Physical Biosensors

A new field of research at the Department for Integrated Sensor Systems is the development of physical biosensors. These electrochemical sensors incorporate the general components of a biosensor: two closely associated elements, a biological recognition element that interacts with the analyte of interest, and a transducer which further receives and delivers the measured signal.

Physical biosensors, including potentiometry, amperometry, and conductometry, are self-contained integrated devices that are based on the measurement of the current resulting from the oxidation or reduction of an electroactive biological substance. The determination of analytes and their concentrations are essential for a wide range of applications, including environmental monitoring, drug screening, disease diagnosis, treatment and quality control. Since the last century electrochemical biosensors have been widely used to detect analytes and determine their concentrations. The relatively simple setup, the high sensitivity and selectivity as well as the small size and price of these sensor devices make them ideal for research and commercial applications (e.g. Glucose-biosensor).

Furthermore, the usage of screen-printed electrodes combined with a great variety of available electrode modifications for the analyte detection offer many possibilities for environmental monitoring. The research focus at DISS is on the development of voltammetric biosensors for the quantification of specific microorganisms, chemical compounds (e.g. pesticides, herbicides, etc.) as well as hormones in the field of water economics.

Developed sensors 

System for impedance tomography in soils 

Electrical impedance tomography (EIT) is a non-invasive measurement method for the spatially resolved determination of the electrical conductivity distribution in an examination volume. It offers great potential for applications in environmental monitoring, especially for the characterization of soils, substrates and water distributions. In this thesis, a compact, portable solution for the impedance tomographic detection of conductivity changes is presented, which was specially developed for field use. 

The measurement system is based on a multi-channel‑impedance spectrometer with a flexibly configurable electrode arrangement, which feeds low-frequency alternating currents into the medium and records the resulting potential distributions at the edge electrodes. From the measured boundary potentials, the complex conductivity inside the medium is determined by means of inverse reconstruction algorithms. To solve the inverse problem, finite element models and regularized reconstruction methods are used. The results are visualized in the form of two-dimensional sections and three-dimensional volume models, including with the help of isosurfaces. 

Experimental investigations show that the system can reliably detect and localize conductivity contrasts, for example in the case of inserted objects or in the case of time-varying moisture distributions. This makes the impedance tomography platform particularly suitable for the analysis of water transport, soil heterogeneity and hydraulic properties. The compact design, the modular architecture and the mobile control system open up new possibilities for the practical use of the EIT in environmental and agricultural monitoring. 

Miniaturized potentiostat for electrochemical measurements 

Electrochemical sensors are particularly attractive for environmental monitoring applications due to their high sensitivity, low cost and good miniaturizability. In particular, portable measuring systems are required for the detection of organic pollutants, drug residues or redox-active substances, which enable on-site analysis without complex laboratory equipment. In this thesis, a miniaturized potentiostat is presented, which was specially developed for mobile electrochemical measurements. 

The sensor system integrates all the essential functional units of a classic potentiostat in a compact, energy-efficient design. It supports common electrochemical measurement methods such as cyclic voltammetry and SquareWave voltammetry and covers a wide current and potential range. The power supply and data communication are provided via a USB interface, which means that the device can be operated directly with mobile devices such as smartphones or tablets. Specially developed application software enables intuitive control of the measurement sequences as well as the graphical display and storage of the measurement results. 

Comparative measurements with commercial laboratory potentiostats show a good agreement of the current‑voltage characteristics as well as a sufficiently low noise behavior for environmental analytical applications. The miniaturized potentiostat developed thus represents a powerful and cost-effective alternative to classic laboratory equipment and is particularly suitable for mobile measurement campaigns, field analyses and decentralized environmental monitoring systems. 

Contact: Martin Brandl