Biomedical Engineering Reference
In-Depth Information
(a)
signal
change
transducer
transducer
(b)
signal
change
transducer
transducer
transducer
(c)
signal
change
transducer
transducer
(d)
signal
change
pre-incubation
transducer
transducer
biorecognition element (e.g., capture antibody)
secondary biorecognition element (e.g., detection antibody)
analyte (derivative)
label
Fig. 1 Biosensor test formats. a Direct detection, label-free: quantifiable signal response obtained
by binding of analyte. b Sandwich assay, label optional: quantifiable signal response obtained by
binding of a secondary biorecognition element subsequent to analyte binding. c Competitive assay,
label required: quantifiable signal response obtained by binding of a labeled analyte derivative
competing with the analyte for the surface-bound binding sites. d Binding inhibition assay, label
optional: after a preincubation step, in which equilibrium between analyte molecules and unbound
biorecognition elements is achieved, the remaining free biorecognition elements are detected via
immobilized analyte (derivative), allowing calculation of the original analyte concentration
degree of nonspecific binding on the sensing layer [
74
,
80
]. For potential problems
arising from the increased sensing layer thickness in the case of near-surface
transduction principles, see
Sect. 2.2.1
.
2.3 Biosensor Test Formats
2.3.1 Test Formats Derived from Assay Formats
Figure
1
gives an overview of test formats derived from assay formats applied in
biosensor measurements. In principle, four categories of test formats are available:
