System for European Water monitorING

As one of scientific results of SEWING project a theory of ISFET ion-sensitive sensors has been developed. This theory was so far presented in a variety of conference proceedings and now it is being prepared for a final publication in one of the sensor magazines. This theory of ion-selective sensors has become a base of innovative computer models of chemical sensors. These models have found wide application in practice of computer-aided design of sensor systems. The practical results consist of two parts: a model of the internal depletion FET of the ISFET sensor and a model of a ion-selective membrane working as a chemo-electrical transducer. The electrical model was developed in two versions: compatible with SPICE and dedicated to HDL simulators (based on Merckel theory of FET). Both versions are physical. The model of the chemo-electrical transducer was elaborated for pH sensitive ISFETs and for arbitrary ion-selective CHEMFETs. The latter takes the form of a new, so called, super-Nikolski model not known so far in literature. Elaborated scientific results are fundamental, they are of wide interest and have broad applications in chemical sensor systems. They have been implemented in the software controlling the final demonstrator in SEWING project and will be disseminated also in literature. Especially super-Nikolski model is useful for CHEMFET characterization, simulation and data-fusion software. Different models created in this project are available in model libraries and on different software platforms. These models will be developed in the future by extension to other types of sensors. They will be used in new, industrial versions of the SEWING system. More information on the Sewing project can be found at: http://www.sewing.mixdes.org

According to the prototype devices developed under the project, the industrialization phase will be based on the following main points: - Design of a compact and portable on-line analyser, to be powered by low voltage and with the lowest consumption of solutions and washing liquids - Identification and development of a low cost and compact hydraulic to manage the measuring system - Identification and development or a more compact and cheaper electronic to manage signal measurement and system management - Design, development and field test of the industrialized product. The industrialized product will be based on a miniaturized version of the standard SYSTEA's LFA technology. The target of price will be to stay lower of 10.000 euro as list price for the on-line multiparametric device equipped with 6 measuring sensors. The market target will be: environmental and agricultural Authorities, public and private entities that have the need to take under control surface water and groundwater. More information on the Sewing project can be found at: http://www.sewing.mixdes.org

New structures of miniaturized solid-state potentiometric transducers i.e. back-side contact (BSC) and front-side contact (FSC) ion-sensitive field effect transistors (ISFETs) were manufactured by the Institute of Electron Technology+PW (Poland) and LAAS-CNRS (France)+ Microsens (Switzerland), respectively. The performed tests proved good performance and excellent linearity of the pH responses of the ISFETS, which enables the accurate determination of pH. Further deposition of the polyHEMA layer on the gate surface and the chemical modification of the ISFETs i.e. the deposition of ion-selective polymer membranes allowed obtaining sensors - CHEMFETs - sensitive to target ions (NH4+, K+, Na+, NO3-). The procedure of the polyHEMA layer deposition is compatible with the IC technology and is realized using spin-coating technique (industrial method) in the Institute of Electron Technology. Two types of ion-selective membranes (of optimised composition) based on plasticized poly(vinyl chloride) (PVC) and polysiloxane derivative were applied. The method of membrane deposition using an automated dispensing unit (semi-industrial method, PW) and the technology of UV-polymerizable membrane deposition on ISFET wafer using spin-coating set-up (industrial method, LAAS-CNRS and Microsens) were developed, enabling the production of cheap sensors sensitive to: NH4+, K+, Na+ and NO3- ions. Ca+2-sensitive FSC-CHEMFETs have been also prepared by Microsens using the spin-coating industrial technology (these sensors are not yet implemented in the prototype). The working range of the CHEMFETs (linear range of the calibration curves at least 1-4 pX) is appropriate to perform ion monitoring in environmental analysis. An examplary prototype of a portable multisensor analyzer for water quality monitoring based on BSC-CHEMFETs was fabricated by Systea (Italy). Also ion-sensitive FSC-CHEMFETs are ready to be implemented in the measuring system. The multisensor analyzer will be dedicated to the environmental pollution survey of wastewater and natural water resources. More information on the Sewing project can be found at: http://www.sewing.mixdes.org

During the research project three different prototypes of measuring systems were developed: - LFA test unit; - Probe demonstrator; - Final prototype. Each of them was practically used in different stages of research to test the results coming from other groups and to perform measurements on water samples. LFA test unit: The LFA test unit is based on a standard SYSTEA MICROCHEM bench top analyser, which is able to manage automatically a complete measuring sequence using the patented Loop Flow Reactor (LFR) analytical technology. The unit is divided into four main sections: - Hydraulics, mounted in the front view panel - Electronics and actuators, mounted inside the back panel - Internal reagents compartment, accessible from the right side of the unit - Alphanumeric display and membrane keyboard and a printer, mounted at the top front of the instrument. The standard LFR hydraulic manifold unit was modified to integrate: - The two-sides back-planed ISFET measuring flow-cell already developed by Warsaw University. - An Ag/AgCl reference electrode, mounted in the centre of the same measuring head. - N.2 CHEMFET sensors, referenced to the same Ag/AgCl electrode, with standard MOSFET output. Modified Front Side contact Sensors from LAAS partner technology, mounted on a PCB board with rear electrical connectors, were integrated and tested too, using a special customized bigger flow cell already developed by SYSTEA. The LFA test unit is a complete CHEMFET LFA bench-top analyser, which will be used to perform automatic measurement, drifts tests, comparisons on single CHEMFET sensors; the internal electronics and software provide directly output data in concentration unit, with the capability to manage the signal acquisition from two CHEMFET sensors, typically to measure NO3- and NH4+. The measuring unit is fully configurable and open to operators modification of the analytical sequence which manages the hydraulic reactor; using the local keyboard and LCD display, as any other standard SYSTEAs LFA analyser; as an example, it allows: - To polarize the reference electrode and CHEMFETs drain inputs with single predefined voltages - To modify any interval time of the analytical sequence which manages the two CHEMFETs measurement. - To program the opening and closure of any valve included in the loop. - To turn on or off the peristaltic pump in both versus, at two different speed (low and high). - To modify the quantity of solutions which can be injected in the loop reactor. - To perform automatically the standard addition method on each measurement cycle. The unit is configured to manage n.2 injection valves, to perform: - Programmable addition of ISA (Ionic Strength Adjuster) stock solution to the sample, before and after the measurement. - Programmable addition of a stock calibrant solution to the sample, after the sample measurement, to perform standard addition method with CHEMFET sensors. The unit performs after each measurement the automatic calculation of measured concentration; as standard the firmware provides logarithmic calculation, using known addition method, for two CHEMFET chemical sensors choosing between two different algorithms. Another firmware version is available to perform linear calculation using two standard (low, high), for pH ISFET sensors or CHEMFET sensors, which already includes built-in electronic for linearized standard output. The calibration is performed using low and high standard solutions, in order to calculate the CHEMFET sensors slope by the sequential measure of two external standard solutions (low, high), which have to be always chosen divided by a decade (i.e. low 2ppm, high 20ppm). The unit is fully programmable to set any configuration parameter (like added standard solution concentration, volume of added standard or Chemfets polarization electrical parameters). The measured data are shown after the end of the measurement using the LCD display and then automatically printed using the printer mounted on the front panel. Probe demonstrator: The probe demosntrator is a prototype designed to be specifically deployed in water as a probe. The analytical part of the device is based upon a novel patented technology named micro Loop Flow Analysis (uLFA); the main characteristics of this new technology is the extreme compactness (the analytical reactor volume is 5 ml only) and the compatibility to be integrated in submergible measuring devices. The probe is able to mount both types of BSC and FCS CHEMFETs, using the linear modular flow-cell already tested in the measuring stand and in LAAS laboratory. More information on the Sewing project can be found at: http://www.sewing.mixdes.org

A dedicated automatic, computer-controlled stage for measurement of chemical ISFET sensors has been improved, based on standard firmware used in the SYSTEA's LFA analysers. It provides the following procedures: programmable dosage of chemicals, computer-controlled hydraulic system providing the flow of solutions through sensors mounted in flow-cells, programmable supply-measurement equipment for sensor biasing. Results of measurement are generated in XML files and stored in a dedicated database. Dedicated software has been developed for processing the database. Another set of applications has been developed for extracting parameters of the sensor models. It contains a preextraction procedure providing rough values of electrical and chemical model parameters. These parameters are further adjusted by means of optimisation procedure. Two versions of the software have been developed: A prototype software dedicated to Matlab environment, where new algorithms have been implemented, tested, improved and a final C application implemented as a firmware in the final demonstrator. Developed electrical and chemical models appeared to have good numerical properties, were well-conditioned, easy in preextration and final optimisation. More information on the Sewing project can be found at: http://www.sewing.mixdes.org

The prototypes developed are capable to be managed by a local display and keyboard (LFA test unit and final prototype), a printer (LFA test unit) or to provide data to an external PC (probe demonstrator and final prototype) using a RS-232 serial port. The final prototype is equipped with a special application program developed in Viau Basic under Windows XP operating system, which could perform the following main function: - Start of analysis; - Wash of the circuit; - Stop the analysis; - Display of the results; - Record displayed data on a file of the PC. The program can be used locally with the PC directly connected to the measuring device, but it can be also equipped with a set of 2 GSM devices to have the same functionality done remotely. In the future industrialized program other communication devices of higher generation (GPRS, UMTS) will be used. his possibility is developed in laboratory version by TUL partner. More information on the Sewing project can be found at: http://www.sewing.mixdes.org

The final prototype is divided into five main sections: - Hydraulics, mounted on the front side of the internal slid; - Sensors mounted in dedicated flow cell, placed on the right side of the internal slid; - Electronics and actuators, mounted on the right side of the internal slid; - Internal reagents compartment, accessible from the upper side of the unit; - Display and keyboard and printer, mounted on the front panel, which is, can be opened to access the hydraulics and the electronics. The external compartment is IP-55 proof and the unit is designed to be used as a portable and on-line field system, easily powered by an external 12Vdc power supply. The unit is equipped with a standard RS-232 serial port to manage the analyser using a local or a remote device, like a PC or a data-logger. The LFA (Loop Flow Analysis) technology is able to manage automatically a complete measuring sequence using the patented Loop Flow Reactor (LFR) analytical technology. The LFA unit contains as main parts the sensors, the conditioning part electronics and the main processing subsystem. The final prototype integrates: - Up to n.7 Chemfet sensors + Ag/AgCl reference electrode + temperature sensor integrated in a dedicated linear flow-cell or two linear flow-cells connected in series (one for BSC and one for FSC sensors). - The specific A/D acquisition boards developed under the project to manage and read the signals from Chemfets and temperature sensor. It automatically manages the measurement sequence under the specific procedures used by LFA based units and the new computation software developed by SEWING partners. More information on the Sewing project can be found at: http://www.sewing.mixdes.org

One of the key results of the project is software for processing of raw measurement data from several CHEMFET sensors and a temperature sensor. Usage of such software is a must, as real CHEMFET sensors are not sufficiently specific (i.e. they respond not only to their "main ion" but also to some interfering ions), their response curve is non-linear and temperature dependent. There were 3 approaches to design of data processing algorithms. The PW group assumed availability of steady state (current or voltage) readouts from CHEMFETs and a temperature sensor - all located in the reactor of the probe. Initially sensor calibration - water sample measurement cycle was investigated. Finally, an original multistep standard addition type measurement technique was developed, that combines calibration and measurement phases. For NO3, NH4, K and Na sensors (as used in the final demonstrator probe) the first of four steps consists of complete readout from CHEMFETs and a temperature sensor, after water sample (pre-treated with Ionic Strength Adjuster) was placed in the reactor of the probe. Next measurement set is performed after injecting low level of standard liquid (with all the main ions). Then follows injection of high level of the main (most troublesome) interfering ion, i.e. K, and measurement. Finally, injection of high level of the remaining main ions and measurement -complete the cycle. A special purpose optimisation based algorithm has been developed that uses measurement from all sensors in all steps of the measurement cycle and sensor models (also new ones - developed in this project) to perform estimation of main ion concentration in the sample. The algorithm and the software that implements it is data driven, and so it can accept arbitrary number of main ions, sensors (can be redundant if available) if requested via configuration files. The software library has been integrated with the dedicated measurement unit control firmware made by Systea, to provide on-line estimates of ion concentration. Stand-alone off-line processing program has been also provided. The TUL group assumed availability of time responses from the sensors, and used inverse problem solution algorithms to estimate of ion mixture composition. The approach aimed at reducing estimation uncertainty due to CHEMFET measurement inaccuracy. The work ended at the research state, with some publication documenting the results. The UPC group also considered a time evolution of responses from a redundant array of sensors. Using ideas from signal processing (multiple interference cancellation) the group aimed at decreasing of ion content estimation inaccuracy due to sensor non-specifity and measurement error, making some assumptions about statistics of the two sources of inaccuracy. The work ended at the research state with numerous publications documenting acheivements. More information on the Sewing project can be found at: http://www.sewing.mixdes.org

One of the instruments made available from the project partners - the LFA test unit - is tested at our lab for a period of 7-8 months, concerning the parameters NH4-N and NO3-N, using the respective backside contacted ISFET sensors. The results obtained are compared with reference methods used at our lab, according to the German standard methods (DIN). These are: for NO3-N the ion chromatography (IC) and for NH4-N the photometric method. During the testing time the following characteristics are validated: - Sensor conditiong time; - Measuring stability of sensor/system; - The lowest limit of quantification (LOQ); - Accuracy (by means of control and real samples); - Precision / Uncertainty of the system; - Sensor lifetime; - Sensor homogeneity. The results are very satisfactory, special for the nitrate measurement, concerning the stability and life time of the sensors. Also the accuracy and precision of the determination are very good even for real waters, except for effluents from waste water treatment plants. The final improved prototype based on Micromac-1000 device, able to measure four ions simultaneously (NH4+, NO3-, K+ and Na+), was also thoroughly measured and the results are highly satisfactory. More information on the Sewing project can be found at: http://www.sewing.mixdes.org

Two different types of hardware were developed to manage the signal acquisition from Chemfet sensors: - A measuring system developed by Systea based on commercial A/D and D/A boards. This system is applied on the three prototypes developed during the research project (LFA test unit, probe demonstrator and final prototype) and it manages the Chemfet sensors by a specific software procedure developed with PW partners in order to measure the drain current response of voltage driven Chemfets. - A voltage sensing board developed by VTT partner, which will be managed by new dedicated software module developed by UPC partner, using a second parallel board connected through the PC-104 bus to the main CPU unit. The first one is able to measure the drain currents coming from the polarized sensors, while the second one reads directly the drain voltages. The first solution was found most suitable to use it in the final prototype. More information on the Sewing project can be found at: http://www.sewing.mixdes.org

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