platinum coatings for improving performance of implantable microelectrode arrays.

The formation and properties of electrochemical platinum films grown on platinum contacts contained in implantable flexible microelectrodes were investigated. The resulting platinum deposits were obtained by applying cyclic voltammetry to baths containing concentrations around 70 mM of chloroplatinic acid. A pre-activation step was necessary before the platinum-electroplating step in order to achieve good adhesive properties. The benefits of this process were ascribed to higher corrosion resistance, lower impedance and improved adhesion to the sputtered platinum. These improvements can make the application of this electrochemical technique highly useful for increasing the lifetime of implantable microelectrode arrays, such as cuff structures (IEEE Trans. Biomed. Eng. 40 (1993) 640). These medical devices, obtained by semiconductor technology could be used for selective stimulation of nerve fascicles, although, poor long-term performance has been achieved with them. The dissolution rate for platinum thin-film microelectrodes under fixed corrosion test conditions was 38.8 ng/C. Lower rates were observed for electroplated microelectrodes, obtaining a dissolution rate of 7.8 ng/C under analogous experimental ageing conditions. The corrosion behaviour of the electroplated platinum during stimulation experimental conditions was estimated by electrochemical impedance spectroscopy.

Early determination of cystic fibrosis by electrochemical chloride quantification in sweat

A novel and rapid approach to quantify chloride concentration in sweat for early detection of cystic fibrosis (CF) is shown in this work. Disposable screen-printed sensor (SPS) devices capable to induce sweat and measure the chloride concentration are presented. Pilocarpine, which was forced into de skin by means of iontophoresis, has been used to stimulate the sweat glands. Chloride concentration has been directly measured on the skin by potentiometry. The performance of the devices has been tested in synthetic samples, obtaining good agreement with the Nernst equation. Sensors reproducibility has been analyzed in terms of residual standard deviation (RSD), obtaining a value of 8% (n=6 and alpha=0.05). Finally, the application of these sensors in several volunteers has been carried out. The results were compared with the method generally used in hospitals, obtaining deviations minor than 8%.

Development of Durable Nitrate-Selective Membranes for All-Solid State ISE and ISFET Sensors Based on Photocurable Compositions

Novel nitrate-sensitive membranes have been developed using an aliphatic urethane diacrylate photocurable polymer. This polymer has been chosen due to its easy and fast deposition procedure compared with PVC membranes and its compatibility with microelectronic techniques. These membranes were obtained after UV irradiation during no more than 60 seconds. To optimize their composition and evaluate the chemical response ion selective electrodes (ISEs) with solid inner reference were used. Studies of different plasticizers for nitrate PVC membranes and compositions increasing the ratio between oligomer and diluting agent were performed. ISEs developed presented a sensitivity of −56 mV/dec and a lifetime up to one year. Membrane compositions containing dibutyl phthalate and trioctyl phosphate as plasticizers were deposited onto ISFETs. Studies to elongate ISFETs lifetime were carried out modifying the encapsulation methodology, by using the same polymer family. ISFETs showed a sensitivity between 65–69 mV/decade, depending on the plasticizer, and a linear range of 2.4×10−5−0.06 M. The long-term stability of ISFET sensors with trioctyl phosphate plasticizer was up to 10 months, being superior to that described in the literature for PVC membranes and even for other kind of polymers.

Thermal and hydrodynamic studies for micro-channel cooling for large area silicon sensors in high energy physics experiments

Abstract Micro-channel cooling initially aiming at small-sized high-power integrated circuits is being transferred to the field of high energy physics. Todays prospects of micro-fabricating silicon opens a door to a more direct cooling of detector modules. The challenge in high energy physics is to save material in the detector construction and to cool large areas. In this paper, we are investigating micro-channel cooling as a candidate for a future cooling system for silicon detectors in a generic research and development approach. The work presented in this paper includes the production and the hydrodynamic and thermal testing of a micro-channel equipped prototype optimized to achieve a homogeneous flow distribution. Furthermore, the device was simulated using finite element methods.

Application of Isfet based sensors to soil analysis

Standard methods to measure nutrient levels in soil are complex and time consuming due to the extraction and pre-treatment processes involved. The instrumentation used for these measurements is also expensive. Therefore, the use of chemical sensors would be interesting since they can be applied directly to the soil. Thus, it would provide results in real or quasi real time at a moderate cost. The control of these nutrients will permit an optimisation of the overall production process of the crop. Besides, this approach will be useful for reducing the environmental impact caused by excess of nutrients in crop soils. In this work, the use of chemical sensors based on Ion Sensitive Field Effect Transistors (ISFETs) for soil analysis is proposed. These devices are fabricated with microelectronic technology -providing this fact some important advantages- but their mechanism of response are similar to that of Ion selective electrodes (ISEs). Fabrication of pH, Ca 2+ , K + and NO 3 - ISFETs and their evaluation in aqueous solutions is reported. From the preliminary results of their application in soils it is possible to confirm their feasibility as sensors for in-soil monitoring and the promising future applications they have.