Biomedical Engineering Reference
In-Depth Information
microvalves or micropumps) are to be embedded next to the biosensor [
15
].
Polymers allow the use of cheap mass-market replication techniques, such as
hot embossing and injection molding, at low cost. Keeping manufacturing costs
low will also allow a potential use of the resulting biosensor chips as single-use
components, which are usually preferred in biomedical and clinical applications
[
13
].
Another important aspect to consider for biosensor integration is the fact that
usually more than one analyte may have to be detected, and thus the combination
of several biosensors into biosensor arrays would be beneficial to allow multiplex
detection in one measurement cycle. This is a task that can usually be fulfilled by
the biosensor housing. Two potential application scenarios have to be considered
here: more than one analyte (target) is to be detected in one sample (''single
sample-multiple target'' biosensor array) or one marker is to be detected in
multiple samples (''single target-multiple sample'' biosensor array). In both cases
the physical protection of the individual biosensors may be provided by the same
biosensor housing, but the individual biosensor chips have to be separated flui-
dically. This is required not only for the experiment but also for the application of
the sensing layers.
The most commonly found example for the housing strategy in single sample-
multiple target arrays is the creation of more than one transducer structure on a
single substrate and their (potentially permanent) fluidic separation by means of a
polymeric flow cell. Such examples can be found amply in the literature [
93
]. This
strategy is also used for numerous commercialized biosensor systems, such as the
SPR biosensor system of Biacore [
94
] and the SAW biosensor system of SAW
Instruments [
95
]. This setup is especially advantageous if the physical structures
required for biosensor elements (such as electrodes) can be manufactured by
cheap techniques on planar substrates. Potential manufacturing techniques include
screen-printed electrodes [
28
,
36
] or electrodes made by spotting or printing of
conductive polymers [
96
].
If the biosensor has to be created as a single component (maybe because a
nonplanar substrate, such as a fiber, is used), the biosensors are embedded indi-
vidually and assembled in chip format into biosensor arrays. Recently, a strategy
was suggested allowing the embedding of individual biosensors into separate
polymer housings and assembling them into versatile biosensor arrays [
97
].
For this, a disposable polymer microfluidic chip is used which defines the number
of individual biosensors in the array. In the same work, it was also demonstrated
that such a strategy can be complemented by integration of such an array into a
microfluidic environment [
97
]. Especially suitable for such applications is the use
of indirect microfluidic systems that allow an overall biosensor system array to
remain an ''all-disposable'' setup, as the active components responsible for driving
the fluids in the system, i.e., pumps and valves, will not come into contact with the
sample [
98
].
