Hans E. Hummel

Insect antenna as a smoke detector

The larvae of jewel beetles of the genus Melanophila (Buprestidae) can develop only in the wood of trees freshly killed by fire. To arrange this, the beetles need to approach forest fires from as far as 50 kilometres away, . They are the only buprestid beetles known to have paired thoracic pit organs, which behavioural, ultrastructural and physiological experiments have shown to be highly sensitive infrared receptors, useful for detecting forest fires. It has been suggested that Melanophila can sense the smoke from fires, but behavioural experiments failed to show that crawling beetles approach smoke sources. We find that the antennae of jewel beetles can detect substances emitted in smoke from burning wood.

Detection of volatiles released by diseased potato tubers using a biosensor on the basis of intact insect antennae

Comparison of the volatiles emitted by healthy and diseased potato tubers showed that there are volatile patterns specific for infestation by Phytophthora infestans. Some of these marker volatiles can be detected by a biosensor on the basis of intact antennae of the Colorado potato beetle (Leptinotarsa decemlineata). This biosensor shows responses to diseased potato tubers selectively and is not disturbed by odours emitted by healthy and mechanically damaged potato tubers. One single diseased potato tuber can be detected within up to 100 kg potato tubers. So, this biosensor on the basis of intact insect antennae presents a solution to the problem of damageless screening of large numbers of seed potatoes for fungal infestation.

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.

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.

Biosensor for volatiles released by damaged plants

Abstract One of the most crucial problems in biological or biotechnical plant protection is the timing of starting an application. The proposed biosensor measuring overall degree of plant damage is a useful tool for solving the problem. If plants are damaged, for instance by cuts made artificially or by biting or chewing insects, volatile organic compounds (VOCs) will be released to a higher extent and in a different composition compared with undamaged plants. The biosensor based on an electroantennographic technique uses the sensitivity and selectivity of an insects antenna to detect the changes in composition of the VOC. This method is comparatively simple, inexpensive and sensitive (e.g. 1 ppbv cis -3-hexen-1-ol, dynamic range: 1 ppbv-100 ppmv) with respect to usual mass-spectrometric methods of VOC trace analysis. Moreover, the response time (10 ms) and the measurement cycle time (3 min) are short and the biosensor yields an overall parameter easier to deal with than complex mass-spectrometric data arrays. The lifetime of one antennal preparation, however, is 4 h and has to be improved. This paper presents results emerging from laboratory experiments with the Colorado potato beetle ( Leptinotarsa decemlineata Say).

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.

Analysis of volatiles emitted by potato plants by means of a Colorado beetle electroantennographic detector.

An electroantennographic detector based on the antenna of the Colorado potato beetle (Leptinotarsa decemlineata Say, 1824) was used to investigate volatile organic compounds emitted by injured potato plants (Solanum tuberosum L., 1753). Samples were collected on charcoal traps using the CLSA method. Analyses were performed with a GC-EAD-FID setup as well as a GC-MS system. The experiments revealed that several groups of compounds are perceptible to the Colorado potato beetle. The ability of the Colorado potato beetle to detect green leaf odours (e.g. (Z)-3-hexen-1-ol and (E)-2-hexenal), linalool and some terpenes has been noticed before [Visser et al., J. Chem. Ecol. 5 (1979) 13]. In this work the presence of (Z)-3-hexen-1-ol, (E)-2-hexenal and linalool in the potato odour could be confirmed. Moreover, beta-myrcene, benzeneethanol, and several sesquiterpenes (e.g. caryophyllene and germacrene-D) were identified. The GC-EAD experiments reveal that apart from the green leaf odours and linalool prominent reactions of the Colorado bettle antenna are induced by benzeneethanol and the sesquiterpene fraction.

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.

Herbicide dissipation and dynamics modelling in three different tillage systems

Abstract The half-lives (t 50 ) of the herbicides metolachlor, terbuthylazine and isoproturon and the occurrence of desethyl-terbuthylazine and monomethyl-isoproturon were measured in soils managed with three different tillage systems (conventional tillage, ridge tillage and no tillage). The first-order dissipation model was well adapted to the field data. Under the trial conditions, characterised by silty soil, scarce permeability, and reduced rainfall, the tillage system did not substantially influence the dynamics of the herbicides; the t 50 was reduced in no tillage only with metolachlor, the more volatile herbicide. The measured concentrations were then compared with those calculated with SoilFug, a fugacity-based mathematical model; the calculated values approximate the kinetics of both herbicides and metabolites with good precision.