Verlag des Forschungszentrums Jülich
JUEL-4269
Dufaux, Thomas
Design and development of amplifier electronics for silicon-nanowire biosensors
110 S., 2008
Introduction
Bioelectronic sensors represent a major eld of interest in current research. Their ability to detect
and transduce biological processes like DNA-hybridization or electrical cell signals into measurable
currents generates numerous applications. For example, they can be used for non-invasive
monitoring of electrical cell signals in cell cultures or for the detection of very low concentrations
of biological molecules. Several approaches to improve the recording properties of bioelectronic
sensors have been conducted in recent works. The sensors were optimized for higher sensitivities
[1], for a low noise behavior [2] and for high spatial recognition by using large sensor arrays [3].
A common feature of those sensor systems is that they work in environments, which inherently
generate large amounts of noise. At the same time, the sensed signals are very weak and must
be separated from disturbing eects.
Signal processing oers a wide range of methods to enhance data computation. Especially
since the break through of digital signal processing (DSP) methods numerous elds, e.g. telecommunications
showed great bene t from this development. By using DSP the signal detection and
computation can be signi cantly improved. It allows to lter out relevant information, to compensate
measurement errors, or provides a statistical description of signals. These are properties
which are especially interesting for sensor applications, where the information is often masked
by large noise components. The measurement system frequently incorporates additional errors,
which must be separated from the signal of interest, and statistical descriptions can be used to
estimate noise processes or to detect weak signals.
This makes it interesting to use signal theory approaches in conjunction with biological measurements.
Especially in the detection of action potentials of electrically active cells the potential
of signal theory usage was recognized. By using wavelets [4, 5] and nonlinear energy operators
[6], weak action potentials of neuronal cells can be detected. Also in the domain of cell characterization
and molecule detection signal theory approaches can be found. A basic approach for
biological measurements is to observe the resistivity changes of sensors itself [7]. Other methods
gather additional information about the measurement system by quantifying its complex
impedance [8, 9]. The impedance is aected by several elements of the measured system. By
developing models, these parameters can be extracted to deduce further information about the
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bioelectronic system. This was already done for the detection of a protein layer thickness [10] or
to explain cell transfer functions [11].
The objective of this thesis is to develop a measurement system which can be used for current
and future sensor devices in bioelectronic applications. The measurement system should be able
to record resistive changes and to measure the complex system impedance. Furthermore, the
measurement results need to be explained and interpreted by the development of system speci c
models.
This thesis is structured in six chapters. After this introduction, the dierent types of sensors
and measurement approaches are introduced in chapter two. In the third chapter the signal
processing performed by the developed ampli er system is described theoretically. The fourth
chapter deals with the used setup and the measurement processes. The fth chapter presents
results of the development of the ampli er system and some applications. Furthermore, the
measured systems are described by signal theory to allow a deeper understanding. Finally, a
conclusion and outlook for future improvements and measurement approaches is presented in
chapter six.
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