Biomedical Engineering Reference
In-Depth Information
biosensor designs include shape-sensitive alloys, rheological fluids, magnetic particles, or
technologies such as cantilever arrays.
Several approaches are underway which combine either the “passive” materials (Table
7.1) or StRMs with the biological sensing component. This chapter discusses the applica-
tion of those materials that make up the sensing layer in biosensors, and presents the state
of the art in these areas. First some recent studies on cantilever biosensors are discussed.
Then other types of “smart” materials including dendrimers, conducting films and gels,
and StRMs are considered.
7.1.1
Cantilever Arrays
Microcantilevers have been used in the atomic force microscope. Their application in
microbiosensors represents an example of “smart” biosensor technology. These sensors are
arrays of microfabricated flat rods (1 µm thick and less than 100 µm), which can be coated
or patterned with biological molecules (e.g., single-stranded DNA, antibodies, or single-
chain antibody fragments) for detection and binding with specific analytes of interest.
These devices are now commercially available. Ziegler (1) has reviewed the theory, design,
and future prospects of cantilever sensors. Figure 7.2 is a schematic representation of the
principle of cantilever biosensor.
Cantilever biosensors have the advantages of local, high resolution of the response signal
and label-free molecular recognition measurements on a portable device. Also, the very
small size of the sensor can allow for sensitive response and minute levels of reagent
consumption. When a biomolecular interaction such as ligand-analyte binding (anti-
body-antigen or enzyme-substrate complex) is combined with a microcantilever operation,
a highly sensitive biosensor signal is generated. The microcantilevers are usually placed in
piezoelectric cantilever holders and vibrated using external AC voltage. Microcantilevers
Complex
mixture
Biomolecules
Enzymes
Antibodies
Biological sensing layer
Analyte
Signal to
transducer
Cantilever
array
FIGURE 7.2
Schematic representation of a cantilever array biosensor. Microfabricated silicon (flat) rods are coated with
appropriate biomolecule or molecules. Specific interactions are picked up due to ligand-analyte binding result-
ing in specific response.
