Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

BIOSENSOR-BASED TECHNOLOGIES 423
Table 20.3
The ideal characteristics of a biosensor
1. The biorecognition element can be highly specific for the
substrate or antigen
2. Reusable, with multiple readings permitted on a single device
3. High sensitivity
4. Cost-effective
5. Rapid analysis time
6. Use of “on-line” or in situ measurement
7. Results should be in “real-time”
8. Good signal to noise ratio
9. The device should be robust
10. The ability to measure samples in a high-throughput fashion if
required
11. Possibility of incorporation into automated robotic systems
12. Fast turnaround time on analysis
13. Ease of use; ability of use in field by untrained personnel to
provide a measurement
complex matrix (such as fruit or vegetable preparations). This is advantageous over other
optical-measuring techniques where samples have to be specifically pretreated to remove
contaminating colored species prior to analysis.
The correct choice of sensor chip is also an important factor to consider when designing
an assay for any particular analyte. There are many different types of sensor chips that can
be used with a Biacore instrument (Table 20.4). The choice of chip chemistry depends on
many factors, including the application and objective of the test, the chemical characteristics
of the biomolecules of interest, and their specific interactions:
The CM5 chip is the most versatile biosensor chip currently available and is the most
frequently used. Its matrix consists of a completely modified carboxymethylated dextran
covalently attached to the gold surface (Fig. 20.3). Interactions involving small organic
molecules, such as pesticides, large molecular complexes, or whole viruses, can be studied
with this chip. The analytes of interest can be covalently coupled to the sensor surface
through amine, thiol, aldehyde, or carboxyl groups. The chip has a high-binding capacity,
Table 20.4
The surface chemistries of available Biacore chips
Chip type Modification type Applications
CM5 100% carboxylation of dextran surface General use
CM4 30% carboxylation of dextran surface Serum, cell extracts
CM3 100% carboxylation of dextran surface Serum, cell extracts
C1 100% carboxylation of dextran surface Bacteriophage binding
L1 Lipophilic substances Lipid capturing
SA Streptavidin surface Detection of biotin-containing molecules
NTA Nickel–nitrilotriacetic acid Detection of histidine-tagged molecules
HPA Flat hydrophobic surface Used for membrane-associated interactions
Au and SIA None Used in the study of surface chemistry interactions
of self-assembled monolayers and interactions
between surface materials and biomolecules