Biosensors Based on Odorant Binding Proteins - Bioelectronic Nose: Integration of Biotechnology and Nanotechnology - page 166

Chapter 10
Biosensors Based on Odorant Binding Proteins

Krishna C. Persaud and Elena Tuccori

Abstract Both the sensillary lymph of insects and the nasal mucus of vertebrates
contain large amounts of small soluble proteins, odorant-binding proteins that spe-
cifically and reversibly bind odors and pheromones. Proteins from different sources
have affinities toward a wide range of compounds with different sizes and shapes.
They can be easily expressed in heterologous systems, they show high thermal sta-
bility and it is possible to modify their binding sites by site-directed mutagenesis.
We describe the development of an odor sensing biosensor array based on immo-
bilization of odorant binding proteins on to suitable transducers. Using a quartz
crystal microbalance platform as a transduction element, it is possible to detect
and measure quantitatively concentrations of volatile analytes at parts per million
concentrations in air.

10.1 Introduction

A biosensor can be defined as an analytical device that converts a biological interac-
tion into a measurable electrical signal [ 1 ]. Biosensors are commonly composed of
a recognition element (receptor), a signal conversion unit (transducer) and an output
interface. It is possible to classify them on the basis of commonly used receptor and
transducer elements as summarized in Fig. 10.1 . This involves a combination of
two steps: a recognition step and a transduction step. The recognition step involves
a biological sensing element or receptor that can recognize biological or chemical
analytes in solution or in the ambient atmosphere. The receptor may be proteins,
such as antibodies or enzymes, DNA, peptide sequences or whole cells. The recep-
tor elements are in close contact with a transducer that converts the analyte-receptor
interaction into a quantitative electrical or optical signal [ 2 ].
The detection of chemical signals in the environment, which provides informa-
tion on food, mates, danger, predators and pathogens, is essential for the survival of
most mammals and insects. Animals have developed a highly sophisticated olfac-
tory system, able to distinguish between thousands of diverse volatile compounds.