Electrical impedance spectroscopy (EIS) is a non-destructive, rapid and real-time measurement method which does not require special high-tech measurement devices and can be applied to food quality assessment. This method is rapid, effective and affords low-cost investigation of the product. The conventional EIS method requires a set of metal electrodes in direct contact with the medium to be measured. The complicated electrochemical processes on the electrodes-electrolyte interface could substantially affect the value of the impedance measured. The present study sought to explore the possibilities of using the impedance method for quality control in orange juices, to introduce the electrodeless method of electrolyte impedance measurement and to compare this with the conventional impedance methods. The electrical properties of the orange juices were described with the help of an equivalent circuit. An equivalent circuit was designed with constant phase element approximation. The values of the equivalent circuit components were fitted using a non-standard algorithm inspired by the behaviour of actual ant colonies. Implementing the electrodeless method obviated the electrodes phenomena effects and the behaviour of the electrolyte is similar to inductance. The proposed electrodeless method is generally applicable to measuring the electrochemical properties of electrolytes.

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We present a simple narrowband method to detect the amplitude of alternating magnetic fields by a fluxgate sensor using a single lock-in amplifier, improving the common method of using two phase sensitive demodulators (lock-in amplifiers). We eliminated the need for two phase-sensitivite demodulators by processing the reference signals of lock-in amplifier and of the fluxgate excitation unit. This setup can be used as a high-resolution, narrowband spectral analyzer of magnetic fields or as a system for measuring the AC response of magnetic markers. Two methods were introduced and tested; we achieved 2 kHz detecting noise spectral density of 80 pT/¥Hz in the laboratory environment. The method is directly usable for any fluxgate sensor or magnetometer, where the reference signals are available. Using a slow feedback compensatingloop further improves the dynamic range of the instrument.

In vitro neurotoxicity testing and toxicity effect quantification plays an important role in many disciplines of biomedicine as an alternative to in vivo methods. The principle of the majority of in vitro methods corresponds to the basic concept of biosensors, i.e. measured quantity is by means of biological sensing element transformed to physical quantity easily measurable by electrical methods of measurement. Two types of biosensors suitable for neurotoxicity measurements are described in the paper. A common feature for both types is application of a living organism as biological sensing element. In the first type of biosensor the morphology of cell is evaluated using image processing methods known as videometry. In the second type of biosensors the electrical impedance of cells using an improved version of the ECIS (Electric Cell-substrate Impedance Sensing) method is a measure of toxicity effects. The results of experiments with biosensors using videometry and a proposal for improvements of ECIS based biosensors are included in the paper.