Biosensors Based on Odorant Binding Proteins - Bioelectronic Nose: Integration of Biotechnology and Nanotechnology - page 179

Fig. 10.10 Response of a QMB coated with P. dominulus OBP to a pulse 350 ppm of 2-isobutyl-
3-methoxypyrazine in air

The best performance were obtained using covalent immobilization by using self
assembled monolayers rather than direct covalent binding of the proteins.

10.3 Sensor Responses

Although the binding affinities of odorant binding proteins have been characterized
to a range of analytes in solutions [ 49 , 79 , 80 ], there is little data available about
how they interact with ligands in the vapour phase. Here we report our first experi-
ments in this area.
The raw response signal from a QCM with immobilized odorant binding pro-
teins from the Polistes dominulus to 350 ppm of 2-isobutyl-3-methoxypyrazine in
air are shown in Fig. 10.10 . The decrease of the quartz crystals basic oscillator
frequency due to the changes of mass over time is recorded as the sensing signal.
Sensors were stabilized under a constant flow of air before the introduction of target
gas in order to obtain a reference frequency and eliminate the effect of flow dynam-
ics. The baseline frequency was then re-established by a flow of clean air in order
to remove bound analytes. The sensor showed good reversibility as well as stability
over time, although the baseline frequency measured was prone to long term drift.
Control experiments with gold surfaces on bare crystals indicated that responses
specific to the presence of OBPs were being detected.