Peter Schroth

An insect-based BioFET as a bioelectronic nose

Abstract Insects are able to perceive volatiles released by damaged plants in order to find food sources or mating partners. In order to use the highly developed olfactory sense of insects for analytical purposes, the “biological nose” of insects has to be combined with some electronic instrument via a bioelectronic interface to yield a “bioelectronic nose”. In order to combine a field-effect-transistor (FET) with an insect antenna of the Colorado potato beetle ( Leptinotarsa decemlineata ) in an electrically and mechanically stable way, the bioelectronic interface was adapted to the needs of the insect antenna. A mobile biosensor system basing on the pre-adaptation method containing a biologically sensitive field-effect-transistor (BioFET) as sensor head was used for measurements of plant damage in a glasshouse under real world conditions. First measurements with the biosensor showed for ( Z )-3-hexen-1-ol, a marker volatile for plant damage, a dynamic range of 6 orders of magnitude, a threshold of quantification of about 1 ppbv, a limit of detection (i.e., signal-to-noise ratio>3) of about 0.1 ppbv, and is able to detect down to 300 ag ( Z )-3-hexen-1-ol/ml air in a 500 ml sample within a few seconds (ca. 50 ms raise time to 90% signal amplitude, ca. 5 s adaptation time after signal maximum). These characteristics were sufficient to distinguish single mechanically or beetle-damaged plants in background emissions of 1000 undamaged plants in the glasshouse.

Enzyme immobilisation on planar and porous silicon substrates for biosensor applications

Abstract Two methods for the immobilisation of enzymes on silicon-based so-called electrolyte–insulator–semiconductor (EIS) structures are suggested. These EIS structures are used as a basis for potentiometric biosensors. In the first method, heterobifunctional cross-linker molecules are employed to covalently bind enzymes to these capacitive layer structures which possess a planar surface that contains amine groups. Porous EIS sensors which, in comparison to planar sensors, exhibit an enlarged surface area, are used in the second method. For the first time, pH-sensitive Si3N4 was deposited on the walls and bottoms of the SiO2-covered pores. Here, a large amount of enzyme molecules can adsorptively be bound inside the porous structure. Penicillinase is used as a model enzyme. Capacitance–Voltage and Constant Capacitance measurements are performed in order to examine the respective penicillin sensor responses and thus to validate both immobilisation methods. Whereas the sensitivity of the sensors prepared by both methods is nearly identical for low penicillin concentrations up to around 0.25 mM, a difference of the calibration curves in the higher concentration range indicates a larger amount of immobilised enzyme in the case of the porous structures.

A BioFET on the basis of intact insect antennae

Abstract A novel biosensor device on the basis of a FET (field-effect transistor)–insect antenna junction is presented. This biosensor allows the quantitative detection of specific components of host plant odours. The sensor was operated at a fixed working point in the constant voltage mode. As a test odour the gas concentration of Z-3-hexen-1-ol was determined in the concentration range from 0.01 to 100 ppm with short response time of less than 1 s and a high reversibility of the sensor signal in ambient air. Two types of preparation of the biocomponent were examined yielding a whole-beetle-BioFET and an isolated-antenna-BioFET.

Insect-based BioFETs with improved signal characteristics.

Insect-based BioFETs (biologically sensitive field-effect transistors) with improved signal characteristics have been developed. These BioFETs require a specifically adapted signal interfacing between a FET as signal transducer and an intact insect antenna as biocomponent. Therefore, different field-effect transistors have been fabricated in order to study the signal transfer at the bioelectronic interface. As relevant features of the BioFET, its current-voltage characteristics, the transconductance and the signal-to-noise ratio have been investigated as affected by the choice of gate insulator materials and gate dimensions (width-to-length ratio, thickness of the dielectric layers). The performance of the improved FET arrangement in the isolated-antenna BioFET was validated by employing dilution series of the plant odour component Z-3-hexen-1-ol.

The Use of Insect Chemoreceptors for the Assembly of Biosensors Based on Semiconductor Field‐Effect Transistors

The extraordinary sensing abilities of insects have been well-known for many years. The use of their sensitive organs in biosensors is of great interest. This article describes both the signal-generating process inside the sensing organs and how to measure these signals in terms of technical sensing principles. Especially, EAG techniques and a novel BioFET (coupling between an insect antenna and a field-effect transistor) set-up are covered in detail. Possible applications of biosensors based on intact chemoreceptors are given and possible future developments in this area are discussed.

Extending the capabilities of an antenna/chip biosensor by employing various insect species

Abstract Because of their remarkable sensory abilities, insect antennae are very suitable for the construction of highly sensitive biosensors. Odour concentrations down to the low ppb range can easily be detected by means of an antenna/field-effect transistor (FET) junction. In this work, we present measurements performed with different kinds of beetles, namely the Colorado potato beetle ( Leptinotarsa decemlineata Say) and the steelblue jewel beetle ( Phaenops cyanea ). Their ability to specifically detect organic odour molecules, like 1-octen or guaiacol, at concentrations down to the ppb range can lead to interesting applications like the detection of different kinds of fires at an early stage.

Characterising an insect antenna as a receptor for a biosensor by means of impedance spectroscopy

The sensory abilities of insects are of great scientific interest. As an example, a biosensor on the basis of an insect antenna has been developed. With this sensor, organic odour molecules, like cis-3-hexen-1-ol, can be detected in concentrations down to the ppt range. To characterise the insect antenna as the receptor part of the biosensor in more detail, measurements based on impedance spectroscopy have been performed in this work, employing various conditions: the impedance of the antenna was observed to vary with the age, the applied bias voltage and the amount of applied odour. Hence, it could be shown that the antenna is not just a passive electronic device, but reacts actively to some parameters such as voltage or odour concentration.

Linkage of Inanimate Structures to Biological Systems — Smart Materials in Biological Micro- and Nanosystems

Problems and prospects of linking inanimate structures to biological systems are outlined, using the development of a biosensor on the basis of intact insect antennae as an example. The optimisation of a bioelectronic interface between μ-electronics and insect antenna demands materials with well defined surface- and bulk- properties. First approaches to the development of biological robots “Biobots” emphasise the importance of the bioelectronic interface. Considering constraints from demands of the bioelectronic interface is crucial for a design of microsystems containing μ-pumps, μ-valves, and μ-motors supporting biological perceptive systems on a cellular level. So, miniaturised biosensor systems and Biobots might serve as smart devices in areas of obstructed accessibility. This enables applications as a fire extinction system in complex electrical environments like wiring harnesses or as a localisation system for persons buried alive after earthquakes and explosions. Elucidation of the olfactory signalling cascade in insects and mammals is in fast progress. First isolation and cloning work is accomplished already. Thus, synthesis of stabilised protein components of these molecular signal transduction cascades can give way to bioelectronic nanosystems mimicking biological perceptive systems on a molecular level. First approaches to the development of μ-compartments mimicking biological compartimentation in different cellular organelles will need synthetic membrane substitutes and n-electrodes, as well as n-pumps and n-valves. This kind of semi-synthetic receptor cells can yield highly miniaturised sensor systems with biological performance and intimate integration of actuator features leading to applications like single-cell targeted μ-surgery.

Insect chemoreceptors coupled to silicon transistors as innovative biosensors

Applications like the warning about agricultural pest infestations, the detection of spoilt food during storage and transport as well as the monitoring of smoldering fires require highly selective odor sensing techniques. Insect antennae that have been optimized by evolution over million of years are most suitable for such a sensitive and selective detection of certain organic substances in air. The utilization of this highly specialized sense of smell from insects needs in terms of analytical tools, however, an adaptation of the antenna to the microelectronic technique. Therefore, a beetle/FET (field-effect transistor) interface as an innovative biosensor has been developed. This BioFET (biologically sensitive FET) is based on the direct combination of the intact chemoreceptor of an insect with the gate of a FET by means of an electrolyte solution. Depending on the experimental set-up, two different biosensor configurations, namely a whole-beetle BioFET and an isolated-antenna BioFET have been designed. In both configurations, the organic compound that is detected by the beetle initiates a recognition process at its nerve cell membranes, which results in a net potential over the whole insect antenna. Then, this potential drop modified the gate conductivity and consequently, the drain current of the FET. By applying various kinds of insect antennae (e.g. ofthe Colorado potato beetle and the steelblue jewel beetle) different odor concentrations, such as cis- 3-hexen-1-ol, guaiacol and 1-octen can be detected down to the low ppb range.