G.R. Langereis

Using a single structure for three sensor operations and two actuator operations

In many process control applications, a set of separate existing sensor structures is placed in the environment of interest and not much attention is being paid to the integration of these structures and even less to the possibility of combining the measurement results obtained from these sensor structures. However, a new trend in chemical sensing is the development of sensor arrays and the use of more than one transduction principle applied to the same selective layer (J. Janata, M. Josowicz, Chemical sensors, Anal. Chem. 70 (1998) 179R–208R). An integrated sensor structure with the highest level of integration was developed and tested. The structure with a size of 1 mm2 can be accessed by only four contacting leads. By scheduling this structure in different modes, several sensing modes are selected for determining electrolyte conductivity, temperature and hydrogen peroxide concentration, where the latter one represents one example of many species that can be determined amperometrically. In addition, two actuator functions using the same single structure were tested as well: the local environment was thermoresistively heated and a local pH gradient was created by the electrolysis of water. The two actuator operations together with the three sensor operations makes the structure an excellent starting point for many local experiments, which will lead to the determination of more environmental parameters than the number of sensors present in the array.

Measuring conductivity, temperature and hydrogen peroxide concentration using a single sensor structure

Using a single multi purpose sensor structure, consisting of metal films on a substrate only, three electrolyte parameters have been measured. The parameters are temperature, conductivity and hydrogen peroxide concentration, where the latter one represents one example of many species that can be determined amperometrically. The active area of the fabricated devices is about 1 mm/sup 2/.

A demonstration of acquiring specific concentration data by variations in the operating conditions of a non-specific sensor

A method for determining separate ion concentrations using a conductivity sensor was developed and tested. While a single electrical conductivity measurement in a solution does not give information on the present ion types, a range of measurements at various electrolyte temperatures does. Since the temperature dependency of the mobility of an ion is unique for that ion, it appeared to be possible to fit ion concentrations from a set of conductivity measurements while heating the electrolyte. For the calculation of the ion concentrations from conductivity vs. temperature sweep, an estimation algorithm is introduced based on the linear minimum mean square of the error. Errors in the measured conductivity will propagate through the algorithm into errors in the fitted ion concentrations. For the validation of the estimation method, this propagation of errors is also evaluated. The example given merely shows the feasibility of obtaining specific concentration information from an intrinsically non-specific type of measurement, electrolyte conductivity, by using the unique temperature dependence of ionic mobility.

Miniaturized ISFET Interface for the Use on a Serial PC Port

A new interface for using an ISFET (Ion Sensitive Field Effect Transistor) was developed and realized. The advantages of the new design are the small size of the printed circuit board and the low power consumption. This resulted in an electronic circuit small enough to fit in a 25 pins sub-D connector without external power supply. As the circuit is connected to the serial port of the PC, easy interfacing is guaranteed. Furthermore, no hardware calibration is necessary, all calibration can be done by software.