Biomedical Engineering Reference
In-Depth Information
Most chemical SPR sensors are based on the measurement of SPR variations due to
adsorption or a chemical reaction of an analyte with a transducing medium, which results
in changes in its optical properties (32). Applications of these sensors include, amongst
others, monitoring of the concentration of vapors of hydrocarbons, aldehydes, and alco-
hols by adsorption in polyethylene glycol films, and the detection of vapors of aromatic
hydrocarbons by their adsorption in Teflon films (32).
It is, however, in the field of molecular biology that SPR has been most successful, with
applications including immunological analysis, studies of protein-protein interactions,
molecular-biological studies on the mechanisms of gene expression, signal transduction
and cell-cell interactions, screening of new ligands, quantification of protein adsorption
and immobilization, the evaluation of surfaces for biocompatibility, epitope mapping,
determining affinity constants, and the examination of binding kinetics (39). The first
application of SPR to biosensing was demonstrated in 1983 (41). Since then, the technol-
ogy and consequent breadth of applications have continued to develop. This is due in
major part to the fact that it is possible to measure the kinetics of biomolecular interactions
in real time with a high degree of sensitivity; and that no labeling of the biomolecules is
necessary for their detection (39). Furthermore, analysis of receptor-ligand interactions
with a wide range of molecular weights, affinities, binding rates, and in numerous differ-
ent chemical environments is possible (42). Indeed, analyses of analytes with masses rang-
ing from hundreds of daltons to whole cell binding have been reported (42).
Detection methods are most often direct, where analyte quantification is carried out by
direct detection of the binding of the analyte to the immobilized receptor. In cases where
the analyte is small and its binding to the receptor does not produce a measurable increase
in the refractive index, indirect sandwich or competitive assay methods may be used (32).
Table 20.1 lists the most common molecular biological applications of SPR biosensors.
Examples of the
italicized
applications are given below.
As mentioned previously, the use of SPR for the determination of kinetic parameters is
a major contributor to its success as an analytical technology. Early work using SPR for the
determination of reaction kinetics was performed to determine the effect of single base
pair mismatches on DNA hybridization kinetics. In work performed by Gotoh et al. (44),
it was shown that the association kinetics for DNA hybridization were inversely propor-
tional to the number of mismatched base pairs, and that the dissociation kinetics were
even more strongly influenced by the number of mismatches.
In more recent work, the determination of kinetic parameters has proven to be
extremely valuable. Indeed, numerous examples exist in which interaction rates are more
descriptive of a given biological process than the equilibrium binding affinities (42). For
example, Leferink et al. (45) described growth factor interactions with ErbB-1 in which the
TABLE 20.1
SPR Biosensor Applications
Qualitative
Quantitative
Following molecular purification
Active concentration
Specificity
Kinetics
Epitope mapping
Equilibrium constants
Molecular assembly
Thermodynamics
Ligand fishing
Stoichiometry
Small molecule screening
Mechanism
Note:
SPR, surface plasmon resonance.
Source:
Modified from Rich R and Myszka D. 2000. Advances in surface plasmon resonance
biosensor analysis.
Current Opinion in Chemical Biology
11: 54-61.
